FIELD

The present disclosure relates to downhole methods and apparatus for use in the retrieval of casing from a wellbore.

BACKGROUND

In the oil and gas industry, well abandonment must be performed according to strict regulations to minimise risk of fluid leakage into the environment. Current techniques include setting one or more permanent plugs in a wellbore, which may include one or a combination of bridge plugs, cement etc. In many cases the existing casing should be removed, which will typically involve cutting and pulling individual lengths of the casing, allowing a rock-to-rock well barrier (e.g., cement plug) to be established to minimise any leak path.

In many wells, the casing will be secured in place using a cement sheath surrounding the casing. Additionally, or alternatively, other binding mechanisms may be present, such as caused by debris, geological movement, bore collapse and the like. Thus, significant axial forces may need to be applied to remove individual casing sections, with such forces being applied by one or a combination of hydraulic pressure, tensile pulling force and the like. As such, in many known techniques very short lengths of casing may be capable of being retrieved at a time, requiring multiple trips to retrieve the desired total casing length.

Other wellbore operations may preferably require existing casing to be retrieved, for example in slot recovering operations.

SUMMARY

It should be noted that terms such as“upward”, “upper”, “uphole”, “shallower” and similar as used herein may not be limited to the vertical direction but instead are made with respect to a direction towards an entry point of the wellbore. Similarly, terms such as“downward”,“downhole”,“lower”,“deeper” and the like are made with respect to a direction away from the entry point of the wellbore. An aspect of the present disclosure relates to a method for use in retrieving casing from a wellbore, comprising:

running a tool string having a casing cutter, a casing anchor and a jarring apparatus into the cased wellbore;

operating the casing anchor to anchor the tool string to the casing;

operating the casing cutter to cut through the casing to divide an upper casing portion from a lower casing portion;

applying tension to the tool string to apply a pulling force on the upper casing portion; and

operating the jarring apparatus to generate repeated jarring forces within the jarring apparatus which are applied into the upper casing portion, wherein the pulling force and jarring forces assist in freeing the upper casing from the wellbore.

An aspect of the present disclosure relates to a method for use in retrieving casing from a wellbore, comprising:

running a tool string having a casing cutter, a casing anchor and a jarring apparatus into the cased wellbore;

operating the casing anchor to anchor the tool string to the casing;

operating the casing cutter to cut through the casing to divide an upper casing portion from a lower casing portion;

configuring the jarring apparatus from a non-jarring configuration into a jarring configuration in which first and second jarring portions of the apparatus become rotatable relative to each other; and

establishing relative rotation between the first and second jarring portions to generate repeated jarring forces within the jarring apparatus which are applied into the upper casing portion.

An aspect of the present disclosure relates to a method for use in retrieving casing from a wellbore, comprising:

running a tool string having a casing cutter, a casing anchor and a jarring apparatus into the cased wellbore;

operating the casing anchor to anchor the tool string to the casing;

operating the casing cutter to cut through the casing to divide an upper casing portion from a lower casing portion; applying tension to the tool string to apply a pulling force on the upper casing portion and to configure the jarring apparatus into a jarring configuration in which first and second jarring portions of the apparatus become rotatable relative to each other; and

establishing relative rotation between the first and second jarring portions to generate repeated jarring forces within the jarring apparatus which are applied into the upper casing portion, wherein the pulling force and jarring forces assist in freeing the upper casing from the wellbore.

An aspect of the present disclosure relates to a method for use in retrieving casing from a wellbore, comprising:

running a tool string having a casing cutter, a casing anchor and a jarring apparatus into the cased wellbore;

operating the casing anchor to anchor the tool string to the casing;

operating the casing cutter to cut through the casing to divide an upper casing portion from a lower casing portion;

applying tension to the tool string to apply a pulling force on the upper casing portion and to configure the jarring apparatus into a jarring configuration; and

generating repeated jarring forces within the jarring apparatus while applying tension within the tool string.

Thus, repeated jarring is achieved while tension is provided within the tool string, such that the simultaneous pulling force and the application of jarring forces, which may be applied via the casing anchor, assist in freeing the upper casing from the wellbore.

Known jarring tools may include linear jars. Such linear jars will typically require potential energy generated in a tool string to be rapidly released to accelerate a hammer against an anvil. In this respect the nature of linear jars is such that at the point of triggering and impact any tension applied in an associated tool string drops to zero, such that the present synergistic effect of simultaneous pulling and repeated jarring is simply not possible. Further, linear jars are typically reset by setting weight down, again requiring the loss in any tension and increasing the potential complexity of operation and control, for example by an operator at surface. The method may comprise maintaining tension within the tool string following the jarring apparatus being configured into its jarring configuration and initiating the generation of jarring forces. That is, tension may be continuously applied during the reconfiguring of the jarring apparatus and in the transition into the generation of jarring forces. Alternatively, tension may be at least partially relieved following reconfiguring of the jarring apparatus into its jarring configuration, with tension then reapplied before or during the generation of jarring forces.

The method may comprise providing a drive to the jarring apparatus to generate repeated jarring forces. The drive may comprise a rotary drive, for example from a connected running string, work string, motor and/or the like. The drive may comprise a linear drive, such as from a linear motor or the like.

In some examples the magnitude of each jarring force generated may be a function of the tension applied within the tool string. Additionally, or alternatively, the magnitude of each jarring force generated may be a function of a force mechanism, such as a spring assembly. The force mechanism may be provided as part of the jarring apparatus.

The method may comprise generating repeated jarring forces within the jarring apparatus by causing repeated impact between respective impact surfaces. In some examples the jarring forces and any resultant vibration need not strictly be created by more complex fluid based systems, such as systems which might function on the basis of creating pressure pulses and the like.

In some examples impact may be achieved in an axial direction. For example, the respective impact surfaces may be arranged for relative axial movement therebetween. Alternatively, or additionally, impact between the respective impact surfaces may be achieved in a rotary direction.

The method may comprise causing relative reciprocating movement between the respective impact surfaces to cause multiple impacts and thus generate repeated jarring forces. Such reciprocating movement may be in a linear direction, rotary direction, and/or the like. In one example the method may comprise applying tension to the tool string to apply a pulling force on the upper casing portion and to configure the jarring apparatus into a jarring configuration in which the first and second jarring portions of the apparatus become rotatable relative to each other. The method may comprise establishing relative rotation between the first and second jarring portions to generate repeated jarring forces within the jarring apparatus which are applied into the upper casing portion, wherein the pulling force and jarring forces assist in freeing the upper casing from the wellbore.

Thus, the jarring apparatus may be operated by the combination of applied tension and the relative rotation between the first and second jarring portions, both being parameters that may be readily controlled by an operator, and indeed parameters that may be used for performing or implementing other elements or steps of the present method. This may therefore provide a simple and efficient method for use in assisting the retrieval of casing.

The magnitude of the jarring forces applied may be a function of the applied tension, whereas the jarring frequency may be a function of the speed of relative rotation between the first and second jarring portions. As such, the jarring operation may be infinitely variable, in particular using parameters readily controllable by an operator.

The pulling force on the upper casing portion may act to dislodge the upper casing portion in an upward direction, with the jarring forces applied by the jarring apparatus providing a vibratory assistance. For example, the vibration effect provided by the jarring apparatus may function to assist in breaking-up and/or dislodging material, such as cement, debris, mud solids, collapsed bore material etc., behind the casing, to reduce binding friction of the upper casing portion, and/or the like.

The method may comprise continuously applying tension and thus the pulling force on the upper casing portion while generating jarring forces. In some examples a constant or substantially constant tension may be applied. Alternatively, a variable tension may be applied. The method may comprise running the tool string into the wellbore on a running string. The running string may comprise any suitable running string, such as slickline, wireline, coiled tubing, drill pipe and the like.

The running string may define a fluid conduit to permit flow of fluid between surface and the tool string. Such fluid flow may be provided for one or a number of purposes, which will be described in more detail below. However, in some examples such fluid flow may be for use in operating one or more components of the tool string, for use during casing cutting operations, for use in providing an upward hydraulic driving force to the upper casing portion, and/or the like.

The running string may be configured to apply at least one of tension and rotation to the tool string. In this example the running string may function as a work string. The running string may be configured to apply both tension and rotation to the tool string. Thus, dual actuation operations may be provided along a common transmission medium (i.e., the running string), thus providing a relatively simple method of operation.

The method may comprise applying a pulling force on the tool string via the running string, wherein said pulling force applies tension in the tool string to configure the jarring apparatus into its jarring configuration and apply the pulling force on the upper casing portion.

However, in other examples tension in the tool string may be applied or generated via a tensioning apparatus. Such a tensioning apparatus may be deployed with the tool string. The tensioning apparatus may be arranged to grip a surrounding structure (for example via the casing anchor), and include a force mechanism arranged to pull on the tool string (relative to any anchor point with the surrounding structure) and apply a tension therein. In some examples the force mechanism may comprise a jacking mechanism configured to provide an axial stroking function. The jacking mechanism may be hydraulically operated, mechanically operate and/or the like.

The method may comprise rotating the running string to apply relative rotation between the first and second jarring portions when the jarring apparatus is in the jarring configuration. In some examples, the method may comprise providing relative rotation between the first and second jarring portions via a downhole motor, such as a downhole electric motor, hydraulic motor and/or the like.

The first jarring portion of the jarring apparatus may be coupled to an upper portion of the tool string, and the second jarring portion may be coupled to a lower portion of the tool string. In this respect, when the jarring apparatus is configured in its jarring configuration the upper and lower tool string portions may be rotatable relative to each other. The upper tool string portion, and thus the first jarring portion, may be coupled to a running string. The method may comprise rotating the upper tool string with the running string, thus providing relative rotation between the first and second jarring portions when the jarring apparatus is in its jarring configuration.

The method may comprise running the tool string into the wellbore with the jarring apparatus in a non-jarring configuration, in which the first and second jarring portions are rotatably coupled together. In this example the jarring apparatus, when in its non jarring configuration, may be capable of transmitting torque across the first and second jarring portions. For example, the method may comprise transmitting torque from a drive source, such as a running string, on one axial side of the jarring apparatus to driven elements, such as the cutter, on an opposite axial side of the jarring apparatus.

The method may comprise releasing a rotatable coupling between the first and second jarring portions to configure the jarring apparatus into its jarring configuration. The releasable rotatable coupling may comprise a shear arrangement. The releasable rotatable coupling may comprise a spline arrangement.

The method may comprise establishing relative axial movement (e.g., telescoping) between the first and second jarring portions to release the rotatable coupling. For example, the method may comprise disengaging a spline arrangement by relative axial movement between the first and second jarring portions. Relative axial movement may be provided by applying tension through the tool string, for example via a running string. In some examples the second jarring portion may be axially secured within the wellbore, for example via the casing anchor (or a separate casing spear, described below), with the first jarring portion being pulled axially, for example via a running string, to establish relative axial movement between the first and second jarring portions.

The method may comprise releasing an axial coupling between the first and second jarring portions to configure the jarring apparatus in its jarring configuration. Release of the axial coupling may then permit relative axial movement between the first and second jarring portions to be achieved to release a rotatable coupling, such as a spline arrangement. The method may comprise releasing an axial coupling by applying an axial tension within the tool string above a threshold value. This axial coupling may thus define a triggering mechanism within the jarring apparatus.

The rotatable coupling between the first and second jarring portions may be resettable. Such an arrangement may facilitate reconfiguring the jarring apparatus back to its non jarring configuration. Thus, the method may comprise reconfiguring the jarring apparatus into its non-jarring configuration by resetting the rotatable coupling therebetween. The method may comprise reconfiguring the jarring apparatus into its non-jarring configuration by setting weight down on the jarring apparatus.

In some examples, the method may comprise resetting an axial coupling between the first and second jarring portions.

The method may comprise establishing relative rotation between the first and second jarring portions to cause repeated impact between first and second impact surfaces within the jarring apparatus. Thus, mechanical impact between separate impact surfaces within the jarring apparatus may generate the jarring forces.

The method may comprise establishing relative rotation between the first and second jarring portions to operate a lifting assembly within the jarring apparatus, wherein such operation of the lifting assembly causes the first and second impact surfaces to be cyclically separated and subsequently impacted together. The lifting assembly may comprise a first lifting structure provided on the first jarring portion and a second lifting structure provided on the second jarring portion. The first and second lifting structures may be configured to cooperate during relative rotation therebetween to causes first and second impact surfaces to be cyclically separated and subsequently impacted together. The first and second lifting structures may comprise cooperating cam profiles.

In one example, the first and second lifting structures may also define the first and second impact surfaces. However, in other examples the first and second lifting structures may be provided separately or remotely from the first and second impact surfaces.

In some examples, the jarring apparatus may comprise a jarring mass that is caused to axially reciprocate within the jarring apparatus by the lifting assembly during relative rotation between the first and second jarring portions. The jarring mass may comprise one of the first and second impact surfaces. The jarring mass may define a jarring hammer configured to strike or impact an anvil portion within the jarring apparatus, wherein the anvil portion defines the other of the first and second impact surfaces.

The method may comprise applying the axial tension within the tool string through the lifting assembly. However, in other examples the method may comprise limiting the axial loading applied through the lifting assembly. For example, the method may comprise using a thrust assembly interposed between the first and second jarring portions to divert axial loading above a threshold value from the lifting assembly.

The casing anchor may define a casing spear.

The method may comprise operating the casing anchor to anchor the tool string to the casing prior to the step of cutting the casing with the casing cutter. However, in other examples the method may comprise operating the casing anchor after the step of cutting the casing.

The method may comprise extending slips of the casing anchor into gripping engagement with the casing.

The method may comprise hydraulically operating the casing anchor to engage the casing. Such hydraulic operation may be provided by pumping a fluid through the tool string. The method may comprise operating the casing anchor to engage the casing by applying tension through the tool string. In this example the tension applied within the tool string to set the casing anchor may be below a threshold for configuring the jarring apparatus into its jarring configuration.

The method may comprise initially pre-setting the casing anchor into initial gripping engagement with the casing, and then subsequently fully setting the casing anchor by increasing the gripping engagement force. The method may comprise initially hydraulically operating the casing anchor to provide the pre-set. Alternatively, or additionally, the method may comprise mechanically pre-setting the casing anchor, for example via a drag-block arrangement and/or the like. The method may comprise fully setting the casing anchor by applying tension through the tool string. Such tension may be accommodated by the initial pre-set of the casing anchor.

The casing anchor may be configured to be unset. In one example the casing anchor may be unset by relieving tension within the tool string, for example by setting weight down.

The casing cutter may comprise one or more cutting blades. The method may comprise extending the casing cutter into engagement with the casing and rotating said casing cutter to cut the casing. Such rotation may be provided by a rotational drive, such as a downhole motor. However, in some examples the casing cutter may be rotated by a connected running string on which the tool string is deployed.

The casing cutter may comprise a hydraulic action cutter, such as a fluid jet cutter. The casing cutter may comprise a flow-propelled cutter. The casing cutter may comprise an explosive cutter. The casing cutter may comprise a projectile based cutter.

The method may comprise flowing fluid through the tool string and outwardly into an annulus region defined between the tool string and the casing during operation of the casing cutter. The fluid flow may provide one or more functions, such as lubricating the cutter, cooling the cutter, removing swarf and other debris produced during cutting, and the like. The casing cutter may be configured to be retracted. In one example the casing may be retracted by reducing or ceasing fluid flow through the tool string.

In examples where the casing anchor is set prior to the cutting operation, the casing anchor may be configured to permit the casing cutter to be rotated by the running string, for example via a swivel connection. In some examples the casing anchor may permit relative rotation with the remainder of the tool string to permit a drive torque to be transmitted past the casing anchor, for example from a running string on one side of the casing anchor to the casing cutter on an opposite side of the casing anchor. The method may comprise rotatably locking at least a portion of the tool string to the casing anchor during the step of configuring the jarring apparatus into its jarring configuration. In one example, the method may comprise rotatably locking the second jarring portion of the jarring apparatus to the casing anchor during the step of configuring the jarring apparatus into its jarring configuration. Such an arrangement may thus allow relative rotation between the first and second jarring portions to be achieved. The method may comprise rotatably locking at least a portion of the tool string to the casing anchor via a clutch, spline or the like.

In examples where the casing anchor is set prior to the cutting operation, the casing anchor may be configured to provide and maintain in use a degree of centralisation to the casing cutter within the casing.

In other examples, the rotatable securing of the tool string, particularly the second jarring portion, may be achieved by setting a secondary anchor, which will be described in more detail below.

The method may comprise setting a packer on the tool string to sealingly engage the casing above the cutter. The method may comprise hydraulically setting the packer, for example by fluid flow through the tool string. The method may comprise setting the packer by applying tension through the tool string.

In examples where the packer is set prior to the cutting operation, the packer may be configured to permit the casing cutter to be rotated by a running string, for example via a swivel connection. Prior to setting the packer fluid flow externally of the tool string along an annulus defined between the tool string and the casing may be permitted. The annulus defined between the tool string and the casing may be identified as the tool annulus herein. Thus, any fluid delivered through the tool string, for example to pre-set or set the casing anchor, to extend the cutter etc. may be returned to surface along the tool annulus. However, after setting the packer such flow externally of the tool string along the tool annulus may be restricted.

The method may comprise setting the packer prior to operating the casing cutter. In this respect, any fluid returns past the set packer along the tool annulus will be prevented.

The method may comprise providing a diversion flow path internally of the tool string that provides a flow by-pass past the packer. The diversion flow path may facilitate fluid in the tool annulus on one side of (e.g., below) the set packer to enter the tool string, and said fluid to exit the tool string and into the tool annulus on an opposite side of (e.g., above) the tool annulus. The method may comprise permitting flow by-pass when the packer is set and the casing cutter is operated to cut the casing. In this respect, fluid returns from the cutting operation may be permitted towards surface.

The diversion flow path may be provided in a cross-over sub within the tool string which permits contra flow, for example downward flow from surface towards the cutter and upward or return flow through the diversion flow path back towards surface.

The diversion flow path may be closed during running of the tool string into the wellbore, and subsequently opened when required. The diversion flow path may alternatively be open during running of the tool string into the wellbore.

The method may comprise retaining cutting debris from fluid returns within a filter mechanism within the diversion flow path. The tool string may comprise a junk basket for filtering and retaining debris from fluid returns. This may minimise the requirement for treating the returned fluid at surface.

In some examples flow returns to surface during the cutting operation may be monitored and information from this monitoring derived. For example, a change in a parameter of the flow, such as flow rate, pressure etc., may provide a tell-tale that the casing has been successfully cut, with at least a proportion of the fluid flow passing behind the cut casing.

The method may comprise closing the diversion flow path following the cutting operation. Such closure of the diversion flow path may be provided by any suitable actuation method or mechanism, for example by applying tension through the tool string. The method may comprise closing the diversion flow path during operation of the jarring apparatus. In one example, the operation to reconfigure the jarring apparatus into its jarring configuration may also close the diversion flow path.

The closed diversion flow path, in combination with the set packer may prevent any return flow past the packer, thus facilitating the application of an upward fluid pressure force applied on the tool string. Such an upward fluid pressure force may thus provide assistance in upwardly dislodging the upper casing portion by use of a piston effect.

The method may comprise flowing fluid from the tool string and into the tool annulus and subsequently through the cut formed in the casing (i.e., the cut created between the upper and lower casing portions) into an outer annulus externally of the casing. This outer annulus may be identified herein as the casing annulus. This casing annulus may be defined between the casing and an outer surrounding structure. This outer surrounding structure may be an outer casing. This outer surrounding structure may be an open-hole face (i.e., rock face) of the wellbore. The casing annulus may be initially at least partially filled by cement, debris or other particles which provide a binding effect between the casing and the outer surrounding structure. The present method may desirably remove this binding effect by the combination of applied pulling force and vibration.

This step of flowing fluid into the casing annulus may be performed when the packer is set and the diversion flow path is closed, thus preventing fluid form being diverted, instead, upwardly through the tool annulus.

The step of flowing fluid into the casing annulus may provide an upward fluid pressure force applied on the upper casing portion. Such an upward fluid pressure force may thus provide assistance in upwardly dislodging the upper casing portion by use of a piston effect. The step of flowing fluid into the casing annulus may also function to flush the casing annulus, and assist in the removal or disruption of cement, debris etc..

The method may comprise looking for a return of the fluid in the casing annulus at surface. Such return flow may provide an indication of sufficient disruption of any cement, debris etc. with the casing annulus.

The method may comprise operating a secondary casing anchor to engage the casing, and provide or assist in anchoring the tool string to the casing. The secondary casing anchor may form part of the tool string. The secondary casing anchor may form part of the jarring apparatus. The secondary casing anchor may define a casing spear.

The secondary casing anchor may be set prior to reconfiguring the jarring apparatus into its jarring configuration. In some examples, the setting of the secondary casing anchor may facilitate reconfiguring of the jarring apparatus.

The method may comprise operating the secondary casing anchor to engage the casing by applying tension through the tool string. In this example, the tension applied within the tool string to set the secondary casing anchor may be below a threshold for configuring the jarring apparatus into its jarring configuration. The tension applied within the tool string may be permitted by reaction off the previously set casing anchor.

The method may comprise applying a tension within the tool string which applies an axial force within the secondary casing anchor above a trigger threshold value. Thus, the secondary casing anchor may remain unset until the trigger threshold value has been exceeded, thus permitting other operations to be facilitated by lower tension applied within the tool string, such as the setting of the original casing anchor, setting of a packer etc.

The secondary casing anchor may comprise an anchor actuator that operates one or more slips to be extended into engagement with the casing. For example, the anchor actuator may comprise an axially moveable kick-out tool which, when moved axially, causes or permits radial movement of the one or more anchor slips. Axial tension within the tool string may apply an axial force on the anchor actuator in a direction to bias the one or more slips towards engagement with the casing. The secondary casing anchor may comprise a trigger mechanism that may resist movement of the anchor actuator in response to the applied axial force until the trigger threshold value is reached and/or exceeded.

The trigger mechanism may comprise a releasable lock, such as releasable dogs, a shear arrangement and/or the like.

The trigger mechanism may comprise a biasing arrangement configured to resist the axial force applied on the anchor actuator. The method may comprise applying axial tension in the tool string that is sufficient to overcome the resistance provided by the biasing arrangement to provide suitable operation of the anchor actuator. The biasing arrangement may comprise a spring, such as a Belleville spring stack. The biasing arrangement may be suitably tuned to the specific operation, for example by providing a desired trigger threshold. Further, the biasing arrangement may be tuned to accommodate other factors, such as the weight of the tool string, which in some examples may be suspended through the biasing arrangement.

The secondary casing anchor may provide a more ensured anchor point for performing the jarring operation. That is, jarring operations may be performed without relying or only relying on the originally set casing anchor. For example the method may comprise using the secondary casing anchor as a reaction point to apply a tension through the jarring apparatus (e.g., between the first and second jarring portions) to permit this jarring apparatus to be configured into its jarring configuration. Further, the secondary casing anchor may continue to provide an anchor and axial reaction point to facilitate continued application of applied tension during a jarring operation. Furthermore, the secondary casing anchor may function to rotatably lock the second jarring portion relative to the casing thus permitting relative rotation between the first and second jarring portions to be achieved. In this respect, the requirement to rotationally lock the tool string to the originally set casing anchor, for example via a clutch mechanism, might not be required.

In some examples, the secondary casing anchor may be provided to facilitate the combined use of different apparatus. For example, an existing cut-and-pull tool may include features such as a casing anchor, cutter, packer and the like, without any jarring apparatus. The method may thus comprise forming a tool string by coupling the existing cut-and-pull tool to a jarring apparatus and secondary casing anchor. In this respect, the provision of the secondary casing anchor may provide assurances that a sufficient or suitable casing anchor may be achieved, without relying on or over stressing a casing anchor on the existing cut-and-pull tool. Further, the secondary casing anchor may function to more robustly accommodate torque loading during rotary based jarring.

The secondary casing anchor may be configured to be unset. In one example the secondary casing anchor may be unset by relieving tension within the tool string, for example by setting weight down.

The method may comprise locating the tool string above a barrier set in the casing. Such a barrier may prevent any downward flow of fluid past the barrier. The barrier may provide a support for a plug later set in the casing, for example following removal of the upper casing portion. The method may comprise setting the barrier. The barrier may be set via a barrier tool provided on the tool string. Alternatively, the barrier may be set prior to running the tool string into the wellbore.

The method may comprise displacing (e.g., pulling) the upper casing portion upwardly through the wellbore toward surface. The method may comprise displacing the upper casing portion toward surface by pulling the tool string out of the hole (e.g., on the running string) with the upper casing string connected thereto, for example via the casing anchor and/or the secondary casing anchor where present. The method may comprise operating the jarring apparatus while displacing the upper casing portion toward surface. As such, vibratory assistance may be achieved during the retrieval process, facilitating easier pulling, for example by reducing binding friction, further dislodging material in the casing annulus, and/or the like.

By use of the tool string to both cut, jar and pull the upper casing portion the method may be performed during a single trip, thus providing significant operational advantages and efficiencies in comparison with techniques which might require multiple trips to perform different operations to enable casing removal.

The method may comprise dividing the retrieved upper casing portion at surface during the retrieval process in a known manner. Where the initial cutting and jarring operations have sufficiently freed the upper casing portion from the wellbore, the method may comprise immediately retrieving the upper casing portion. Sufficient freeing of the upper casing portion from the wellbore may be recognised via one or more factors or indicators, such as upward displacement caused by the overpull or tension applied on the tool string during the jarring operation. Further, sufficient freeing of the upper casing string may be recognised by the ability to pull the casing string from the wellbore within any operational constraints of associated lifting equipment, for example provided on a rig, platform, vessel or the like.

The method may comprise retaining the tool string engaged with the casing following the cutting operation, and displacing the upper casing portion by applying an upward pull on the tool string, for example via a running string. The casing anchor and/or the secondary casing anchor, where present, may thus not be disengaged from the upper casing portion. This method step may thus involve pulling the upper casing string from its lower end.

In an alternative example, the method may comprise releasing the tool string from the casing and moving the tool string upwardly to a shallower depth in the wellbore. Such releasing of the tool string may comprise one or more of un-setting the casing anchor, un-setting the secondary casing anchor, where present, retracting the casing cutter and retracting the packer. The method may comprise re-engaging the tool string with the upper casing portion at the shallower depth, for example by re-setting the casing anchor and/or the second casing anchor where present, and subsequently displacing the upper casing portion by applying an upward pull on the tool string, for example via a running string, optionally with simultaneous jarring. Such an example may thus involve pulling the upper casing from an anchor point towards it upper end. Such an arrangement may facilitate easier handling of the upper casing portion at surface. Further, such an arrangement may facilitate casing pulling while minimising the added weight of any running string.

Where the initial cutting and jarring operations have not sufficiently freed the upper casing portion from the wellbore, the method may comprise releasing the tool string from the casing and moving the tool string upwardly to a shallower depth in the wellbore. The method may comprise re-engaging the tool string with the upper casing portion at the shallower depth, for example by re-setting the casing anchor and/or the second casing anchor where present. The method may comprise operating the jarring apparatus to provide jarring and vibration at this shallower depth. The method may comprise applying this further jarring at the shallower depth without also further cutting the upper casing portion. This further jarring applied at the shallower depth may be sufficient to free the upper casing portion, allowing the upper casing portion to be pulled on the tool string. In this respect, the tool string may remain engaged with the upper casing portion at the shallower depth to facilitate pulling, or alternatively may be disengaged and reengaged at a location further towards the upper end of the upper casing portion.

In some examples the method may comprise applying jarring of the upper casing portion at multiple shallower depths within the wellbore (for example progressively shallower depths) to assist in freeing of the upper casing portion from the wellbore.

Where the initial cutting and jarring operations have not sufficiently freed the upper casing portion from the wellbore, the method may comprise running or moving the tool string to a depth in the wellbore which is above the initial cut, and repeating the method steps of at least anchoring the tool string to the casing and operating the casing cutter to cut through the casing to divide the upper casing portion. This arrangement may therefore provide a shorter length of casing to be pulled. In some examples the method may comprise repeating the steps of configuring the jarring apparatus into its jarring configuration and applying jarring to the shorter casing length. Further method steps define above may be repeated, as required.

In the examples described the method may be performed to retrieve a casing from a wellbore. However, the same method may be applied to the removal of any tubing within a wellbore, provided the tool string can be deployed therein. As such, although the term “casing” is used herein, this should be understood to mean any tubular structure located within a wellbore, and might include, for example, liner etc.

An aspect of the present disclosure relates to a downhole apparatus for use in retrieving casing from a wellbore, the apparatus comprising:

a casing cutter operable to cut a casing within the wellbore;

a casing anchor operable to engage a cut section of casing in the wellbore; and a jarring apparatus for applying a jarring force to the casing.

Features of the downhole apparatus may be provided in accordance with the details described above in connection with the method aspect.

The downhole apparatus may be used in performing the method of any other aspect.

The jarring apparatus may comprise first and second jarring portions and may be configurable into a jarring configuration by applying an axial tension within the jarring apparatus. In some examples this arrangement may be such that first and second jarring portions of the jarring apparatus become rotatable relative to each other to generate repeated jarring forces within the jarring apparatus.

The jarring apparatus may comprise first and second jarring portions or assemblies axially moveable relative to each other between first and second axial configurations.

The jarring apparatus may comprise a thrust assembly interposed between the first and second jarring assemblies to limit relative axial movement therebetween at the second axial configuration and permit axial loading in one axial direction to be transferred between the first and second jarring assemblies via the thrust assembly.

The jarring apparatus may comprise a jarring mass axially moveable within the jarring apparatus in reverse first and second directions, and a force mechanism for biasing the jarring mass in its first axial direction and for biasing the first and second jarring assemblies in a direction towards their first axial configuration.

The jarring apparatus may comprise a lifting assembly operable by relative rotation between the first and second jarring assemblies to cyclically lift the jarring mass in the second axial direction against the bias of the force mechanism and release the lifted jarring mass to permit the jarring mass to be driven by the force mechanism in the first direction.

It should be understood that the term“lift” or“lifting” with reference to the jarring mass is not intended to be limited to an increase in vertical height, but is instead used to define any displacement of the jarring mass in the second direction against the bias of the force mechanism, irrespective of the orientation of the jarring apparatus. In a similar manner, the release and movement of the jarring mass in the first direction may be defined as a dropping motion of the jarring mass.

In use, a repeated jarring force may be generated by the reciprocating axial motion of the jarring mass as it is cyclically lifted and released by the lifting assembly during relative rotation between the first and second jarring assemblies. In particular, the movement of the jarring mass in the first direction under the action or drive of the force mechanism may permit a jarring force to be generated. As such, the jarring force may be a function of the bias force provided by the force mechanism. The provision of the force mechanism to bias the jarring mass in the first direction may provide an internal or on-board energy source for use in delivering the desired jarring force. Such an arrangement may allow any forces applied within or through the lifting assembly to be a function of the capacity or rating of the force mechanism. This may contribute to providing a degree of protection to the lifting assembly.

As jarring forces are generated by relative rotation between the first and second jarring assemblies, the jarring apparatus may be defined as a rotary jarring apparatus.

The thrust assembly limits relative axial movement between the first and second jarring assemblies at their second axial configuration, which may also be defined as a limit position or configuration. In this respect, relative axial movement of the first and second jarring assemblies in a direction from the first axial configuration will be limited at the second axial configuration. The thrust assembly may permit relative axial movement between the first and second jarring assemblies in a direction from the second axial configuration towards the first axial configuration. As such, the thrust assembly may be considered to be axially unidirectional.

When the thrust assembly is engaged at the second axial configuration axial load transference in one axial direction is permitted. This axial direction may be the direction of relative movement between the first and second jarring assemblies to be reconfigured from the first axial configuration to the second axial configuration. The load transference via the thrust assembly in this regard may prevent or divert any excessive axial loading between the first and second assemblies from being transmitted through the force mechanism and applied within the lifting assembly, thus providing a degree of protection to the lifting assembly. In this respect, the thrust assembly may function or define a load limiter. In the specific application of casing retrieval, this load limit function may provide significant advantages, especially considering the possible applied force that may be suspended or applied through the jarring apparatus including not only the weight of the casing but also the required overpull to displace the casing upwardly through the wellbore.

As presented above, the force mechanism provides a dual biasing function: biasing the jarring mass in its first axial direction; and biasing the first and second jarring assemblies in a direction towards their first axial configuration.

The force mechanism may be energised by movement of the jarring mass in its second direction and relative axial movement between the first and second jarring assemblies towards their second configuration.

The force mechanism may be of a displacement type, which generates a force as a function (linearly or otherwise) of its displacement. The force mechanism may be displaced in a common direction by movement (lifting) of the jarring mass in its second axial direction and by relative axial movement of the first and second jarring assemblies towards their second configuration. In this way, the biasing force may increase by lifting of the jarring mass and by relative movement between the first and second jarring assemblies towards their second configuration.

The force generated within the force mechanism may thus be a function of the relative axial movement of the first and second jarring assemblies towards their second configuration. A user may therefore be provided with a degree of control of the jarring force by controlling the relative axial displacement between the first and second jarring assemblies. However, the thrust assembly, by limiting relative axial movement between the first and second jarring assemblies at the second configuration, may provide a limiting effect on the displacement within the force mechanism and thus the force permitted to be generated. Any further increasing force applied between the first and second jarring assemblies may then be accommodated via the thrust assembly, preventing the further generation of force within the force mechanism, other than via the lifting assembly. As noted above, this limiting effect of the thrust assembly may provide a degree of protection to the lifting assembly during its operation. In some examples the lifting of the jarring mass may establish a relatively small displacement of the force mechanism compared to that caused or permitted by relative axial movement of the first and second jarring assemblies towards their second configuration. In this case, the force generated within the force mechanism may be primarily a function of the relative displacement of the first and second jarring assemblies towards their second configuration, such that providing a limit to that relative displacement via the thrust assembly provides significant protection within the jarring apparatus.

Initial relative axial movement of the first and second jarring assemblies from their first configuration towards their second configuration may be permitted without corresponding operation (e.g., displacement) of the force mechanism. In some examples this initial relative movement between the jarring assemblies may permit another operation to be facilitated without being retarded by the force mechanism. For example, the initial relative movement between the first and second jarring assemblies may function to release a rotary coupling between the first and second jarring assemblies, which will be described in further detail below.

In some examples, the force mechanism may be inactive until the first and second jarring assemblies have achieved sufficient relative axial movement towards their second configuration to begin displacing the force mechanism. In an alternative example, the force mechanism may be preloaded such that operation may be permitted without any required displacement by relative axial movement between the first and second jarring assemblies. In such an alternative example any displacement by the relative axial movement between the jarring assemblies will function to increase the force developed in the force mechanism for use in a jarring operation.

The force mechanism may be interposed (e.g., axially interposed) between one of the first and second jarring assemblies and the jarring mass. The force mechanism may be operated on opposing sides or ends (e.g., axial sides or ends) thereof by one of the first and second jarring assembles and the jarring mass.

The force mechanism may directly bear on or engage one of the first and second jarring assemblies. In some examples the force mechanism may be engaged with one of the first and second jarring assemblies via a force load shoulder. The force load shoulder may continuously engage the force mechanism. Alternatively, where initial relative movement between the first and second jarring assemblies is permitted before operation of the force mechanism, the force load shoulder may be initially separated from and pick-up or engage the force mechanism during the course of relative movement between the first and second jarring assemblies in a direction towards the second configuration. In some examples the force load shoulder may be adjustable to provide flexibility in setting the pick-up point.

The force mechanism may directly bear on or engage the jarring mass. Alternatively, the jarring apparatus may comprise a bearing structure, such as a bearing sleeve, rod, arm or the like, which is interposed between the force mechanism and the jarring mass.

The force mechanism may comprise any suitable device, apparatus, assembly or means which is cable of functioning as described herein. In some examples the force mechanism may comprise a spring mechanism, such as a mechanical spring, gas spring or the like.

The jarring apparatus may comprise an arresting mechanism configured to arrest movement of the reciprocating mass when moving in the first axial direction under the action of the force mechanism. The arresting mechanism may be configured to rapidly arrest or decelerate the jarring mass. Such a rapid arrest may assist to provide a jarring force. That is, the jarring force may be a result of a force generated upon arresting the jarring mass when moving in its first direction.

The arresting mechanism may be provided by opposing impact surfaces. In examples where a jarring force is provided by impact within the apparatus, the jarring mass may be defined as a hammer. In one example the jarring mass may comprise a first impact surface, and one of the first and second jarring assemblies may comprise a second impact surface, wherein the first and second impact surfaces are configured to be impacted together when the jarring mass is driven in its first direction under the action of the force mechanism. In such an example, lifting of the jarring mass in its second direction by the lifting assembly may cause the first and second impact surfaces to separate. The first impact surface may be integrally formed with the jarring mass. Alternatively, the first impact surface may be provided on a separate component, such as an impact or hammer head, which is coupled to the jarring mass.

The first and second impact surfaces may be provided separately from the lifting assembly. This may increase the longevity of the lifting assembly, by avoiding the lifting assembly having to perform a dual function of lifting and impacting.

In other examples the arresting mechanism may not rely on, or entirely on, an impact between two surfaces. For example, the arresting mechanism may comprise a damping mechanism, such as a fluid damper, spring system or the like. In this example jarring may be achieved through reciprocating motion of the jarring mass. The jarring mass may thus be operated to reciprocally wobble, shake, agitate or like

The thrust assembly may comprise respective loading faces on the first and second jarring assemblies, wherein the respective loading faces are axially engaged when the first and second jarring assemblies reach their second axial configuration.

The thrust assembly may permit the first and second jarring assemblies to be rotatable relative to each other when in their second configuration.

The thrust assembly may comprise a thrust bearing or bearing assembly.

The lifting assembly may comprise a first lifting structure rotatably and axially fixed relative to one of the first and second jarring assemblies and a second lifting structure rotatably fixed and axially moveable relative to the other of the first and second jarring assemblies, wherein the second lifting structure acts axially, directly or indirectly, on the jarring mass. The first and second lifting structures may be configured to cooperate during relative rotation therebetween to cause the second lifting structure to be axially moved in cyclical lifting and dropping phases. During the lifting phase the second lifting structure may cause the jarring mass to be lifted in its second direction. The dropping phase of the first and second lifting structures may coincide with releasing the jarring mass. However, in some alternative examples release of the jarring mass may occur prior to the dropping phase between the first and second lifting structures. This may provide a degree of protection to the first and second lifting structures, which will be described in further detail below.

The dropping phase of the first and second lifting structures may be considered to function to reset the lifting structures in preparation for a subsequent lifting phase.

Loading may be applied between the first and second lifting structures which is a function of the biasing force provided by the force mechanism (via the jarring mass and second lifting structure). In this respect such loading may be controlled by appropriate selection of the force mechanism and by virtue of the load limiting effect of the thrust assembly. This may assist to increase the longevity of the first and second lifting structures, and thus of the lifting assembly.

The second lifting structure may be rotatably coupled to its associated jarring assembly via a connection which permits the second lifting structure to move axially. In this respect the associated jarring assembly is the jarring assembly to which the second lifting structure is connected. The connection may include, for example, a keyed connection, splined connection, castellated connection or the like.

The second lifting structure may be integrally formed with the jarring mass. Alternatively, the second lifting structure may be separately formed from the jarring mass. The second lifting structure may directly bear on or engage the jarring mass. Alternatively, the jarring apparatus may comprise a bearing structure, such as a bearing sleeve, rod, arm or the like, which is interposed between the second lifting structure and the jarring mass.

The first lifting structure may be permanently axially connected to its associated jarring assembly. In this respect the associated jarring assembly is the jarring assembly to which the first lifting structure is connected.

The first lifting structure may be releasably axially connected to its associated jarring assembly. Axial release of the first lifting structure may effectively permit axial release of the jarring mass to thus be driven in its first direction by the force mechanism. The force mechanism may thus also cause the first and second lifting structures to be moved in the same first direction. In some examples one or both of the first and second lifting structures may be permitted to move axially further than the jarring mass in the first direction. This may function to decouple the effect of the force mechanism from applying loading between the first and second lifting structures after a degree of axial movement in the first direction has been achieved. In one example an arresting mechanism (e.g., impact surfaces) may provide such a decoupling function.

In one example the first lifting structure may be axially releasable from its associated jarring assembly prior to initiation of the dropping phase. Accordingly, release of the jarring mass to generate a jarring force may not be initiated or caused by transition of the lifting structures to the dropping phase, thus affording protection to the lifting structures and contributing to addressing or at least mitigating problems associated with prior art rotary jarring tools. This may assist to prolong the operational life of the lifting structures.

Axial release of the first lifting structure may function to release or reduce, for example significantly reduce, loading applied between the first and second lifting structures prior to initiation of the dropping phase. This arrangement may assist to minimise wear and/or risk of damage or failure occurring within the lifting structures.

The first lifting structure may remain axially released relative to its associated jarring assembly during a transition from the lifting phase to the dropping phase. In some examples the first lifting structure may remain axially released relative to its associated jarring assembly during at least a portion, for example the entirety of the dropping phase. Accordingly, the dropping phase may be initiated and optionally completed with minimised loading applied between the first and second lifting structures, which may assist to provide protection to the lifting structures and prolong their operational lifespan.

The first lifting structure may become axially fixed relative to its associated jarring assembly in advance of a subsequent lifting phase. The first lifting structure may become axially fixed relative to its associated jarring assembly upon initiation of a subsequent lifting phase. The first lifting structure may become axially fixed relative to its associated jarring assembly during the course of a subsequent lifting phase. In some examples the first lifting structure may be axially released relative to its associated jarring assembly prior to completion of the lifting phase. In such an arrangement relative axial displacement between the first and second lifting structures may continue under reduced loading to complete the lifting phase.

The first and second lifting structures may comprise inter-engaging profiles which cooperate during relative rotation of the lifting structures to cause the cyclical lifting and dropping phases. The inter-engaging profiles may be configured such that a surface area of contact therebetween reduces as the lifting phase progresses. When exposed to load such a reducing surface area of contact results in increasing stresses applied between the inter-engaging profiles of the first and second lifting structures. As such, axially releasing the first lifting structure prior to completion of the lifting phase may prevent excessive loading being applied over the reducing surface area of contact, reducing stresses applied and minimising wear and risk of damage or failure.

The inter-engaging profiles may permit at least one cycle of lifting and dropping phases for a single 360 degrees of relative rotation between the first and second lifting structures. In one example the inter-engaging profiles may permit multiple cycles (such as 2, 3, 4 etc.) of lifting and dropping phases for a single 360 degrees of relative rotation.

The inter-engaging profiles may be configured for rotating sliding engagement therebetween. The inter-engaging profiles may be defined by circumferential ramp structures. In one example the inter-engaging profiles may comprise rotary cam surfaces. In such examples the first and second lifting structures may define respective first and second lifting cams. The number of individual cam profiles provided on each lifting structure may dictate the number of lifting and dropping phases provided for a single 360 degrees of relative rotation between the lifting structures.

The inter-engaging profiles may comprise or be defined by a track and follower arrangement.

The inter-engaging profiles of the first and second lifting structures may be prevented from axial impact during or following the dropping phase. Such an arrangement may function to minimise wear and/or damage to the inter-engaging profiles. In one example one or both of the first and second lifting structures may comprise a no-go profile which functions to prevent axial impact of the inter-engaging profiles following the dropping phase. In some examples the first lifting structure may include a no-go profile, such as an annular lip, ring or the like, configured to interact with the second jarring assembly to prevent axial impact between the inter-engaging profiles of the first and second lifting structures.

The inter-engaging profiles may remain separated during a portion of relative rotation between the first and second lifting structures following the dropping phase. Such relative rotation without contact may define a transition phase between the dropping phase and a subsequent lifting phase. The inter-engaging profiles may be brought into contact during relative rotation to initiate a subsequent lifting phase.

The first lifting structure by being axially releasable relative to its associated jarring assembly may be defined as a shuttle lifting structure.

The lifting phase may be achieved during a first relative rotational displacement between the first and second lifting structures.

The dropping phase may be achieved substantially instantaneously upon completion of the lifting phase. Alternatively, the dropping phase may be achieved during a second relative rotational displacement between the first and second lifting structures.

The jarring apparatus may comprise a locking system for selectively axially fixing and releasing the first lifting structure relative to its associated jarring assembly. The locking system may be operated by relative rotational movement between the first and second jarring assemblies. Operating the first and second lifting structures and also the locking system by the relative rotation between the first and second jarring assemblies may facilitate simplified establishing of appropriate sequencing or timing of the lifting and dropping phases and the fixing and releasing of the first lifting structure. In this respect, a common datum of the relative positioning of the first and second jarring assemblies may be utilised. In some examples the locking system may be operable in response to relative axial displacement of the first and second lifting structures, wherein said relative axial displacement is provided in response to relative rotation between the lifting structures.

The locking system may comprise a mechanical locking system for mechanically locking and releasing the first lifting structure relative to its associated jarring assembly. The mechanical locking system may comprise a mechanical latch or the like.

The locking system may comprise a hydraulic locking system for hydraulically locking and releasing the first lifting structure relative to its associated jarring assembly. The hydraulic locking system may be interposed, for example radially interposed, between the first and second jarring assemblies.

One of the first and second jarring assemblies may comprise a mandrel, and the other of the first and second jarring assemblies may comprise a housing assembly. The mandrel may extend at least partially within the housing assembly. The mandrel may be composed of a unitary or multiple components. Similarly, the housing assembly may be composed of unitary or multiple components.

An aspect of the present disclosure relates to a jarring apparatus for use in the retrieval of a casing from a wellbore, the jarring apparatus comprising:

first and second jarring portions rotatable relative to each other to generate repeated jarring forces within the jarring apparatus; and

a casing spear operable to engage a casing within a wellbore.

The casing spear may function to anchor the jarring apparatus within the casing. The casing spear may function as a conduit to transmit the jarring forces into the casing.

The first and second jarring portions may be initially rotationally locked, and configured to be unlocked (and thus arranged in a jarring configuration) by applying an axial tension within the jarring apparatus.

The casing spear may be operated to engage a casing by applying an axial tension within the jarring apparatus. In the aspects and examples defined above reference is made to retrieval of casing from a wellbore. However, the subject matter being disclosed may also be applied in alternative applications, not necessarily associated with pulling casing. For examples, described methods and apparatus may be suitable for use in performing any other wellbore retrieval operation, such as in wellbore fishing operations.

As an example, an aspect of the present disclosure relates to a jarring apparatus comprising:

first and second jarring portions rotatable relative to each other to generate repeated jarring forces within the jarring apparatus; and

an anchor operable to engage a surrounding structure within a wellbore.

In one example the surrounding structure may comprise a pipe structure, such as casing, liner tubing, drill pipe, coiled tubing and/or the like.

The anchor may comprise a radially expandable anchor.

The anchor, when in engagement with a surrounding structure, may provide a reaction point for suitable operation of the jarring apparatus, for example to permit the jarring apparatus to be reconfigured between non-jarring and jarring configurations.

The anchor, when in engagement with a surrounding structure, may provide a transmission medium for use in transmitting jarring forces originating within the jarring apparatus into the surrounding structure.

An aspect of the present disclosure relates to a method for applying jarring within a wellbore, the method comprising:

running a jarring apparatus into a wellbore;

setting an anchor of the jarring apparatus against a surrounding structure;

establishing relative rotation between first and second jarring portions of the jarring apparatus to generate repeated jarring forces within the jarring apparatus.

The jarring forces may be transmitted into the surrounding structure via the anchor.

The method may be used in fishing operations in a wellbore. The method may be used in cementing operations within a wellbore, for example in assisting in a more complete placing of cement behind a tubular, such as a casing string.

It should be understood that the features defined in relation to one aspect may be applied in relation to any other aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1A is a diagrammatic illustration of a retrieval tool assembly, shown deployed in a wellbore in an initial configuration;

Figure 2A diagrammatically illustrates an example jarring tool apparatus which may be used in the tool assembly of Figure 1 , shown in a non-jarring configuration;

Figure 2B illustrates a cam assembly of the jarring tool of Figure 2A;

Figure 2C illustrates the jarring tool of Figure 2A in a jarring configuration;

Figures 1 B to 1 F diagrammatically illustrate a sequential operation of the retrieval tool assembly of Figure 1 A, during the removal of a section of casing from a wellbore;

Figure 3 illustrates an optional additional step within the sequence of Figures 1A to 1 F;

Figure 4A provides a flow chart setting out an example sequence of operations in using the tool assembly of Figure 1 in cutting and freeing a section of casing from a wellbore;

Figure 4B provides a flow chart setting out an example retrieval process of a casing which has been previously cut within a wellbore; Figure 5A diagrammatically illustrates a casing spear apparatus which may be used in combination with a jarring apparatus for gripping a section of casing, wherein the casing spear apparatus is illustrated in a retracted configuration;

Figure 5B diagrammatically illustrates the casing spear apparatus of Figure 5A in an extended configuration;

Figures 6A and 6B illustrate a further example jarring apparatus which may be used in the tool assembly of Figure 1 , shown in non-jarring and jarring configurations, respectively;

Figure 7 A is a cross-sectional view of a further example jarring apparatus;

Figure 7B is an enlarged split view of the portion of the apparatus of Figure 7A contained within the broken outline;

Figure 8 is an exploded view of a rotary connection between a jarring mass of the apparatus of Figure 7 A and an outer housing;

Figures 9 and 10 illustrate separate lifting structures of a lifting assembly of the apparatus of Figure 7A;

Figures 11A to 11 D illustrate a rotary sequence of cooperation between the separate lifting structures of the lifting assembly;

Figure 12 is an exploded view of a rotary valve of the jarring apparatus of Figure 7A;

Figures 13A to 13D are sectional views through line 13-13 of Figure 7B, and illustrate sequential stages of operation of the rotary valve;

Figures 14A to 14B illustrate a releasable axial connection of the apparatus of Figure 7A, shown in different configurations;

Figures 15A to 21 C illustrate the jarring apparatus of Figure 7 A in sequential stages of operation; and Figures 22 and 23 provide diagrammatic illustrations of alternative examples of a jarring apparatus.

DETAILED DESCRIPTION FO THE DRAWINGS

Figure 1A provides a diagrammatic illustration of a tool string 1100 shown in an initial Run-in-Hole (RIH) configuration, deployed on a running string 1101 into a section of casing 1102 which is located within a wellbore 1104. A casing annulus 1106 defined between the casing 1102 and the wellbore 1104 may be filled with cement and/or debris which binds the casing 1102 to the wellbore 1104. In the present example the tool string 1100 is configured for use in retrieving a portion of the casing 1102 from the wellbore 1104, for example as part of an abandonment operation, slot recovery operation and the like.

The tool string 1100 comprises a casing cutter tool 1108, a casing anchor 1110 and a jarring apparatus 1112. The tool string 1100 further includes a packer 1114 and a flow diverter 1116 that includes an inlet 1118 and outlet 1120, and a filter mechanism in the form of a junk catcher 1122. The tool string 1100 also includes a clutch mechanism 1124 which is configured to operatively engage the casing anchor 1110. When in the illustrated RIH configuration the casing cutter 1108, casing anchor 1110 and packer 1114 are retracted. Further, the jarring apparatus 1112 is in a non-jarring configuration, and the clutch 1124 is disengaged from the casing anchor 1110. Further, the inlet 1118 and outlet 1120 of the flow diverter 1116 are closed. However, in other examples the inlet 1118 and outlet 1120 are initially opened.

The running string 1101 is a tubular structure capable of delivering fluid to the tool string 1100 from surface. The running string 1101 in the present example is also capable of providing a pulling force on the tool string 1100 to apply a tension therein, and also to provide a rotary drive to the tool string 1100 for operation of both the casing cutter 1108 and the jarring apparatus 1112. The running string 1101 may thus also be defined as a work string. The running string 1101 may be provided by drill pipe, coiled tubing or the like.

In the present example the jarring apparatus 1112 is configured to generate repeated jarring forces in response to a rotational drive input, in this case provided by the running string 1101. Multiple different forms of jarring apparatus may be provided, with some examples provided herein. Further, which such rotary driven jarring is exemplified, non-rotary jarring apparatus may alternatively be used while still achieving the significant benefits of the present disclosure.

An example jarring apparatus 1112 is diagrammatically illustrated in Figure 2A in which the jarring apparatus 1112 is initially configured in an initial non-jarring configuration. The jarring apparatus 1112 comprises a first jarring portion in the form of a mandrel 1202, and a second jarring portion in the form of an outer housing assembly 1204. The mandrel 1202 is rotatably secured to the running string 1101 and may extend below the jarring apparatus 1112 to engage other elements of the tool string 1100, such as the clutch mechanism 1124 and the flow diverter 1116. The outer housing assembly 1204 is coupled to other elements of the tool string, such as the casing anchor 1110. In some examples the outer housing 1204 of the jarring apparatus 1112 may provide a housing component of other elements of the tool string 1100, such as the casing anchor 1110.

The jarring apparatus 1112 further comprises a lifting mechanism 1206 which includes a first annular cam profile 1208 provided on or with the mandrel 1202 and a second annular cam profile 1210 provided on or with the housing 1204. As illustrated in Figure 2B, the annular cam profiles 1208, 1210 each include a plurality of circumferentially arranged ramped cam teeth. When in the non-jarring configuration of Figure 2A the first and second annular cam profiles 1208, 1210 are axially separated and disengaged and held in this separated position via a locking mechanism 1212 which axially and rotationally locks the mandrel 1202 and the housing 1204. Thus, when in this configuration torque applied by the running string 1101 (Figure 1A) may be transmitted through the jarring apparatus 1112.

The jarring apparatus 1112 may be reconfigured into a jarring configuration by applying an overpull via the running string 1101 , which thus pulls the mandrel 1202 axially relative to the housing 1204, which in use may be axially secured to the casing 1102 via the casing anchor 1110, described in more detail below. Upon reaching a threshold axial trigger force the locking mechanism 1212 will be released, as illustrated in Figure 2C, allowing the first and second cam profiles 1208, 1210 to be axially engaged. The housing 1204 may be held static or otherwise impeded in the wellbore 1104 (for example via the casing anchor 1110 and clutch mechanism 1124) and tension is applied within the mandrel 1202 via the connected running string 1101 which generates an axial load between the cam profiles 1208, 1210. The mandrel 1202 may then be rotated relative to the housing 1204, thus causing the ramped cam teeth of the first and second cam profiles 1208, 1210 to slide over each other in a cyclical axial lifting and dropping motion, with each drop causing the profiles 1208, 1210 to rapidly impact against each other and generate a jarring force. The jarring force is proportional to the tension applied in the running string 1101 , and a jarring frequency may be provided which is a function of the rotational speed and the number of cam teeth present.

A sequence of operation of the tool string 1100 for use in removing a portion of the casing 1102 will now be described with reference to Figures 1 B to 1 F. Referring initially to Figure 1 B, the tool string 1100 is run into the wellbore 1104 until located at the required depth. Although not shown in Figure 1 B, a plug may be set below the tool string 1102, thus isolating the lower regions of the casing 1102. The plug may be set via a plug setting tool on the tool string 1100, or alternatively may have been set prior to running the tool string 1100.

Fluid is then pumped from surface through the running string 1101 and the tool string 1100, and into the tool annulus 1223 between the tool string 1100 and the casing 1102, as indicated by arrows 1220, for return to surface. Fluid passes through an internal restriction 1222 which generates a back pressure within the tool string 1100 which causes the casing cutter 1108 to be radially expanded into engagement with the casing 1102. The elevated internal fluid pressure also provides an initial or pre-set of the casing anchor 1110, for example by driving a cone 1224 under anchor slips 1226 which become radially extended to engage the casing 1102.

In the subsequent step, illustrated in Figure 1C, an axial tension is applied through the tool string 1100 by pulling via the running string 1101 in the direction of arrow 16, with the pre-set casing anchor 1110 providing a reaction anchor point. This axial tension further sets the casing anchor 1110 by increasing the gripping force between the anchor slips 1226 and the casing 1102. This axial tension also causes the packer 1114 to become set, providing a seal within the tool annulus 1223 above the cutter 1108. Further, the axial tension also opens the inlet 1118 and outlet 1120 of the flow diverter 1116, thus providing a flow path past the set packer 1114. In the present example the axial tension applied at this stage may not be sufficient to reconfigure the jarring apparatus 1112 into its jarring configuration. In one example the axial tension at this stage may be applied by an overpull in the running string 1101 in the region of 89kN (20klbf).

Subsequent to this, as illustrated in Figure 1 D, the running string 1101 is rotated in the direction of arrow 1230 to rotatably drive the extended cutter 1108 to initiate cutting of the casing 1102 to form a first cut region 1231. At the same time fluid is circulated down through the tool string 1100 and into the tool annulus 1223 to function to cool and lubricate the casing cutter 1108. Returns are diverted past the set packer 1114 via the flow diverter 1116, as illustrated by arrows 1232, with debris produced by the cutting action retained in the junk catcher 1122. The returns may then re-enter the tool annulus 1223 above the packer 1114 and flowed to surface. When the casing 1102 is fully cut this may produce an upper casing portion 1102a and a lower casing portion 1102b. Further, at the point the casing 1102 is divided a change in a parameter of the fluid returns at surface may be identified (such as flow rate, pressure etc.), which might reflect a proportion of the fluid flow diverting behind the casing 1102 provide a suitable tell-tale that cutting has been achieved.

It should be noted that in the present example both the set casing anchor 1110 and the packer 1114 permit the tool string 1100 to be rotated despite their engagement with the casing 1102. This may be permitted via a swivel interface or the like. The casing anchor 1110 and/or the packer 1114 may provide a centralising function to assist in maintaining the cutter 1108 in a centralised position within the casing 1102, thus assisting in providing a more efficient cutting action.

In a subsequent step, as illustrated in Figure 1 E, rotation and fluid flow may be temporarily ceased and an overpull again applied via the running tool 1102, in this case with a greater force than previously applied, to release the locking mechanism 1212 (Figure 2A) of the jarring apparatus 1112. This causes the jarring apparatus 1112 to be configured into its jarring configuration, which is illustrated in Figure 2C. In one example the axial overpull may be in excess of 222kN (50klbf).

This overpull also closes the inlet 1118 and outlet 1120 of the flow diverter 1116, thus preventing, in combination with the packer 1114, any return flow along the tool annulus 1223. Further, the applied overpull also engages the clutch 1124 such that the outer housing portion 1204 (Figure 2A) of the jarring apparatus 1112 becomes rotatably fixed relative to the casing anchor 1110 and thus the upper casing portion 1102a.

With the overpull maintained the running string 1102 is again rotated, as illustrated by arrow 1230, thus generating repeated jarring forces within the jarring apparatus 1112 which are delivered into the upper casing portion 1102a. Simultaneously, fluid is delivered through the tool string 1100 and into the casing annulus 1106 via the first cut region 1231 , as illustrated by arrows 1234. This fluid may thus provide a hydraulic force on the upper casing portion 1102a and the tool string 1100 (facilitated by the packer 1114) which may provide a piston effect and contribute to the axial force seeking to dislodge the upper casing portion 1102a upwardly from the wellbore 1104. Thus, the axial overpull applied via the running string 1102, the jarring forces from the jarring apparatus 1112 and the hydraulic piston effect may work together to assist in freeing the upper casing portion from the wellbore.

The fluid within the casing annulus 1106 may eventually return to surface, assisting to dislodge and/or flush cement, debris etc. from the casing annulus 1106 and assist to free the upper casing portion 1102a. Furthermore, returning fluid at surface from the casing annulus 1106 may provide a good indication that the upper casing portion 1102a might be sufficiently released from the wellbore 1104 to permit retrieval.

The overpull applied via the running string 1101 may be varied (for example up to and beyond 4.45MN (1 Mlbf)), which may thus have an influence on the magnitude of the individual jarring forces generated. Furthermore, the rotational speed of the running string 1101 may be varied (for example from less than 1 RPM to more than 200 RPM) to vary the jarring frequency.

When the upper casing portion 1102a is sufficiently free this may be retrieved to surface, as illustrated in Figure 1 F, which illustrates the lower casing portion 1102b left within the wellbore 1104. In the example of Figure 1 F a barrier 1236 is shown within the lower casing portion 1102b, which barrier 1236 may have been set before or after retrieval of the upper casing portion 1102a. Further operations may then be performed, such as retrieving further lengths of casing, setting permanent barriers in the wellbore 1104, drilling a side-track bore from the now uncased wellbore section, etc. In some operations the upper casing portion 1102a may not be readily freed and pulled from the wellbore 1104, despite initially performing the disclosed highly effective cut and pull method. In this eventuality further steps may be performed during the single trip. For example, as illustrated in Figure 3 the tool string 1100 may be entirely unset and returned to its initial configuration of Figure 1A. The tool string 1100 may then be moved to a shallower position in the wellbore 1104. At this point different options may be available. For example the jarring apparatus 1112 may be further operated to vibrate the upper casing portion 1102a at the shallower location. Indeed, the tool string 1100 may be progressively moved to shallower positions in the wellbore 1104 to apply jarring at each shallower location, which may result in freeing of the upper casing portion 1102a. However, in some circumstances an operator may consider it appropriate to reposition the tool string 110 at a shallower location, and repeat the various method steps described above to form a second cut region 1238 above the first cut region 1231 , thus effectively seeking to retrieve a shorter length of casing in one pull.

Figures 4A and 4B provide flow charts of an example method for retrieving casing from a wellbore in accordance with the present disclosure. Referring initially to Figure 4A, a tool string (such as tool string 1100 described above) is run to the required depth in a wellbore, as in step 1240. Anchor slips, a packer and a casing cutter are extended in step 1242. The tool string is rotated in step 1244 to cut the casing and subsequent to this in step 1246 a jarring tool within the tool string is triggered to be configured into a jarring configuration. Flow is then delivered through the tool string, as in step 1248, and an axial pulling force and rotation is applied to the tool string to axially pull against the casing and to operate the jarring tool to generate jarring force and apply vibration to the casing, as in step 1250.

A determination is then made in step 1252 as to whether the cut casing is sufficiently free, and if the determination is positive a pull-out-of-hole (POOH) procedure is initiated, as in step 1254 and as will be descried with reference to Figure 4B. If the determination at step 1252 is negative step 1256 is performed in which the jarring tool is disengaged and the slips, packer and cutter are retracted, with the tool string moved to a shallower location within the wellbore, as in step 1258. Following this, as in step 1260, the slips are again set and the jarring tool is triggered, with rotary jarring and axial pulling applied in step 1262.

A further determination is then made in step 1264 as to whether the cut casing is now sufficiently free, and if the determination is positive the pull-out-of-hole (POOH) procedure of step 1254 is performed. However, if the determination in step 1264 is negative step 1266 is performed in which the jarring tool is disengaged and the cutter is extended, with the procedure then returning to step 1244 to provide a further cut to the casing at the shallower location.

In some examples, however, multiple cycles of moving the tool string and jarring at progressively shallower depths may be initiated before any further casing cuts are made.

Reference is now made to Figure 4B which exemplifies the POOH procedure in step 1254. In this respect the tool string may be disengaged and pulled to the top region of the casing, as in step 1268. The slips may then be extended to engage this top end of the casing, as in step 1270, with the casing then pulled with optional jarring applied, as in step 1272. In step 1274 the top of the casing may be suspended from rig equipment, such as slips within a rotary table, with the tool string then retrieved in step 1276. The casing may then be pulled and broken out using conventional rig equipment, as in step 1278.

In the examples presented above the tool string comprises a casing anchor. In other examples a secondary casing anchor may be used to provide further assured operation of at least the jarring apparatus. Such an example secondary casing anchor 1280 is illustrated in Figures 5A and 5B, wherein the secondary casing anchor 1280 is shown in a retracted configuration in Figure 5A, and in an extended configuration in Figure 5B. The secondary casing anchor 1280 may be defined as a casing spear.

In the present example the casing spear 1280 is located within the tool string 1100 such that the jarring apparatus 112 is located on one axial side of the casing spear 1280, and the casing anchor 1110, packer 1114 and cutter 1108 are located on an opposite axial side of the casing spear 1280. In the present example the casing spear 1280 provides a rotary coupling between the tool string components on opposite axial sides thereof.

The casing spear 1280 includes a housing 1282 and a plurality of anchor slips 1284 which are extendable form the housing 1282. The casing spear 1280 further includes an actuator which includes an activator cone 1286 mounted on a spear mandrel 1288 which is secured to the jarring apparatus 1112, specifically to the outer housing 1204 (See Figure 2A) of the jarring apparatus 1112. The casing spear 1280 further comprises a power spring 1290 (e.g., a Belleville spring stack) which biases the spear mandrel 1288 and activator cone 1286 towards the position illustrated in Figure 5A. This power spring 1290 also carries the weight of the casing spear housing 1282 and slips 1284, and all the lower components of the tool string 1100, including the casing anchor 1110, packer 1114 and the casing cutter 1108.

When an operator wishes to activate the casing spear 1280 an upward pulling force will be applied, for example via a connected running string, with the pulling force reacted off the casing anchor 1110 when set. When the pulling force is sufficient to compress the power spring 1290 the spear mandrel 1288 may drive the cone 1286 under the slips 1284 causing these to be radially extended, as illustrate in Figure 5B. Thus, the casing spear 1280 may function to anchor the tool string 1100 to a surrounding casing. In this example the set casing spear 1290 may provide a suitable reaction point to permit a larger overpull to be applied and trigger the jarring apparatus 1112.

In the example described above the power spring 1290 may be selected to provide a desired resistance to movement of the casing spear mandrel 1288, which may thus set a trigger or threshold activation force. The rating of the power spring 1290 in this regard may also take into account the weight suspended therefrom.

In the example described above the pulling force to activate the casing spear 1280 is reacted off the casing anchor 1110. However, in other examples the casing spear may be initially pre-set to provide an initial gripping of a surrounding casing, before the setting overpull is applied. In this respect the initial pre-set may be achieved by a hydraulic actuator, for example. In some examples, the casing spear 1280 may be provided to facilitate the application of a jarring apparatus to an existing cut-and-pull tool, which may include features such as the casing anchor 1110, cutter 1108, packer 1114 and the like, without any jarring apparatus. In this respect the casing spear 1280 may facilitate connection of the jarring apparatus 1112 to the existing cut-and-pull tool. The provision of the casing spear may provide assurances that a sufficient or suitable casing anchor may be achieved, without relying on or over stressing the casing anchor 1110 on the existing cut-and-pull tool.

In the example of Figures 5A and 5B a jarring apparatus 1112 is provided in combination with an anchor 1280 which in the present example is defined as a casing spear by virtue of the exemplified use in pulling casing. However, the present disclose extends to the provision of a jarring apparatus 1112 in combination with an anchor 1280 which may be suitable for use in engaging any surrounding structure, such as any tubular or other apparatus, open rock face and/or the like.

An alternative example of a jarring apparatus, in this case identified by reference numeral 10, is diagrammatically illustrated in cross-section in Figure 3A. The jarring apparatus 10, which is only partially shown in Figure 3A, is illustrated in a non-jarring configuration.

The jarring apparatus 10 comprises a first jarring portion or assembly in the form of a mandrel 12, and a second jarring portion or assembly in the form of an outer housing assembly 14. The jarring apparatus 10 is configured such that relative rotation established between the mandrel 12 and outer housing assembly 14 causes reciprocating motion of a jarring mass 24 to generate repeated linear jarring forces. In this regard, as jarring is achieved through relative rotation, the apparatus 10 may be defined as a rotary jarring apparatus. In use, the mandrel 12 may be rotated by the running string 1101 (Figure 1A).

In the present example, the jarring apparatus 10 is arranged to provide axial jarring forces in the direction of arrow 16, which may be defined as an uphole direction. In use, an axial pulling force may be applied to the mandrel 12 via the running string 1101 in the direction of arrow 16 during the jarring operation, and a load/resistance applied to the housing in the direction of arrow 17, such as from engagement of the casing anchor 1110 with the casing (Figure 1A). Such loading through the apparatus 10 may contribute to the generation of a jarring force. However, in the present example the jarring apparatus 10 incorporates features to provide a degree of protection from excessive loading or overloading.

The mandrel 12 includes a tubular structure which extends into the outer housing assembly 14. A first or upper end of the mandrel 12 may include a suitable connector (not shown) for facilitating connection with the running string 1101. The mandrel 12 may be provided as a unitary component, or may be composed of multiple connected components. Similarly, the housing assembly 14 may be provided as a unitary component, or may be composed of multiple connected components.

The apparatus 10 further comprises a thrust assembly 18 interposed between the mandrel 12 and housing 14. In the illustrated example the thrust assembly 18 includes a first thrust shoulder 20 provided on the mandrel 12, and a second thrust shoulder 22 provided on the housing 14. In the configuration shown in Figure 3A the first and second thrust shoulders 20, 22 are axially separated and thus disengaged. However, as will be described in more detail below, relative axial movement between the mandrel 12 and housing 14 (in the relative direction of arrows 16, 17) will eventually bring the first and second thrust shoulders 20, 22 into engagement, such that axial loading (in the relative direction of arrows 16, 17) may be transmitted between the mandrel and 12 and housing 14 via the thrust assembly 18, thus diverting such loading from other components within the apparatus 10. In this respect the thrust assembly may function or define a load limiter. The thrust assembly 18 permits rotation between the first and second thrust shoulders 20, 22 when engaged, such that the thrust assembly 18 may function as a thrust bearing.

The jarring mass 24 is radially positioned between the mandrel 12 and housing 14, and is axially moveable in reverse directions (directions 16, 17) relative to both the mandrel 12 and housing 14. The jarring mass 24 is rotatably fixed relative to the mandrel 12 via a rotary connection 26, such as a keyed or splined connection. However, in other examples the jarring mass may alternatively be rotatably fixed relative to the housing 14. The jarring mass 24 includes a first impact surface 28, and the housing 14 includes a second impact surface 30, wherein, in use, reciprocating axial movement of the jarring mass 24 causes the first and second impact surfaces 28, 30 to axially impact together, thus generating repeated axial jarring forces within the apparatus 10. In an alternative example the mandrel 12 may comprise an axial impact surface, alternative or in addition to the impact surface provided on the housing 14. As the jarring mass 24 is responsible for generating impact within the apparatus 10, the jarring mass may thus also be defined as a hammer.

A force mechanism 32 in the form of a power spring (e.g., a Belleville spring stack) is provided within the apparatus 10, and is configured, in use, to bias the jarring mass 24 to move axially in the direction of arrow 16, and thus to bias the first and second impact surfaces 28, 30 into engagement. As will be described in more detail below, relative movement between the mandrel 12 and housing 14 in the direction of arrows 16, 17, will cause the spring 32 to be engaged and compressed by an annular shoulder 34 on the mandrel 12. In this respect, the force generated by the spring 32 against the jarring mass 24 is a function of the compression or displacement of the spring 32. In some examples the spring 32 may be uncompressed until engaged by the mandrel. However, in other examples the spring may carry a degree of pre-compression.

The jarring apparatus 10 further includes a lifting assembly 36 which is operable by relative rotation between the mandrel 12 and housing 14 to cyclically lift the jarring mass 24 in the direction of arrow 17 against the bias of the spring 32, and release the lifted jarring mass 24 to permit the jarring mass to be driven by the spring 32 in the direction of arrow 16, causing the impact surfaces 28, 30 to rapidly engage to establish a jarring force. Any suitable form of lifting assembly 36 may be provided to function to cyclically lift and release the jarring mass 24 in the manner described.

In the present example the lifting assembly 36 includes a first lifting structure 38 rotatably and axially fixed relative to the housing 14, and a second lifting structure 40 rotatably fixed, but axially moveable, relative to the mandrel 12. In the present example the second lifting structure 40 is integrally formed with the jarring mass 24, and is thus rotatably connected to the mandrel 12 via rotatable connection 26. In other examples the second lifting structure 40 may be separately formed and rotatably coupled to the jarring mass 26. In further examples the second lifting structure 40 may be separately rotatably coupled to the mandrel 12. In such examples the jarring mass 24 may not necessarily be rotatably coupled to the mandrel 12.

The lifting structures 38, 40 include cooperating cam structures that cooperate during relative rotation therebetween to cause the second lifting structure 40 to be axially moved in cyclical lifting and dropping phases, thus effecting axial reciprocating movement of the jarring mass 24. The cam structures may be provided as in the example of Figure 2, or may be provided in accordance with later described examples.

Loading may be applied between the first and second lifting structures 38, 40 which is a function of the biasing force provided by the spring 32. In this respect such loading may be controlled by appropriate selection of the spring 32, by the extent of compression of the spring 32 caused by relative movement between the mandrel 12 and housing 14, and by virtue of the load limiting effect of the thrust assembly 18, which will be described in more detail below. This may assist to increase the longevity of the first and second lifting structures, and thus of the lifting assembly.

The jarring apparatus 10 further includes a releasable rotary connection 42 between the mandrel 12 and housing 14. In the present example the releasable rotary connection 42 includes a splined connection. When the apparatus 10 is configured as shown in Figure 3A, the releasable rotary connection 42 is engaged, and the mandrel 12 and housing 14 are rotatably coupled. Such a configuration may thus prevent any jarring to occur, to the extent that this configuration may be defined as a non-jarring configuration. Further, the rotary connection may allow torque to be transmitted between the mandrel 12 and housing 14.

When jarring is to be performed, the mandrel 12 is axially moved by a pull force applied in the direction of arrow 16 by the connected running string 1101 (Figure 1A) to disengage the rotary connection 42, as illustrated in Figure 3B, thus permitting relative rotational movement to be achieved to operate the lifting assembly 36 and lift/drop the jarring mass 24 to generate jarring. Such axial movement, in addition to releasing the rotary connection 42, causes the annular shoulder 34 of the mandrel 12 to pick up and energise the spring 32, thus establishing the bias force acting against the jarring mass 24 in the direction of arrow 16. Although not shown, the apparatus 10 may further comprise a releasable axial connection between the mandrel 12 and housing 14 which first needs to be disengaged to allow the relative axial movement. Such a releasable axial connection may be releasable upon application of a threshold release force applied between the mandrel 12 and housing 14.

In the configuration of Figure 3B the mandrel 12 has been moved until the thrust assembly 18 is engaged, such that further axial loading applied between the mandrel 12 and housing (e.g., by increasing an overpull on the mandrel 12 from the running string 1101) will be transmitted via the thrust assembly 18 and thus diverted from the spring 32 and the lifting assembly 36. In this configuration the spring 32 may be considered to provide its maximum bias force, subject to any minor variation caused by the cyclical lifting of the jarring mass 24 by the lifting assembly 36, which will be described further below.

While Figure 3B illustrates the thrust assembly 18 fully engaged, it should be understood that jarring may be effected at any stage following release of the rotary connection 42 and energising of the spring 32. In this respect, the extent of axial loading applied between the mandrel 12 and housing 14, prior to engagement of the thrust assembly 18, will dictate the level of bias force developed by the spring 32 and thus the level of jarring forces created within the apparatus 10. In this respect, a user may control the jarring force output by controlling the overpull on the mandrel 12, up until the load limit has been reached via engagement of the thrust assembly 18. This can provide a significant degree of operational flexibility within the apparatus 10, while minimising risk of overloading.

Another example of a jarring apparatus, in this case represented by reference numeral 100, is illustrated in Figure 7 A in cross-section, which is similar in many respects to apparatus 10 first shown in Figure 3A.

The apparatus 100 comprises a first jarring assembly in the form of a mandrel 102, and a second jarring assembly in the form of a housing assembly 104. The mandrel 102 and housing assembly 104 in the present example are each composed of multiple connected components. As in the previous example, the apparatus 100 is configured such that relative rotation established between the mandrel 102 and housing 104 causes repeated jarring forces to be generated, and as such the apparatus 100 may also be defined as a rotary jarring apparatus. In use, the mandrel may be rotated by the running string 1101 (Figure 1A), applying the generated jarring forces to the casing 1102.

In the present example the jarring apparatus 100 is arranged to provide axial jarring forces in the direction of arrow 16, which may be defined as an uphole direction. As such, the jarring may be defined as upjarring. An axial pulling force may be applied to the mandrel 102 in the direction of arrow 16 during the jarring operation. As in the previously described example, such loading through the apparatus 100 may contribute to the generation of a jarring force, and the jarring apparatus 100 incorporates features to provide a degree of protection from excessive loading or overloading.

The mandrel 102 includes a tubular structure which extends into the outer housing assembly 104. A first or upper end of the mandrel 102 includes a suitable connector 106 for facilitating connection with the running string 1101. A releasable rotary connection 107 is provided between the mandrel 102 and housing 104. In the present example the releasable rotary connection 107 includes a splined connection, and when the apparatus 100 is configured as shown in Figure 7A, the releasable rotary connection 107 is engaged, and the mandrel 102 and housing 104 are rotatably coupled. Such a configuration may thus prevent any jarring to occur, to the extent that this configuration may be defined as a non-jarring configuration. Further, the rotary connection may allow torque to be transmitted between the mandrel 102 and housing 104. When jarring is required, axial movement between the mandrel 102 and housing 104 in the relative direction of arrows 16, 17 will cause the rotary connection 107 to be disengaged.

To aid the current description an enlarged split view of the jarring apparatus 100 in region 7B of Figure 7A is illustrated in Figure 7B, reference to which is now made.

As in the previously described example, the apparatus 100 includes a thrust assembly (or thrust bearing) 108 interposed between the mandrel 102 and housing 104. In the illustrated example the thrust assembly 108 includes a first thrust shoulder 110 provided on the mandrel 102, and a second thrust shoulder 112 provided on the housing 104. The first thrust shoulder 110 is provided on a coupling 111 which provides a connection between separate mandrel components. As will be described in further detail below, the coupling 111 also includes an impact surface 214 which is configured to impact against a matching impact surface 216 on the housing 104 to provide a secondary linear impact function within the apparatus 100.

In the configuration shown in Figure 7B the first and second thrust shoulders 110, 112 are axially separated and thus disengaged. However, as will be described in more detail below, relative axial movement between the mandrel 102 and housing 104 (in the relative direction of arrows 16, 17) will eventually bring the first and second thrust shoulders 110, 112 into engagement, such that axial loading (in the relative direction of arrows 16, 17) may be transmitted between the mandrel 102 and housing 104 via the thrust assembly 108, thus diverting such loading from other components within the apparatus 100. In this respect the thrust assembly may function as or define a load limiter.

The apparatus 100 further comprises a jarring mass 114 radially positioned between the mandrel 102 and housing 104, and being axially moveable in reverse directions (directions 16, 17) relative to both the mandrel 12 and housing 14. The jarring mass 114 may be of any required length, for example in accordance with a desired weight to be provided, and in the present example the apparatus 100 is illustrated axially split over the length of the jarring mass 114 to reflect the non-specific length requirement of the mass 114.

The jarring mass 114 includes a first impact surface 116 (provided on an impact insert), and the housing 104 includes a second impact surface 118 (also provided on an impact insert), wherein, in use, reciprocating axial movement of the jarring mass 114 causes the first and second impact surfaces 116, 118 to axially impact together, thus generating repeated axial jarring forces within the apparatus 100. In an alternative example the mandrel 102 may comprise an axial impact surface, alternative to or in addition to the impact surface provided on the housing 104. As the jarring mass 114 is responsible for generating the impact within the apparatus 100, the jarring mass may thus also be defined as a hammer.

A force mechanism in the form of a power spring 120 (e.g., a Bellville spring stack) is provided within the apparatus 100, and is configured, in use, to bias the jarring mass 114 to move axially in the direction of arrow 16, and thus to bias the first and second impact surfaces 116, 118 into engagement. A mass pusher sleeve 122 extends between the spring 120 and the jarring mass 114, such that the spring 120 may act indirectly on the jarring mass 114, and vice versa. In the present example the mass pusher sleeve 122 extends past a coupling 124 of the housing 104, and as also shown in the exploded view of Figure 8, the mass pusher sleeve 122 is rotatably connected to the coupling 124 via a first castellated connection 126, and also to the hammer via a second castellated coupling 128.

The mandrel 102 carries a spring pick-up ring 130 which defines an annular shoulder 132. In the initial configuration of Figure 7B the mandrel 102 is positioned within the housing 104 such that the annular shoulder 132 is separated from the spring 120. As will be described in more detail below, relative movement between the mandrel 102 and housing 104 in the direction of arrows 16, 17, will cause the annular shoulder 132 to engage and compress the spring 120. In the present example a thrust bearing 134 is interposed between the spring 120 and spring pick-up ring 130, which transmits axial loading while accommodating relative rotation between the spring 120 and the spring pick-up ring 130. The force generated by the spring 120 against the jarring mass 114 (via the pusher sleeve 122) is thus a function of the compression or displacement of the spring 120 caused by movement of the mandrel 102 in the direction of arrow 16. In some examples the spring 120 may be uncompressed until engaged by the mandrel. However, in other examples the spring may carry a degree of pre-compression.

The spring pick-up ring 130 may be adjustably mounted on the mandrel 102, which may allow a user to set the spring pick-up point within the apparatus 100. Furthermore, in some examples the spring pick-up ring 130 may be releasably secured to the mandrel 102, for example via a shear pin connection. Such a releasable connection may permit the spring pick-up ring 130 to be released upon exposure to an over-load condition within the apparatus, thus providing a degree of load protection.

The apparatus 100 further comprises a lifting assembly or mechanism 136 which includes a first lifting cam structure 138 rotatably fixed to the outer housing 104 (in a manner described later), and a second lifting cam structure 140 rotatably fixed relative to the mandrel 102 via keys 142. The keys 142 are engaged within axial key-ways 144 within the mandrel 102 such that relative axial movement is permitted between the second lifting cam structure 140 and the mandrel 102. A cam pusher sleeve 146 extends axially between the second lifting cam structure 140 and the jarring mass 114. As will be described in detail below, relative rotation between the mandrel 102 and housing 104 causes the first and second lifting cam structures 138, 140 to cooperate to cause cyclical lifting and dropping of the second lifting cam structure 140, thus facilitating lifting and dropping of the jarring mass 114 to generate impact between the impact surfaces 116, 118.

Reference is additionally made to Figure 9 which is a perspective view of the first lifting cam structure 138, and Figure 10 which is a perspective view of the second lifting cam structure 140. The first lifting cam 138 includes a first rotary cam profile 148 which in the present example includes two circumferentially distributed cam lobes 150 each having a gradual ramp or rising portion 152, and a drop-off or falling portion 154, with a base portion 156 circumferentially positioned between each cam lobe 150. The second lifting cam 140 includes a complimentary second rotary cam profile 158, and thus includes two circumferentially distributed cam lobes 160 each having a gradual ramp or rising portion 162, and a drop-off or falling portion 164, with a base portion 166 circumferentially positioned between each cam lobe 160.

The complementary rotary cam profiles 148, 158 inter-engage and cooperate upon relative rotation therebetween to cyclically cause the cam structures 138, 140 to be displaced in one axial direction in a lifting phase, and to be displaced in a reverse axial direction in a dropping phase, as illustrated in Figures 11A to 11 D. In this respect, Figure 11A illustrates initial engagement of the respective ramp portions 152, 162 at the start of a lifting phase, with relative rotation therebetween permitting the cooperating ramp portions 152, 162 to circumferentially slide relative to each other and axially drive the cam structures 138, 140 apart towards a peak separation, as shown in Figure 11 B. As the cam structures 138, 140 progress towards the illustrated peak position in Figure 11 B the area of contact therebetween reduces, thus causing the stresses induced in the cam structures 138, 140 to increase. As will be described herein, the jarring apparatus 100 provides measures to minimise such stresses within the cam structures 138, 140 thus prolonging their operational life span.

Following completion of this lifting phase the drop-off portions 154, 164 become aligned, allowing the cam structures 138, 140 to “drop” and cause reverse axial displacement in a dropping phase, as illustrated in Figure 11C. The cam structures 138, 140 are arranged within the jarring apparatus 100 such that at this dropping phase the first and second cam profiles 148, 158 are prevented from axial engagement or impact therebetween. That is, immediately following the dropping phase an axial separation gap 168 is provided between the first and second cam profiles 148, 158. This is achieved, at least in part, in the present example by the provision of a no-go profile in the form of an annular lip 170 provided on the first cam structure 138 which engages a corresponding axial shoulder 172 on the housing 104 (see Figure 7B). Alternatively, or additionally, a no-go profile may be provided on the second cam structure 140 to provide this function.

Following this dropping phase the cam lobes 150, 160 become aligned with the opposing base portions 156, 166, as illustrated in Figure 11 D, without contact therebetween, as noted above (i.e., the axial separation gap 168 is maintained). Further relative rotation may provide a transition from the completed dropping phase to initiation of a subsequent lifting phase, with the cycle of Figures 11A to 11 D being repeated, causing cyclically lifting and dropping of the cam structures 138, 140. In the present example, with each cam structure 138, 140 comprising two cam lobes 150, 160, the cams structures 138, 140 will undergo two cycles of lifting and dropping for each full 360 degrees of relative rotation therebetween. The provision of more or less cam lobes 150, 160 on each cam 138, 140 may facilitate more or less cycles for each full 360 degrees of relative rotation.

Loading may be applied between the first and second cam structures 138, 140 which is a function of the biasing force provided by the spring 120. In this respect such loading may be controlled by appropriate selection of the spring 120, by the extent of compression of the spring 120 caused by relative movement between the mandrel 102 and housing 104, and by virtue of the load limiting effect of the thrust assembly 108, which will be described in more detail below. This may assist to increase the longevity of the first and second cam structures 138, 140, and thus of the lifting assembly 136.

Referring again to Figure 7B, the first cam structure 138 is positioned radially between the mandrel 102 and the housing 104, and is sealed relative to the mandrel 102 via inner seals 174, and sealed relative to the housing 104 via outer seals 176. The first cam structure 138 is rotatably fixed relative to the housing 104, specifically to a coupling portion 180 of the housing 104, which will be described in more detail below. A spring 182 biases the first cam structure 138 towards the second cam structure 140.

The first cam structure 138 is configured to be selectively axially fixed and released relative to the housing 104 via a hydraulic locking system. The hydraulic locking system functions to fix the first cam structure 138 relative to the housing 104 during the lifting phase between the first and second cam structures 138, 140, which thus permits the cooperation of the first and second cam profiles 148, 158 to cause the jarring mass 114 to be lifted in the direction of arrow 17 by the second cam structure 140, against the bias of the spring 120, and thus axially separate the first and second impact surfaces 116, 118. The hydraulic locking system also functions to release the first cam structure 138 relative to the housing 104 prior to completion of the lifting phase between the cam structures 138, 140, with such axial release permitting the spring 120 to drive the jarring mass 114 in the direction of arrow 16 and cause the impact surfaces 116, 118 to be rapidly impacted together, to generate a jarring force.

In the present example, the hydraulic locking system 186 includes a hydraulic chamber 184 which is defined radially between the mandrel 102 and housing 104, and axially between the first cam structure 138 and the coupling portion 180. A valve assembly 186 is provided between the hydraulic chamber 184 and a flow path 188 extending through the mandrel 104, wherein the valve assembly 186 is configurable between open and closed positions by relative rotation between the mandrel 102 and housing 104. When the valve assembly 186 is in its closed position fluid communication between the hydraulic chamber 184 and flow path 188 is prevented, thus hydraulically locking the hydraulic fluid in the hydraulic chamber 184, effectively axially fixing the first cam structure 138 relative to the housing 104. When the valve assembly 186 is in its open position fluid communication between the hydraulic chamber 184 and flow path 188 is permitted, allowing fluid to be displaced from the hydraulic chamber 184, and effectively axially releasing the first cam structure 138 from the housing 104.

Reference is additionally made to Figure 12 which is a perspective exploded view of the valve assembly 186 and the first cam structure 138. The valve assembly 186 in the present example is provided in the form of a rotary plug valve and comprises a valve sleeve 190 which is rotatably fixed to the coupling portion 180, and thus to the housing 104, via a castellated coupling 192. In this example the valve sleeve 190 is coupled with the first cam structure 138, and thus provides a rotary connection between the housing 104 and the first cam structure 138. The valve sleeve 190 includes two circumferentially arranged (in this case diametrically opposed) ports 194 extending radially therethrough.

The valve assembly 186 further comprises a valve selector portion 196, which is formed by the mandrel 102, and includes a single port 198 extending radially through the valve selector portion 196 (two diametrically opposed ports could be provided in the selector portion 196). When the mandrel 102 and housing 104 are in the illustrated relative axial configuration of Figure 7B, the port 198 in the valve selector portion 196 is axially misaligned from the ports 194 in the valve sleeve 190, which is also illustrated in the cross-sectional view of Figure 13A, with the spring 182 removed for clarity. However, when the mandrel 102 is moved in the direction of arrow 16 to prepare for jarring, the ports 194, 198 will become axially aligned and thus allow the valve assembly 186 to become operational. In this respect, and with additional reference to the sequence of Figures 13B-D (also taken along line 13-13 assuming the ports 194, 196 have become axially aligned), relative rotation between the valve sleeve 190 and valve selector portion 196 in accordance with relative rotation between the mandrel 102 and the housing 104 will cause cyclical alignment and misalignment of the ports 194, 198 to effectively open and close the valve assembly 186. By appropriate timing between the lifting and dropping phases of the first and second cam structures 138, 140 within the lifting assembly 136, and of the opening and closing of the valve assembly 186, suitable operation of the jarring apparatus 100 may be achieved. In this respect, such timing may be readily facilitated by virtue of both the lifting assembly 136 and valve assembly 186 being commonly operated by relative rotation between the mandrel 102 and housing 104.

Referring again to Figure 7B the jarring apparatus 100 further comprises a releasable axial connection 200 between the mandrel 102 and housing 104 which first needs to be disengaged to allow relative axial movement therebetween. The axial connection 200 includes a circumferential array of dogs 202 which are positioned radially between the mandrel 102 and housing 104. In the connected configuration shown in Figure 7B the dogs 202 are received within a circumferential groove 204 in an outer surface of the mandrel, and held in place by the radial constraint of the housing 104. Upper and lower springs 206, 208 are positioned on either side of the dogs 202, and function to bias the dogs 202 towards the illustrated central position, such that the springs 206, 208 function to retain the mandrel 102 in position relative to the housing 104. In this position the mandrel 102 may be permitted to move in reverse axial directions relative to the housing 104, albeit resisted by the springs. As such, the connection may be considered to be a compliant connection. The housing 104 further includes upper and lower circumferential grooves 210, 212 which are positioned on either side of the dogs 202 when in the illustrated initial connected configuration.

The process of releasing the axial connection, in reverse directions, is illustrated in Figures 14A and 14B. Referring first to Figure 14A, a release of the mandrel 102 in the direction of arrow 16 is illustrated, which corresponds to the direction to release the rotary connection 107 (Figure 7A) between the mandrel 102 and housing 104, and permit the spring 120 to be compressed in preparation for rotary jarring. The housing 104 is held stationary (e.g., axially secured to the casing) and an axial pulling force is applied on the mandrel 102 in the direction of arrow 16, which causes the mandrel 102 and dogs 202 to move in the same direction, compressing upper spring 206. Such movement of the mandrel 102 will eventually cause the dogs 202 to become aligned with upper circumferential groove 210 in the housing 104, permitting the dogs to be released from the groove 204 in the mandrel 102, thus achieving disconnection. At this point the pulling force on the mandrel 102 will rapidly cause the mandrel 102 to move in the direction of arrow 16, radially constraining the dogs 202 in place within the upper groove 210, effectively deactivating the connection 200. In the example presented, the upper spring 206 primarily dictates the required threshold pulling force which must be exceeded to achieve disconnection.

The connection 200 may be subsequently reset, by relieving any pulling force on the mandrel 102, and/or by setting a pushing force on the mandrel 102, to re-align the groove 204 on the mandrel 102, along the dogs 202 to be released and return to the initial position.

The connection 200 may also permit axial release in a reverse direction, which is illustrated in Figure 14B. The housing 104 is held stationary (e.g., by engagement with an object, suspended load etc.) and an axial pushing force is applied on the mandrel 102 in the direction of arrow 17, which causes the mandrel 102 and dogs 202 to move in the same direction, compressing lower spring 208. Such movement of the mandrel 102 will eventually cause the dogs 202 to become aligned with lower circumferential groove 212 in the housing 104, permitting the dogs 202 to be released from the groove 204 in the mandrel 102, thus achieving disconnection. At this point the pushing force on the mandrel 102 will rapidly cause the mandrel 102 to move in the direction of arrow 17, radially constraining the dogs 202 in place within the lower groove 212, effectively deactivating the connection 200. In the example presented, the lower spring 206 primarily dictates the required threshold pushing force which must be exceeded to achieve disconnection.

In the present example the ability to permit the described reverse axial release of the mandrel 102 in the direction of arrow 17 may function to provide a linear jar within the apparatus 100. In this respect, and again with reference to Figure 7B, the apparatus 100 includes the pair of secondary impact surfaces 214, 216 which are caused to impact together upon axial release of the mandrel 102 in the direction of arrow 17.

Referring again to Figure 7B the apparatus 100 incorporates various features which permits cooling of the various components during use, for example the impact surfaces 116, 118, lifting assembly 136 and spring 120. For example, the mandrel 102 includes a number of cooling ports 220 which permit fluid flowing through the apparatus 100 when in use to also function as a cooling medium. Furthermore, the mandrel 102 may also include ports (which may or may not be commonly used as cooling ports 220) to prevent hydraulic locking between the mandrel 102 and housing 104.

A full cycle of operation of the apparatus 100 will now be described with reference to Figures 15A to 21C.

Referring initially to Figure 15A an overpull is applied on the mandrel 102 in the direction of arrow 16 (via the running string 1101 of Figure 1A), which causes the axial connection 200 to be released (as described above with reference to Figure 14A), and the rotary connection 107 between the mandrel 102 and housing 104 to be disengaged. In the illustrated configuration of Figure 15A a very high overpull has been imparted, such that in addition to the spring 120 being compressed, the thrust assembly 108 has been engaged. As such, the apparatus 100 is shown operated in its load limit configuration. When in the configuration of Figure 15A the valve assembly 186 is also operationally aligned, which is also shown in the cross-sectional view of Figure 15B, taken along line 15B-15B of Figure 15A (with the spring 182 removed in Figure 15B for clarity). In this regard the valve assembly 186 is in an open configuration, with the port 198 in the valve selector portion 196 aligned with one of the ports 194 of the valve sleeve 190. As such, the first lifting structure 138 of the lifting assembly 136 is axially released relative to the housing 104. Although the first lifting structure 138 may be considered to be axially released from the housing 104 when the valve assembly 186 is open, the first lifting structure 138 is nevertheless biased axially towards the second lifting structure 140 by virtue of the action of the spring 182.

The corresponding configuration of the lifting assembly 136 is illustrated in Figure 15C, wherein the first and second cam profiles 148, 158 of the lifting structures 138, 140 respectively are not engaged (separation gap 168).

Rotation of the mandrel 102 relative to the housing 104, caused by rotation of the running string 1101 , eventually causes the valve assembly 186 to close by misalignment of the ports 194, 198, as illustrated in Figures 16A and 16B, wherein Figure 16B is a sectional view taken through line 16B-16B of Figure 16A. The first lifting structure 138 thus becomes hydraulically locked relative to the housing 104. When in this configuration the second lifting structure 140 has rotatably progressed as shown in Figure 16C, but the first and second cam profiles 148, 158 remain separated and non-engaged (separation gap 168). As an example, the mandrel 102 may have been rotated by around 40 degrees relative to the initial position of Figure 15A to reach this stage in which the valve assembly 186 becomes closed.

Continued rotation of the mandrel 102, illustrated in Figure 17A, maintains the valve assembly 186 in its closed configuration, as illustrated in Figure 17B, which is a sectional view taken through line 17B-17B of Figure 17A, and eventually brings the cam profiles 148, 158 of the lifting assembly 136 into engagement, as illustrated in Figure 17C. Specifically, opposing ramp portions 152, 162 become engaged in preparation to initiate the lifting phase. When in the configuration illustrated in Figure 17A, the jarring mass 114 is positioned such that the impact surfaces 116, 118 remain engaged. As an example, the mandrel 102 may have been rotated by around 77 degrees relative to the initial position of Figure 15A to reach this stage. Further rotation of the mandrel 102, illustrated in Figure 18A, maintains the valve assembly 186 in its closed configuration, as illustrated in Figure 18B, which is a sectional view taken through line 18B-18B, and causes the ramp portions 152, 162 of the first and second lifting structures 138, 140 to slide over each other and cause relative axial displacement of said lifting structures 138, 140 to provide the lifting phase, as illustrated in Figure 18C. By virtue of the first lifting structure 138 being hydraulically locked and axially fixed to the housing 104 the axial separation between the lifting structures 138, 140 causes the jarring mass to be moved axially in the direction of arrow 17 against the bias of the spring 120, causing the first and second impact surfaces 116, 118 to become axially separated. As an example, the mandrel 102 may have been rotated by 128 degrees relative to the initial position of Figure 15A to reach this stage.

Further rotation of the mandrel 102, illustrated in Figure 19A, causes the ports 194, 198 of the valve assembly 186 to start to become aligned, as illustrated in Figure 19B, which is a sectional view taken through line 19B-19B, thus reconfiguring the valve assembly 186 into its open configuration. This establishes communication between the hydraulic chamber 184 and the flow path 188, axially releasing the first lifting structure 138 from the housing 104. This axial release of the first lifting structure 138 permits the loading and potential energy stored within the spring 120 to rapidly drive the jarring mass 114 in the direction of arrow 17 and cause the impact surfaces 116, 118 to be rapidly impacted together, generating a jarring force. As an example, the mandrel 102 may have been rotated by 129 degrees relative to the initial position of Figure 15A to reach this stage of generating a jarring force within the apparatus 100.

As illustrated in Figure 19C, the ramp profiles 152, 162 of the first and second lifting structures 138, 140 remain engaged. However, the axial release of the first lifting structure 138 from the housing 104 relieves or reduces, for example significantly reduces, loading applied between the lifting structures 138, 140, thus minimising stress therein. The timing of axial release of the first lifting structure 138 may be selected to be such that a relatively large surface area of contact between the ramp profiles 152, 162 exists during the initial lifting and loading phase, again assisting to control levels of stresses applied in the lifting assembly 136. The configuration of the apparatus 100 upon further rotation of the mandrel 102 is illustrated in Figure 20A. As shown in Figure 20B, which is a sectional view taken through lines 20B-20B in Figure 20A, the valve assembly 186 remains opened, with the ports 194, 198 still aligned during this further rotation. The further rotation also causes the second lifting structure 140 to further rotate relative to the first lifting structure 138, causing the ramp profiles 152, 162 to reach the peak position, as illustrated in Figure 20C, reflecting the maximum axial displacement between the lifting structures 138, 140. As the valve assembly 186 remains open during this phase of rotation loading applied between the reducing contact area between the ramp profiles 152, 162 is minimised, thus minimising stresses within the lifting assembly 136. As an example, the mandrel 102 may have been rotated by 168 degrees relative to the initial position of Figure 15A to reach this stage of the ramp profiles 152, 162 peaking.

Further rotation of the mandrel 102, for example now 180 degrees relative to the initial position of Figure 15A, will cause the first and second lifting structures 138, 140 to effectively drop (i.e., the first lifting structure 138“drops” relative to the second lifting structure 140 under the bias of spring 182), returning the apparatus 100 to the initial configuration. This dropping phase is illustrated in Figures 21A-C. Continuous rotation of the mandrel 102 will cause continuous cycles of jarring, as described above. In this respect the jarring frequency will be a function of the number of cam profiles provides on the lifting structures 138, 140, and the rotational speed of the mandrel 102. The jarring frequency may also be influenced by the number of ports provided in the valve assembly 186. In use, the jarring frequency may be readily adjusted by adjusting the rotational speed of the mandrel 102.

The timing of the lifting and dropping phases of the lifting structures 138, 140 and the opening and closing of the valve assembly 186 may be readily adjusted to achieve the desired operation of the apparatus 100. For example, delaying the opening of the valve assembly 186 may permit a greater separation between impact surfaces 114, 116 to be achieved, and thus more energy to be generated by the spring 120.

The common operation of the valve assembly 186 and the lifting assembly 136 by the relative rotation between the mandrel 102 and the housing 104 may facilitate the appropriate timing of operation to be readily achieved and adjusted, for example by simple relative alignment of the different components on the mandrel 102 and/or housing 104.

In the examples provided above jarring is achieved by providing impact between impact surfaces. However, jarring may also be achieved without necessarily requiring such impact. Examples of jarring apparatuses which function to provide jarring without impact are illustrated in Figures 22 and 23.

Referring first to Figure 22, a rotary jarring apparatus 910 is illustrated which is similar in most respects to apparatus 10 first show in Figure 3A, and as such like features share like reference numerals, incremented by 900. Thus, the apparatus 910 includes a mandrel 912 located within a housing 914, a thrust assembly 918, a jarring mass 924, force mechanism 932 and lifting mechanism 936. However, in the present example the lifting assembly 936 includes a first lifting structure rotatably and axially fixed relative to the mandrel 912 (but alternatively could be connected to the housing 914), and a second lifting structure rotatably fixed, but axially moveable, relative to the housing 914 (but alternatively could be rotatably fixed to the mandrel 912). Further, the jarring mass 924 is rotatably connected to the housing 914 (but alternatively could be rotatably connected to the mandrel 912).

Furthermore, instead of impact surfaces, the apparatus 910 includes an arresting mechanism in the form of a gas spring 8 provided between the jarring mass 924 and the housing 914. A similar gas spring may also or alternatively be provided between the jarring mass 924 and the mandrel 912. In use, relative rotation between the mandrel 912 and housing 914 operates the lifting mechanism 936 to“lift” the jarring mass 924 against the bias of force mechanism 932, and subsequently allow the jarring mass to“drop” and be driven by action of the force mechanism 932. Such movement of the jarring mass 924 under the drive of the force mechanism 932 may be arrested by the gas spring 8, thus generating a jarring effect. Continuous operation may thus generate repeated jarring effects.

Figure 23 illustrates a similar jarring apparatus 1010 to that shown in Figure 34. However, in this example an arresting mechanism is provided in the form of a mechanical spring 9, such as a Belleville spring stack. It should be recognised that the examples provided herein are indeed only exemplary, and that various modifications may be made thereto.