NO318590B1 - Down-hole equipment - Google Patents

Description

The present origin relates to down-hole equipment, i.e. equipment that is used downhole in a borehole in connection with the extraction of hydrocarbon fuel reserves.

In particular, the invention relates to a downhole casing unscrewing assembly as stated in the independent claim 1.

Brochure 4035B from Tri-State Oil Tools describes a prior art casing unscrewing assembly in accordance with the preamble of the appended claim 1. This prior art casing unscrewing assembly includes upper and lower anchor sections for gripping the casing section to be separated. A torque generator and clutch is located between the two armature sections to provide a means for rotating the armature sections relative to each other and thereby unscrewing the threaded connection between the casing sections. The operating conditions are such that the bottom anchor and associated casing sections will mainly remain fixed inside the borehole while the top anchor and associated casing section rotate relative to it. For each cycle of the torque generator, the armatures make half a turn relative to each other. As the torque generator is operated and the upper anchor and associated casing section is rotated through 180° inside the borehole, the work string connecting the upper anchor to the surface must be allowed to rotate at the surface. Furthermore, as the casing section is unscrewed and separated, the work string must be allowed to move up the hole. The work string can be moved in this way using either the torque generator or equipment placed at the surface. However, the need to move the work string in the rotational and axial directions reduces the efficiency of the assembly from Tri-State Oil Tools resulting in compound casing unscrewing operations. The present invention seeks to overcome these problems.

A downhole anchor has been provided, for use in a borehole, consisting of an elongated housing, gripping means which are movable relative to said housing between a released position and a gripping position in which the gripping means can engage with an inner surface of the borehole, and a hydraulic chamber inside said housing in fluid communication with a surface of gripping elements, where applying pressure to hydraulic fluid inside said hydraulic chamber causes the gripping member to move from the released position to the gripping position.

Thereby, the anchor in accordance with this invention achieves its gripping function with hydraulic organs, instead of with hydraulic-mechanical organs in known anchors, i.e. the hydraulic force acts directly on the gripping organs without an intermediate mechanical transmission. By means of this arrangement, the hydraulic fluid can directly push the gripping members into engagement with the inner surface of the borehole, without the use of an intermediate transmission or connection.

It should be noted that when the borehole is set with casing, the inner surface of the borehole will consist of the inner surface of the casing.

Advantageously, the arrangement is such that the supply of pressure to said hydraulic fluid causes the gripper to move radially in relation to the axis of the housing, without accompanying axial movement of the gripper. The casing would usually be positioned between its longitudinal axis substantially parallel to that of the borehole.

The gripping means preferably consist of a plurality of gripping elements placed for radial movement inside the borehole. Two or more gripping elements can be separated along the longitudinal axis of the housing. In addition, or instead, two or more gripping elements can be placed around the longitudinal axis of the said housing. In the preferred embodiment, a set of three gripping elements is placed around the longitudinal axis of the housing at an angle of 120° relative to each other; it is preferred that two of the aforementioned set of three gripping elements are placed, the two sets being separated from each other along the longitudinal axis of the housing. When two sets of three gripping elements are fitted, it is preferred that the second set is fitted around the longitudinal axis of the housing with an angularly offset design in relation to the first set, where the angle between the two sets is preferably 60°.

It is desirable that it is placed on pressing members to press the gripping member towards the released position. The impressed members are preferably a leaf spring. It is highly desirable that the gripping elements are fixed to a pair of leaf springs.

Each gripping element preferably consists of a blade and at least one plunger, which blade has at least one serrated outer edge portion adapted to grip the inner surface of the borehole. The blade may be fitted with a recess for receiving each stamp. The hydraulic pressure preferably acts on a surface of the blade within each recess to push the blade away from the housing and away from the one or more pistons. Typically, the blade and one or each piston will be positioned such that the blade is pushed away from the top of the one or each piston. Thereby, the blade in this design acts like a hydraulic cylinder.

A downhole torque generator is also provided, for use in a borehole, consisting of an elongated first shaft, and an elongated second shaft, each shaft having a hole located through its length, where the hole in the first shaft is in

fluid communication with the hole in the second shaft, and the first shaft is connected to the second shaft by a torque-generating connection, after which the application of an axial tensile force and/or axial compression force to said shafts causes said first and second shafts to rotate in relative to each other around the aforementioned torque-generating connection.

The first shaft is preferably placed in the form of a tubular housing placed around the second shaft with a torque-generating connection, and the second shaft acts as a drive shaft. It is also preferred that the torsion is generated by an axial compression force, which is produced by hydraulic pressure inside the holes in the shafts.

The torque-generating connection preferably consists of helical grooves placed on one of said shafts (preferably the second shaft), which is received in a corresponding helical recess in the second of said shafts (preferably the first shaft). In the preferred arrangement, if the shafts are pulled together, they will rotate relatively in one direction and will move completely away from each other, and if the shafts are pushed together, they will rotate relatively in an opposite direction and will move axially toward each other; the shafts can be relatively moved between a retracted position in which the combined length of the shafts is a minimum; and an extended position, in which the combined length of the shafts is a maximum. Stop means may be provided to limit movement of the shafts past the contracted and extended positions. It is preferred that at least part of the second shaft is received inside the first shaft.

It is desirable that pressing means are provided to press the shafts towards the retracted position. An annular chamber may be located between the interior of the first shaft and the exterior of the part of the second shaft that is inside the first shaft, and the pressing members may be located in this annular chamber. It is particularly preferred that the pressing members are a stack of disc springs. Preferably, a piston is placed inside the hole in the first shaft, which piston is adapted to apply an axial compression force against the pressing members. The piston can be connected to the other shaft by means of a screw thread.

If a hydraulic fluid is pumped through the hole in the first shaft to the hole in the second shaft, and through the hole in the second shaft, the first and second shafts will remain in the retracted position, because there will be no relative rotary motion, due of the power of the pressed organs. If the hole in the second shaft is blocked - or, more commonly, a blockage is formed downstream of the second shaft - pressure will build up in the hole, and will apply a force to the piston. This force will eventually overcome the pressing force of the pressing member, causing the first and second shafts to rotate relative to each other, moving them to the extended position. If the fluid pressure is removed, the pressing members will force the first and second axles back to the retracted position.

The initiation of relative rotary motion can thus be achieved by selecting the relative size of the holes in the shafts to produce a pressure drop to act on the piston to overcome the force of the pressing members. This can be done, for example, by reducing the size of the hole in the second shaft.

There is further provided a downhole clutch assembly, for use in a borehole, consisting of an elongated drive shaft and an elongated driven shaft, each shaft having a hole located longitudinally therethrough, which hole in the drive shaft is in fluid communication with the hole in the driven shaft , and connecting means for connecting the drive shaft to the driven shaft, which connection means is such that rotation of the drive shaft in a first direction causes the driven shaft to rotate with the drive shaft, and rotation of the drive shaft in a direction opposite to the first direction does not cause the driven shaft rotates with the drive shaft.

The connecting member preferably consists of: a flange on the driven shaft, which flange is axially movable along the driven shaft and is rotatably fixed in relation to this; a plurality of detents on the flange for engagement with a plurality of cooperating detents on the drive shaft; and urging means for pressing the detents on the collar into engagement with the detents on the drive shaft; wherein the detents and the pressing force are such that when the drive shaft is rotated in the said first direction, the detents are held in engagement, whereby rotary motion of the drive shaft is transmitted to the driven shaft through the flange, and when the drive shaft is rotated in the opposite direction to the first direction, the collar is moved axially from the drive shaft, and the detents on the flange disengage from the detents on the drive shaft, whereby rotary movement of the drive shaft is not transferred to the flange. This can be achieved by suitable design of the latches; in one direction the latches are angled in relation to each other so that during rotary movement these slide over each other and push the flange axially against the spring force.

It should be noted that the flange could instead be located on the drive shaft, in which case the detents on the drive shaft would instead be located on the driven shaft.

Furthermore, a downhole swivel is provided, for use in a borehole, consisting of a first elongate coupling part and a second elongate coupling part mountably secured to the first elongate coupling part, where the first and second coupling parts are each fitted with a hole lying through them, which hole in the first coupling part is in fluid communication with the hole in the second coupling part, and the first and second coupling parts are each provided with means for connecting additional equipment thereto.

The second coupling part, which is preferably located at the bottom when in use, is provided with a shoulder adapted to meet a surface inside the borehole to prevent further movement of the said swivel piece down the borehole.

It is desirable that the first elongate part is rotatably secured to the second rotatable part by means of a set of axial thrust plates.

The means for connecting additional equipment are usually screw joints. The shoulder is advantageously used to abut against the upper part of the well casing, to prevent further downward movement of the swivel in relation to the well casing.

Furthermore, a fishing socket tool has been installed to retrieve downhole equipment, consisting of a socket shaft adapted for fixed placement on other downhole equipment; a sleeve housing located over at least a portion of the sleeve shaft; gripping means for gripping the downhole equipment to be retrieved, which sleeve housing has locking means adapted to lock the gripping members in a gripping position, and the sleeve housing is axially movable relative to the shaft from a release position, in which the locking means does not lock the gripping members to the gripping position and a locking position, in which the gripping means locks the gripping means in the gripping position; and a release member axially movable relative to the sleeve shaft and the housing, said release member being movable into contact with the sleeve housing to move the sleeve housing to the release position.

The fishing muff tool is also known as a fishing tool. A wide range of downhole equipment can be retrieved with the fish socket tool: it is particularly suited to removing casing from a well, as part of the screw-out assembly.

The fishing sleeve tool preferably has a centrally located hole axially in the shaft.

Devices are preferably placed to prevent rotary movement between the sleeve shaft and the sleeve housing. These members desirably consist of a plurality of interlocking grooves placed on an outer surface of the sleeve shaft and on an inner surface of the sleeve housing. This arrangement enables a torque to be transmitted from the sleeve shaft to the sleeve housing, and to the gripping member through the locking member. In this way, the fishing socket tool can be used to rotate the downhole equipment to be retrieved. This is particularly applicable when the downhole equipment to be retrieved must be rotated to remove it from other downhole equipment.

Stop means may be provided to prevent movement of the housing past the lock and release positions.

The release element preferably consists of a tubular element with a diameter substantially equal to the diameter of the sleeve housing. This enables one end of the release element to bump against one end of the sleeve housing when this is moved into contact with the sleeve housing. In the preferred embodiment, the release element is fixedly attached to downhole equipment separate from the rest of the fishing socket tool.

In accordance with the invention, a downhole casing unscrewing assembly is provided as indicated in the characteristic of independent claim 1.

Advantageous embodiments of the invention appear from the independent claims.

Advantageously, the downhole casing unscrewing assembly is in the form of an elongate shaft with a hole located longitudinally therethrough, which hole is adapted to receive hydraulic fluid used to operate the assembly.

The anchor members and the torque-generating members form parts of the extended shaft. The torque generating members are ideally located between the first and second anchor members.

Advantageously, the first and second anchor means consist of an elongated housing, gripping means movable relative to said housing between a released position and a gripping position in which the gripping means can engage an inner surface of the borehole, and a hydraulic chamber inside said housing, in fluid communication with a surface of said gripping member, whereupon application of pressure to said hydraulic fluid within said hydraulic chamber causes gripping members to move from said released position to said gripping position.

The anchor members thereby receive their gripping function with hydraulic members, instead of with hydraulic-mechanical members with known anchors, i.e. the hydraulic force acts directly on the gripping member without an intermediate mechanical connection. By means of this arrangement, the hydraulic fluid can directly push the gripping members into engagement with the inner surface of the borehole, without the use of an intermediate connection or transition.

Advantageously, the arrangement is such that the supply of pressure to said hydraulic fluid causes the gripper to move radially in relation to the axis of the housing, without accompanying axial movement of the gripper. The casing would usually be positioned between its longitudinal axis substantially parallel to that of the borehole.

The gripping means preferably consist of a plurality of gripping elements placed for radial movement inside the borehole. Two or more gripping elements can be separated along the longitudinal axis of the housing. In addition, or instead, two or more gripping elements can be placed around the longitudinal axis of the said housing. In the preferred embodiment, a set of three gripping elements is placed around the longitudinal axis of the housing at an angle of 120° relative to each other; it is preferred that two of the aforementioned set of three gripping elements are placed, the two sets being separated from each other along the longitudinal axis of the housing. When two sets of three gripping elements are fitted, it is preferred that the second set is fitted around the longitudinal axis of the housing with an angularly offset design in relation to the first set, where the angle between the two sets is preferably 60°.

It is desirable that it is placed on pressing members to press the gripping member towards the released position. The impressed members are preferably a leaf spring. It is highly desirable that the gripping elements are fixed to a pair of leaf springs.

Each gripping element preferably consists of a blade and at least one plunger, which blade has at least one serrated outer edge portion adapted to grip the inner surface of the borehole. The blade may be fitted with a recess for receiving each stamp. The hydraulic pressure preferably acts on a surface of the blade within each recess to push the blade away from the housing and away from the one or more pistons. Typically, the blade and one or each piston will be positioned such that the blade is pushed away from the top of the one or each piston. Thereby, the blade in this design acts like a hydraulic cylinder.

Advantageously, the downhole torque generator comprises first and second elongate shafts, each shaft having a longitudinally through hole, the hole in the first shaft being in fluid communication with the hole in the second shaft, and the first shaft being mounted on the second shaft at a torque-generating connection, where the application of an axial tensile force and/or an axial compression force on said shafts causes said first and second shafts to rotate relative to each other around said torque-generating connection.

The first shaft is preferably placed in the form of a tubular housing placed around the second shaft with a torque-generating connection, and the second shaft acts as a drive shaft. It is also preferred that the torsion is generated by an axial compression force, which is produced by hydraulic pressure inside the holes in the shafts.

The torque-generating connection preferably consists of helical grooves placed on one of said shafts (preferably the second shaft), which is received in a corresponding helical recess in the second of said shafts (preferably the first shaft). In the preferred arrangement, if the shafts are pulled together, they will rotate relatively in one direction and will move completely away from each other, and if the shafts are pushed together, they will rotate relatively in an opposite direction and will move axially toward each other; the shafts can be relatively moved between a retracted position in which the combined length of the shafts is a minimum; and an extended position, in which the combined length of the shafts is a maximum. Stop means may be provided to limit movement of the shafts past the contracted and extended positions. It is preferred that at least part of the second shaft is received inside the first shaft.

It is desirable that pressing means are provided to press the shafts towards the retracted position. An annular chamber may be located between the interior of the first shaft and the exterior of the part of the second shaft that is inside the first shaft, and the pressing members may be located in this annular chamber. It is particularly preferred that the pressing members are a stack of disc springs. Preferably, a piston is placed inside the hole in the first shaft, which piston is adapted to apply an axial compression force against the pressing members. The piston can be connected to the other shaft by means of a screw thread.

If a hydraulic fluid is pumped through the hole in the first shaft to the hole in the second shaft, and through the hole in the second shaft, the first and second shafts will remain in the retracted position, because there will be no relative rotary motion, due of the power of the pressed organs. If the hole in the second shaft is blocked - or, more commonly, a blockage is formed downstream of the second shaft - pressure will build up in the hole, and will apply a force to the piston. This force will eventually overcome the pressing force of the pressing member, causing the first and second shafts to rotate relative to each other, moving them to the extended position. If the fluid pressure is removed, the pressing members will force the first and second axles back to the retracted position.

The initiation of relative rotary motion can thus be achieved by selecting the relative size of the holes in the shafts to produce a pressure drop to act on the piston to overcome the force of the pressing members. This can be done, for example, by reducing the size of the hole in the second shaft.

The casing unscrewing assembly preferably further includes a downhole clutch assembly which is disposed between the torque generating member and the first anchor member, which allows the torque generating member to apply a torsional force to the first anchor member in one direction, and does not allow the torque generating member to generating member to supply a torsional force to the first anchor member in the opposite direction.

The downhole mounted clutch assembly preferably consists of an elongate drive shaft and an elongate driven shaft, which drive shaft and driven shaft each have a hole extending longitudinally therethrough, and the hole in the drive shaft is in fluid communication with the hole in the driven shaft, and connecting means for connecting the drive shaft to the driven shaft, said connecting means being such that rotation of the drive shaft in the first direction causes the driven shaft to rotate with the drive shaft, and rotation of the drive shaft in a direction opposite to the first direction does not cause the driven shaft to rotate with the drive shaft. In practice, the drive shaft is located at the end of the clutch device against the torque-generating member, and the driven shaft is located at the end of the clutch device against the first anchor member.

The connecting member preferably consists of: a flange on the driven shaft, which flange is axially movable along the driven shaft and is rotatably fixed in relation to this; a plurality of detents on the flange for engagement with a plurality of cooperating detents on the drive shaft; and urging means for pressing the detents on the collar into engagement with the detents on the drive shaft; wherein the detents and the pressing force are such that when the drive shaft is rotated in the said first direction, the detents are held in engagement, whereby rotary motion of the drive shaft is transmitted to the driven shaft through the flange, and when the drive shaft is rotated in the opposite direction to the first direction, the collar is moved axially from the drive shaft, and the detents on the flange disengage from the detents on the drive shaft, whereby rotary movement of the drive shaft is not transferred to the flange. This can be achieved by suitable design of the latches; in one direction the latches are angled in relation to each other so that during rotary movement these slide over each other and push the flange axially against the spring force.

It should be noted that the flange could instead be located on the drive shaft, in which case the detents on the drive shaft would instead be located on the driven shaft.

It is desirable that the casing stripping assembly further includes a downhole swivel for use in a borehole, consisting of a first elongate connecting part and a second elongate connecting part rotatably fitted to the first elongate connecting part, the first and second elongate connecting part each being fitted with a hole located longitudinally therethrough, which hole in the first connecting part is in fluid communication with the hole in the second connecting part and the first and second connecting parts are each provided with means for connecting further equipment thereto.

The second connecting part, which is placed at the bottom in use, is preferably placed with a shoulder adapted to meet a surface inside the borehole to prevent further movement of the said swivel piece down the borehole. The shoulder provides an excellent means for locating the unscrewing assembly in the correct portion of the casing after it has been cut at the correct position with a cutting assembly.

It is desirable that the first and elongated part is rotatably secured to the second rotatable part by means of a set of axial washers.

Means for connecting additional equipment are usually screw joints. The shoulder is advantageously used to abut against the upper part of the well casing, to prevent further downward movement of the swivel in relation to the well casing.

The unscrewing assembly further preferably includes an upper idle damper tube positioned above the swivel. The upper external plain coupling consists of first and second elongate shafts each of which has a hole located longitudinally through them, which hole in the first shaft is in fluid communication with a hole in the second shaft. The first and second shafts are axially movable relative to each other between a retracted position, in which the total length of the lower idle damper tube is a minimum, and an extended position in which the total length of the lower idle damper tube is a maximum. The purpose of the upper external plain coupling is to allow upward movement which takes place as the first casing section is disengaged from the second casing section.

The unscrewing assembly is preferably fitted with a fish socket tool, so that the casing can be pulled off and retrieved from the borehole in one easy trip. The fishing sleeve tool is also known in the art as a fishing tool. The fishing socket tool is preferably placed between the upper external plain coupling and the swivel.

In the preferred embodiment, the fishing socket tool consists of: a socket shaft adapted for fixed attachment to one end of the upper outer plain coupling and at the other end to the swivel; a sleeve housing situated over at least parts of the sleeve shaft; gripping means for gripping the casing, wherein the sleeve housing has locking means adapted to lock the gripping members in the gripping position, and the sleeve housing is axially movable relative to the shaft from a release position, in which the locking means does not lock the gripping members in the gripping position and a locking position which the gripping means lock in the gripping means in the gripping position; and a release element axially movable relative to the socket shaft and the housing, which release element is movable into contact with the socket housing to move the socket housing into the release position.

Devices are preferably placed to prevent rotary movement between the sleeve shaft and the sleeve housing. These members preferably consist of a plurality of interlocking grooves placed on an outer surface of the sleeve shaft and on an inner surface of the sleeve housing. This arrangement enables torque to be transmitted from the sleeve shaft (ie via the upper outer plain coupling) to the sleeve housing and the gripping members through the locking member. In this way, the fishing socket tool can be used to rotate the casing that is gripped.

The sleeve shaft is preferably fitted with a centrally located hole axially through the shaft, which hole is in fluid communication with the holes in the upper outer plain coupling and the swivel piece.

Stop means may be fitted to prevent movement of the housing past the locking and release positions.

The release element preferably includes a tubular element with a diameter substantially equal to the diameter of the sleeve housing. This enables one end of the release element to bump against one end of the sleeve housing when this is moved into contact with the sleeve housing. In the preferred embodiment, the release element is secured to the upper outer plain coupling. It is particularly preferred that the sleeve shaft is connected to one of the first and second shafts of the upper outer plain coupling, and the release element is connected to the other of the first and second shafts of the upper outer plain coupling.

In a preferred embodiment, the unscrewing assembly further includes a lower outer idle damper pipe placed between the torque generating member and the second anchor member. The lower outer plain coupling consists of first and second elongate shafts each having a through hole in the longitudinal direction, which hole in the first shaft is in fluid communication with the hole in the second shaft. The first and second shafts are axially movable relative to each other between a retracted position, in which the total length of the lower plain coupling is a minimum, and an extended position, in which the total length of the lower plain coupling is a maximum. The purpose of the lower plain coupling is to compensate for the increase in length of the torque-generating member as torque is generated, to prevent the anchor member from moving axially. The distance between the retracted and extended position of the lower outer plain coupling is preferably substantially equal to the distance between the retracted and extended position of the torque generating member. In the preferred arrangement, the second axle is comprised of an outer housing, and the first axle is located within the outer housing.

Lubrication is optionally provided between the first and second shafts of the lower outer plain coupling, and the internal hydraulic pressure is such that it pushes the lower outer plain coupling to the retracted position. When the first shaft in the lower outer plain coupling is pushed downward by the torque generating member, the frictional forces into the outer plain coupling tend to push the second armature downward. However, the internal hydraulic pressure tends to close the outer plain coupling, and this creates an upward force on the outer housing that balances the downward movement resisting a frictional force. The external plain coupling's rotary drive can usually be a hexagon or a slot, and is preferably immersed in an oil bath.

It is preferred that the first shaft of the lower external straight coupling is connected to the second shaft of the torque-generating member and the second shaft of the lower external straight coupling is connected to the housing of the second anchor member.

It is desirable to place valve means to allow filling of the equipment as it runs into the borehole. Valve members can be fixedly attached to the second anchor member on the opposite side of the torque-generating member. However, it is preferred that the valve member is fixedly located above the upper external smooth coupling under a circulation piece (circulation piece is discussed in more detail below).

The valve members preferably consist of an elongated valve body and a valve element inside the valve body. The valve body is fitted with a hole located throughout in the longitudinal direction, which hole is in fluid communication with the hydraulic chamber in the second anchor member. The valve body can also include at least one port situated from the hole in the valve body to the borehole.

The valve element is preferably movably placed inside the hole in the valve body. The valve element can be movable corresponding to fluid flow through the hole. The valve element can be fixed to the valve body with a break pin, so that it does not move relative to it until the fluid flow reaches a predetermined amount - and when the fluid flow reaches the predetermined amount, the break pin is broken, and the valve element begins to move relative to to the valve body. The valve element moves to close one or each port, preventing hydraulic fluid from leaving the valve body and entering the borehole. This allows hydraulic pressure to build up inside the unscrewing assembly.

In a preferred embodiment, the casing unscrewing assembly further includes an elongated circulation piece. If the valve member is placed below the second anchor member, the circulation piece can be placed immediately above the upper external plain coupling. If the valve element is placed above the upper external plain coupling (which is preferred), the circulation piece can be placed immediately above the valve element.

The circulation piece will be activated after the casing is unscrewed when it is desired to pull the unscrewing assembly and related equipment out of the borehole. The circulation piece includes a hole located longitudinally therethrough in fluid communication with the hole in the other components of the casing-unscrewing assembly. The circulation piece also includes a radial hole in fluid communication with the hole in the longitudinal direction of and with the interior of the borehole. However, a sealing element usually prevents fluid communication between the radially and longitudinally located holes. The sealing member may be held in place by a break pin, and the break pin may be broken by applying a sufficient downward force to the sealing member. This power can be supplied, e.g. by dropping a ball from the surface.

Reference is now made to the attached drawings where:

Figure IA shows a schematic view of a borehole in which a first embodiment of the unscrewing assembly in accordance with the invention is placed; Figure 1B is a schematic view of a borehole in which is placed a second embodiment of a unscrewing assembly in accordance with the present invention; Figure 2A is a cross-section of an upper idle damper tube for use in a unscrewing assembly in accordance with the invention, in an extended position; Figure 2B is a cross-section of an upper idle damper tube for use in a unscrewing assembly in accordance with the invention, in a retracted position; Figure 3 is a cross-section of a swivel for use in a unscrewing assembly in accordance with the invention; Figure 4 is a cross-section of an anchor member for use in a unscrewing assembly in accordance with the invention, showing gripping members in a released position; Figure 4A is a view along lines A-A in Figure 4, enlarged in relation to Figure 4; Figure 4B is a view along lines B-B in Figure 4, enlarged in relation to Figure 4; Figure 4C is a view along the lines C-C of Figure 4, enlarged in relation to Figure 4; Figure 4D is a cross section of parts of the anchor member shown in Figure 4, illustrating a leaf spring and a spring block in the body; Figure 4E is an enlarged side view of the leaf spring, spring block and retaining pins for the anchor member shown in Figure 4; Figure 4F is a view similar to Figure 4, showing the gripping member in the gripping position; Figure 5A is a cross-section of a clutch assembly for use in a unscrewing assembly in accordance with the invention; Figure 5B is a view along lines B-B in Figure 5A; Figure 5C shows a detent construction provided on the clutch assembly shown in Figure 5A; Figure 6A is a cross-section of a torque generator for use in a unscrewing assembly in accordance with the invention, in an extended position; Figure 6B is a cross-section of a torque generator for use in a unscrewing assembly in accordance with the invention, in a retracted position; Figure 7A is a cross-section of a lower idle damper tube for use in a unscrewing assembly in accordance with the invention, in an extended position; Figure 7B is a cross-section of a lower idle damper tube for use in a unscrewing assembly in accordance with the invention, in a retracted position; Figure 8 is a cross-section of a valve member for use in a unscrewing assembly in accordance with the invention; Figure 9 is a cross-section of a circulation piece for use in a unscrewing assembly in accordance with the invention; Figure 10 is a cross-section of a modification showing an upper idler damper tube, a fish socket tool for removing a casing stub, and a swivel;

Figure 1 IA is a cross-section showing the fishing socket tool in Figure 10 enlarged.

Figure 1 IB is a view along lines B-B in Figure 1 IA; and

Figure 11C is a cross-section showing the lower part of the fishing socket tool in Figure 1 IA enlarged.

Reference is made to Figure IA, which is not to the correct scale, showing a borehole 10 situated through a hydrocarbon-fluid bearing formation 12. In the area of the formation 12, the inner surface of the borehole 10 is set with a casing 14. The casing 14 has a first casing pipe part 14a (or casing pipe stump), at the top of the borehole 10, and a second casing pipe part 14b further down than the first casing pipe part 14a. The first and second casing parts 14a and 14b are usually connected by a casing 14c, which has screw threads (not shown) which engage with corresponding threads on the parts 14a and 14b (not shown), after which the parts 14a and 14b can be connected. The first casing part 14a has an upper edge 14b.

A drill string 16 is located from the surface 18 of the formation 12 and carries a first embodiment of a screw assembly generally marked 20 at the end thereof. The unscrewing assembly 20 consists of, in sequence from top to bottom, a circulation piece 900, a bypass valve member 800 (Figure 8), an upper dead-end damper tube 200 (Figures 2A and 2B), a swivel piece 300 (Figure 3), an upper anchor 400 (Figure 4 , 4A, 4B, 4C, 4D, 4E, and 4F), a clutch assembly 500 (Figures 5A, 5B, and 5C), a torque generator 600 (Figures 6A and 6B), a lower outer idle damper tube 700 (Figures 7A and 7B), and a lower anchor 400' (Figure 4). A shut-off cap (not shown) is placed at the lower end of the anchor 400'.

Figure 1B illustrates a second embodiment of the unscrewing frame assembly 20' in formation. Figure IB is identical to Figure IA, with the exception that the bypass valve member 800 is placed below the lower anchor 400', and like reference numbers have been used to refer to like parts. The first embodiment shown in Figure IA is preferred

that shown in Figure 1B because there is less weight hanging on the shaft of the torque generator 600; there is less hydraulic pressure acting on the torque generator 600 before the bypass valve 800 closes; there is less likelihood of the anchor blades of the anchors 400 and 400' being driven out when the assembly 20 is pulled out of the borehole 10.

In the following description, it will be assumed that the bypass valve member 800 is placed in the position shown in figure IA.

Referring to Figures 2A and 2B, the upper outer plain coupling 200 consists of a first shaft 202 and a second shaft in the form of an outer housing 204. The first shaft 202 has an internal hole 206, which is in fluid communication with an internal hole 208 in the outer housing 204. An end of the first shaft 202 remote from the outer housing 204 is fitted with a threaded recess 210 by means of which the first shaft 202 is connected to the drill string 16. An end of the outer housing 204 remote from the first shaft 202 is fitted with a screw-threaded projection 152 by means of which the outer housing 204 is in connection with the swivel piece 300.

The upper outer plain connector 200 is shown in a retracted position in Figure 2B and in an extended position in Figure 2A. In Figure 2A, the outer plain connector is 18 inches (0.46 m) longer than in Figure 2B. The hydraulic sealing diameter is designed to ensure that there is a slight offset against the coupling being closed by internal pressure.

The shaft 202 consists of an upper shaft part 212 firmly attached to a lower shaft part 214 by means of threads. The outer housing 204 consists of an upper body part 216, a middle body part 218 and a lower body part 220: the upper body part 216 is connected to the middle body part by threads; and the middle body part 218 is connected to the lower body part 220 with threads. A sealing ring 222 is placed on the upper shaft part 216 for sealing between the upper body part 216 and the upper shaft part 212. A sealing ring 234 is placed on the lower shaft part 214 for sealing between the middle body part 218 and the lower shaft part 214. ring 224 is provided on the lower shaft portion 114 for sealing between the lower shaft portion 114 and the lower body portion 220. It should be noted that the sealing rings 222, 224 and 234 are capable of withstanding the operating pressure of the unscrewing assembly 20 (and all subsequently described sealing rings which is exposed to the operating pressure of the reduction position 20 is also capable of withstanding this operating pressure). The sealing rings 222,224 and 234 (and the subsequently described sealing rings) do not prevent relative sliding movement (axial or rotary) between the two surfaces they seal between. The sealing diameter of the three seals may be designed to provide a hydraulic pressure for the outer plain coupling 200 to cause it to close when pressurized. This causes the swivel pieces 300 to be lifted off the upper edge 14d as the first casing part 14a is released.

An annular chamber 226 is defined between the upper shaft portion 212 and the middle body portion 218; and an annular chamber 228 is defined between the lower shaft portion 214 and the middle body portion 218. The annular chambers 226 and 228 are prevented from communicating with each other by the lower shaft portion 214.

Ports 230 are placed in the upper shaft part 212 to provide fluid communication between the hole 206 and the annular chamber 226. Ports 232 are placed in the middle body part 218 to provide fluid communication between the annular chamber 228 and the interior of the borehole 10.

With reference to figure 3, the swivel piece 300 consists of a first elongated connecting part 302 and a second elongated connecting part 304. The first connecting part 302 is fitted with a hole 306 situated longitudinally through it. The hole 306 is in fluid communication with a hole 308, which is located longitudinally through the second connection part 304. The first connection part 302 is provided with a screw-threaded recess 310 for connection with the screw-threaded projection 252 on the upper external plain coupling 200. The second connection part 304 is fitted with a screw-threaded part 312 for connection with an upper anchor 400.

The upper end of the second connecting part 304 is placed with a along the periphery

horizontal shoulder 316 which is dimensioned so that it can meet the upper edge 14d of the first casing part 14. The part of the swivel piece which, in use, is placed under the shoulder 316 is dimensioned so that it can fit through the casing parts 14a and 14b, as shown in Figure 1. The first connecting part 302 is rotatably attached to the second connecting part 304 by means of bearing arrangements mainly labeled 314. The bearing arrangements consist of a plurality of single axial thrust plates in a sealed

oil bath. Although other bearing arrangements can be used (such as roller bearings or ball bearings), single axial thrust plates provide the highest axial load capacity.

The first connecting part 302 consists of upper and lower parts 318 and 320, respectively, which are connected by screw threads. The lower connecting part 304 consists of upper and lower parts 322 and 324, respectively, which are connected by screw threads. A sealing ring 326 is placed on the lower first connecting part for sealing between the lower first connecting part 320 and the lower second connecting part 324. A piston 328 is placed between the lower first connecting part 320 and the upper second connecting part 322. The piston 328 is placed above the bearing arrangement 314. A sealing ring 330 is placed on the piston 328 for sealing between the piston 328 and the upper second connecting part 322. A further sealing ring 332 is placed on the piston 328 for sealing between the lower first connecting part 320 and the piston 328.

With reference to figures 4, 4A, 4B, 4C, 4D, 4E and 4F, the upper anchor 40 is shown, which consists of an elongated housing 402 with holes 404 located in a continuous longitudinal direction. One end of the housing 402 is fitted with a screw-threaded recess 406 which is connected to the screw-threaded projection 312 on the swivel piece 300.

The housing 402 is provided with a plurality of radially located holes 408, which communicate at one end with the hole 404. Gripping means are provided at the other end of the holes 408: the gripping means consist of a plurality of gripping elements 410 (which are not shown in figure 4B): each gripping element consists of six piston elements 410a and a blade 410b; each blade 410b is provided with a serrated outer surface 410c. The blade 410b is fitted with six cylindrical recesses 410b, which respectively receive one of the piston elements 410a. A surface 410e on each of the depressions 410b sits on top of one of the piston elements 410a, respectively. A sealing ring 41 Of is placed on the blade 410b, in each recess 410b, for sealing between the blade 410a and the outer surface of the piston elements 410a. The bottom of each piston element 410a is clamped against the housing 402, and an O-ring seal 41 Og is placed on the bottom of each piston element 410a to seal between said bottom and the housing 402.

Each piston element 410a has a hole 411 situated through it: the hole 411 in each piston element 410a has an inner part 41 la and an outer 41 lb. The outer part 41 lb of each hole 411 has a larger diameter than the inner part 41 la, which thus forms a shoulder 410h on each piston element 410b. A PTFE disk 440 is placed on the shoulder 410h.

Each piston element 410a is clamped to the housing 402 by a respective piston retaining bolt 442. Each piston retaining bolt 442 has a substantially circular cross-section and consists of an inner part 442a and an outer part 442b. The outer part 44b has a larger diameter than the inner part 442a, so that the bolt 442 has a T-shaped cross-section. The outer portion 442b of each bolt 442 abuts one of the respective PTFE washers 440 to clamp each piston member 410b to the housing 412. The inner portion 442a of each bolt 442 is located within the hole 448 and is secured to the wall of the hole 408 with a screw thread. Each bolt 442 can be tightened with a hex key, which can be placed in a hex hole provided on the top of each bolt 442. Each bolt 442 is provided with a centrally located hole 442c which communicates at one end with one of the holes 408, and communicates with it other end with the outer part 41 lb of the hole 411.

There are a total of six gripping elements 410 placed on the anchor 400, each of which consists

of six piston elements 410a and a blade 410b. Three of the gripping elements 410 are arranged around the axis of the housing 402 at an angle of 120° to each other, shown in Figure 4A. The other three gripping elements 410 are also placed around the axis of the housing 402 at an angle of 120°, and are axially separated from the first three gripping elements 410. The second set of three gripping elements 410 is placed 60° offset in relation to the first set with gripping elements 410, so that if the first set of gripping elements 410 became

offset towards the second set of gripping elements 410 by moving it axially to the right in Figure 4, there would be an angle of 60° between each gripping element 410. It should be noted that this is not the arrangement actually shown in Figure 4; for clarity, in Figure 4, the gripping elements 410 of the first and second sets are shown at an angle of 0° to each other.

The gripping elements 410 are movable between a release position, as shown in Figure 4, and a gripping position, as shown in Figure 4F. The direction of movement of the gripping elements 410, between the releasing position and the gripping position, is completely radial in relation to the longitudinal axis of the housing 402. The gripping elements 410 can be moved from the released position to the gripping position by increasing the pressure in the holes 408. Each gripping element 410 is connected to a pair of leaf springs 414, which press them towards the released position.

The end of the upper armature 400 remote from the threaded recess 406 is provided with a threaded projection 452 for connection with the clutch assembly 500.

Stop means are placed to limit the movement of each of the gripping elements 410. The stop means is placed between the six piston elements 410a, and consists of

stop members 416 fitted to each gripping member 410, and three stop screws 418 fixed to the housing 402. Each stop member 416 is fitted with a stop shoulder 416a and each stop screw 418 is fitted with a stop surface 418a. The outwardly directed radial movement of the blade 410b of the gripping members 410 is limited by the mutual engagement of the stop shoulders 416a and 418a.

Each gripping element 410 is set in its own blade pocket 420, so that there are a total of six blade pockets. Each blade pocket 420 is fitted with a spring recess 422 located along the two longitudinally located edges thereof. One of the leaf springs 414 is received in each spring recess 422 and located along the longitudinally extending edge of the leaf pocket 420. Each end of each leaf spring 414 abuts an upper surface 422a of its spring recess 422, as shown in Figure 4D. A spring block 424 is fixedly attached to the middle part of the blade 410b, along opposite edges thereof, as shown in Figure 4C. Each of the spring blocks 424 is located within one of the spring recesses 422 below the centrally located portion of the leaf springs 414. The blade 410b is fixedly attached to the spring blocks 424 by retaining pins 426. This arrangement is shown in Figure 4E, where for clarity only one leaf spring 414, spring block 424 and retaining pins 426 are shown. The retaining pins 426 are held in place by the plugs 428.

When the hydraulic pressure in the holes 408 is increased, an outwardly directed radial force pushes against the surface 41 Oe of the cylinder recess 41 Od. This force acts to push the blades 410b radially outward; the spring blocks 424 are pushed with the leaves 41 Ob by means of their connection to the leaves 410b by the retaining pins 426. This exerts a force at the center of the leaf springs 414, which is opposed by the spring force in the leaf springs 414 because these are held at their ends by the surface 422a. When the hydraulic force is greater than the spring force of the leaf springs 414, the leaf springs 414 deform and the leaves 410b move radially outward.

Referring to Figures 5A, 5B and 5C, a clutch assembly 500 consists of an elongated drive shaft in the form of a housing 502 and an elongated driven shaft in the form of a driven housing 504. The drive housing 502 is provided with a longitudinally moving hole 506 The hole 506 is in fluid communication with a hole 508, which is located longitudinally through the driven housing 504. Coupling means are provided to connect the greenhouse 502 to the driven housing 504. The coupling means consists of flange 510, pressing means in the form of a spring 512 , a plurality of detents 514 on the flange 510, and a plurality of detents 516 on the housing 502. The flange 510 is placed on the driven housing 504 using an axial slot design. This prevents rotation of the flange 510 in relation to the driven housing 504. Figure 5B shows how the grooves 510a on the flange 510 lock together with the grooves 504a on the driven housing 504.

The flange 510 is axially movable relative to the driven housing 504. The design of the detents 514 and 516 is such that when the housing 502 is rotated in one direction, the detents engage with each other, assisted by the spring 512, causing the driven housing 504 to rotate with the greenhouse 502.

The latches 514 and 516 are thus formed so that when the housing 502 is rotated in an opposite direction, the latches 514 slide over the latches 516, thereby pushing the flange 510 axially against the spring force of the spring 512, so that the driven housing 504 does not rotate with the housing 502.

This ratchet construction is shown in greater detail in Figure 5C. The greenhouse 502 and the flange 510 have been "unwrapped" in Figure 5C to show the construction more closely. Each detent 514 and 516 has a surface - 514a and 516a, respectively - that has an angle of 15° to the longitudinal axis of the clutch assembly 500, and a further surface - 514b and 516b, respectively - that has an angle of 45° to the longitudinal axis of the clutch assembly 500. When torque is applied to rotate flange 510 and housing 502 relatively in one direction, detent surfaces 514b and 516b meet and can slide over each other, when torque is applied to rotate flange 510 and housing 502 relatively in the opposite direction , the 15° detent pawls 514a and 516a meet each other, but these cannot slide over each other and serve to prevent relative rotation in the opposite direction.

The driven housing 504 is fitted with a screw-threaded recess 518 which is connected to the screw-threaded projection 452; the housing 502 is fitted with a threaded projection 520 for connection with the torque generator 600.

The driven housing 504 consists of an upper driven housing part 522 and a lower driven housing part 524, which are connected by screw threads. The greenhouse 502 consists of an upper greenhouse part 526 and a lower greenhouse part 528, which are connected by screw threads. The flange 510 is placed on the lower driven housing part 524.

A sliding coupling 534 is located inside the upper housing part 526 between the lower driven housing part 524 and the lower housing part 528. A sliding ring 532 is arranged at the upper end of the sliding coupling 534, between the upper greenhouse part 526 and the lower driven housing part 524. A sliding ring 536 is arranged at the lower end of the sliding coupling 534 between the sliding coupling 534 and the lower greenhouse part 528. A sealing ring 530 is arranged on the sliding coupling 534 for sealing between the sliding coupling 534 and the upper housing 526.

With reference to figures 6A and 6B, the torque generator 600 consists of a first elongated shaft in the form of a housing 602 and a second elongated shaft in the form of a drive shaft 604. The housing 602 is arranged with a through hole 606 located in the longitudinal direction. The hole 606 is in fluid communication with a hole 608, which is located longitudinally through the drive shaft 604. The housing 602 is fitted with a screw-threaded recess 622 which is connected to a screw-threaded projection 520. The drive shaft 604 is fitted with a screw-threaded projection 610 for connection with a screw-threaded recess 710 on the lower idle damper pipe 700.

The drive shaft 604 is arranged with external helical grooves 612 along parts of its outer surface. The helical grooves 612 can be received in corresponding helical grooves (not shown) in the inner surface of the housing 602. An annular space 614 is defined between portions of the outer surface of the drive shaft 604 and portions of the inner surface of the housing 602. The annular space 614 contains pressing members in the form of a leaf spring stack 616 (the leaf spring stack 616 is not shown in Figure 6B, for reasons of clarity). A piston 618 is arranged at an upper end of the annular space 614, and is movable axially into the housing 606. The piston 618 is arranged with a hole 620, which is in connection with the holes 606, 608 after which fluid can flow through the hole 606 to hole 608 via hole 620.

The torque generator 600 is movable between a retracted position shown in Figure 6B, and an imaginary position shown in Figure 6A. If the hole 608 is blocked, applying increasing pressure to the hole 606 will cause the piston 618 to move downward (ie, to the right in Figure 6A) against the spring force of the leaf spring stack 616. This will cause the drive shaft 604 to rotate relative to the housing 602, at by means of the helical grooves 612 and their corresponding recesses. In this way, the torque generator 600 can be moved from the retracted position to the moved position.

If the pressure in the hole 606 is removed, the torque generator 600 will move back to the retracted position, using the displaced force in the spring 616 against the piston 618.

A sealing ring 624 is provided on the piston 618 for sealing between the piston 618 and the housing 602. An adjustment ring 626 is provided at the upper end of the leaf spring stack 616. Sliders 628 are provided along the leaf spring stack 616 at intervals. A shoulder washer 630 is provided at the lower end of the leaf spring stack 616, and sets the lower position of the leaf spring stack 616. Inclined washers (ie, shims) are provided within each pair of leaf springs in the stack 616 to ensure that they cannot be compressed beyond 75 % of full compression capacity; this helps to prevent permanent settling and/or failure of the leaf springs and to keep the leaf spring deflection within an acceptable load range.

With reference to figures 7A and 7B, the lower outer idler damper tubes 700 consist of a first elongated inner shaft 702 and a second elongated shaft in the form of an outer housing 704. The first elongated shaft 702 is arranged with a through hole 706 located in the longitudinal direction. The hole 706 is in fluid communication with the hole 708, which is located longitudinally through the housing 704. The first elongate shaft 702 is provided with a screw-threaded recess 710 for connection to the screw-threaded projection 610. The housing 704 is provided with a screw-threaded projection 712 for connection with the second appeal 400<*>.

The shaft 702 consists of an upper shaft part 716, a middle shaft part 718 and a lower shaft part 720: the upper shaft part 716 is fixed to the middle shaft part 718 by screw threads; and the middle shaft part 718 is fixed to the lower shaft part 720 with screw threads. The housing consists of six housing parts 722,724, 726, 728, 730 and 732, each of which is connected to its neighboring housing part by screw threads.

An annular chamber 714 is defined between the upper shaft portion 716 and the housing portion 726; a compensating piston 734 is arranged inside the annular chamber 714 and divides the chamber 714 into two sub-chambers 714a and 714b. An annular chamber 736 is arranged between the upper shaft part 718 and the housing part 724. An annular chamber 738 is arranged between the middle shaft part 718 and the housing part 726; ports 740 are provided in the housing portion 726 and allow fluid communication between the annular chamber 738 and the interior of the borehole 10. An annular chamber 742 is provided between the middle shaft portion 718 and the housing portion 730; ports 748 allow fluid communication between hole 706 and annular chamber 742. An annular chamber 744 is disposed between lower shaft portion 720 and housing portion 730; ports 746 allow fluid communication between the annular chamber 744 and the interior of the borehole 10.

A sealing ring 750 is placed on the upper shaft part 716 for sealing between the upper shaft part 716 and the housing part 702. A sealing ring 752 is placed on the middle shaft part 718 for sealing between the middle shaft part 718 and the housing part 718. A sealing ring 754 is placed on the lower shaft part 720 for sealing between the lower shaft part 720 and the housing part 732. A sealing ring 756 is placed on the compensating piston 734 in sealing between the compensating piston 734 and the housing part 726; and a sealing ring 758 is placed on the compensating piston 734 for sealing between the compensating piston 734 and the upper shaft part 716. A sealing ring 760 is placed on the lower shaft part 720 for sealing between the lower shaft part 720 and the housing part 730.

The cross-sectional shape of the portion of the outer surface of the shaft 702 is hexagonal, and the cross-sectional shape of the inner surface of the housing 704 is hexagonal. This design serves to prevent relative rotary movement between the shaft 702 and the housing 704. In particular, this design prevents relative rotary movement between the upper shaft part 716 and the housing part 724.

The lower idle damper tube 700 is movable between an extended position as shown in Figure 7A and a retracted position as shown in Figure 7B. When the lower idle damper pipe 700 is in the extended position, the torque generator 600 will be in the retracted position, and when the lower idle damper pipe 700 is in the retracted position, the torque generator 600 will be in the extended position.

When the lower idle damper tube 700 is in the retracted position, the annular chambers 714a and 742 are at their maximum volume, and the annular chambers 736, 738 and 744 are at their minimum volume; and when the lower idle damper tube is in the extended position, the annular chambers 714a and 742 are at their minimum volume, and the annular chambers 736, 738 and 744 are at their maximum volume. Sub-chambers 714b remain at the same volume regardless of stroke position, i.e. sub-chamber 714b has the same volume when the lower idle damper tube 700 is in the extended position as when the lower idle damper tube 700 is in the retracted position.

The lower idle damper tube 700 is lubricated, and is located with lubricating fluid in the annular chamber 714a and 736. Internal hydraulic pressure in the hole 706 results in a force that causes the housing 704 and shaft 702 to retract. The arrangement is such that when the first elongate shaft 702 is subjected to a downward force from the torque generator 600, the downward force on the housing 704 formed by friction between the hexagonal part of the shaft 702 and the housing part 704 is exactly met by an upward force on the housing 704 formed by the pressure in the fluid in the hole 706 which communicates with the chamber 742.

The anchor 400' is connected to the lower idle damping pipe 700. The construction of the lower anchor 400' is preferably exactly the same as the construction of the upper anchor 400. Thereby, the screw-threaded recess 406 in the anchor 400' will be connected to the screw-threaded projection 712, and the threaded projection 452 and the lower anchor 400' will be connected to the shut-off cap, which is of a conventional design.

With reference to Figure 8, valve members 800 are shown. The valve members 800 consist of a valve body 802 with a through hole 804 located in the longitudinal direction, the valve body 802 includes ports 806 which can communicate with the hole 804. A movable valve element in the form of a piston 808 is placed inside the valve body 802; a piston 808 is movable axially in relation to the valve body 802. The piston 808 is originally fixed to the valve body 802 by means of breaking pins 810. The piston 808 has a through hole 812 situated in the longitudinal direction which is in fluid communication with the hole 804. The piston 808 is fitted with a hole 814 which is in fluid communication with the hole 806 for the body 802.

The valve body 802 consists of an upper body part 818 and a lower body part 820: the upper body part 818 is fixed to the lower body part 120 by screw threads.

The piston 808 is movable inside the lower body part 820. Sealing rings 824,826 are placed between the piston 808 and a valve flange 840, which is placed inside the lower body part 820. Four O-rings 842, 844, 846 and 848 act as static seals around the valve flange 840 on a sealing house 850.

An internal filter 828 is placed in the hole 804 above the piston 808. A filter 830 is placed in the ports 806.

A nozzle arrangement 832 is located in the hole 810 of the piston 808.

The upper half of the valve member 800 shown in Figure 8 shows the piston 808 in a first position with the break pin 810 intact; and the lower half of figure 8 shows the piston 808 in a second position in which this has been moved axially in relation to the first position, and the breaking pin 810 has been broken. The breaking pin 810 can be broken by increasing the fluid flow through the hole 804, 810, 814 and 806. When the breaking pin 810 is broken, the piston 808 is moved axially in a downward direction (i.e. to the right in Figure 8), and this takes the hole 814 out of alignment with the hole 806 , so that fluid can no longer flow through the valve member 800.

The valve member 800 is fitted with a screw-threaded recess 816 which is connected to a screw-threaded projection 906 of the circulation piece 900.

With reference to Figure 9, the circulation piece 900 consists of an elongated body 902 with a through hole 904 located in the longitudinal direction. The body 902 has a screw-threaded projection 906 which can be fixed to the screw-threaded recess 816 of the bypass valves 800. The circulation piece 900 includes a hole 908, which is located radially from the hole 904. However, the fluid communication between the hole 904 and the hole 908 is prevented by a valve element 910 which is fixed to the body 902 with a breaking pin 912.

Four sealing rings 914 are placed on the valve body 910 for sealing between the valve body 910 and the body 902.

If a sufficient force is applied to the valve body 910 to break the breaker pin 912 - e.g. by dropping a ball (not shown) to the seat 910a in the valve body 910 - then the valve body 910 can move downwards (ie to the right in Figure 9), which will produce fluid communication between the hole 904 and the hole 908. The hole 908 is in fluid communication with the borehole 10.

Operation of the unscrewing assembly will now be described.

Before the unscrewing assembly 20 is inserted, a pipe cutter (not shown) is inserted into the borehole 10 and the upper casing part 14a is cut off at a correct position to form the upper chamber 14d. The unscrewing assembly 20 is then lowered into the borehole 10 with the drill string 16 to the shoulder 316 when the swivel piece 300 meets the upper edge 14b of the first casing section 14a. The weight of the equipment below the upper outer plain coupling is set down on the upper edge 14b of the first casing section 14a - for an OD 8 inch (20 cm) unscrewing assembly this weight would be approximately 11,500 Ibs (5200 kg). The equipment is moved down an additional 18 inches (0.46 m), which is the distance between the retracted and unretracted positions of the upper outer plain link 200. As the upper outer plain link 200 reaches the fully retracted position, the weight on the upper edge 14d increase. This should be allowed to increase to approximately 30,000 Ibs (13,600 kg). The equipment should then be raised approximately 9 inches (0.23 m) when the weight of the upper edge 14b should drop back to 11,500 Ibs (5200 kg). The shoulder 316 of the swivel piece 300 is now set on the upper edge 14d of the first casing section 14a.

The drilling fluid now flows through the screw assembly 20. This will flow through holes 904, 804, 812, 814 and 806 to the wellbore area 10. The flow rate will gradually be brought up to 125 to 150 U.S. gallon per minute (473-568 l/min). The breaker pin 810 will break at this flow rate (depending on the mud density) which will cause the piston 808 to move downward and will block fluid communication between the hole 812 and the hole 816. This results in a pressure build-up in the unscrewing assembly 20.

The anchors 400 and 400' require an internal pressure of approximately 10 to 30 psi (68.9-10 - 206.9-10 Pa) for the gripping elements 412 to overcome the force of the leaf springs 414 and move from the release position to the gripping position. The valve member 800 requires approximately 50 psi for the valve to close. The closing speed of the valve is set low to minimize the initial pressure shock. It should be noted that the pop off valve (not shown) of the slurry pump (not shown) on surface 18 should be set to the maximum pressure value possible for a flow rate of 200 U.S. gallon per minute, to ensure that the valve 800 will close and to have the maximum pressure available for the unscrewing assembly 20; ideally 5000 psi should be made available.

As the pressure increases with the valve member 800 closed, the hydraulic anchors 400 and 400' will grip the first casing section 14a and the second casing section 14b, respectively. The grip force will increase as the pressure increases.

When the pressure is approximately 175 - 285 psi, the piston 618 of the torque generator 600 will be able to overcome the displacing force of the leaf spring pack 616. A pressure of 550 - 660 psi is required to fully compress the leaf spring pack 616. Thus, as the pressure increases above 175 - 285 psi, the force from the piston 618 will begin to generate a torque caused by the housing 602 of the torque generator 600 being rotated relative to the drive shaft 604; the direction of operation is counterclockwise when viewed down the hole. As the pressure

increases, the grip that the two anchors 400 and 400<*> have on the grooved pipe sections 14a and 14b should become higher than the generated torque, so that slippage at the anchors 400 and 400' should not occur.

The connection between the first and second casing sections 14a and 14b will begin to loosen at a certain pressure, which is dependent on the tightening torque and the amount of corrosion/mud in the threads. It is expected that a total pressure of 5000 psi will be sufficient to loosen most casing connections that will occur in this area.

As the torque is generated, the torque generator 600 moves from the retracted position to the extended position resulting in an increase in its length of approximately 18 inches (0.46 m). At the same time, the lower idle damper tube 700 moves from the extended position to the retracted position to compensate for the increase in the length of the torque generator 600.

When the hole 706 is pressurized (eg, to 5000 psi), the annular chamber 742 is also pressurized through the ports 748. The sealing ring 760 is eg. 150 mm in diameter, while the sealing rings 752 and 754 e.g. is 95 mm in diameter. The high pressure acting on the sealing ring 754 - through the lower end of the hole 706 - will push the outer housing to the right (in Figures 7A and 7B) with a force of 54,934 Ibs (5000 • PI. (95<2>) / ( 4 x 25.4<2>)). As the chamber 742 is pressurized, the pressure will also push the outer housing 704 to the left with a force of 82,020 Ibs (5000.POI.(150<2->95<2>) / (4 x 25.4<2>)) . Thereby there is a net force on the left of 27086 Ibs. The lower housing section 732 is connected to the armature 400', so this net hydraulic force pulls down on the inner shaft 702. This internal pressure balances the axial frictional drag created between the inner shaft 702 and the outer housing 704 due to the torsional force acting on it. notched cross-section of the inner shaft 702 and the outer housing 704. This frictional force would otherwise tend to push the armature 400' downward, but is compensated by the force balanced inside the outer plain coupling 700.

The lower armature 400', the lower idle damper tube 700, and the drive shaft 604 of the torque generator 600 should not rotate during torque generation. The housing 602 of the torque generator 600 should rotate, along with the driven housing 502 of the clutch assembly 500, the housing 504 of the clutch assembly 500, and the upper armature 400. The upper casing section 14b should also rotate to unscrew it from the casing 14c. The lower connecting part 304 of the swivel joint 300 will rotate relative to the upper connecting part 302, by means of bearing arrangements 314. When the torque generator 600 has reached the extended position, the pressure should be reduced back to zero gauge pressure on the surface pump. This will cause the spring force in the spring 616 to push the piston 618 upwards and move the torque generator 600 from the extended position to the retracted position. The torque generator will reach the retracted position at a pressure of approximately 175 - 285 psi, at which pressure the gripping member 412 of the anchors 400 and 400' will still engage the inner surface of the first and second casing sections 14a and 14b.

During the pressure reduction, the movement of the torque generator 600 from the extended position to the retracted position will result in a torque in a direction opposite to the torque generated during the pressure increase. This could result in a retraction of the first casing section 14a on the flange 14c. However, the clutch device 500 prevents this, because the shaft 602 of the torque generator 600 rotates in the opposite direction during pressure reduction, and the drive shaft 502 of the clutch device 500 is unable to drive the driven shaft 504.

When the pressure reaches zero gauge pressure at the surface, the first cycle of the unscrewing assembly will be complete and the first casing section 14a will have been unscrewed by about half a turn. The cycle should then be repeated until the first casing section 14a is loose, ie less than 550 - 660 psi is required. Usually this is about eight cycles, although this will vary with the type of flange thread. It should be noted that the maximum pressure required during each cycle is reduced as the connection between the first casing section 14a and the flange 14c, or between the second casing section 14b and the flange 14c, becomes looser.

It is possible to determine when the connection is loose, because only 550 - 660 psi will be required to move the torque generator from the retracted position to the extended position (ie, as soon as it is only necessary to overcome the spring force of the spring stack 616).

When the upper casing sequence 14a is unscrewed, the housing 204 of the upper external plain coupling 200 will move upwards in relation to the shaft 202, i.e. towards the retracted position.

A ball (not shown) is dropped directly into the borehole, which lands on the seat 910a and causes the breaker pin 912 to break and move the valve element 910 downward, thereby providing fluid communication between the hole 904 and the interior of the borehole 10. The purpose of the circulation piece 900 is to ensure that the drill string 16 is retrieved in a dry state - the fluid in the string 16 is emptied via the hole 908 - and to prevent the anchors from opening when removed from the drill hole 10.

After the first casing section 14a has been unscrewed, it can be removed from the borehole using a standard spear arrangement (not shown).

In one modification, the write-off assembly may include a mechanically or hydraulically actuated spear of suitable design between the swivel piece 300 and the upper outer plain coupling 200. In this modification, the swivel piece 300 will not need the outer shoulder 316; the landing shoulder could instead be located on the casing retrieval spear.

Referring to Figures 10, 1IA, 1IB and 11C, a modification is shown including a fishing socket tool 950 between the upper outer plain connector 200 and the swivel 300. Many of the parts shown in Figures 10 and 11 are identical to the parts shown in Figures 2A, 2B and 3, and like parts are marked with like reference numbers. The upper external plain coupling 200 is inverted so that the bypass valve 800 above the upper external plain coupling 200 needs to have a box-box transition to connect this to the projection 252 on the upper external plain coupling 200.

The purpose of the fishing sleeve tool 950 is to enable the casing stub 14a to be removed from the borehole 10 after it has been detached (but not freed) from the rest of the casing 14. The advantage of the fishing sleeve tool 950 is that the casing stub 14a can be released and removed from the borehole 10 in a single trip , instead of in two trips.

The fishing socket tool 950 includes a release element in the form of a damper tube 904, which is firmly attached with screw threads to the body part 216 in the upper external plain coupling 200, and a socket shaft in the form of a slotted sub 952, which is arranged at one end with a threaded projection 954 by means of which the sub 952 is connected to the threaded recess 210 of the upper outer plain coupling 200. The length of the damper tube 974 is such that the stroke of the upper outer plain 200 is reduced from 18 inches (45.7 cm) to 16 inches (40.6 cm). The sub 952 is provided with a centrally located axial hole 976, which provided fluid communication between the holes 206 and 306. The other end of the slotted sub 952 is provided with a threaded projection 956 by means of which the sub 952 is connected to the threaded recess 310 on the swivel piece 300.

The fishing socket tool 950 further consists of a grooved housing 958 which surrounds parts of the grooved sub 952. Part of the outer surface of the grooved sub 952 is arranged with grooves 960, which are located axially on the sub 952. Parts of the inner surface of the grooved housing 958 is provided with grooves 962, which are located axially on the housing 958. The grooves 960 and 962 engage in locking engagement, whereby the sub 952 can be moved axially in relation to the housing 958, but cannot be moved rotating in relation to the housing 958. The housing 958 is fixed to a gripper housing 964. The slotted housing 958 and the gripper housing 964 together form a sleeve housing.

Gripper in the form of a gripper 966 is placed inside the gripper housing 964. The gripper 966 is axially movable inside the gripper housing 964, but this is prevented from moving past the end of the gripper housing 964 by a stopper 964a placed on the end of the gripper housing 964. A ring 968 is arranged to continue rotating movement from the gripper housing 964 to the gripper 966. The ring 968 has a conventional design and can consist of e.g. a simple cylinder ring with a key or finger (not shown) located downwardly into a slot machinery into the wall of gripper 966 and partially milled into the inner diameter of gripper housing 964.

The inner surface of the gripper housing 164 is provided with conical surfaces 964b, formed on the left-hand spiral threads, and the outer surface of the gripper 966 is fitted with the conical surface 966a, also with the left-hand spiral threads. The tapered surfaces 964b are in contact with the tapered surfaces 966a. The surfaces 964b and 966a are designed so that as the surfaces 964b are moved upwards in relation to the surfaces 966a, the surfaces 964b are pushed inwards on the surfaces 966a, thereby causing the gripper 966 to grip an object arranged inside it. The downward movement of surfaces 964b relative to surface 966a releases pressure on gripper 966. Braided threads are provided on the inside of gripper 966, which are also left-handed spirals; and this helps to release the gripper 966 from the casing section to rotate to the right, because the drill pipe used is right-hand threaded.

A stop ring 970 is screwed onto the outer surface of the sub 952, and a burst washer 972 is placed immediately above the stop ring 970 to prevent the stop ring 970 from being unscrewed. The slotted housing 958 is axially movable relative to the sub 952. The stop ring 970 defines one of the limitations to the movement of the slotted housing 958, and an upper surface of the first elongate connecting member 302 defines the second limitation of movement of the slotted housing 958 housing 958. In total, the slotted housing can move about 2 inches (5.1 cm).

The slotted housing 958 is slotted 958a to allow fluid to escape as it enters the annular slot between the unscrewing assembly 20' and the casing stub 14a. It should be noted that this feature is only necessary if the depreciation assembly 20<*> is used. There is no need for the unscrewing assembly 20, where the overflow valve 900 is placed above the upper external plain coupling 200.

A spring 980 is placed between the slotted housing 958 and the slotted sub 952. The spring 980 presses the slotted housing 958 against the stop ring 970 as the fishing socket tool 950 is lowered into the well. This ensures that the shock tube 974 can impact the housing 958. It also ensures that a shoulder 958b of the slotted housing 958 is always kept in a position separate from the shoulder 302a of the first elongate connecting part 302. This is important if it becomes necessary to release the gripper 966 from an unretrievable casing section. When the gripper 966 is locked by pulling up the sleeve gripper housing 964 (as described above), the spring 980 will be compressed to the position shown in Figure 1 IA.

The operation of the fishing socket tool 950 will now be described.

The unscrewing assembly 20 (or 20') is lowered from the surface and usually so that the shoulder 316 contacts the casing stub 14a. The slotted housing 958, the gripper housing 964 and the gripper 966 are moved along the outside of the casing stub 14a. As the outer plain connector 200 moves to the fully closed position, the shock tube 974 is forced downward into contact with the slotted housing 958. After the shock tube 974 contacts the housing 958, this housing 958 pushes downward relative to the sub 952, and also pushes the gripper housing 964 (which is fixed to the housing 958) downwards, which ensures that the surface 964b does not press against the surfaces 966a so that the gripper 966 does not grip the casing stub 14a. However, the gripper 966 will be in frictional contact with the casing, even though the casing is free between surfaces 964b and 966a.

The unscrewing assembly 20 (or 20') is then pulled eight inches (20.3 cm) to its center stroke position, and the unscrewing assembly 20 cycle takes place as described above. After 8-10 cycles (ie after 8-10 half rotations), the remaining required torque to complete the unscrewing of the liner stub 14a is relatively low (for example 5% of the original break-out torque); at the same time that the fishing socket tool 950 can be activated by pulling the unscrewing assembly 20 (or 20') upwards, so that the upper external plain coupling 200 is brought to the extended position. The assembly can further be pulled up to pull the gripper housing 964 upwards and cause the surface 964b to move upwards relative to the surfaces 966a, as the gripper 966 has frictional contact with the casing. This causes the surfaces 964b to abut against the surface 966a and causes the gripper 966 to grip the casing stub 14a. When the gripper has been sufficiently locked to the casing stub 14a, the torque to the left can be applied from the surface to complete the unscrewing of the casing stub 14a. This torque will be transferred from the gripper housing 964 to the gripper 966 at the ring 968, through the key or finger of the ring 968. When the casing stub 14a has been completely unscrewed, the unscrewing assembly 20 (or 20') can be removed from the borehole 10 together with the casing stub 14a, which will be held in the gripper 966.

The gripper 966 can be released in the event that the casing cannot be retrieved. If the casing threads are still engaged, a downwardly directed force can be applied to the shock tube 974, so that it hits the top of the housing 958 as the upper external plain coupling 200 is closed. This should break the state between surfaces 966a and 964b. The drill string is then rotated to the right (clockwise). As the string is rotated to the right, the gripper 966 is raised along the outer diameter of the casing, and the torque is transmitted through the ring 968. The assembly should be pryed upwards to compensate for the relative movement of the gripper 966 until it is released. The system should not be pressurized or circulated during this phase. The presence of the spring 980 prevents the shoulder 958b in the housing 958 from being dropped onto the shoulder 302a. This ensures that the force is transferred to the sleeve grip housing 964.

Other arrangements, such as J-slots or breaker pins, may be used to control the operation of socket tool 950.

The particular method of operation described above allows the weight of the tool to be transferred through the swivel to the casing.

If the borehole is not vertical, there is a possibility that the lower idle damping pipe 700 will not be in the intended extended position after it has been lowered into the borehole. To solve this problem, a break pin (not shown) can be placed on the lower dead stop damper tube 700 to hold it in the extended position when it is initially fed into the borehole 10. During the first pressure cycle, the break pin will break so that the lower dead stop damper tube 700 can moved to the retracted position.

Although the operation of downhole casing unscrewing assemblies 20 is described above by means of releasing first and second casing sections 14a, 14b, the principal function of assembly 20 is to rotate the first section relative to the second section and allow relative axial movement. Whether or not the rotation frees two casing sections depends on the arrangement of the encountering casing threads. Accordingly, an embodiment of the present invention by casing unscrewing assembly can be used to connect as well as disconnect casing sections.

Claims (23)

1. A downhole casing unscrewing assembly (20) for rotation, within a wellbore (10), of a first threaded casing section (14a) relative to an oncoming second threaded casing section (14b), said assembly (20) comprising first anchor means (400 ) adapted to firmly engage the first casing section (14a), second anchor means (400') adapted to firmly engage the second casing section (14b), torque generating members (600) disposed between the first and second anchor member (400,400') and adapted to generate a torsional force between the first and second anchor members (400,400'), thereby releasing the first casing section (14a) from the second casing section (14b), a downhole clutch assembly (500) disposed between the torque generating member (600) and the first anchor member (400) which allows the torque generating member (600) to apply a torsional force to the first anchor member (400) in one direction and does not allow the torque oment-generating member (600) to supply a torsional force to the first anchor member (400) in the opposite direction, characterized in that a downhole swivel piece (300) is placed above the first anchor (400) and that the upper idler damper pipe (200) is placed over the swivel (300). 2. A downhole casing unscrewing assembly according to claim 1, characterized in that the upper idler damper tube (200) consists of first and second elongate shafts (202,204) each of which has a hole (206,208) located throughout in the longitudinal direction, which hole (206) in the first shaft ( 202) is in fluid communication with the hole (208) in the second shaft (204) and the first and second shafts (202,204) are axially movable relative to each other between a retracted position in which the total length of the external plain coupling ( 200) is minimal, and an extended position, in which the total length of the external tight coupling (200) is maximal. 3. A downhole casing unscrewing assembly according to claim 1 or 2, characterized by a fish socket tool (950) positioned above the first anchor (400). 4. A downhole casing unscrewing assembly according to claim 3, characterized by a fish socket tool (950) located between the upper dead-end damper pipe (200) and the swivel (300). 5. A downhole spring tube unscrewing assembly according to claim 4, characterized by a release element (974) in the fish socket tool (950) fixedly attached to the upper external plain coupling (200). 6. A downhole casing unscrewing assembly according to claim 5, characterized in that a fish socket tool shaft (952) in the fish socket tool (950) is connected to one of the first and second shafts (202, 204) in the upper idler damper pipe (200) and the release element (94) is connected to the second of the first and second shafts (202, 204) of the upper idler damper pipe (200). 7. A downhole casing unscrewing assembly according to any one of the preceding claims, characterized in that a lower idle damper pipe (700) is placed between the torque generating member (600) and the second anchor member (400'). 8. A downhole spring tube unscrewing assembly according to claim 7, characterized in that the lower idler damper tube (700) consists of first and second elongate shafts (702, 704) each of which has a through hole (706, 708) located in the longitudinal direction, which hole (706) in the first shaft (702) is in fluid communication with the hole (708) in the second shaft (704) and the first and second shafts (702, 704) are axially movable relative to each other between a retracted position, in which the total length of the lower idle damper tube (700) is minimal, and an extended position in which the total length of the lower idle damper tube (700) is maximum. 9. A downhole casing unscrewing assembly according to claim 8, characterized in that the second shaft (704) in the lower idle damping pipe (700) consists of an outer housing and the first shaft (702) in the lower idle damping pipe (700) is located inside the outer House. 10. A downhole casing skimming assembly according to claim 9, characterized in that lubrication is placed between the first and second shafts (702,704) in the lower idle damping pipe (700), and the internal hydraulic pressure urges the lower idle damping pipe (700) to the retracted position. 11. A downhole casing unscrewing assembly according to claim 10, characterized in that the relative rotary movement between the first and second shafts (702, 704) in the lower idle damper pipe (700) is prevented by anti-rotation means. 12. A downhole casing unscrewing assembly according to claim 11, characterized in that the anti-rotation member is immersed in an oil bath. 13. A downhole steering tube unscrewing assembly according to claims 11 or 12, characterized in that the anti-rotation member is a slot. 14. A downhole bearing pipe unscrewing assembly according to any one of claims 7-13, characterized in that the first shaft (702) in the lower idle damper pipe (700) is connected to the torque-generating member (600) where the second shaft (704) in the lower the idle damping pipe (700) is connected to the second anchor member (400'). 15. A downhole casing unscrewing assembly (20) according to any one of the preceding claims, characterized by valve means (800) arranged to allow filling of the assembly (20) with fluid as the assembly is introduced into the hole (10). 16. A downhole casing unscrewing assembly according to claim 15, characterized by valve body (800) consisting of an elongated valve body (802) and a valve element (808) inside the valve body (802), where the valve body (802) is fitted with a through hole located in the longitudinal direction (804), which hole (804) is in fluid communication with the second anchor member (400'). 17. A downhole casing unscrewing assembly according to claim 16, characterized in that the valve body (802) includes at least one port (806) located from the hole (804) in the valve body (802) to the borehole (10). 18. A downhole casing unscrewing assembly according to claims 16 or 17, characterized in that the valve body (808) is movably placed inside the hole (804) in the valve body (802). 19. A downhole spring tube unscrewing assembly according to claim 18, characterized in that the valve body (808) is movable corresponding to fluid flow through the hole (804). 20. A downhole casing unscrewing assembly according to claim 19, characterized in that the valve element (808) can be fixed to the valve body (802) with a breaking pin (810) or is spring-loaded so that the valve element (808) is not moved relative to it before the fluid flow reaches a predetermined value. 21. A downhole casing pipe unscrewing assembly according to any one of claims 15-20, characterized in that the valve member (800) is placed above the first anchor member (400). 22. A downhole casing unscrewing assembly according to claim 21, characterized by a circulation piece (900) placed immediately above the valve member (800). 23. A downhole casing unscrewing assembly according to claim 22, characterized in that the circulation piece (900) consists of a hole (904) located throughout in the longitudinal direction in fluid communication with the holes in the other components of the casing unscrewing assembly; a radial hole (908) in fluid communication with the longitudinally located hole (904) and with the interior of the borehole (10); and a sealing element (910) which normally prevents fluid communication between the radially and longitudinally disposed holes (908, 904), which sealing element (910) is held in place by a break pin (912) which can be broken by applying a sufficient downwardly directed force against the sealing element (910).