APPARATUS AND METHOD FOR SETTING A TUBING ANCHOR AND TENSIONING TUBING STRING THEREABOVE

Abstract

A tensioning tool for connection with a tubing hanger and tubing string suspended from the tubing hanger retained in a dognut by a hanger retainer. Preferably the hanger retainer is temporarily engaged to the top of the tensioning pup for release therefrom once a lower end of the tubing has been fixed by a tubing anchor and the tubing has been lifted a tensioning distance. The hanger retainer is then engaged with the tubing hanger for suspending the tensioned tubing from the dognut locked in the wellhead. The dognut and the hanger retainer have co-operating locking faces which prevent rotation of the hanger retainer in the dognut once the locking faces are mated which assists in maintaining torque applied to the tubing string which may have been applied to rotationally set the tubing anchor. More preferably, the tensioning pup has a series of gradations marked on the pup for measuring the amount of tension applied to the tubing string.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is a regular application claiming priority of U.S. Provisional Patent application Ser. No. 60/574,203 filed on May 26, 2004, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the invention relate to production of oil and gas from a wellbore and more particularly to apparatus for tensioning production tubing to prevent wear due to compression of at least a portion of the tubing string during production.

BACKGROUND OF THE INVENTION

In conventional oil and gas production, once a wellbore has been drilled, cased and perforated, a production tubing string is lowered into the wellbore to produce the hydrocarbons therethrough. A rod string extends through the production tubing string to either a reciprocating pump or a progressive cavity pump (PCP), positioned at a downhole end of the production tubing. In the case of a PCP, the rod string is used to rotate a rotor within a stator in the PC pump, to pump the hydrocarbons to surface. A top drive is typically used to rotate the rod string. In the case of a reciprocating pump, the rod string is reciprocated axially within the tubing string, typically by a pumpjack. Further, in the case of the reciprocating pump, an anchor is set at the lower end of the production tubing to prevent a corresponding axial movement of the pump barrel during reciprocation of the rod string.

The length of the production tubing may be greater than 1000 ft and, more typically, is at least 3000-4000 ft long, depending upon the depth of the wellbore. Typically, the weight of the tubing string hanging in the wellbore places at least the portion of the tubing string closest to surface, in tension. In such long strings of jointed tubing and particularly when using a reciprocating pump, it is not unusual that the production tubing string closest to the tubing anchor rests on the anchored pump barrel causing a portion of the tubing string to go into compression and buckle slightly. Buckling of the tubing string may result in contact with the rod string resulting in wear as the rod string is actuated. Excessive wear may eventually compromise the structural integrity of the production tubing necessitating frequent replacement. Tripping the production tubing string in and out of the wellbore to effect said replacements results in cessation of production and costly downtime and servicing.

Typically, the tubing string may be tensioned approximately 1 inch for every one thousand feet of tubing in order to alleviate buckling. Conventional methods of tensioning tubing include lowering the tubing string to a desired depth, setting a tubing anchor at a lower end of the tubing to fix the position of the lower end of the tubing string and then pulling up to stretch the tubing. Once the tubing is stretched, a set of shorty slips are used to hold the tubing string in place. The pulling apparatus is disconnected so that a dognut can be threaded onto the tubing string. The pulling apparatus must then be reinserted in order to lift the tubing string to release the shorty slips. The tubing string must be lifted at least 3 inches, and more typically 5-6 inches to effectively release the shorty slips. In the case of shallow wells, there is not enough stretch in the tubing string to permit sufficient lifting and therefore attempts to straighten the tubing may result in tearing out the threaded joints.

Further, even in deeper wellbores where there is sufficient slack to permit lifting high enough to set and release the slips, the methods are fairly crude and inaccurate and do not always have a successful outcome, the tubing string being tensioned too much or not enough.

SUMMARY OF THE INVENTION

In one embodiment, a tensioning tool engages a form of tubing hanger, hanger retainer and dognut from which a tubing string is suspended, to permit lowering of the tubing, setting of a tubing anchor and lifting of the tubing hanger and tubing string to be stretched or tensioned. Measuring means are provide to determine a tensioning distance to which the tubing string and hanger are lowered such that when lifted, adequate tensioning of the tubing is achieved without over-stretching the tubing. A retainer is provided for engaging between the tubing hanger and the dognut, lockingly supported in a wellhead bowl, for supporting the tubing string in the dognut following tensioning of the tubing string. The form of tubing hanger and retainer minimize over tensioning and enable support and anti-rotation of the tubing hanger and tubing string.

Preferably, the tool comprises a tensioning pup that engages the tubing hanger and which is marked with a series of evenly spaced gradations for measuring the tensioning distance. A hanger retainer or nut is engaged with a top of the tubing hanger once the tubing has been tensioned permitting the tensioned tubing to be suspended from the hanger nut in the dognut.

In the case where the tubing anchor is rotationally set, at least some of the torque applied to the tubing string to set the anchor is maintained by the tubing hanger and retainer in order to keep the tubing anchor actuated. Mating circumferential locking faces are machined on an inner radial face of the dognut and an outer face of the hanger retainer which, when aligned and mated, rotationally lock the hanger nut in the dognut preventing release of at least some of the torque applied to the tubing string.

Thus in a broad aspect of the invention a tensioning tool for tensioning a tubing string suspended in a wellbore casing by a tubing hanger supported in a dognut in a wellhead and anchored at a downhole end by a tubing anchor comprises: a tensioning pup adapted for engaging the tubing hanger for lifting the tubing hanger and tubing string suspended therefrom for tensioning the tubing string; means for measuring a tensioning distance applied for tensioning the anchored tubing string; and a retainer adapted for re-engaging the tubing hanger in the wellhead dognut when the tubing string is in tension. Preferably, a tensioning pup is engaged with the tubing hanger for supportably lifting and lowering the tubing hanger and tubing string suspended therefrom, the tensioning pup being marked with a series of gradations at evenly spaced intervals for measuring the tensioning distance therewith. The hanger retainer is preferably a nut for threaded engagement with the top end of the tubing hanger. More preferably, the hanger nut has a circumferential locking face which engages a circumferential locking face formed in the dognut for rotationally locking the tubing hanger and tubing string from rotation once tensioned.

Further, a method of tensioning a tubing string suspended in a wellbore is provided wherein the tubing string has an upper end at a wellhead and a lower end having a tubing anchor, the wellhead having a bowl for lockably supporting a dognut therein, the method comprising: supporting the tubing string at the wellhead with the upper end of the tubing string projecting from the wellhead; fitting the upper end of the tubing string with a tubing hanger for suspending the tubing string therefrom, the tubing hanger having a threaded top end; fitting a dognut over the top end of the tubing hanger, the dognut having a bore and a top end having a first circumferential locking face extending radially outwards from the bore; releasing the tubing string at the wellhead; lowering the tubing hanger and the tubing string so as to engage the dognut in the wellhead bowl; continuing to lower the tubing hanger and tubing string so that the top end of the tubing hanger is below the top end of the dognut by a tensioning distance, the lower end of the tubing string being substantially at a target depth; setting the tubing anchor to fix the position of the lower end of the tubing string at the target depth in the wellbore; pulling up the tubing hanger and tubing string at least the tensioning distance to tension the tubing string and expose the top end of the tubing hanger; engaging a hanger retainer having a second circumferential locking face extending radially outwards therefrom to the top end of the tubing hanger for supporting the tubing string therefrom; aligning the first and second circumferential locking faces; and lowering the hanger retainer supporting the tubing hanger and tubing string into the dognut for suspending the tensioned tubing string therefrom, the first and second circumferential locking faces being mated together for preventing rotation of the hanger retainer within the dognut.

Preferably, a tensioning pup is engaged with the tubing hanger for supportably lifting and lowering the tubing hanger and tubing string suspended therefrom, the tensioning pup being marked with a series of gradations at evenly spaced intervals for measuring the tensioning distance therewith. The hanger retainer is preferably a nut for threaded engagement with the top end of the tubing hanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is an exploded schematic view of a tensioning tool according to an embodiment of the invention, the tool being adapted for use to tension production tubing suspended from a tubing hanger, to remove buckling therein;

FIG. 1b is a cross-sectional view according to FIG. 1a, along section lines A-A, illustrating mating circumferential locking faces of a hanger retainer and a modified dognut;

FIG. 2a-c are partial longitudinal sectional views of the tensioning tool according to FIG. 1, in use to tension the production tubing, and more particularly,

FIG. 2a illustrates a first step of engaging the tensioning tool according to FIG. 1 into a top end of a tubing string, the tensioning tool and tubing string being lowered to a predetermined position prior to fixing the position of the lower end of the production tubing;

FIG. 2b illustrates a second step wherein the dognut has been locked into place in the wellhead and the production tubing is tensioned by lifting the tubing at a top end to position the tensioning tool at a predetermined position;

FIG. 2c illustrates a third step wherein a hanger retainer carried on the tensioning tool engages a modified dognut for locking the production tubing into the tensioned position;

FIG. 3 is a longitudinal sectional view of the wellhead illustrating the engaged hanger retainer and modified dognut positioned in the wellhead following tensioning of the production tubing suspended therefrom;

FIG. 4a is a partial longitudinal sectional view according to FIG. 2b illustrating the second step in tensioning the tubing string;

FIG. 4b is a partial longitudinal sectional view according to FIG. 2c illustrating the third step in tensioning the tubing string; and

FIG. 4c is a partial perspective sectional view according to FIG. 4b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1a, an embodiment of a tensioning tool 1 comprises a tubing hanger 2 from which production tubing (not shown) is suspended, a tensioning pup 3, threadably connected to the tubing hanger 2, a modified dognut 4 positioned about the tensioning pup 3 and being axially moveable thereover and a hanger retainer 5, preferably a hanger nut, positioned on the tensioning pup 3 and being axially moveable over the tensioning pup 3.

In the preferred embodiment and in a connecting position, the hanger nut 5 is threaded for operational engagement in a secured position with an upper, outer threaded surface 66 at the top end 6 of the tubing hanger 2. The top end 6 of the tubing hanger 2 is sized to fit axially upwardly through the dognut 4 for exposing the outer threaded surface 66 above the dognut 4 for engagement with the hanger nut 5. When engaged, the nut 5 may seat on a shoulder 16.

Further, the tensioning pup 3 is threaded at an upper portion 7, adjacent a top end 8 of the tensioning pup 3, for temporarily retaining the hanger nut 5 thereon during connection of the tensioning tool 1 to the tubing hanger 2. The tensioning pup 3 has a threaded portion 17 adjacent a bottom end 18 for connection to a threaded bore 19 of the tubing hanger 2. The production tubing (not shown) is suspended from the tubing hanger 2.

As shown in FIGS. 1a and 1b, the hanger retainer 5 is machined with an radially outward extending outer circumferential locking face 11 about an upper outer edge 12. The dognut 4 is machined having an inner circumferential locking face 13 formed to extend radially outwards from an upper, inner edge 14. One embodiment of the locking faces 11,13 is a form of compatible spline having a variable radial extent to lock relative rotation. Once the circumferential locking faces 11,13 are engaged, the hanger retainer 5 and dognut 4 are fixed to prevent independent rotation of the hanger retainer 5, and supported tubing hanger 2 and tubing string 20, within the dognut 4 and to suspend the tubing hanger 2 and string 20 from the hanger retainer 5, supported in the dognut 4.

The tensioning pup 3 is conveniently marked along a length with a series of gradations 10 used to measure the amount of tension or stretching applied to the tubing string 20. Typically, the gradations 10 are marked in 1 inch intervals.

In Use

Having reference to FIGS. 2a-c and in use, a tubing string 20 of production tubing is lowered into the wellbore 21 to the final section of tubing 20 with the lower end of the string at about a target depth. The string 20 is hung in a wellhead 9 from slips (such as shorty slips not shown). The tubing hanger 2 is threaded onto the final piece of tubing 20. The dognut 4 is then set onto the tubing string 20 over the tubing hanger 2. The hanger nut 5 is temporarily suspended above the dognut such as by threaded connection to threads 7 at the top end 8 of the tensioning pup 3. A seal 15, typically an O-ring, is placed over the tensioning pup 3 for sealing between the tubing hanger 2 and the dognut 4 when installed. The tensioning pup 3 is then threaded into internal threads 17 in the tubing hanger 2.

The tensioning pup 3 and tubing string 20 are lifted to release and remove the slips (not shown), after which the tubing string 20 is lowered. The dognut 4 is landed into the bowl in the wellhead 9 and preferably that his time the dognut 4 is locked into place in the wellhead 9 by setting a plurality of dogs 22. The tubing string 20 is further lowered a tensioning distance (FIG. 2a) as measured on the series of gradations 10 on the tensioning pup 3. One approach is to mark the tensioning distance from 0″ as the top end 6 of the tubing hanger 2 when the tensioning pup 3 is threaded thereto. For example, as the tensioning pup 3 is typically graded in 1 inch intervals, in order to stretch the tubing by 5 inches the tubing string 20 is lowered a relative tensioning distance from 0″ to the 5 inch gradation on the tensioning pup 3 as viewed above the top end 6 of the tubing hanger 2 and relative to some datum such as the dognut 4.

A tubing anchor 30 is set at a lower end 31 of the tubing string 20 to fix the position of the lower end 31 of the tubing string 20 in the wellbore 21 at the target depth.

In the case of a rotationally actuated tubing anchor 30, the tensioning pup 3 is rotated to set the tubing anchor 30. It may be necessary, depending upon the type of tubing anchor 30 used to hold at least some of the torque on the tubing anchor 30 to keep the tubing anchor 30 engaged with the wellbore 21 until the tensioning operation is completed or thereafter.

As shown in FIG. 2b, and once the tubing anchor 30 has been set, the tubing string 20 is lifted or pulled up to stretch the tubing string 20 suspended therefrom. The tubing 20 is pulled upwards the tensioning distance and a further distance sufficient to expose the threaded top end 6 of the tubing hanger 2 through the dognut 4. The O-ring 15 and hanger nut 5, which is released from the threads 7 at the top end 8 of the tensioning pup 3, are pushed down to the dognut 4. The hanger nut 5 is threaded onto the top end of the tubing hanger 2.

As shown in FIG. 4a, the hanger nut 5 is tightened onto the tubing hanger 2, preferably until the hanger nut 5 is adjacent or stops against shoulder 16 on the tubing hanger 2. Typically, at this point the circumferential locking face 11 of the hanger nut 5 sit a small distance of approximately ±4″ above the dognut 4. In other words the top end 6 of the tubing hanger 2 is slightly over-tensioned more than the tensioning distance to facilitate engaging the hanger retainer. The outer circumferential locking face 11 of the hanger nut 5 is aligned to mate with the inner circumferential locking face 13 of the dognut 4.

As shown in FIGS. 2c, 3 and 4b-c, the tubing hanger 2 and string 20 is lowered the last small distance downwards through the dognut 4, compressing the O-ring 15 to seal against the tubing hanger 2. The circumferential locking faces 11,13 on the hanger retainer or nut 5 and the dognut 4 mate and act to rotationally lock the tubing hanger 2 into the dognut 4, retaining at least some of the torque applied to the tubing string 20 in the case where rotation is used to set the tubing anchor 30 and to suspend the tubing string 20 from the hanger nut 5 supported in the dognut 4. There may be some residual rotation of the top end 6 of the tubing hanger 2 to seat the shoulder 16 into the hanger nut 5.

Once the tensioning operation is completed, the pulling tool is removed and the tensioning pup 3 is unthreaded and removed from the tubing hanger 2 and such production equipment as is required is connected thereto.

Claims

1. A tensioning tool for tensioning a tubing string suspended in a wellbore casing by a tubing hanger supported in a dognut in a wellhead and anchored at a downhole end by a tubing anchor comprising:

means adapted for engaging the tubing hanger for lifting the tubing hanger and tubing string suspended therefrom for tensioning the tubing string;

means for measuring a tensioning distance applied for tensioning the anchored tubing string; and

means adapted for engaging the tubing hanger in the dognut when the tubing string is in tension.

2. The tensioning tool as described in claim 1 wherein the means adapted for engaging the tubing hanger and for measuring the tensioning distance of the tubing hanger and anchored tubing string is a tensioning pup adapted for connection to the tubing hanger at a lower end and a lifting means at an upper end, the tensioning pup having a series of evenly spaced gradations marked thereon for measuring the amount of tension applied to the tubing hanger and suspended tubing string.

3. The tensioning tool as described in claim 1

wherein the dognut further comprises a bore for positioning the dognut about the tensioning pup and being axially moveable thereon and having a profiled inner circumferential locking face formed about an upper inner edge; and

the means adapted for engaging the top end of the tubing hanger in the dognut comprises a hanger retainer adapted for engagement with the top end of the tubing hanger and having an outer circumferential locking face about an upper outer edge,

wherein, in a secured position the hanger retainer is moving axially over the tensioning pup for connection to engagement means at the top end of the tubing hanger, the hanger retainer, tubing hanger and suspended tubing being lowered into and engaged in the dognut for supporting the tubing hanger and tensioned tubing therefrom and aligning and mating the circumferential locking faces of the hanger retainer and the donut, preventing release of the hanger retainer from the dognut.

4. The tensioning tool as described in claim 3 further comprising:

a temporary engagement means formed at an outer upper end of the tensioning pup; and

wherein in a connecting position, the hanger retainer is temporarily engageable at the upper end of the tensioning pup by the outer engagement means during connection of the tensioning pup to the tubing hanger; and in the secured position, the hanger retainer is releasable from the upper end of the tensioning pup for moving axially thereover for connection to the engagement means at the top end of the tubing hanger.

5. The tensioning tool as described in claim 4 wherein the engagement means at the outer upper end of the tensioning pup and the top end the tubing hanger are a plurality of threads formed thereon and the hanger retainer is threaded for engagement therewith.

6. The tensioning tool as described in claim 1 further comprising a seal formed about the hanger retainer for sealing between the hanger retainer and the dognut in the secured position.

7. A tensioning tool for tensioning a tubing string suspended in a wellbore casing by a dognut supported in a wellhead, the tubing string being anchored at a downhole end by a tubing anchor comprising:

a tubing hanger having a top end movable through the dognut;

a tensioning pup adapted at a lower end for supportable connection to the tubing hanger and tubing string suspended therefrom and adapted for connection to a lifting means at an upper end for lifting the tubing hanger and suspended tubing string for tensioning the tubing string; and

a retainer for engaging the top end of the tubing hanger in the dognut once the subbing string is in tension.

8. The tensioning tool as described in claim 7 further comprising a series of gradations marked on the tensioning pup for measuring the amount of tension placed on the tubing string.

9. The tensioning tool as described in claim 7

wherein the dognut further comprises a bore for positioning the dognut about the tensioning pup and being axially moveable thereon and having a profiled inner circumferential locking face formed about an upper inner edge; and

the means adapted for engaging the top end of the tubing hanger in the dognut comprises a hanger retainer adapted for engagement with the top end of the tubing hanger and having an outer circumferential locking face about an upper outer edge,

wherein, in a secured position the hanger retainer is moving axially over the tensioning pup for connection to engagement means at the top end of the tubing hanger, the hanger retainer, tubing hanger and suspended tubing being lowered into and engaged in the dognut for supporting the tubing hanger and tensioned tubing therefrom and aligning and mating the circumferential locking faces of the hanger retainer and the donut, preventing release of the hanger retainer from the dognut.

10. The tensioning tool as described in claim 9 further comprising:

a temporary engagement means formed at an outer upper end of the tensioning pup; and

wherein in a connecting position, the hanger retainer is temporarily engageable at the upper end of the tensioning pup by the outer engagement means during connection of the tensioning pup to the tubing hanger; and in the secured position, the hanger retainer is releasable from the upper end of the tensioning pup for moving axially thereover for connection to the engagement means at the top end of the tubing hanger.

11. The tensioning tool as described in claim 10 wherein the engagement means at the outer upper end of the tensioning pup and the top end the tubing hanger are a plurality of threads formed thereon and the hanger retainer is threaded for engagement therewith.

12. The tensioning tool as described in claim 7 further comprising a seal formed about the hanger retainer for sealing between the hanger retainer and the dognut in the secured position.

13. A method of tensioning a tubing string suspended in a wellbore, the tubing string having an upper end at a wellhead and a lower end having a tubing anchor, the wellhead having a bowl for lockably supporting a dognut therein, the method comprising:

supporting the tubing string at the wellhead with the upper end of the tubing string projecting from the wellhead;

fitting the upper end of the tubing string with a tubing hanger for suspending the tubing string therefrom, the tubing hanger having a threaded top end;

fitting a dognut over the top end of the tubing hanger, the dognut having a bore and a top end having a first circumferential locking face extending radially outwards from the bore;

releasing the tubing string at the wellhead;

lowering the tubing hanger and the tubing string so as to engage the dognut in the wellhead bowl;

continuing to lower the tubing hanger and tubing string so that the top end of the tubing hanger is below the top end of the dognut by a tensioning distance, the lower end of the tubing string being substantially at a target depth;

setting the tubing anchor to fix the position of the lower end of the tubing string at the target depth in the wellbore;

pulling up the tubing hanger and tubing string at least the tensioning distance to tension the tubing string and expose the top end of the tubing hanger;

engaging a hanger retainer having a second circumferential locking face extending radially outwards therefrom to the top end of the tubing hanger for supporting the tubing string therefrom;

aligning the first and second circumferential locking faces; and

lowering the hanger retainer supporting the tubing hanger and tubing string into the dognut for suspending the tensioned tubing string therefrom, the first and second circumferential locking faces being mated together for preventing rotation of the hanger retainer within the dognut.

14. The method as described in claim 13 wherein the tubing anchor is set rotationally, further comprising:

applying torque to the tubing string for setting the tubing anchor;

maintaining at least some of the torque on the tubing string while tensioning the tubing string, engaging the hanger retainer in the dognut,

wherein the mated first and second locked circumferential locking faces maintain the at least some of the torque by preventing rotation of the hanger retainer within the dognut.

15. The method as described in claim 13, following fitting the dognut over the tubing hanger, further comprising:

engaging a tensioning pup with the tubing hanger for supportably lifting and lowering the tubing hanger and tubing string suspended therefrom.

16. The method as described in claim 15 further comprising: lowering the tubing hanger a tensioning distance by lowering the tensioning pup as measured against a series of gradations at evenly spaced intervals along the tensioning pup for measuring the relative tensioning distance.

17. The method as described in claim 16 wherein the gradations are spaced at one inch intervals.

18. The method as described in claim 15 wherein the tensioning pup has outer engagement means formed at a top end for temporarily retaining the hanger retainer thereon prior to engaging the hanger retainer with the tubing hanger.

19. The method as described in claim 18 wherein the hanger retainer is a hanger nut and wherein the top end of the tubing hanger is a plurality of threads for threadably engaging the hanger nut thereon.