WELL ABANDONMENT AND SLOT RECOVERY

The present invention relates to apparatus and methods for well abandonment and slot recovery and in particular, though not exclusively, to single trip casing cutting and pulling system which can retrieve the seal assembly on the same trip.

When a well has reached the end of its commercial life, the well is abandoned according to strict regulations in order to prevent fluids escaping from the well on a permanent basis. In meeting the regulations it has become good practise to create the cement plug over a predetermined length of the well and to remove the casing. Current techniques to achieve this may require multiple trips into the well, for example: to pull the wear bushing from the wellhead; to pull the seal assembly from the wellhead; to set a bridge plug to support cement; to cut the casing above the plug; to pull the cut casing from the well; and create a cement plug to cement across to the well bore wall. The cement or other suitable plugging material forms a permanent barrier to meet the legislative requirements.

Each trip into a well takes substantial time and consequently significant costs. Combined casing cutting and pulling tools have been developed so that the cutting and pulling of the casing can be achieved on a single trip. Such a tool is the TRIDENT® System to the present Applicants, Ardyne Technologies Limited.

US 6,629,565 to Smith International, Inc. discloses a well abandonment process and apparatus for cutting and retrieving an offshore well casing, the process comprising : making a trip to the well wherein all of the following steps are performed, the steps comprising : pulling a seal assembly from the wellhead, cutting the casing, griping the casing, and retrieving the seal assembly and cut casing. Thus this advantageously combines the steps of cutting and pulling the casing along with pulling the seal assembly to save a further trip into the well. In US 6,629,565 a casing cutting and pulling tool is suspended from an offshore vessel or platform by connection to a drill pipe. At the top of the casing cutting and pulling tool, there is a seal assembly retrieval tool mounted in the drill string, which is used to pull the seal assembly of interior casing or intermediate casing in a wellhead. Below the seal assembly retrieval tool, the casing cutting and pulling tool also has a bumper jar, a spear, a long stroke bumper jar, a mud motor and a casing cutter, all connected to each other in series in the order given.

In one embodiment, the procedure for operation of the system is as follows. Trip in the hole until the seal assembly retrieving tool is landed on the seal in the wellhead. It is important to allow for enough space out to trip seal assembly into riser. Next, engage the seal assembly with the seal assembly retrieval tool. Then pull the seal assembly with the casing cutting and pulling tool up into riser. The casing cutter is then spotted at the desired cutting depth. With the casing cutter in the correct location, a slight left-hand torque is applied to engage the spear (1/4 turn) to grip the casing. The casing is then cut and the spear is disengaged by a right- hand torque to release its grip on the casing. The casing cutting and pulling tool is then pulled out of the hole until the spear is just below the wellhead. A left-hand torque is then applied to engage the spear to grip the casing. Next, the casing cutting and pulling tool is pulled out of the hole with the casing. The seal assembly and seal assembly retrieval tool are then laid out at the surface. The casing cutting and pulling tool is then pulled further out of the hole until the casing hanger is landed out on rotary table. It should be spaced out so that the spear can be racked in the derrick. The spear is then disengaged and racked back in the derrick. Finally, the casing is rigged up and laid down on the derrick. Since the spear is engaged to grip the casing before the casing is cut with the casing cutter, the casing may be cut in tension. In particular, with the spear engaged, the operator of the casing cutting and pulling tool may pull up on the drill pipe so that the casing experiences an applied pressure in tension. With tension pressure applied to the casing during the cutting procedure, the chances of a successful cut are greatly increased. Once the seal assembly is pulled the casing may be cut with the spear at any depth below the wellhead. There are a number of disadvantages in the apparatus and process described in US 6,629,595. While it states that once the seal assembly is pulled the casing may be cut with the spear at any depth below the wellhead, this is not the case as the maximum depth will be limited to the distance between the spear and the seal assembly retrieval tool as the drill string is stopped when the seal assembly retrieval tool reaches the seal assembly. At this point only shallower depths can be achieved and even this is limited by the requirement for sufficient space out to trip the seal assembly through the riser. Additionally, the seal assembly must remain attached to and supported by the drill string during the cutting of the casing. This means that the drill string cannot be fully rotated from surface to rotate the cutting blades and cut the casing. As described above, only quarter turns are therefore achievable. This limits the operating modes available for use on the cutting and pulling tool. In particular a mud motor has to be present on the drill string to rotate the cutter. Further, as some operators stipulate that the seal assembly must be in place during cutting for safety reasons, pulling the seal assembly so that the casing can be cut with the spear at any depth below the wellhead is not permissible. It is therefore an object of at least one embodiment of the present invention to provide a one trip casing cutting and pulling system which also retrieves the seal assembly and which obviates or mitigates one or more disadvantages of the prior art.

It is therefore an object of at least one embodiment of the present invention to provide a method of cutting and pulling casing which retrieves the seal assembly on the same trip as the cut and pull operation and which obviates or mitigates one or more disadvantages of the prior art. According to a first aspect of the present invention there is provided a casing cutting and pulling assembly located on a drill string comprising : a casing spear to anchor to casing in a well bore;

a casing cutter configured to cut the casing; and

a wear bushing and seal assembly retrieval device, the retrieval device comprising a modified wear bushing and a running tool:

the modified wear bushing configured to locate in a wellhead housing, having an axial throughbore for the unimpeded passage of the drill string therethrough, a latching mechanism for connecting the modified wear bushing to a seal assembly, and a formation on a wall of the throughbore; and

the running tool being configured to mount in the drill string and having a shoulder protruding from an outer surface thereof to contact the formation and support the modified wear bushing on run-in and retrieval; wherein when the wear bushing and seal retrieval device is landed in the wellhead housing, the running tool can be run deeper in the well to position the casing cutter at multiple locations in the casing with the seal assembly remaining in the wellhead housing.

In this way, casing can be cut and pulled at any position in the well with the seal assembly remaining in place until the cut casing is pulled, at which time the seal assembly is pulled as the running tool is tripped through the wellhead. Thus casing cutting and pulling with seal assembly retrieval is achieved on a single trip.

Preferably the modified wear bushing has a substantially cylindrical body and at least a portion of an outer surface of the body has a profile to match an inner surface of a seal assembly into which the retrieval device is deployed. In this way the wear bushing and seal assembly retrieval device can be modelled from a standard wear bushing for the seal assembly.

Preferably the latching mechanism comprises a plurality of pins which are biased radially outwardly and sized to locate in a receptacle of the seal assembly. In this way, the seal assembly automatically couples to the wear bushing and seal assembly retrieval device when the modified wear bushing lands in the wellhead housing.

Preferably, the running tool comprises a sub with a substantially cylindrical body having a bore therethrough and the shoulder is a rim around the circumference of the body directed radially outwards. In this way the shoulder contacts the formation of the modified wear bushing and picks it up together with the seal assembly when the drill string is tripped from the well. The shoulder may be a stop collar. Preferably the shoulder has an outer diameter greater than an inner diameter of the throughbore of the modified wear bushing. In this way, the shoulder will contact a lower side of the formation and raise the modified wear bushing and the seal assembly to surface. Preferably the formation of the modified wear bushing is arranged above the shoulder on the drill string.

Preferably, the running tool is releasably coupled to the modified wear bushing. The releasable coupling may be a shear bolt which is released by shearing when the modified wear bushing is landed in the wellhead housing. In this way, the modified wear bushing is positively landed and latched to the seal assembly when the drill string is run in the well.

Preferably the casing spear and casing cutter are located on the drill string below the running tool. In this way, the casing spear and casing cutter can be operated at any depth below the wellhead. Preferably casing cutter is operated by full rotation of the drill string. The unimpeded passage of the drill string through the modified wear bushing allows rotation also and therefore a motor is not required to operate the casing cutter.

Preferably a packer is located on the drill string below the running tool. More preferably, the packer is a mechanical tension-set retrievable packer. In this way, the packer can be set by pulling or releasing tension on the drill string. Preferably, the casing spear is located between the mechanical tension-set retrievable packer and the casing cutter. In this way, casing can be cut under tension and a circulation test can be performed.

According to a second aspect of the present invention there is provided a method of retrieving a seal assembly from a wellhead on the same trip as cutting and pulling casing, the method comprising the steps:

(a) locating a running tool of a wear bushing and seal assembly retrieval device according to the first aspect, a casing spear and a casing cutter in order on a drill string wherein the running tool supports the modified wear bushing;

(b) running the drill string through the wellhead and into a wellbore;

(c) landing the modified wear bushing in the wellhead housing and latching the modified wear bushing to the seal assembly;

(d) running the drill string through the modified wear bushing when the seal assembly is in the wellhead housing and latched to the modified wear bushing; (e) locating the running tool, casing spear and casing cutter below the wellhead at a position at which casing is to be cut;

(f) cutting the casing;

(g) pulling the drill string through the modified wear bushing to contact the shoulder of the running tool with the formation of the modified wear bushing so as to pick-up the modified wear bushing together with the seal assembly attached thereto and thereby pull the seal assembly from the wellhead;

(h) locating the casing spear towards an upper end of a cut section of casing and gripping the cut section of casing with the casing spear;

(i) pulling the drill string so as to recover the cut section of casing together with the modified wear bushing and the seal assembly. In this way, the drill string can operate below the wellhead without any restriction on depth or operating configuration so that casing can be cut at any location and the seal assembly is automatically retrieved when the string is pulled out of the wellhead. Further the seal assembly may remain in place in the wellhead during casing cutting.

Preferably the method includes at step (a), releasably coupling the modified wear bushing to the running tool and by step (d) decoupling the modified wear bushing from the running tool. In this way the modified wear bushing is carried into the wellbore and positively located in the wellhead housing.

Preferably the method includes the step of rotating the drill string through the modified wear bushing when the seal assembly is in the wellhead housing. In this way, tools which operate by revolutions of the drill string can be used in the well bore. Preferably the drill string is rotated to operate the casing cutter. Alternatively, the casing cutter can be operated by a motor arranged on the drill string. Preferably step (e) includes actuating the casing spear to anchor the drill string to the casing in the well bore to hold the casing in tension during step (f). In this way the casing is advantageously cut in tension.

Preferably the method includes at step (a) locating a packer on the drill string below the running tool. Preferably the method includes the further step of actuating the packer to seal an annulus between the drill string and casing in the well bore. Preferably the method includes the step of setting down weight on the drill string to set the packer. Alternatively the method includes the step of applying an upward force or tension to the drill string to set the packer. In this way, a mechanical tension-set packer may be used.

Preferably the method includes the step of performing a circulation test to determine circulation behind the cut tubular at surface. This provides a positive circulation test and the cut casing section, can be removed. Preferably the circulation test is performed between steps (g) and (h). This provides the necessary access behind the cut tubular to determine if circulation occurs. The method may include the further steps of pulling the drill string through the modified wear bushing when the modified wear bushing is in the wellhead housing to locate the casing cutter at a shallower depth in the casing and cutting the casing at the shallower depth. This will be needed in the event that the circulation test is negative, there being no circulation behind the cut tubular. The method may include repeating the circulation test and cutting casing at increasingly shallower depths until a positive circulation test occurs and a section of cut tubular can be removed from the wellbore. In the description that follows, the drawings are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results.

Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein including (without limitations) components of the apparatus are understood to include plural forms thereof. Furthermore, relative terms such as", "lower", "upper, "up", "down" and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations. Likewise, the term "inlet" shall be construed as being an opening which, dependent on the direction of the movement of a fluid may also serve as an "outlet", and vice versa. There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

Figures 1A to IF provide schematic illustrations of a casing cutting and removal assembly in a method according to an embodiment of the present invention; and

Figure 2 is a part cross sectional view through a wear bushing and seal assembly retrieval device for use in a casing and pulling assembly according to an embodiment of the present invention.

Referring to Figures 1A to IF there is illustrated a casing and pulling assembly, generally indicated by reference numeral 10, including a casing cutter 12, a casing spear 14, a wear bushing and seal assembly retrieval device 16 which comprises a modified wear bushing 18 and a running tool 20, mounted in order upon a drill string 22, according to an embodiment of the present invention.

The casing and pulling assembly 10 is used to cut and remove a casing section 24 from a well 26. The well shown in Figures 1A to IF is a typical arrangement in which a wellhead 28 provides access to a subsea well 26. For simplicity only two casings are shown, with an inner casing string 30 supported from a casing hanger 32 mounted in the wellhead housing 34. A seal assembly 36 is used to seal the annulus 38. As is known in the art a wear bushing 18 is landed in the wellhead 28, see Figure IB, against the casing hanger 32 to protect the seal assembly 36 and the casing hanger 32 from damage when a drill string 22 is run in or pulled out through the wellhead 28. The drill string 22 is run from a rig/platform or vessel 42 through a riser 44. In Figures 1A to IF, the wear bushing 18 is a modified wear bushing according to an embodiment of the present invention and a running tool 20, for the modified wear bushing 18, is shown on the drill string 22 at a location deeper in the well 26 with the seal assembly 36 remaining in the wellhead housing 34, at Figure 1C, according an embodiment of the present invention.

Reference is now made to Figure 2 of the drawings which illustrates a wear bushing and seal assembly retrieval tool 16 comprising a modified wear bushing 18 and accompanying running tool 20. The retrieval tool 16 is shown in the wellhead 28, with like parts to those of Figures 1A to IF given the same reference numeral to aid clarity. It will be appreciated by those skilled in the art that the shape and configuration of the wellhead housing 34, seal assembly 36 and casing hanger 32 will vary depending on the manufacturer. Flowever, those shown in Figure 2 include the main characteristics including a groove 44 in the seal assembly 36, used for locating and retrieving the seal assembly 36.

In the present invention, the modified wear bushing 18 has an outer shape to match the inner shape of the wellhead 28. In this regard the wear bushing 18 is formed in three parts, so that it can be adapted for different wellhead 28 designs. Flowever, it may be of unitary or multiple part construction. A seal retrieval portion 46 sits between a lower portion 48 shaped to land on the casing hanger 32 and an upper portion 50 to protect the seal retrieval portion 46 and seal assembly 36. Each part 46,48,50 of the wear bushing provides a central throughbore 52 for the passage of the drill string 22.

The upper portion 50 includes a formation or downward facing shoulder 54 being an annular rim or ledge around an inner surface 56 of the wear bushing 18. There is also a shear bolt 58 (one is shown but there may be more spaced around the circumference) which provides the releasable connection to the running tool 20.

The seal retrieval portion 46 has a latching mechanism 45 which includes seal assembly retrieval fingers 60 which are biased in a radially extended position to sit in the groove 44 of the seal assembly 36. There are eight seal assembly retrieval fingers 60 arranged circumferentially around the wear bushing 18, though the any number may be selected. Each finger 60 is biased radially outwards by an individual spring 62. Each finger 60 has a distal end 64 shaped to match the profile of the groove 44 and an orientation pin 66 to ensure the profiles align for engagement to provide maximum loading when the seal assembly 36 is to be retrieved. The latching mechanism 45 automatically connects the modified wear bushing 18 to the seal assembly 36 when the modified wear bushing lands in the wellhead 28.

Now considering the running tool 20. This has a cylindrical body 68, with connections (not shown) to be made-up in the drill string 22. Towards an upper end 70, there is a formation or shoulder 72. Shoulder 72 is formed from a section 74 of the body 68 having a greater diameter than the remaining body 68 and diameter of the drill string. The diameter of the section 74 is sized to match the diameter of the throughbore 52 of the modified wear bushing 18. The section 74 therefore forms a protrusion which provides a hard shoulder 72 in the form of a upward facing ledge or rim at its upper end and a sloped surface 78 at its lower end 80 to ease passage through the well 26. It is also seen that the shear bolt 58 is fastened into the section 74 with the formation 54 of the wear bushing 18 being supported on the shoulder 72 of the running tool 20. This may be considered as the run-in configuration and is shown in Figure IB.

As shown in Figure IB the casing cutting and pulling assembly 10, in a preferred embodiment, has arranged from a first end 82, the casing cutter 12, an anchor mechanism being the casing spear 14, a mechanical tension-set retrievable packer 86 and the wear bushing and seal retrieval device 16. The casing cutter 12, casing spear 14 and mechanical tension- set retrievable packer 86 may be formed integrally on a single tool body or may be constructed separately and joined together by box and pin sections as is known in the art. Two parts may also be integrally formed and joined to the third part. This arrangement may be the TRIDENT® casing cutting and pulling system offered by Ardyne, UK and Norway. A detailed description of a suitable casing cutter 12 and casing spear 14 is found in GB2543410 to the present Applicants and incorporated herein by reference. A detailed description of a suitable packer 86 is found in GB2548727 to the present Applicants and incorporated herein by reference. It will be appreciated by those skilled in the art that other casing cutters, casing spears and packers may be used.

Referring to Figure 1A, there is illustrated the well 26 prior to deployment of the casing cutting and pulling assembly 10. The seal assembly 36 is in place on the wellhead 28 to seal the annulus 38 to the casing string 30. A cement plug 88 is shown in the casing string 30. Referring to Figure IB of the drawings, the casing cutting and pulling assembly 10 is run-in the well 26, through the wellhead 28 and into the casing string 30 until the wear bushing and seal assembly retrieval device 16 lands in the wellhead 28.

On landing in the wellhead housing 34, the modified wear bushing 18 will contact the casing hanger 32 and the latching mechanism 45 will engage the fingers 60 in the groove 44 of the seal assembly 36. The modified wear bushing 18 is therefore coupled to the seal assembly 36. Continued weight on the string 22 will cause the bolt 58 to shear and the running tool 20 will be released from the modified wear bushing 18 and be free to travel through the bore 52 of the wear bushing 18 and into the casing string 30. Note that the seal assembly 36 remains in position in the wellhead housing 34 maintaining the seal on the annulus 38. The modified wear bushing 18 acts as a standard wear bushing preventing damage to the seal assembly 36 and casing hanger 32.

The drill string 22 is free to travel any distance into the casing string 30, its movement not being restricted by the wear bushing and seal assembly retrieval device 16, as in the prior art. This is illustrated in Figure 1C. The standard steps of casing cutting and pulling can now be undertaken. The drill string 22 is positioned in the well so that the blades 90 of the casing cutter 12 are at a desired location to cut the casing 30. At this position, the casing spear 14 is hydraulically actuated to grip the casing surface 92 to secure the axial position of the tool 10 in the wellbore and the string 22 rotated from the rig 42 to operate the cutter 12. Note that the casing 30 is held in tension when the casing cutter 12 is operated. Also of note is that as the running tool 20 is located adjacent the other components 12,14,86 of the assembly 10, it is kept clear of and below the wellhead 28. In this way, the annulus 38 is kept sealed with the seal assembly 36 in place in the wellhead 28 during cutting of the casing 30. This is a requirement for some operators. This is shown in Figure ID. If it is a requirement of the casing cutter 12 that the seal assembly 36 is removed for the passage of fluid, for example, the running tool 20 can be located higher in the drill string 22 so that the seal assembly 36 is raised before the cutting position is reached.

The use of a mechanically set retrievable packer 86 allows rapid setting of the packer 86 by pulling of the string 22 against the set casing spear 14, if a kick occurs in the well 26 for any reason. The mechanical tension-set retrievable packer 86 will rapidly set to seal the well 26 and is a safety feature. When the casing cutter 12 has finished cutting the casing, the casing cutter is deactivated and we have a cut section of casing 24 ready for removal. The drill string 22 with the assembly 10 is now pulled out of the well 26 until the running tool 20 arrives in the wellhead 28 whereupon the shoulder 72 on the running tool 20 will abut the formation 54 on the modified wear bushing 18 and pick-up the modified wear bushing 18 together with the seal assembly 36. This is shown at Figure IE. At this point, the packer 86 can be set to seal the casing 30 and perform a circulation test. Fluid pressure applied through the drill string 22 will exit the casing at the cut 94 and can be detected in the annulus 38 at surface. A positive test indicates that the annulus behind the casing 24 is free of debris which may cause the casing 24 to stick when removed. The cut casing section 24 can now be removed.

Tension applied to the drill string 22 is released to thereby unset the packer 86. The casing spear 14 is released by setting down weight on the drill string 22. The drill string 22 is now pulled out of the well 26 to locate the casing spear 14 at an upper end of the cut section of casing 24. In this position the casing spear 14 is activated to grip the casing section 24 and by pulling the drill string 22 and the casing cutting and pulling assembly 10 from the well 26, the seal assembly 36 is retrieved together with the cut section of casing 24. This is illustrated in Figure IF. The wellbore now contains the casing stub 96 and cement plug 88. The entire procedure has been completed on a single trip.

In the event that the circulation test is negative, that is a pressure increase is not seen at surface, then it is assumed that cement or other debris is located in the annulus between the cut casing 24 and the formation which will prevent movement and subsequent recovery of the cut casing section 24. The drill string 22 and casing cutting and pulling assembly 10 are then pulled up the casing to locate the blades 90 of the casing cutter 12 at a location higher in the well, shallower depth, on the cut casing section 24. The steps of cutting, testing and pulling can be repeated safe in the knowledge that the seal assembly 36 remains in the wellhead 28.

The principal advantage of the present invention is that it provides a casing cutting and pulling assembly which automatically retrieves the seal assembly on the same trip in the well.

A further advantage of an embodiment of the present invention is that it provides a method of cutting and pulling casing which allows the seal assembly to remain in position during the cut and then retrieves the seal assembly on the same trip in the well.

A still further advantage of an embodiment of the present invention is that it provides a casing cutting and pulling assembly which retrieves the seal assembly on a single trip without interfering with the cutting and pulling operation.

The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended. For example, the shoulder and the formation may be provided with mating profiles so that they lock when engaged to prevent relative rotation. The shoulder on the running tool may be a number of blocks which are biased radially outwards to prevent the shoulder catching when run in the wellbore. Further it will be appreciated that the non-essential method steps may be added to, changed or removed for a single trip.