Patent Application
20120312549
This invention relates to a method and apparatus for use in retrieving tubulars from bores. Aspects of the invention relate to the retrieval of cut casing from boreholes drilled to access subsurface hydrocarbon-bearing formations.
Wells drilled to access subsurface formations may be lined with tubular members, typically metal tubular lengths joined together by threaded connectors. In the oil and gas exploration and production industry, an initial section of the well bore is drilled and then lined with a string of tubular members, known as casing, which extends from the end of the bore to the surface of the earth. Cement may then be circulated into the annulus between the casing and the bore wall. The set cement provides support for the bore wall and prevents fluid migration along the annulus. The drilling of the bore is then continued beyond the end of the first casing. A second casing string is then run into the bore. This string also extends from the end of the bore to surface. Again, cement is circulated into the annulus between the casing string and the bore wall. However, the volume of cement is selected to be sufficient only to fill the annulus between the second string and the surrounding unlined bore wall; the annulus between the first and second casing strings is left substantially free of cement.
This process is repeated until the desired depth is reached, and the upper end of the bore is lined by numerous casing strings, the smallest diameter innermost casing extending from surface to the end of the bore.
At some point in the life of the well, for example prior to abandonment or in the course of workover procedures, it may be desired to remove portions of some of the casing strings. Generally, no attempt is made to retrieve the cemented casing sections. Rather, the innermost casing is cut above the cemented section, and the cut section retrieved. However, this may not be straightforward. Solid material may have gathered or settled in the annulus between the cut casing and the surrounding casing during the life of the well. Also, corrosion between the casings may cause adjacent casings to become fixed relative to one another.
Thus, a typical procedure for retrieving casing may involve the following steps:
If the cut casing does not come free a second cut may be made in the casing, closer to surface.
In anticipation of difficulties in retrieving a cut casing, the operator may incorporate a jar in the fishing BHA. Alternatively, the present applicant's Agitator (Trade Mark) tool may be incorporated in the BHA. As described in U.S. Pat. No. 7,077,205, the disclosure of which is incorporated herein in its entirety by reference, a flow pulsing tool such as the applicant's Agitator tool may be used in conjunction with an extension and retraction means, such as a shock tool, to vary the tensile load applied to a stuck object, such as a cut casing section. Operation of the applicant's Agitator tool, further details of which are described in U.S. Pat. No. 6,279,670, the disclosure of which is also incorporated herein in its entirety by reference, requires circulation of fluid through the tool. Thus, fluid is pumped down the work string, passes through the Agitator tool, and passes though outlet ports in the fishing BHA and into the annulus above the casing spear.
According to the present invention there is provided a tubular retrieval method including applying a cyclically varying fluid pressure to the interior of a section of cut bore lining tubular.
According to another aspect of the invention there is provided tubular retrieval apparatus comprising:
The pressure pulses or varying pressure will tend to push the tubular being retrieved free from the surrounding larger diameter tubular. As the pressure pulses are applied to the cut section, the pressure will be applied to a relatively large area; potentially the cross-sectional area of outer tubular surrounding the cut tubular, and at least the cross-sectional area of the cut tubular. The varying pressure may also assist in dislodging solids which have settled or otherwise lodged in the annulus between the cut tubular and the surrounding tubular. Furthermore, the varying pressure may assist in establishing fluid circulation in the annulus, assisting retrieval of the cut tubular.
An upper seal may be configured for location above the cut, and may configured for location towards the upper end of the cut tubular. A lower seal may be configured for location below the cut.
The apparatus may include a support member configurable to engage the cut tubular, typically an upper end of the tubular. The support member may be utilised to apply a pulling force to the tubular, and the support member may be tubular and configured to carry fluid. The support member may include a gripping device to engage the cut tubular, and the gripping device may incorporate or be provided in combination with the upper seal.
The pressure pulse-generating device may be located above the cut tubular. The device may be configured for mounting in a support member engaging the tubular.
The pressure pulse-generating device may take any appropriate form. In one embodiment the device is configured to act on fluid being circulated in the bore above the cut tubular and to generate pressure pulses or pressure variations in the circulating fluid. The fluid may be circulated through a tubular support member and an annulus between the support member and the surrounding tubular. The apparatus may be configurable to provide communication between the circulating fluid and the isolated section of cut tubing, whereby the pressure pulses or pressure variations are applied to fluid in the isolated section.
The pressure pulse-generating device may be fluid actuated, and may be adapted to be actuated by fluid being circulated in the well bore. The device may include a positive displacement motor, such as a Moineau principle motor. The device may include a valve operable to vary a fluid flow area, and thus vary the pressure in fluid being passed through the valve. The valve may be configured to rotate or oscillate. The device may produce a variation on the fluid pressure above or below the valve. The apparatus may be configurable to provide fluid communication between the fluid above the valve and the isolated section of cut tubing. Alternatively, or in addition, the apparatus may be configurable to provide fluid communication between the fluid below the valve and the isolated section of tubing.
The apparatus may be configured to permit fluid to pass from an outlet of the pressure pulse-generating device into an annulus between the device and the surrounding tubular. The fluid may pass from the device outlet to the annulus via a flow port. The flow port may be nozzled or otherwise restricted. The flow port may be configured to be opened and closed. In one embodiment, the pulse-generating device may be de-activated by closing the flow port.
These and other aspects of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Reference is first made to
The inner casing 20 is mounted within an outer casing 22. A lower portion of an annulus 24 between the casings 20, 22 has been filled with cement 26. The upper part of the annulus 24 is free of cement, however over the life of the well the upper end of the inner casing 20 is likely to have become fixed relative to the outer casing 22 through corrosion and the presence of mud solids 28 that have settled between the casing strings.
The apparatus 10 comprises a positive displacement motor section 30 positioned above a valve assembly 32. The positive displacement motor and valve assembly are similar to the motor and valve described in U.S. Pat. No. 6,279,670. Thus, as fluid is passed through the motor 30, a rotor is subject to rotation and also oscillates within the motor stator. The lower end of the rotor provides mounting for an upper valve plate configured to co-operate with a stationary lower valve plate. As the rotor rotates and oscillates, openings in the valve plates are moved into and out of alignment, thus varying the flow area through the valve assembly 32.
The fishing BHA 14 also includes a section of pipe 38 mounted to the lower end of the valve assembly 32 and which extends downwards to provide mounting for the casing spear 16 and pack-off element 18. The pipe 38 provides fluid communication between the outlet of the valve assembly 32 and the isolated section of the inner casing 20A. Also, the pipe 38 defines a nozzled port 40 which provides fluid communication between the pipe 38 and the upper annulus 44 between the work string 12 and the apparatus 10 and the outer casing 22.
In use, an operator wishing to retrieve the inner casing 20 will first determine the height of the cement 26 in the annulus 24 between the casings 20, 22. The operator will then determine where the inner casing should be cut, this normally being a short distance above the upper end of the cement 26. The operator will then set a packer 34 within the inner casing 20, below the location where the cut is to be made. This seals off the bore of the inner casing 20. A cutter (not shown) is then run into the bore to produce a casing cut 36. The work string 12 carrying the fishing BHA 14 is then run in to the bore and the casing spear 16 and pack-off element 18 set at the upper end of the inner casing 20.
Tension is then applied to the work string 12 from surface, which tension is thus applied to the cut section of the inner casing 20. In addition, surface pumps are started and cause fluid to be pumped down the work string 12 and through the fishing BHA 14. The passage of fluid through the motor section 30 causes the rotor to rotate and produces relative movement of the valve plates within the valve assembly 32. Thus, the rotary valve within the valve assembly 32 opens and closes, providing a varying fluid pressure below the valve assembly 32, which varying fluid is applied to the cut section of casing. Initially, it is likely that the settled solids and other material 28 in the annulus 24 will prevent circulation of the fluid from the inner casing 20, through the cut 36, and up through the annulus 24. Accordingly, the pulsing pressure will create an upward force acting over the cross-section of the inner casing 20. There is also a pulsed fluid pressure force acting through the cut 36 and tending to dislodge the settled solids 28. The pressure pulses will also tend to vibrate the casing, further assisting in reducing friction and dislodging the solids 28.
The nozzled port 40 allows fluid circulation and operation of the motor 30 while the annulus 24 remains blocked above the cut 36, the nozzling of the port 40 maintaining a back pressure within the cut section of casing.
In due course the cut section of casing will break free, and at some point it is likely that the pulsing fluid pressure will dislodge the solids 28 to achieve circulation through the annulus 24, which will facilitate movement of the inner casing 20 relative to the outer casing 22.
Once the inner casing 20 has been freed from the outer casing 22, retrieval is relatively straightforward.
In an alternative arrangement, the nozzled port 40 incorporates a valve which may be opened and closed from surface by the operator. When closed, the valve prevents flow through the port 40. Thus, if the valve is closed and the annulus 24 above the cut 36 is blocked, there is no circulation route for fluid being pumped from surface. In this situation the motor 30 will not operate, although fluid pressure may still be transmitted through the motor 30 to the cut section of casing below the apparatus 10. Accordingly, it is possible for the operator to turn the apparatus on and off by opening and closing the valve.
Reference is now made to
In the illustrated arrangement, there is again an outlet port 140 provided below the valve assembly 132, however the port 140 is not nozzled, allowing relatively free flow to the upper annulus 144. However, a pressure transfer pipe 52 extends from above the valve assembly 132 to a point in the pipe 138 above the casing spear and pack-off element 116, 118. The point where the pressure transfer pipe 52 enters the pipe 138 is isolated from the port 140 by a seal 54.
During operation of the apparatus 50, the pressure pulses generated above the valve assembly 132 are transferred through the pipe 52 and the casing spear 116 to the cut section of inner casing 120.
Use of the apparatus 50 is otherwise similar to the apparatus 10 described above. However, the apparatus 50 offers the additional advantage that there is no requirement to elevate the back pressure downstream of the valve assembly 132 (achieved by nozzling the port 40 in the first embodiment), which increases the surface pump requirements.
It will be apparent to those of skill in the art that the above described arrangements allow an operator to introduce pressure pulses below the casing spears 16, 116 and act on the full area of the casing string 20, 120. Also, the pulses below the spears 16, 116 assist in directly pushing the casing 20, 120 free. Furthermore, applying pressure pulses through the casing cut 36, 136 will assist in dislodging solids 28, 128 in the annulus 24, 124 in order to establish circulation and free the inner casing 20, 120.
It will be apparent to those of skill in the art that the above described embodiments are merely exemplary of the present invention, and that various modification and improvements may be made thereto, without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0920346.4 | Nov 2009 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2010/002140 | 11/19/2010 | WO | 00 | 5/18/2012 |
