Closed system hydraulic expander

[0001] 1. Field of the Invention

[0002] The present invention generally relates to an apparatus and methods for wellbore completion. Particularly, the invention relates to an apparatus and methods for expanding a first tubular against a second tubular. More particularly, the invention provides a closed system expander tool for selectively expanding a portion of a tubular.

[0003] 2. Description of the Related Art

[0004] Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a section of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus known in the art, the casing is cemented into the wellbore by circulating cement into the annular space defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.

[0005] It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed or hung off of the existing casing by the use of slips, which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever decreasing diameter.

[0006] Apparatus and methods are emerging that permit tubulars to be expanded in situ. The apparatus typically includes expander tools which are fluid powered and are run into the wellbore on a working string. The hydraulic expander tools include radially expandable members which, through fluid pressure, are urged outward radially from the body of the expander tool and into contact with a tubular therearound. As sufficient pressure is generated on a piston surface behind these expansion members, the tubular being acted upon by the expansion tool is expanded past its point of elastic deformation. In this manner, the inner and outer diameter of the tubular is increased in the wellbore. By rotating the expander tool in the wellbore and/or moving the expander tool axially in the wellbore with the expansion member actuated, a tubular can be expanded into plastic deformation along a predetermined length in a wellbore.

[0007] Multiple uses for expandable tubulars are being discovered. For example, an intermediate string of casing can be hung off of a string of surface casing by expanding an upper portion of the intermediate string into frictional contact with the lower portion of surface casing therearound. This allows for the hanging of a string of casing without the need for a separate slip assembly as described above. Additional applications for the expansion of downhole tubulars exist. These include the use of an expandable sand screen, employment of an expandable seat for seating a diverter tool, and the use of an expandable seat for setting a packer.

[0008] There are problems associated with the expansion of tubulars. One problem particularly associated with the use of rotary expander tools is the likelihood of obtaining an uneven expansion of a tubular. In this respect, the inner diameter of the tubular that is expanded tends to initially assume the shape of the compliant rollers of the expander tool, including imperfections in the rollers. Moreover, as the working string is rotated from the surface, the expander tool may temporarily stick during expansion of a tubular, then turn quickly, and then stop again. This spring-type action in the working string further creates imperfections in the expansion job.

[0009] Another obstacle to smooth expansion relates to the phenomenon of pipe stretch. Those of ordinary skill in the art will understand that raising a working string a selected distance at the surface does not necessarily translate in the raising of a tool at the lower end of a working string by that same selected distance. The potential for pipe stretch is great during the process of expanding a tubular. Once the expander tool is actuated at a selected depth, an expanded profile is created within the expanded tubular. This profile creates an immediate obstacle to the raising or lowering of the expander tool. Merely raising the working string a few feet from the surface will not, in many instances, result in the raising of the expander tool; rather, it will only result in stretching of the working string. Applying further tensile force in order to unstick the expander tool may cause sudden recoil, causing the expander tool to move uphole too quickly, leaving gaps in the tubular to be expanded.

[0010] The same problem exists in the context of pipe compression. In this respect, the lowering of the working string from the surface does not typically result in a reciprocal lowering of the expander tool at the bottom of the hole. This problem is exacerbated by rotational sticking, as discussed above. The overall result of these sticking problems is that the inner diameter of the expanded tubular may not have a uniform circumference.

[0011] Additionally, the timing of various events downhole must be carefully orchestrated to achieve a smooth expansion. For example, initiation of axial translation of the expander tool should be coordinated with the gradual increase in pressure under the expander members to develop a gradual transition zone early on in the expansion process. If too little pressure is applied during axial translation, the engagement of the expandable tubular to the supporting tubular will be compromised. On the other hand, if too much pressure is applied during axial translation, the expander tool may stall or the transition zone will be too abrupt thereby compromising the strength of the expandable tubular due to excessive wall thinning.

[0012] Furthermore, some expander tools may collect cement and debris in the hydraulic chamber beneath the expander members. This is because these expander tools supply fluids to the hydraulic chambers via a hole in the mandrel of the tool. The hole provides a path through which cement may potentially enter the tool. Cement setting up behind the expander members may prevent retraction of the expander members on retrieval.

[0013] There is a need, therefore, for an improved apparatus for expanding a portion of casing or other tubular within a wellbore. Further, there is a need for an apparatus which will aid in the expansion of a tubular downhole and which avoids the potential of pipe-stretch/pipe-compression by the working string. Further still, there is a need for an apparatus which will aid in developing a gradual transition zone for expansion. Further still, there is a need for an apparatus that will reduce the potential for cement or debris to collect in the expander tool.

[0014] The present invention provides an apparatus and method for expanding a first tubular against a second tubular. In one aspect, an expander tool includes a mandrel coupled to a first spline assembly such that an annular space is formed between the same. Seals are placed between the mandrel and the first spline assembly to retain a fluid in the annular space. The fluid may be used to actuate one or more expander members disposed on the first spline assembly. The first spline assembly is rotatably connected to a second spline assembly which is also coupled to the mandrel. In another aspect, the expander tool may include a torque anchor connected to the second spline assembly, thereby preventing the second spline assembly and the first tubular from rotating.

[0015] The first tubular may be expanded against the second tubular by rotating the mandrel. Rotating the mandrel also rotates the first spline assembly which in turn rotates the expander members. Additionally, rotating the mandrel causes a first seal to advance axially relative to a second seal, thereby increasing the pressure in the annular space. When the pressure reaches a predetermined level, the expander members are actuated and begin to extend radially toward the first tubular and expand the first tubular against the second tubular.

[0016] In another aspect still, a closed system hydraulic expander tool may be used to perform the expansion process. The closed system hydraulic expander tool includes a rotatable tubular coupled to a first extendable housing and a second housing. The first extendable housing being movably coupled to the second housing. One or more expander members are disposed in the first extendable housing. The expander members are actuated by a fluid contained in a fluid chamber formed between the tubular and the first extendable housing. A torque anchor may be used to rotationally fix the second housing.

[0017] In another aspect still, the second housing of the expander tool may comprise an extendable housing. The second extendable housing being rotatably connected to the first extendable housing and threadedly coupled to the tubular. Upon actuation, the tubular and the first extendable housing are rotated. The rotation causes the second extendable housing to ride along the threads, thereby causing the second extendable housing to retract and extending the first extendable housing. The extension of the first extendable housing increases the pressure in the fluid chamber by compressing the fluid in the fluid chamber.

[0018] In another aspect still, the first extendable housing is movably connected to the second housing using a threaded connection. Upon actuation, the tubular and the first extendable housing are rotated. The threads of the first extendable housing ride along the threads of the second housing, thereby extending the first extendable housing. The extension of the first extendable housing increases the pressure in the fluid chamber by compressing the fluid in the fluid chamber.

[0019] So that the manner in which the above recited features and advantages of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

[0020] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0021] FIG. 1A-B is a cross-sectional view of a wellbore having an upper string of casing and a lower string of casing being lowered into the upper string of casing. In this view, the lower string of casing serves as the expandable tubular. Also depicted in FIG. 1A-B is an expander tool of the present invention for expanding the lower string of casing.

[0022] FIG. 2A-B depicts the wellbore of FIG. 1. In this view, the expander tool has been actuated and the lower string of casing has been expanded into the upper string of casing.

[0023] FIG. 3 presents an exploded cross-sectional view of a lower portion of the expander tool of the present invention.

[0024] FIG. 4 presents an exploded cross-sectional view of an upper portion of the expander tool of the present invention.

[0025] FIG. 5 presents an exploded cross-section view of lower portion of the expander tool after the lower string of casing has been expanded into the upper string of casing.

[0026] FIG. 6A presents a partial schematic view of another embodiment of the present invention.

[0027] FIG. 6B presents a partial schematic view of the embodiment of FIG. 6A near the end of the expansion process.

[0028] FIG. 1A-B presents a cross-sectional view of a wellbore 100 having an upper string of casing 110 and a lower string of casing 120. The lower string of casing 120, or liner, is being lowered into the wellbore 100 co-axially with the upper string of casing 110. The lower string of casing 120 is positioned such that an upper portion 120U of the lower string of casing 120 overlaps with a lower portion 110L of the upper string of casing 110. A collett (not shown) may be used to support the lower string of casing 120 on a working string 170.

[0029] In the example of FIG. 1A-B, the lower string of casing 120 serves as an expandable tubular. In particular, the lower string of casing 120 will be hung off of the upper string of casing 110 by expanding the upper portion 120U of the lower string of casing 120 into the lower portion 110L of the upper string of casing 110. However, it is understood that the apparatus and method of the present invention may be utilized to expand downhole tubulars other than strings of casing.

[0030] A sealing member 222 is preferably disposed on the outer surface of the lower string of casing 120 in order to seal an annular area between the tubulars 110, 120 as the upper portion of the lower string 120 is expanded. In the preferred embodiment, the sealing member 222 defines a matrix formed in grooves (not shown) on the outer surface of the lower string of casing 120. However, other configurations are permissible, including one or more simple rings formed circumferentially around the lower string of casing 120.

[0031] The sealing member 222 is fabricated from a suitable material based upon the service environment that exists within the wellbore 100. Factors to be considered when selecting a suitable sealing member 222 include the chemicals likely to contact the sealing member, the prolonged impact of hydrocarbon contact on the sealing member, the presence and concentration of erosive compounds such as hydrogen sulfide or chlorine, and the pressure and temperature at which the sealing member must operate. In a preferred embodiment, the sealing member 222 is fabricated from an elastomeric material. However, non-elastomeric materials or polymers may be employed as well, so long as they substantially prevent production fluids from passing upwardly between the outer surface of the lower string of casing 120U and the inner surface of the upper string of casing 110 after the expandable section 120U of the casing 120 has been expanded.

[0032] Also positioned on the outer surface of the lower string of casing 120 is at least one slip member 224. The slip member 224 is used to provide an improved grip between the expandable tubular 120U and the upper string of casing 110 when the lower string of casing 120 is expanded. In this example, the slip member 224 defines a plurality of carbide buttons interspersed within the matrix of the sealing member 222. However, any suitable placement of a hardened material which provides a gripping means for the lower string of casing 120 into the upper string of casing 110 may be used. For example, a simple pair of rings having grip surfaces (not shown) formed thereon for engaging the inner surface of the upper string of casing 110 when the lower string of casing 120 is expanded would be suitable. The size, shape and hardness of the slips 224 are selected depending upon factors well known in the art such as the hardness of the inner wall of casing 110, the weight of the casing string 120 being hung, and the arrangement of slips 224 used.

[0033] In order to expand the lower string of casing 120 seen in FIG. 1A-B, an expander tool 300 is provided. For clarity purposes, portions of the expander tool 300 have been enlarged as seen in FIGS. 3 and 4. Therefore, FIG. 1A-B will be described in conjunction with reference to FIGS. 3 and 4, with like elements similarly labeled. Similarly, FIG. 2A-B will be described in conjunction with reference to FIG. 5.

[0034] The expander tool 300 includes a rotatable mandrel 310 connected to a top connector 315 at an upper end and a bottom connector 320 at a lower end. Torque screws 325 are used to connect the mandrel 310 to the top connector 315 so that the top connector 315 may transfer torque to the mandrel 310.

[0035] A lower spline assembly 330 is coupled to a lower portion of the mandrel 310 using a first spline connection 332. The lower spline assembly 330 includes a lower inner spline 336 at least partially disposed in a lower outer spline 334. The lower inner spline 336 forms the expander body which houses one or more expander members 350. Preferably, each spline 334, 336 are tubular shaped and are coupled to each other using a second spline connection 338. Specifically, the second spline connection 338 consists of grooves formed on an inner surface of the lower outer spline 334 which mate with splines formed on an outer surface of the lower inner spline 336. The first spline connection 332 coupling the lower spline assembly 330 to the mandrel 310 includes splines formed on an inner surface of a lower portion of the lower outer spline 334 which mates with grooves formed on an outer surface of the mandrel 310. The first and second spline connections 332, 338 allow the mandrel 310 to transfer torque to the lower inner spline 336 when the mandrel 310 is rotated. The second spline connection 338 also allows the lower inner spline 336 to extend and/or retract axially relative to the lower outer spline 334.

[0036] The expander tool 300 contains an annular space 340 formed between the lower inner spline 336 and the mandrel 310. The annular space 340 acts as a fluid chamber for containing hydraulic fluid used to actuate one or more of the expander members 350 disposed in the lower inner spline 336. Seals 355, 360 are used to prevent fluid leakage from the annular space 340. An upper seal 355 attached to the mandrel 310 is disposed between the mandrel 310 and the lower inner spline 336. Because the upper seal 355 is attached to the mandrel 310, the upper seal 355 does not move axially during operation. A lower seal 360 attached to the lower inner spline 336 is disposed between the mandrel 310 and the lower inner spline 336. By attaching the lower seal 360 to the lower inner spline 336, the lower seal 360 travels with the lower inner spline 336 during operation. To effectively retain the fluid, the lower seal 360 contacts a profile 365 of predetermined length formed on an outer surface of the mandrel 310. The profile 365 allows the lower seal 360 to seal in the fluid as it travels with the lower inner spline 336. When lower seal 360 moves past the end of the profile 365, the fluid is allowed to drain out of the annular space 340.

[0037] Fluid may be introduced into the annular space 340 through one or more fill ports 370 disposed in the lower inner spline 336 prior to lowering the expander tool 300 into the wellbore 100. The pressure in the annular space 340 may be controlled using a pressure regulator 375. Preferably, the pressure regulator 375 is disposed above the expander members 350 of the expander tool 300.

[0038] The lower inner spline 336 has a plurality of recesses 380 to hold a respective expander member 350 capable of extending radially. In one embodiment, the expander member 350 is an expander pad 350 having a slightly barreled outer surface and a flat inner surface. The expander pad 350 is supported on a piston 382 and may be disposed within a cartridge 384 to facilitate replacement. The cartridge 384 is then attached to the recess 380 in the lower inner spline 336. The back of the piston 382 is exposed to the fluid pressure in the annular space 340. As the pressure is increased, the fluid forces the pistons 382 from the recesses 380. This, in turn, causes the expander pads 350 to contact the lower string of casing 120.

[0039] Although two expander pads 350 are shown in FIG. 1A-B, additional expander pads 350 may be added to the expander tool 300. Preferably, the expander tool 300 contains three expander pads 350. It must be noted that other expander members, including expander pads and expander rollers of various shapes and sizes, are suitable for use with the expander tool 300 of the present invention.

[0040] The expander tool 300 further includes an upper spline assembly 430 for axial translation of the expander members 350. Specifically, the upper spline assembly 430 includes an upper outer spline 434 coupled to an upper inner spline 436 using a third spline connection 438. The third spline connection 438 allows the upper inner spline 436 to extend/retract axially relative to the upper outer spline 434. A lower portion of the upper inner spline 436 is rotatably connected to an upper portion of the lower inner spline 336 using a thrust bearing assembly 440. The thrust bearing assembly 440 allows the lower and upper spline assemblies 330, 430 to rotate independently of each other. Although a thrust bearing assembly 440 is used, other apparatus capable of allowing the spline assemblies to rotate independently as known to a person of ordinary skill in the art are also applicable.

[0041] A lower portion of the upper inner spline 436 has threads 450 that engage helical threads 455 formed on an outer surface of the mandrel 310. Alternatively, a nut (not shown) having threads may be attached to the upper inner spline 436 for engaging the mandrel 310. The helical threads 455 are formed along a predetermined length of the outer surface of the mandrel 310. An upper portion of the upper outer spline 434 connects the upper spline assembly 430 to a torque anchor 500, thereby causing the upper spline assembly 430 to be rotationally fixed within the wellbore. In this manner, as the mandrel 310 is rotated, the threads 450 of the upper inner spline 436 may ride along the helical threads 455 of the mandrel 310 and axially advance the upper inner spline 436.

[0042] A torque anchor 500 suitable for use with the expander tool 300 of the present invention is seen in FIG. 1A-B. The torque anchor 500 is in the run-in position. In this view, the torque anchor 500 is in an unactuated position in order to facilitate run-in of the expander tool 300 and the lower casing string 120. The torque anchor 500 defines a body having sets of wheels 510, 520 radially disposed around its perimeter. The wheels 510, 520 reside within wheel housings 530, and are oriented to permit axial (vertical) movement, but not rotational movement of the torque anchor 500. Sharp edges (not shown) along the wheels 510, 520 aid in inhibiting rotational movement of the torque anchor 500. In the preferred embodiment, four sets of wheels 510 and 520 are employed to act against the upper casing 110 and the lower casing 120 strings, respectively. Although wheels 510, 520 are presented in the FIG. 1A-B, other types of slip mechanisms may be employed with the torque anchor 500 without deviating from the aspects of the present invention.

[0043] The torque anchor 500 is run into the wellbore 100 on the working string 170 along with the expander tool 300 and the lower casing string 120. The torque anchor 500 is attached below the top connector 315 using a bearing assembly 505. When the torque anchor 500 is activated, the bearing assembly 505 allows the torque anchor 500 to remain stationary while the top connector 315 and the mandrel 310 rotates. In the run-in position, the wheel housings 530 are maintained essentially within the torque anchor body 500. Once the lower string of casing 120 has been lowered to the appropriate depth within the wellbore 100, the torque anchor 500 is activated. Fluid pressure provided from the surface through the working string 170 acts against the wheel housings 530 to force the wheels 510 and 520 outward from the torque anchor body 500. Wheels 510 act against the inner surface of the upper casing string 110, while wheels 520 act against the inner surface of the lower casing string 120. This activated position is depicted in FIG. 2A. In the activated position, the torque anchor 500 is rotationally fixed relative to the upper string of casing 110.

[0044] In operation, the expander tool 300 of the present invention is run into the wellbore 100 on the lower end of a working string 170. As seen in FIG. 1, the working string 170 is temporarily connected to the lower string of casing 120 in order to accomplish the expansion operation in a single trip. In this manner, the lower string of casing 120 can be introduced into the wellbore 100 at the same time as the expander tool 300. A collet (not shown) disposed near the end of the working string 170 may optionally be used to releasably connect the lower string of casing 120 to the expander tool 300. Further, the collet may be landed into a radial profile (not shown) within the lower string of casing 120 to support the lower string of casing 120. The collet is mechanically or hydraulically actuated as is known in the art, and supports the lower string of casing 120 until such time as the lower string of casing 120 has been expandably set by actuation of the expander tool 300.

[0045] FIGS. 1A-B, 3, and 4 show the expander tool 300 of the present invention in the unactuated position. Prior to lowering the expander tool 300, a predetermined amount of hydraulic fluid is injected into the annular space 340 through one or more fill ports 370. In the unactuated position, the pressure inside the annular space 340 is insufficient to actuate the expander pads 350. The expander pads 350 reside in the recesses 380 until the fluid pressure in the annular space 340 rises above the actuation pressure. The expander tool 300 is lowered with the lower spline assembly 330 in a retracted position and the upper spline assembly 430 in an extended position. The torque anchor 500 is activated after the expander tool 300 reaches the predetermined depth in the upper string of casing 110 as seen in FIG. 2A.

[0046] Actuation of the expander tool 300 begins with the rotation of the working string 170. Rotating the working string 170 causes the top connector 315 to rotate, which, in turn, rotates the mandrel 310. The first spline connection 332 transfers the torque from the mandrel 310 to the lower spline assembly 330, thereby causing the expander pads 350 to rotate about the inner surface of the lower string of casing 120.

[0047] Rotating the mandrel 310 also initiates the axial advancement of the expander pads 350. As the mandrel 310 rotates, the threads 450 on the upper inner spline 436 ride along the helical threads 455 of the mandrel 310. Being rotationally fixed, the upper inner spline 436 is advanced axially relative to the upper outer spline 434 and the mandrel 310 as its threads 450 engage the threads 455 of the mandrel 310. Connected to the upper inner spline 436, the lower inner spline 336 and the expander members 350 are pulled along by the upper inner spline 436. Even though the lower inner spline 336 is traveling axially, it must be noted that the lower inner spline 336 continues to rotate with the mandrel 310 due to the thrust bearing assembly 440.

[0048] The axial advancement of the lower inner spline 336 triggers an increase in hydraulic pressure in the annular space 340. As discussed above, the upper seal 355 is located on the mandrel 310 and thus remains stationary axially relative to the moving lower inner spline 336. On the other hand, the lower seal 360 is located on the lower inner spline 336 and thus travels with the lower inner spline 336 along the mandrel 310. Consequently, axial advancement of the lower seal 360 relative to the upper seal 355 compresses the fluid in the annular space 340, thereby causing a gradual increase in hydraulic pressure in the annular space 340. The pressure increase under the pads 350 provides the pressure necessary for expansion. The pressure gradually extends the pads 350 against the lower string of casing 120. This gradual expansion against the lower string of casing 120 creates a gradual transition zone of expansion as seen in FIGS. 2B and 5. The pressure continues to rise until it reaches the optimum expansion pressure. Once reached, the pressure regulator 375 activates and bleeds off fluid in the annular space 340 to regulate the pressure in the annular space 340. It is contemplated that more than one pressure regulator 375 may be used in order to achieve the desired transition zone profile. Disposed above the expander pads 350, the pressure regulator 375 may discharge the fluid ahead of the expander members 350 so that they may provide additional lubricant for the expansion pads 350.

[0049] FIGS. 2A-B and 5 show the expander tool 300 near the end of the expansion process. At this point, the upper spline assembly 430 is in a retracted position and the lower spline assembly 330 is in an extended position. The lower inner spline 336 has moved the lower seal 360 past the profile 365 on the mandrel 310. Disengaged from the profile 365, the lower seal 360 is no longer capable of retaining fluid in the annular space 340. The leakage of fluid relieves the pressure in the annular space 340, thereby deactivating the expander pads 350. After the expander members 350 have returned to their respective recess 380, the torque anchor 500 is deactivated and the collett is released from the lower string of casing 120. Thereafter, the expander tool 300 may be retrieved by pulling on the working string 170.

[0050] It is believed that by controlling the expansion pressure through the axial advancement of the expander members 350, a gradual transition zone for expansion is more easily achieved. Because the pressure is now a direct function of axial movement of the expander members 350, the timing of pressure and rotation from the surface is no longer necessary. Any sudden torque increase, due to pipe drag, is translated into axial movement of the expander members 350, which, in turn, gradually increases the pressure in the expander tool 300. Therefore, there is no time lag between the expander members' 350 axial advancement and the application of pressure. Further, the gradual increase in pressure behind the expander members 350 results in a less abrupt transition zone from the unexpanded portion to the expanded portion. As a result, the thinning effect on the transition zone is minimized and the overall strength of the lower string of casing 120 is conserved.

[0051] It is contemplated that rotation of the mandrel 310 is accomplished by rotating the working string 170 from the surface. However, rotation may also be achieved by activation of a downhole rotary motor, such as a mud motor (not shown).

[0052] FIG. 6A partially shows another embodiment of an expander tool 600 according to aspects of the present invention. In this embodiment, the expander members 650 may be advanced using a rotationally fixed sleeve 608 coupled directly to the lower inner spline 636.

[0053] Similar to the previous embodiment, the expander tool 600 includes a lower spline assembly 630 coupled to a mandrel 610 using a first spline connection (not shown). The lower spline assembly 630 includes a lower inner spline 636 coupled to a lower outer spline (not shown) using a second spline connection (not shown). An annular space 640 is formed between the lower inner spline 636 and the mandrel 610. The annular space 640 is sealed using an upper seal 655 and a lower seal (not shown). The lower inner spline 636 houses the expander members 650 used to expand the lower string of casing 620. The expander tool 600 further includes a torque anchor 700 attached below the top connector (not shown) using a bearing assembly (not shown).

[0054] To advance the expander members 650, a tubular sleeve 608 is connected to the torque anchor 700 at one end and coupled to the lower inner spline 636 at another end. Specifically, the sleeve 608 is connected below the torque anchor 700, thereby rotationally fixing the sleeve 608 when the torque anchor 700 is activated. An inner diameter of the sleeve 608 is such that the lower inner spline 636 may be received in an annular area 677 between the sleeve 608 and the mandrel 610. At the other end of the sleeve 608, threads 720 are formed on an inner surface thereof. Alternatively, a nut (not shown) having threads may be attached to the end of the sleeve 608. Preferably, the threads 720 on the sleeves 608 are disposed proximate the upper seal 655 of the expander tool 600. The threads 720 mate with threads 730 formed on a predetermined length of an outer surface of the lower inner spline 636. The distance between the threads 720 on the sleeve 608 and the torque anchor 700 should be at least the predetermined length of the threads 730 on the lower inner spline 636.

[0055] In operation, the expander tool 600 is run into the wellbore in the unactuated position shown in FIG. 6A. The torque anchor 700 is activated after the expander tool 600 reaches the predetermined depth in the upper string of casing.

[0056] Actuation of the expander tool 600 begins with the rotation of the working string (not shown). Rotating the working string causes the top connector to rotate, which, in turn, rotates the mandrel 610. The first spline connection transfers the torque from the mandrel 610 to the lower spline assembly 630, thereby causing the expander members 650 to rotate about the inner surface of the lower string of casing 620. In this embodiment, expander pads 650 are used to expand the lower string of casing 620.

[0057] Rotating the mandrel 610 also initiates the axial advancement of the expander pads 650. As the mandrel 610 rotates, the threads 730 on the lower inner spline 636 engage the threads 720 of the sleeve 608. Because the sleeve 608 is rotationally fixed, the threads 730 of the lower inner spline 636 ride along the threads 720 of the sleeve 608, thereby axially advancing the lower inner spline 636 relative to the mandrel 610. In this manner, the expander pads 650 are advanced in the wellbore.

[0058] As discussed above, the axial advancement of the lower inner spline 636 triggers an increase in hydraulic pressure in the annular space 640. Specifically, the upper seal 655 remains stationary axially relative to the moving lower inner spline 636, while the lower seal travels with the lower inner spline 636 along the mandrel 610. Consequently, axial advancement of the lower seal relative to the upper seal 655 reduces the annular space 640 and compresses the fluid in the annular space 640. Compression of the fluid causes a gradual increase in hydraulic pressure in the annular space 640. The pressure increase under the pads 650 provides the pressure necessary for expansion. The pressure extends the pads 650 radially against the lower string of casing 620. This gradual expansion against the lower string of casing 620 creates a gradual transition zone of expansion.

[0059] The pressure continues to rise until it reaches the optimum expansion pressure. Once reached, the pressure regulator 675 activates and bleeds off fluid in the annular space 640 to regulate the pressure in the annular space 640. Thus, even though the annular space 640 continues to compress, the optimum expansion pressure may be maintained by the pressure regulator 675. It is contemplated that more than one pressure regulator 675 may be used in order to achieve the desired transition zone profile. Disposed above the expander pads 650, the pressure regulator 675 may discharge the fluid ahead of the expander pads 650 so that they may provide additional lubricant for the expansion pads 650.

[0060] The expander pads 650 are advanced until the threads 720 of the sleeve 608 are below the threads 730 on the lower inner spline 636. Without threads 730 to engage the sleeve 608, the lower inner spline 636 is unable to advance further as illustrated in FIG. 6B. At the same time, the lower seal has moved beyond the profile on the mandrel 610, thereby allowing hydraulic fluid to drain from the annular space 640. The expander pads 650 deactuate as the fluid pressure behind the piston 682 decreases, thereby allowing the piston 682 to return to the recess 680.

[0061] After the expander pads 650 have returned to their respective recess 680, the torque anchor 700 is deactivated and the collett is released. Thereafter, the expander tool 600 may be retrieved by pulling on the working string.

[0062] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.