IN AN ANNULUS

The invention relates to a packer arranged to establish a barrier in an annulus, the annulus being downhole in a well, for example.

Background

Packers can be used to seal and isolate one area from another. For example, a packer can be used in an annulus to isolate areas along pipes. Isolation like that typically takes place by one or more packers (downhole packers) being positioned and set in the annulus. Such packers are referred to as annulus packers.

Annulus packers are often used in wells in the oil and gas industry. For example, after drilling and in various operations in a petroleum well, it is known to isolate a portion of the well by providing a gas- and liquid-tight barrier in an annulus between the inside of a casing of the well and the outside of a downhole tool, a well pipe or the like. The packer is provided on a tool in a non-expanded state before the tool is lowered into the well. When the tool is positioned in the well, the packer is subjected to an axial load so that the packer expands, and a barrier is provided in the annulus.

Known packers for such purposes typically comprise a packer element made of rubber, the packer element having a rectangular cross section and rounded outer edges. The dimensions and the shape of the cross section may vary, depending on, among other things, the diameters of the casing and the downhole tool, and the pressure and the environment in the well. The isolation may take place with one single packer or with a plurality of packers. The plurality of packers may be positioned in series.

The isolation may be permanent or temporary. A packer for permanent isolation in a well is referred to as a "permanent packer" in technical language. A packer for temporary isolation, called a temporary packer, may be pulled out of the well after a certain time, for example after a pressure-testing of a well.

The temporary packer may comprise, for example, a packer element and an expansion ring which cooperate to provide radial expansion of the packer under axial compression in the annulus. The packer element is typically formed from an elastic material. The expansion ring is typically formed from a non-elastic material, for instance metal. When an elastic packer element is subjected to a mechanical axial load, the packer element is transformed, and tensions arise in the elastic material. By transformation is meant, herein, that the elastic element changes its shape when an external force is applied to it and is substantially returned to its original shape when the external force is removed. The external force is in this context axially directed.

When a mechanical load is applied to the packer, the packer element expands in a radial direction so that a barrier is provided in the annulus while the axial width is simultaneously being reduced. The axial load may be of several hundred tonnes. To have a controlled expansion of the packer element, and to avoid destructive deformation of the packer element, it is known to provide the packer with control rings made of metal. When the packer element expands, the control rings are forced outwards in a radial direction and suffer a permanent deformation. Since the control rings are deformed, the packer may only be used once.

It is a known problem that the energy supplied to the packer element during setting may give a destructive deformation of the packer element. By a destructive deformation is meant, herein, a permanent deformation or structural damage to the packer element allowing the packer element to be used only once.

Patent document GB2357098 discloses a packer as indicated above. When the packer is subjected to an axial force, the packer element and the control rings are forced radially outwards so that the packer element and the control rings come into contact with a surrounding casing. The control rings are subjected to a plastic deformation, meaning that the packer must be pulled out of the well after a sealing is opened, for instance after pressure testing of a well. If several pressure tests are required in different positions in a well bore, the packer must be replaced with a new packer between every repositioning and test.

The plastic deformation of the support rings as described above is a disadvantage. Another disadvantage is that the packers are often complicated and comprise several parts, the actual packer element being one of many elements thereof.

Patent document US7304098 discloses an annular packer comprising a packer element and an internal centre ring arranged to establish the inner diameter of the packer element. The packer further comprises two end rings I backup rings. The centre ring is shown with an inner diameter that is larger than the inner diameter of the packer element. The centre ring has an angular cross section with one straight radial face and two adjacent faces resting against a corresponding groove in the packer element.

Patent document US2018209241 discloses an annular packer comprising a packer element with two internal supporting rings and two elastic supporting rings along the radial outer edges of the packer element.

Patent document US3554280 discloses a deformable packer element comprising an annular recess in which an expansion ring is positioned. Each end of the packer element is tapered. A complementary support member comprising a metallic support ring is positioned to each of the tapered surfaces. When an axial force is applied to the packer, the support members are pushed outwards, and the packing element is pushed inwards. The metallic support rings are pushed outwards, and a plastic deformation takes place.

Problems with the prior art include that the packers are complicated and/or require great axial force for setting and/or require supporting rings that suffer permanent deformation during setting so that the packers cannot be reused. If several barriers are to be established in a well, the tool will therefore have to be pulled out of the well and the packer must be replaced between each setting.

A problem with prior art packers, is that the packer element is subject to damage during setting because of large internal stresses when the packer element expands in a radial direction. Such damage is typically cracking of the surface of the packer element. If even a smallest crack occurs, the crack may easily expand and cause destruction of the packer element. If a crack and subsequent destruction occur, a retraction of the tool out of the well may not be possible. If a crack occurs, material from the packer may flow through the control ring and into an adjacent back up ring making it difficult, if not impossible, to retract or reverse the backup ring, meaning that the tool is stuck in the well. There is a need for solutions that can simplify the isolation of wells and reduce the costs.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art. The object is achieved through the features that are specified in the description below and in the claims that follow.

Summary of the invention

The invention is defined by the independent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect the invention relates to a packer for sealing an annulus between a downhole tool and a casing in a well bore, where the packer is arranged for being positioned between two back-up rings having a contact surface, the packer comprising:

- an elastic packer element having an internal annular recess with a triangular cross section having a first internal sliding surface and a second internal sliding surface; and

- an elastic expansion ring being positioned in the internal annular recess, the expansion ring having a triangular cross section with a first external sliding surface for being in sliding contact with the first internal sliding surface, and a second external sliding surface being in sliding contact with the second internal sliding surface. The packer element further comprises an annular support surface arranged to absorb an axial force from the contact surface of the backup ring.

By cross section may be understood a peripheral cross section showing the mass of the packer, and/or the packer element and/or the expansion ring.

A problem with prior art packers, is that the packer element is subject to damage during setting because of large internal stresses when the packer element expands in a radial direction. Such damage is typically cracking of the surface of the packer element. If even a smallest crack occurs, the crack may easily expand and cause destruction of the packer element. To avoid such cracks and destruction, prior art packer elements are typically protected by metallic support rings. The support rings may be positioned adjacent to the packer element or to an adjacent support element. When the packer is set, the support rings undergo a permanent deformation. This means that a prior art packer, due to possible cracks and the deformed support rings can only be set once.

The packer element described herein is a resettable packer. The resettable feature is possible because the packer is not subject to cracks and/or suffering a permanent destructive deformation or structural damage during setting. By destructive deformation is meant, herein, a permanent deformation or structural damage. Said packer may therefore be set and reset multiple times. In what follows, it is explained more specifically how the invention solves the problems associated with cracks and internal stress.

Experience shows that the destructive deformation of a packer element can be reduced if the packer element has an internal radial/annular recess. If the radial recess houses an expansion ring, as is described herein, a controlled expansion may be provided in addition. An effect of the internal annular recess and the expansion ring being positioned therein, is that the expansion ring may support and guide the packer element in a radial direction when an axial force is applied to the packer.

The first internal sliding surface and the second internal sliding surface of the packer element are adapted for sliding contact with the corresponding first external sliding surface and the corresponding second external sliding surface of the expansion ring.

When the packer that is described herein is to be set, the internal sliding surfaces will rest against and slide along the external corresponding sliding surfaces on the expansion ring. This sliding helps to guide the packer element in an outward radial direction when the packer element is subjected to an axial load/compression. By the expansion ring being able to give the packer element an internal sliding support, the axial force required for setting and transforming the packer element may be reduced.

The forces applied to the packer are absorbed and distributed in such a way that stresses inside the packer element is reduced and transferred to the centre of the packer element. Since the packer element is not subject to damage, no support rings are required, and the packer may be set and reset multiple times.

The packer described herein is formed from an elastic material that can provide a constant volume when the material changes its shape. When the packer is to be set, the packer surrounds a portion of a downhole tool.

The internal recess of the packer element and the support from the expansion ring may contribute to the centre of the packer element being subjected to minimal forces and thereby also absorbing minimal energy in the transformation phase. This allows the axial setting force to be reduced as described above. When the packer has been set and transformed, the tensions in the packer will typically be greatest at the edges/corners between the curved outer and inner surfaces and the side faces, whereas the centre of the packer element may be maintained as a low-energy area with minimal tensions. Thereby the packer may provide the greatest possible strength through the transformation.

The internal sliding surfaces in the recess and on the expansion ring may be plane. Said sliding surfaces may be isosceles. Said sliding surfaces may be curved, and in this embodiment, the angle may be measured along a secant extending from the start and the end of the curvature.

An effect of the expansion ring being elastic, is that the expansion ring can change its form and absorb internal forces applied to the packer element, and thereby reduce the internal stress in the packer element during setting of the packer. When the internal stress is reduced the risk of internal damage on the packer element is also reduced.

Another effect of the expansion ring being elastic, is that the expansion ring may fill the recess in the packer ring at least close to 100 %, giving the packer element an internal and flexible support during transformation.

An effect of the annular support surface described herein, is that a backup ring may be positioned in direct contact with the packer element, eliminating the need for a support ring. Since no support ring is required, the packer may be set and reset multiple times.

By backup ring is herein understood a ring arranged to transfer and distribute an axial load to the packer element. The backup ring is typically extendable in a radial direction. The backup ring typically comprises a steel ring formed by one or more elements. When an axial load is applied to the backup ring, the outer diameter of the backup ring increases. When said load is removed, the backup ring returns to the original shape and outer diameter.

Another effect of the annular support surface is that the axial load applied to the packer is transferred in an axial direction. This enables a controlled elastic transformation of the packer element. When the load is absorbed in the axial direction, the forces acting on the packer element is clearly defined, so that an axial compression and radial extension can be achieved with a minimum of stress inside the packer element.

The annular support surface may be adapted to a specific backup ring. The cross section of the packer element may therefore be subject to a variety of embodiments.

The packer element may be formed by elastomers or polymer materials. In a preferred embodiment, the packer element may be formed by materials such as HNBR (hydrogenated nitrile butadiene rubber), FKM (fluorocarbon-based fluoroelastomer materials), FFKM (perfluoroelastomer) or Alfas® fluoropolymer materials.

The effect of the technical features that are described above is that a resettable packer may be provided. By resettable means that the packer can be set with a small axial force and can be set and reset several times without suffering permanent destructive deformation or structural damage.

A key element for enabling the resettable feature, is that the packer is made from elastic material only, and does not comprise any element that deforms plastically during setting, for instance metal. When the packer is made of elastic material only, the packer may return to its original form and any contact between the packer element and the enclosing tube/casing may cease when the axial load eases. When there is no contact between the packer element and the enclosing tube/casing, the packer may be repositioned and set and reset in at least one other position.

Another key element is that no control ring is required for supporting the packer element or protecting the packer element from an adjacent back-up ring or like versa.

The packer element and the expansion ring that are described herein can give optimum support when the packer is being set, and approximately 100 per cent filling of the recess when the packer has been set. Thereby the invention provides a controlled setting and resetting of the packer, without damage being caused to the packer element or the expansion ring.

Compared with prior-art expanding packers, the packer that is described herein has the following advantages:

The axial setting force is between 50 and 70 per cent smaller, so that the inner tensions in the packer element can be reduced.

The packer element can expand more than a conventional packer. This gives increased flexibility because one packer dimension can be used in applications with different sizes of the annulus between the packer and the surrounding pipe. The axial expansion may typically be between 20 and 40 per cent, and the outer diameter of the packer may typically increase by between 7 and 11 per cent. How much the packer expands, depends on the size of the annulus between the packer and the surrounding pipe, that is to say the difference between the outer diameter of the packer and the inner diameter of the pipe.

Increased radial flexibility can provide a satisfactory seal/barrier in the annulus with just one packer element, whereas when a packer according to prior art is used, a plurality of packers must often be used in series to achieve equivalent sealing. Thereby the invention also contributes to a shorter and more compact packer.

The packer can be set and reset with reduced risk of destructive deformation of the packer element. Thereby the packer can be reused, which gives a more cost-effective sealing of a well.

The packer may comprise a lubricant between the internal sliding surfaces and the external sliding surfaces.

An effect of the lubricant is that friction between the adjacent sliding surfaces may be reduced. A preferrable friction coefficient between the sliding surfaces is less than 0,3p. Less friction means that less axial force is required to set the packer. Adding the lubricant may ensure a constant and correct friction coefficient. The lubricant may be grease. The lubricant may be applied during assembly of the packer, when the expansion ring is positioned in the recess.

A mutual angle between the first internal sliding surface and the second internal sliding surface may be in the range of 65 degrees to 85 degrees inclusive.

The geometry of the recess and the angle of the sliding surfaces have turned out to be of great importance to how large an axial force is required to be to transform and expand the packer element radially.

A small angle between the sliding surfaces, for example of 20-40 degrees, may give less destructive deformation, but the power requirement during setting is great, and the risk of damage to the packer element and/or the expansion ring during setting and resetting of the packer is large.

A gentle angle between the sliding surfaces, for example of 100-140 degrees, gives a small radial guiding effect for the packer element, and a radial void may be created at the periphery of the expansion ring. If the packer element is to fill this void, there is a great risk that the packer element may be subjected to a large and destructive deformation.

Through data simulations and practical tests, the applicant has found that an annu- la r/radia I recess which has a triangular cross section, in which the angle between the surfaces of the groove is between 65 and 85 degrees, and a corresponding expansion ring, which fills out the groove more than 95 % when the packer is unloaded, require less energy for the expansion of the packer element than solutions in which the angle is outside the interval from 65 to 85 degrees. The smallest force requirement appears to be achieved when the angle is approximately 70 degrees.

When the triangular groove has a 70-degree angle, the internal sliding surfaces of the packer element can slide along the external sliding surfaces of the expansion ring in a radial direction with the lowest possible force.

The packer element may have a modulus of elasticity which is larger or equal to a modulus of elasticity for the expansion ring.

An effect of this feature, is that the deformation of the expansion ring may be similar to or less than the deformation of the packer element. This feature is useful for best possible guiding of the packing element. Since the expansion ring is elastic, the expansion ring may absorb some of the energy supplied to the packer element, so that material tensions in the packer element can be reduced. The expansion ring may typically be subjected to a limited deformation which may help to further reduce the forces required for setting the packer element.

The packer element has a radial height, and the recess may have a depth which is between 1/3 and 2/3 of the radial height of the packer element.

An effect of said depth range is that the transfer of forces is optimized, i.e. the ratio between the material left at the periphery of the packer element is ideal compared to the depth of the recess, for reducing the risk of, or even preventing, damage to the packer element.

The recess may comprise a bottom groove between the internal sliding surfaces, the bottom groove being rounded and having a radius of between 2.3 and 3.5 millimetres. The bottom groove may be positioned in a centre portion of the packer element.

An effect of said groove and radius range, is that a curved groove has less risk for crack than a sharp groove.

The first external sliding surface and the second external sliding surface may be connected by a rounded top portion with a radius that is at least 2 per cent larger than that of the rounded bottom groove in the packer element.

Thereby a clearance may be provided between the rounded top portion and the rounded bottom groove when, in use, the expansion ring is installed in the packer element. An advantage of this clearance is that the expansion ring may have a free space for a certain radial expansion so that the axial forces on the packer can be reduced during setting.

The packer element may be symmetric. The recess may be symmetric. The symmetry may be around a plane arranged perpendicularly to a centre axis of the packer element.

An effect of the packer element being symmetric is that the packer element may get a symmetric expansion when subjected to an axial force. A symmetric expansion is advantageous because it contributes to the external surface of the packer element being displaced in parallel towards the casing by the expansion, so that a simultaneous and even contact arises between the external surface of the packer element and the internal surface of the casing. The angle between the first external sliding surface and the second external sliding surface may be between 0 and 3 degrees smaller than the angle between the first internal sliding surface and the second internal sliding surface belonging to the packer element.

When the angle between the sliding surfaces on the expansion ring is equal or smaller than the angel between the internal sliding surfaces in the recess, as described above, the top portion of the expansion ring may easily be positioned in the centre of the bottom grove during assembly of the packer.

The annular support surface may be plane. The annular support surface may comprise a curved cross section. The annular support surface may comprise a surface being arranged perpendicular to a centre axis of the packer element.

In a second aspect, the invention relates to a downhole tool including the packer in accordance with the first aspect of the invention, the packer being adapted for a plurality of settings and/or resettings.

An effect of a downhole tool being equipped with the packer, is that downhole operations may be executed more efficiently. Since the packer is resettable, the packer may for instance be used for multiple pressure tests in a well, without pulling the downhole tool out of the well between the settings of the packer.

In a third aspect, the invention relates to a method for setting and resetting the packer in accordance with the first aspect of the invention, the method comprising the steps of: a. positioning the packer on a downhole tool; and b. positioning the downhole tool in a casing.

The method may further comprise the step of: c. applying an axial load to the packer so that the packer element expands in a radial direction and forms a barrier between the downhole tool and the casing.

Even further, the method may comprise the step of: d. reducing the axial load on the packer so that the radial expansion of the packer el- ement ceases.

The method may further comprise the step of: e. moving the downhole tool to another position in the casing and repeating the steps a-d, or moving the downhole tool out of the casing.

The method that is described herein makes it possible to provide one or more barriers in a petroleum well by reusing one and the same packer.

Specific description

Various embodiments will now be described, only as examples, with reference to the accompanying drawings, in which:

Figure 1 shows a cross section of a packer according to the invention;

Figure 2 shows a cross section of a packer element belonging to the packer;

Figure 3 shows a cross section of an expansion ring belonging to the packer;

Figure 4 shows, on a larger scale, a peripheral section of the packer element;

Figure 5 shows a peripheral section of the expansion ring;

Figures 6a-6c show, on a smaller scale, a sequence for setting the packer;

Figure 7 shows a section of a downhole tool including the packer; and

Figure 8 shows on a larger scale a cross section of the packer element and a backup ring.

Reference is made first to figures 1-5. An annular packer 1 comprises a packer element 10 and an expansion ring 20. The packer 1 is symmetric around a centre plane CP which is perpendicular to a centre axis CA of the packer 1. The packer element 10 has a rectangular peripheral cross section with a width B and a height H. The packer element 10 includes an internal recess 11. The recess 11 is shown as a triangular recess, the width of the recess 11 being reduced in an outward radial direction. The recess 11 comprises a first internal sliding surface 110 and a second internal sliding surface 111, which are facing each other and have an angle A10 between them.

The packer element 10 has an internal diameter D10 which, in the figure, is equal to an internal diameter D20 of the expansion ring 20. In an embodiment not shown, the diameter D10 of the packer element 10 may be larger than the diameter D20 of the expansion ring 20.

The two internal sliding surfaces 110, 111 are connected to each other via a bottom groove 112 which has a radius Rll. In the figures, the internal sliding surfaces 110, 111 and an internal surface 15 are connected by a rounded edge 115 with a radius R12. The rounded bottom groove 112 and the two rounded edges 115 contribute to reducing the internal tensions in the packer element 10.

The expansion ring 20 is shown with an external triangular cross section which corresponds to that of the internal recess 11. The expansion ring comprises a width B20 and a first external sliding surface 210 and a second external sliding surface 211, which are facing away from each other and have an angle A20 between them.

The packer 1 is assembled by the expansion ring 20 being pushed into the packer element

10 with the help of a tool (not shown). A lubricant may be applied to the internal recess

11 and/or to the expansion ring 20 during assembly, to ensure a low friction between the internal sliding surfaces 110, 111 of the packer element 10 and the external sliding surfaces 210, 211 of the expansion ring 20 during setting of the packer.

The packer element 10 further comprises on each side an external annular support surface 17 arranged to absorb an axial force from a contact surface 71 of a backup ring 70, as shown in figure 8. The annular support surface 71 can be adapted to different backup rings 70.

Reference is now made to figures 6a, 6b and 6c. Here, it is shown how the technical features of the invention provide a controlled setting of the packer 1. The packer 1 is mount- ed on a downhole tool 80 which is surrounded by a pipe 99. The downhole tool 80 comprises a displaceable body 85 which is arranged to apply an axial force to the packer 1. The packer 1 rests, in an axial direction, against two plane contact surfaces 70 faces belonging to the downhole tool 80. The displaceable body 85 may be a backup ring. Said backup ring may be positioned on either side of the packer 1 (not shown).

As illustrated, no support ring (not shown) is required, since the stress inside the packer 1 is less than a prior art packer (not shown).

In figure 6a, the packer 1 is unloaded (F = 0 %), and the packer element 10 and the expansion ring 20 have their original shapes.

In figure 6b, the body 85 is being displaced and the packer 1 is subjected to an axial force (F = 50 %). The packer element 10 is compressed in the axial direction. The internal sliding surfaces 110 and 111 of the packer element 10 slide along the external supporting sliding surfaces 210, 211 belonging to the expansion ring 20. Thereby the packer element 10 gets an internal support, while, at the same time, the expansion ring 20 guides the packer element 10 in a radial direction. The expansion ring 20 is compressed somewhat so that the surfaces 210, 211 form a curved surface.

Because of the support from the expansion ring 20 and its shape, the energy that will have to be supplied to the packer element 10 for the packer 1 to be set, may be reduced. The packer element 10 will, in the main, absorb energy in, at and near a contact surface 17.

Figure 6c shows the packer 1 when it has been set and transformed and forms a barrier in an annulus 95 between the downhole tool 80 and the pipe 99. The expansion ring 20 now fills the internal recess 11 of the packer element 10. The expansion ring 20 has been subjected to a minor deformation because it has absorbed energy which would otherwise have been absorbed by the packer element 10 and subjected the packer element 10 to increased internal tension. The energy of the packer element 10 is, in the main, concentrated along the outer edges X. Without the expansion ring 20 and the specific geometry of the expansion ring 20 and the recess 11, the energy at the corners of the packer ele- merit 10 would have become so great that there would have been a great risk of cracks along the outer edge of the packer element 10.

Figure 7 shows a downhole tool 80 including the packer 1, the downhole tool 80 being positioned in a pipe 99 and the packer 1 forming a barrier between the downhole tool 80 and the pipe 99.

Figure 8 shows an alternative embodiment of the packer 1, where two back up rings 70 are positioned directly to the packer 1 in two annular recesses 19 in the packer element 10. Each recess 19 comprises an external annular support surface 17 arranged to absorb the axial force from the contact surface 70 of a backup ring 70. The backup ring 70 comprises a spring element 72 arranged to expand radially when the packer 1 is set in the well. Positioning the backup ring 70 directly to the packer 1 as illustrated is possible because of the effect of technical features described in the first aspect of the invention.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative embodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive.

The use of the verb "to comprise" and its different forms does not exclude the presence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.