TUBING ANCHOR AND FORCE GENERATOR COMBINED WICH SUCH AN ANCHOR

Abstract: A tubing anchor (1) comprises a body (5); a plurality of slips (21) mounted on the body for radial movement into and out of engagement with the tubing and a drive sleeve (26) mounted on the body for axial movement relative thereto. A piston and cylinder actuator (8, 4) has a piston rod (10) connected to the drive sleeve (26) by dogs (27) for moving the drive sleeve relative to the body in a first direction. Mating cam surfaces (28 and 29) on the drive sleeve and slips respectively cause radial outward movement of the slips in response to axial movement of the drive sleeve. Interengaging surfaces (33 and 34) on the body and the slips respectively are provided for transferring axial load applied to the body in a second direction, opposite to the first direction, to the slips to force the slips in the second direction thereby increase the radially outwardly force on the slips produced by the interengagement of the respective cam surfaces of the slips and the drive sleeve.

Description: TUBINGANCHOR ANDFORCEGENERATORCOMBINEDWICH SUCHAN ANCHOR This invention relates to a tubing anchor, that is to say a device which can be set inside tubing to provide an anchor against which a force may be applied to be transmitted by the anchor to the tubing. The invention also relates to a force generator tool incorporating such a tubing anchor. It should be appreciated that whilst a primary use for the proposed tubing anchor is as part of a force generator tool the tubing anchor may find other applications and the scope of the present invention is not limited to the force generator application. It is an established technique in the oil and gas industry to apply a force in the up-hole or down¬ hole direction to a component located within a section of tubing forming part of a well. Where the well is substantially vertical and/or only moderate forces are required a number of options well known to those skilled in the art are available including, for example, the use of wire lines to exert an upward force and the use of the weight of a tubing string to exert a downward force. However, where large forces are required, particularly in portions of a bore which deviate from the vertical, specialist tools are required to generate the required force. A prior art tool of this type is described in EP-A-0477452. The tool described m EP-A-0477452 includes an anchoring mechanism which, upon pressurisation of the handling string to which the tool is connected engages the wall of the tubing within which the tool is located to provide an abutment against which the force generated by a force generating mechanism of the tool can react. Typically, the tool .of EP-A-0477452 is run into a well on a handling string until t engages an item to be shifted, e.g. a sleeve valve which is stuck. The handling string is then pressurised to actuate the anchor mechanism to lock the tool to the well casing and the handling string is then further pressurised to operate the force generator mechanism to apply a force to the item to be acted upon, the reaction force from the force generating mechanism being transferred by the anchor mechanism to the well casing. Whilst the device of EP-A-0477452 provides a solution to the problem of applying a substantial force to an item in a well, the force which can be effectively applied by this tool is limited by the ability of the anchor mechanism of the tool to grip the well casing. As a practical matter, it is believed that the anchor mechanism proposed limits the total force which the tool can produce to a value substantially less than that required for many operations. The present invention provides a tubing anchor which is able to resist substantially higher axial loads than those which can be resisted by the anchor mechanism of EP-A-0477452 and yet which can readily be set in a well casing, and subsequently released, after the tool has been run into the well bore on coiled tubing. The tubing anchor of the present invention is accordingly particularly suitable for use in a force generator of a general type described in EP-A-0477452 and enables the force generating portion of the tool to be designed to produce substantially higher axial forces than those which can be produced, for a given tubing pressure, by the tool of EP-A-0477452. The present invention also provides a force generator incorporating the novel tubing anchor referred to above. Because the novel tubing anchor is capable of resisting substantially larger axial loadings than known tubing anchors suitable for incorporation within a force generating tool, the force generating portion of the tool of the preferred embodiment is designed to produce a substantially higher axial force, at any given handling string pressure, than the device of EP-A-0477452. According to one aspect of the present invention there is provided a tubing anchor comprising a body; a plurality of slips mounted on the body for radial movement into and out of engagement with a tube within which the tubing anchor is located; a drive sleeve mounted on the body for axial movement relative thereto; mating cam surfaces on the drive sleeve and slips respectively whereby axial movement of the drive sleeve relative to the body in a first direction causes radially outward movement of the slips by virtue of relative axial movement of the cam surfaces of the drive sleeve and slips respectively; and interengaging surfaces on the body and the slips respectively for transferring axial load applied to the body m a second direction, opposite to the first direction, to the slips to force the slips m the second direction thereby increasing the radially outwardly force on the slips produced by the mterengagement of the respective cam surfaces of the slips and the drive sleeve. Accordingly, m a preferred embodiment of the present invention the tubing anchor may be run into a well bore on, for example, coiled tubing and may be set by moving the drive sleeve m the first direction to move the slips radially outwardly mto engagement with the surroundmg casing. The slips, having been moved mto contact with the casing, will fix the anchor relative to the casing. Any load subsequently applied to the anchor n the second direction will be applied to the slips thereby forcing them further along the cam surface of the drive sleeve and thus radially outwardly mto engagement with the casing. The force with which the slips engage the casing is accordingly mcreased by the axial load applied to the anchor m the second direction. Preferably, the interengaging surfaces of the body and the slips are themselves cam surfaces whereby axial load transferred to the slips from the body m the second direction will itself produce a radially outward force on the slips by virtue of the camming action of the interengaging surfaces. Preferably, means are provided for effecting a direct tensile connection between the handling string upon which the anchor is mounted and the drive sleeve in order to move the drive sleeve in the second direction thereby releaving the radially outward cam force applied to the slips to release the grip between the slips and the surrounding tubing. In the event that the tubing anchor is used as part of a force generator tool, the force generator portion of the tool is designed to produce a force which reacts against the tubing anchor in the second direction. In order to produce a very large force the force generator preferably comprises a multiplicity of similar stages each comprising an annular piston working within a cylinder, each annular piston being connected to the next adjacent annular piston by a piston rod and each cylinder being connected to each adjacent cylinder by a wall portion which sealingly receives the adjacent piston rod. Means are provided for hydraulically interconnecting the working chambers of the pistons and cylinders such that upon pressurisation of the handling string to which the tool is connected each working chamber is pressurised. The fluid pressure in each working chamber acts on the annular piston associated therewith to generate a force. Because the pistons are rigidly interconnected by their associated piston rods the forces produced are additive to produce a total force which is substantially higher than the force which is generated by any individual piston and cylinder arrangement . Whilst the various piston and cylinder stages can be substantially identical it is preferred that at least the piston rod adjacent the distal end of the tool is of more robust construction than the piston rod nearest the proximal end of the tool. This can be accomplished by making the piston rod at the distal end of the tool with a larger cross-section, and/or of a higher grade material, than the piston rod at the proximal end. With such an arrangement the force which the distal piston rod has to withstand can readily be accommodated. If the distal piston rod is made of a larger cross-section than the proximal piston rod this, will reduce the effective area of the annular piston associated with the distal piston rod. In contrast, the proximal piston rod can be made relatively small in cross-section with a resulting large area available for the piston associated therewith. Similarly, the wall thickness of the cylinders can be varied in the different stages if it is desired to maximize the force- to-weight or force-to-size ratio of the force generating portion of the tool. The cylinder at the distal end of the tool is required to withstand a smaller axial loading than the cylinder at the proximal end of the tool and may accordingly be made with a smaller wall thickness or of a lower grade material than the cylinder at the proximal end of the force generating portion. Accordingly, by appropriate design of the various components each can be designed to produce the maximum contribution to the total force consistent with its position within the assembly of pistons and cylinders: the pistons nearer the proximal end will produce a relatively large contribution to the total force because their piston rods do not need to withstand such a large force as those adjacent the distal end and can accordingly be made of relatively smaller diameter. The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings wherein: FIGURES 1A and 1B illustrate a preferred embodiment to tubing anchor according to the present invention; FIGURES 2A and 2B illustrate a force generating device which may be used in association with the tubing anchor of Figures 1A and 1B to produce a preferred embodiment of force generating tool according to the present invention; and FIGURE 3 shows, on a larger scale, a typical portion of the repeating piston and cylinder arrangement between the lines AA of Figure 2A and BB of Figure 2B. Referring firstly to Figures 1A and 1B, the illustrated tubing anchor 1 comprises a body formed by a top sub 2, a bottom sub 3, a piston sleeve 4 and a piston guide sleeve 5. Prior to use, the piston sleeve 4 is secured to the piston guide sleeve 5 by shear pins 6. The piston guide sleeve 5 is secured to the bottom sub 3 by a screw-threaded interconnection 7. A piston 8 is sliding and sealingly mounted within a cylinder 9 defined within the piston sleeve 4. A piston rod 10 is rigidly connected to the piston 8 and extends from the piston 8 to a terminal end portion 11 which is slidably and sealingly received within a bore 12 provided by the bottom sub 3. The piston 8 and piston rod 10 have communicating axial bores 13,14 which provide a fluid communication from the central bore 15 of the top sub 2 to the central bore 16 of the bottom sub 3. A piston return spring 17 acts on the piston 8 biasing the piston towards the top sub 2. Prior to pressurisation of the system the piston 8 is adjacent the lower face 18 of the top ' sub. The relative position of the various components as illustrated in Figures 1A and 1B occurs after pressurisation of the tool, as more particularly described below. The annular chamber 19 formed between the piston rod 10 and the piston sleeve 4 is vented to the surrounding well bore via a radial passage 20. A multiplicity of slips 21 are mounted on the body. Each slip 21 includes an inner portion 22 which is located within a respective slot 23 provided in the piston guide sleeve. The slots 23 permit some axial movement between the slips 21 and the piston guide sleeve 5. The slips 21 are biased radially inwardly by leaf springs 24 secured to the piston guide sleeve. The radially outer surfaces 25 of the slips are provided with serrated surfaces for engaging the surface of the tubing in which the tubing anchor is located. A drive sleeve 26 is slidably mounted on the piston guide sleeve 5 and is connected to the piston rod 10 by a multiplicity of dogs 27, only one of which is visible in the drawing. The dogs 27 lock the drive sleeve 26 to the piston rod 10 for simultaneous axial movement therewith relative to the remaining components of the tubing anchor. The drive sleeve 26 has, at the lower end thereof, a conically tapered surface 28 which mates with correspondingly tapered surfaces 29 of the slips. The surfaces 28,29 form cam surfaces and operate such that when the slips 21 and drive sleeve 26 are telescoped together a radially outward force is generated on the slips causing the slips to move radially outwardly against the bias of the springs 24. In the initial configuration of the components, as the tool is run into a well, the piston 8 is adjacent the surface 18 at the lower end of the top sub 2 and the upper end 30 of the drive sleeve 26 touches or is located adjacent to a shoulder 31 provided on the piston guide sleeve. In this configuration the slips 21 are retracted under the action of springs 24 such that the outer surfaces 25 of the slips are substantially in alignment with the adjacent outer surface 32 of the bottom sub 3. Accordingly, as the tool is run into the well, it has a substantially uniform outside diameter corresponding to that of the subs 2,3. The bottom sub 3 and the slips 21 have interengaging surfaces 33,34 which can transfer to the slips axial forces applied to the sub 3 in the up-hole direction, i.e. in the direction of the arrow U of Figure 1B, as will be described in more detail hereinafter. The interengaging surfaces 33,34 extend radially with a significant axial component such that they constitute respective cam surfaces. Accordingly, in position of an axial load on the surfaces 34 of the slips 21 by the surface 33 of the bottom sub 3 will produce a radially outward force on the slips 21. The above-described tubing anchor is particularly suitable for use in a force generating tool, and to this end the tubing anchor may have secured to the lower end thereof the force generator 35 illustrated in Figures 2A,2B and 3. This force generator comprises an upper portion 36 which extends from the top end 37 of the tool to the line AA of the Figure 2A and a lower portion 38 which extends from the line BB of Figure 2B to the ' lower end 39 " of the tool. Between the lines AA and BB the tool incorporates at least one and preferably a multiplicity of force generating stages 40. A typical force generating stage is illustrated between the lines AA and BB of Figure 3. The number of force generating stages present in any particular tool will be determined by the available operating pressure and the maximum force which the tool is required to generate. For any particular operating pressure the more force generating stages present the greater will be the total force generated by the tool. The force generator comprises a top piston 41 to which is secured a piston rod 42 having secured thereto, at the end remote from the piston 41 , a guide block 43. The guide block 43 is a free sliding fit within a cylinder 44. The passages 45 permit free flow of fluid past the guide block 43. Accordingly, upon pressurisation of the tool by the supply of hydraulic fluid through the central passage 51 a force will be generated which is substantially equal to the total cross-sectional area of the top piston 41 multiplied by the pressure present within the tool. The piston 41 is screw-threadedly connected to the upper end of the piston rod 42A of the next lower piston and cylinder assembly. Accordingly, the axial force generated by the piston 41 will be applied as an axial loading to the piston rod 42A. The annular chamber 46 formed between the piston rod 42A and the surroundmg cylinder 47 is vented to the surroundmg well bore via radial passages 48. A radial passage 49 connects the chamber 50 located immediately above the top piston" 41 to an axial bore 51 provided m the piston 42A. Referring now to Figure 3 one of the multiplicity of force generating stages 40 which will normally be located between the lines AA and BB of Figures 2A and 2B respectively is illustrated. It is to be understood that whilst the various force generating stages may be identical (which offers particular advantages m terms of reducing production costs by reducing the number of different componentε required) it will general be desirable for there to be slight variations between at least some of the stages. In particular, it is envisaged that whilst the mside diameters of the cylinders 47 will in general remain constant along the length of the tool, the outside diameter of the piston rod 42,42A,42B, etc. may increase towards the lower end of the tool. Whilst this increase will have the undesirable effect of reducing the effective cross-sectional areas of the annular pistons, the increase m diameter will make the piston rods more robust and accordingly more able to withstand the loads imposed on them. It must be remembered that each piston rod has imposed on it the total of the force generated by each force generating stages located above it and accordingly the axial loads on the piston rods increase progressively from the top of the tool towards the lower end thereof. Each force generating stage comprises a piston head 52 which is formed integrally with its associated piston rod 42A,42B, etc. Each piston rod 42A,42B etc. slidingly and sealingly passes through a guide member 53 whereby an annular working chamber 54 is defmed between each piston head 52, the associated up-hole guide member 53, the cylinder 47, and the piston rod 42A,42B etc. Each working chamber 54 is connected to the central bore 51 of the piston rods by a respective radial bore 55. The axial bores 51 of adjacent piston rods interconnect. Accordingly, pressurisation of the chamber 46 results m simultaneous pressurisation of the chamber 50 and all the working chambers 54 of the various force generating stages 40. The force generator by each stage is substantially equal to the pressure withm the annular chamber 54 of that stage multiplied by the cross- sectional area of the annular chamber. Below the l ne BB of Figure 2B the lowermost piston rod 56 is connected to an output member 57 which in use is either abutted directly agamst an item to which force is to be applied, or is connected to another tool which abuts such object. Initially, the output member 57 is secured to the body of force generator 35 by shear pms 58. As illustrated, the shear pms 58 have been sheared and the various components of the force generator are illustrated at approximately half of the available displacement. A return spring 59 is provided to act on the guide member 43 to return the entire stack of pistons and piston rods to the start configuration upon release of hydraulic pressure from the chamber 46. It will be noted that, as illustrated, the axial bore 51 terminates at the output member 57 and no flow passage is provided through the tool. It will be appreciated that, if desired, a selectively operable valve arrangement can be provided at the lower end of the passage 51 enabling flow through the tool if required for operating the tool located beneath the force generator. In use, a force generating tool is produced by securing the force generator 35 to the bottom sub 3 of the tubing anchor. The assembly is run into the well on any suitable handling string. Whilst the handling string may consist of jointed pipes the present invention is of particular advantage when used in association with coiled tubing and in general the tool will be run into the well on coiled tubing. In use, the tool is run to the desired setting depth. Often, this depth will be determined by running the tool down until the output member 57 engages an item to which force is to be applied. However, it should be appreciated that in more general applications of the tubing anchor it is not necessary for the tool to encounter a reactive force to enable it to be set - the tool can be set merely by application of hydraulic pressure. At the required depth hydraulic pressure is increased to act on the piston 8. When the force generated is sufficient to overcome the force of the return spring 17 the piston will move downwardly taking with it the dogs 27 and sleeve 26. The slips 21 cannot move downwardly with the drive sleeve 26 because of the engagement of the surfaces 34 of the slips with the surface 33 of the bottom sub 3. Accordingly, the conically tapered surface 28 of the drive sleeve will be forced to run along the mating cam surface of the slips thereby camming the slips outwardly into engagement with the surrounding casing. Progressively Increasing the pressure within the system will increase the force produced by the piston 8 and will correspondly increase the outward force applied to the slips 21. As system pressure continues to rise the top piston 41 of the force generator, in association with the force generating stages 40 will produce a progressively increasing force applied to the output member 57. When this force is sufficient to overcome the force of the spring 59 and the strength of the shear pins 58, the shear pins 58 will shear allowing the various internal components of the force generator to move downwardly and apply the required force. Progressive increase in pressure will increase the force applied to the output member 57. The reaction force generated by the force generator will be applied to the bottom sub 3 of the tubing anchor which will in turn apply for force via the confronting surfaces 33,34 to the slips 21. This force will tend to drive the slips further along the conical taper 28 of the drive sleeve 26. Also, because of the orientation of the faces 33,34 a direct camming action will be produced tending to move the slips radially outwardly in response to the axially imposed force. Accordingly, as the reaction force applied to the bottom sub 3 increases the force with which the slips 21 engage the surrounding casing will be mcreased. By this arrangement, the tubing anchor is able to withstand a very substantial axial loading m the upward direction. In order to release the assembly pressure is bled off allowing the return spring 59 to return the components of the force generator to the starting position. Similarly, the return spring 17 w ll tend to return the piston 8 and piston rod 10 to the initial position thereby applying an upward force to the dogs 27 which will be applied to the sleeve 26 thereby attending to withdraw the conically tapered portion of the drive sleeve 26 from the slips 21. Provided that the conically tapered portion of the drive sleeve 26 can be withdrawn from the slips the slips will be retracted to their starting position by the springs 24. It will be appreciated, however, that because of the very substantial forces which have been applied to the axial direction of the slips m use the conical portion of the drive sleeve 26 may be ceased to the slips. Under these circumstances, the tool will not free itself as a result of bleeding off of the hydraulic pressure. If this is the case, an axial upward load is applied to the top sub 2 m order to shear the shear pms 6. This will result m compression of the springs 17 solid thereby applying the entire upward load applied to the sub 2 to the piston rod 10. This load will be transferred by the dogs 27 to the drive sleeve 26 resulting m a substantial upward pull on the drive sleeve. This should be sufficient to release the drive sleeve. If necessary, a shock loading may be applied to erk the drive sleeve free. In order to prevent accidental shearing of the pin 6 it is desirable that the force necessary to shear them is greater than the maximum tensile force which may be applied to the top sub 2 by the handling string. If this is the case, shearing of the pm 6 is accomplished by pressurising the tubing string to the maximum available pressure and thereafter applying a tensile force to the sub 2. The shear pms 6 are designed to shear under the combmed effect of maximum hydraulic pressure and a moderate tensile force applied to the top sub 2 yet will not shear under the influence of either hydraulic pressure or tensile strength alone. Whilst the invention has been described with particular reference to a tool which is adapted to exert a downward (push) force, and thus to resist an upward reaction force, it will be appreciated that by appropriate reversal of various components, the mvention may be embodied as a tool adapted to exert an upward (pull) force and to resist the resultant downward reaction force. As an alternative to or m addition to increasmg the diameter of the piston rods towards the lower end of the tool as a means of accommodating the increasing compressive force to which the piston rods are subjected, the material from which the lower piston rods are formed may be of a higher specification that that of the upper piston rods. Additionally, if necessay the wall thickness of the cylinders and/or the specification of the material from which the cylinders are formed may be mcreased towards the upper end of the force generating sections so as to resist the progressively increasing compressive reaction forces imposed on the cylinders towards the upper end of the tool .

Claims: CLAIMS : 1. A tubing anchor comprising a body; a plurality of slips mounted on the body for radial movement into and out of engagement with the tubing; a drive sleeve mounted on the body for axial movement r'elative thereto; means for moving the drive sleeve relative to the body in a first direction; mating cam surfaces on the drive sleeve and slips respectively whereby axial movement of the drive sleeve relative to the body in the first direction causes radially outward movement of the slips by virtue of relative axial movement of the cam surfaces of the drive sleeve and slips respectively; and interengaging surfaces on the body and the slips respectively for transferring axial load applied to the body in a second direction, opposite to the first direction, to the slips to force the slips in the second direction thereby increasing the radially outwardly force on the slips produced by the interengagement of the respective cam surfaceε of the slips and the drive sleeve. 2. A tubing anchor according to Claim 1 wherein the interengaging surfaces of the body and the slips are themselves cam surfaces whereby axial load transferred to the slips from the body in the second direction will itself produce a radially outward force on the slips by virtue of the camming action of the interengaging surfaceε . 3. A tubing anchor according to Claim 1 or Claim 2 wherein the means for moving the drive sleeve comprises: a hydraulic piston and cylinder for producing a force on a piston rod which is connected to the piston and is slideably mounted in the body; and means for connecting the drive sleeve to the piston rod. 4. A tubing anchor according to Claim 3 wherein the piston is captive within the cylinder and including: means for releasably connecting the cylinder to the body whereby, after releaεe of the releasable connection an axial force may be applied to the cylinder in the second direction to apply an axial force to the piston rod in the second direction and thereby exert an axial force on the drive sleeve in the second direction to release the slips . 5. A tubing anchor according to Claim 4 wherein the releasable means compriseε one or more shear elements. 6. A tubing anchor according to any preceding claim in combination with a force generator, the force generator being connected to the tubing anchor whereby reaction forces generated on the body of the force generator are transferred to the body of the tubing anchor in the second direction. 7. A tubing anchor and force generator assembly according to Claim 6 wherein the force generator comprises a plurality of piston and cylinder assemblies, the cylinders being connected to the body of the force generator and the pistons being connected to an output member of the force generator. 8. A tubing anchor and force generator assembly according to Claim 7 wherein the piston rod associated with the force generator piε ' ton nearest 'to the tubing anchor is of less robust construction than the piston rod associated with the force generator piston furthest from the tubing anchor. 9. A tubing anchor and force generator assembly according to Claim 7 or Claim 8 wherein the cylinder associated with the force generator piston neareεt to the tubing anchor is of more robust construction than the cylinder associated with the force generator piston furthest from the tubing anchor.

Inventors: MCGARIAN BRUCE, SIMPSON NEIL ANDREW ABERCROMBI, MCGARIAN, BRUCE, SIMPSON, NEIL, ANDREW, ABERCROMBIE
Applicants: MCGARIAN BRUCE, RED BARON OIL TOOLS RENTAL, SIMPSON NEIL ANDREW ABERCROMBI, MCGARIAN, BRUCE, SIMPSON, NEIL, ANDREW, ABERCROMBIE, THE RED BARON (OIL TOOLS RENTAL) LIMITED
Application year: 1996
Main classification: E21B23
IPC codes: E21B23