Method of removing a downhole casing

Abstract

Method and apparatus for removing a downhole casing from a well on a single trip. A downhole tool assembly is arranged on a work string having a downhole pull tool, a spear tool, motor unit and cutting device. The downhole pull tool is set inside a first casing string and the spear tool, motor unit and cutting device are located inside a second casing string, located through the first casing string. The downhole pull tool and spear tool can be configured to grip the respective casings during cutting of the second casing string. The cut casing section can then be pulled using the downhole pull tool to dislodge the casing section, whereupon via attachment to the spear tool, the cut casing section can be removed from the well. The assembly can be re-set at shallower depths in the event that the cut casing section cannot be dislodged for removal.

Claims

1. A downhole tool assembly for removing a casing from a well by lowering the downhole tool assembly through a first casing wherein the casing to be removed is a second casing located through the first casing in the well, comprising: a downhole pull tool to be located on a work string having a throughbore, the downhole tool having: an anchor mechanism and a piston member axially moveable between an extended position and a retracted position; a spear tool, the spear tool being actuable to grip a cut casing section; and a cutting device; wherein the spear tool is located between the downhole pull tool and the cutting device; and the downhole pull tool includes a rotational mechanism to allow an inner body of the downhole pull tool to rotate relative to an outer body of the downhole pull tool when the anchor mechanism is set to provide through rotation capability so that the cutting device will rotate and cut the second casing by rotation of the work string at surface while the downhole pull tool is anchored to the first casing.

2. A method of removing a casing from a well on a single trip, comprising the steps of: a) providing a downhole tool assembly on a work string, the downhole tool assembly comprising: a downhole pull tool, the downhole pull tool having: an anchor mechanism located on an outer body; a piston member axially moveable between an extended position and a retracted position; and a rotational mechanism, to allow an inner body of the downhole pull tool to rotate relative to the outer body when the anchor mechanism is set; a spear tool; and a cutting device; b) lowering the downhole tool assembly into the well through a first casing wherein the casing to be removed is a second casing located through the first casing in the well; c) gripping the first casing with the anchor mechanism set to hold the outer body of the downhole pull tool stationary; d) after the anchor mechanism is set, rotating the work string at surface to rotate the inner body of the downhole pull tool and the cutting device to cut the second casing with the cutting device; e) gripping the second casing with the spear; f) pulling the cut second casing to dislodge the cut second casing by moving the piston member to the retracted position; and g) removing the cut second casing from the well, wherein: the anchor mechanism of the downhole pull tool grips the first casing while the cutting device is rotated to cut the second casing.

3. A method according to claim 2 wherein the spear tool is in an unset configuration while the cutting device is rotated to cut the casing.

4. A method according to claim 2 wherein in step (d) fluid is pumped into a through bore of the work string to deploy at least one knife in the cutting device.

5. A method according to claim 2 wherein the method includes the step of actuating the anchor mechanism on the downhole pull tool between a set and unset position.

6. A method according to claim 2 wherein the method includes the step of actuating the anchor mechanism to a set position to grip the first casing when the piston member moves from an extended position to a retracted position.

7. A method according to claim 6 wherein the method includes the step of actuating the anchor mechanism to an unset position to release the downhole pull tool from the first casing when the piston member moves from a retracted position to an extended position.

8. A method according to claim 7 wherein the method includes the steps of sequentially actuating the piston member between an extended position and a retracted position to pull the work string in an upward direction in the wellbore.

9. A method according to claim 2 wherein, between steps (e) and (f), the method includes the additional steps of, pulling on stuck cut second casing, moving the downhole tool assembly to a shallower depth, and repeating steps (c) to (e) to remove a shorter section of cut second casing.

10. A method according to claim 9, wherein the method includes repeating the additional step to cut the casing at subsequently shallower depths until the casing can be dislodged and removed from the well.

11. A method according to claim 2 wherein the method comprises monitoring fluid pressure circulating through the work string to determine when the cutting device, downhole pull tool and/or spear tool are actuated.

12. A method according to claim 2 wherein step (g) comprises extracting the work string and the attached cut second casing section from the wellbore by a rig applying an upward force on the work string when the cut second casing has been dislodged.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

(2) FIG. 1 is a sectional view of a typical well with two casing strings installed.

(3) FIG. 2 is a sectional view of the well of FIG. 1 with a downhole tool assembly in a run-in state according to an embodiment of the invention;

(4) FIG. 3 is a sectional view of the well of FIG. 1 with the downhole tool assembly of FIG. 2 in a casing cutting operational state.

(5) FIG. 4 is a sectional view of the well with the downhole tool assembly of FIG. 2 in a spear tool operational state.

(6) FIG. 5 is a sectional view of the well with the downhole system of FIG. 2 in a pulling state.

(7) FIG. 6 is a sectional view of the well of FIG. 1 with a casing string removed; and

(8) FIG. 7 is a sectional view of the well of FIG. 1 with a downhole tool assembly in a run-in state using a downhole pull tool with through-rotation capability.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(9) FIG. 1 shows a typical well 10 with two strings of casing installed. A first section 12 of wellbore 10 is drilled to a first selected depth, after which a first string of casing 14 is run into the well and typically may be a 13⅜ inch casing string. Cement is set over a portion of the outside of the first casing 14, sealing the annulus between the first casing 14 and the first section 12 of wellbore 10.

(10) A second section 16 of wellbore is then drilled to a target depth after the casing 14 is set. A second string of casing 18 is run into the well and typically could be a diameter of 9⅝ inch casing string. The second casing 18 is suspended inside the first casing 14 and cemented to seal the annulus between the second casing 18 and the second section 16 of wellbore 10.

(11) During a well abandonment operation, the second casing 18 or a section of second casing 18 is typically removed before the wellbore is plugged.

(12) FIGS. 2 to 5 are sectional views of a wellbore showing different stages of the casing removal method.

(13) FIG. 2 shows a downhole tool assembly 30 lowered into the annulus 32 of the casing 14. In this example the downhole tool assembly is a casing removal assembly.

(14) The downhole tool assembly comprises a work string 34 with a cutting device 36 at a lower end 34a of the work string. The work string also comprises a motor unit 38, a spear tool 40 and a downhole pull tool 42.

(15) The downhole pull tool 42 may be a Down Hole Power Tool (DHPT) commercially available from Wellbore AS, Norway.

(16) The cutting device 36 has cutting knives which are configured to radially extend from the cutting device 36 to engage the casing. The cutting device is hydraulically actuatable to deploy the knives in response to a fluid pressure in the work string above a preset threshold. Once the knives are deployed the cutting device is configured to be rotated to cut a section of the casing.

(17) The motor unit 38 is a positive displacement motor configured to convert hydraulic force of a pumped fluid through the work string into a mechanical force to rotate the cutting device 36. The motor unit 38 is run above the cutting device in the well.

(18) The spear tool 40 is run above the motor unit 38 and cutting device 36. The spear tool is hydraulically actuable and the spear is set to grip the casing at or above a preset fluid pressure. The spear tool 40 has slips which are configured to contact the inner diameter of a casing to grip the casing in response to fluid pressure above a preset threshold pressure.

(19) When the spear tool 40 is unset, the work string 34 may be picked up by applying an upward force at surface to position the spear tool 40 at a desired location inside a casing string. When the spear tool 40 is set, the work string 34 is picked up to latch the spear. By picking up the set spear the upward pulling force causes the spear tool slips to be wedged or locked between the body of the spear tool and the casing 18 of the wellbore. At this point the spear tool will maintain its grip on the casing 18 even if the fluid pressure in the work string 34 is reduced below the preset threshold pressure.

(20) The downhole pull tool 42 has an anchor mechanism and a piston member. The anchor mechanism has at least one slip which is moveable between a set position and an unset position. In the anchor set position at least one slip engages the inner diameter of the casing 14. In the unset condition the slips are moved away from casing 14 and the downhole pull tool 42 is moveable in the casing annulus 32.

(21) The piston member of the downhole pull tool 42 is connected to the lower work string and is axially movable between an extended position and a retracted position. In a retracted position the work string below the downhole pull tool is pulled upward in the wellbore.

(22) FIG. 3 shows the downhole tool assembly 30 in a casing cutting operation. The work string is lowered to a position where the cutting device 36 is adjacent to a section of casing 18 which is to be cut. Fluid is pumped down the work string 34 to actuate the cutting device to deploy the knives to an extended position to engage the casing.

(23) The fluid flow through the work string creates a differential pressure across the downhole pull tool 42 causing the anchor mechanism to set and grip the first casing string 14. By securing the position of the downhole tool assembly in the wellbore during a casing cutting operation damage to the knives of the cutting device is avoided or mitigated extending the working life of the knives.

(24) The fluid flow through the work string 34 hydraulically actuates the spear tool 40 to grip the casing 18. The fluid pressure actuates the motor unit 38 to rotate the cutting device to allow the cutting device to cut the casing 18 forming a gap 19 in the casing.

(25) The motor unit 38, spear tool 40 and downhole pull tool 42 are held stationary while the cutting device is rotated.

(26) By securing the downhole pull tool to the first casing 14 and the spear tool to the second casing 18 the downhole tool assembly 30 is held rigidly in position during the cutting operation. The position of the first casing 14 and second casing 18 are held relative to one another during the casing cutting operation ensuring a clean cut through the second casing 18 and mitigating damage to the cutting knives.

(27) By providing a downhole pull tool with a motor unit on the same work string the cutting operation and pulling operation may be performed in a single downhole trip.

(28) FIG. 4 shows that once the casing cut has been made the work string 34 is picked up to latch the spear tool 40. By picking up the set spear tool, the upward pulling force causes the slips to be wedged or locked between the body of the spear tool and the casing 18 of the wellbore. At this point the spear tool will maintain its grip on the casing even when the fluid pressure is reduced or stopped.

(29) FIG. 5 shows the downhole pull tool 42 is actuated to move and dislodge the cut casing section 18a. The fluid pressure in the work string is increased to set the anchor mechanism in the downhole pull tool 42 and move the piston member to a retracted or stroked position. The work string 34 below the downhole pull tool 42 and the cut casing section 18a is pulled upward towards the anchored downhole pull tool 42. The cut casing section 18a is pulled upward to dislodge the casing and move the cut casing section 18a away from the remaining section of casing 18b increasing the gap 19.

(30) The fluid pressure is reduced to move the anchor mechanism to an unset position and the piston member to an extended or unstroked position. The downhole pull tool 42 is moved to a higher axial position in the casing 14. The fluid pressure is subsequently increased to set the anchor mechanism and move the piston member to a retracted or stroked position which moves the work string 42 and cut casing section 18a further upwards.

(31) Successive movement of the piston member between a retracted and an extended position moves the work string and cut casing section 18a further upward in the wellbore until cut casing section 18a. At this point, the rig, to which the work string is connected, has sufficient lifting capacity to remove the work siring, downhole assembly and the cut casing section 18a from the wellbore. The downhole pull tool 42 is unanchored from the casing 14 and the spear tool 36 remains anchored to the cut casing section 18a for the lifting operation. FIG. 6 shows the wellbore with the cut casing section 18a and work string 34 removed from the wellbore by a rig.

(32) The downhole pull tool 42 applies a local upward pulling load on the work string 34 and the cut casing section. This mitigates or reduces wear or damage to the work string which may occur if a rig had to apply excessive loads from the surface to dislodge and remove the cut casing section. Once the cut casing section has been dislodged the rig may have sufficient capacity to pull the work string and the casing to surface.

(33) By locating the work string and the downhole tool assembly at the lowest axial position in the wellbore and cutting the casing, the maximum length of cut casing may be removed in a single downhole trip. This avoids multiple trips downhole to remove individual small sections of the casing.

(34) In the event that the cut casing section 18 is immovable due to cement or a blockage between the casing and the wellbore, the work string may be relocated to a higher position in the wellbore and the cutting operation and pulling operation repeated as described above in relation to FIGS. 2 to 6 above. If in this second wellbore axial position the downhole pull tool is unsuccessful in dislodging or lifting the cut casing section, the method of cutting and pulling may be repeated in further axial positions until a cut casing section may be removed.

(35) By systematically checking whether a cut casing section may be removed the maximum length of casing that may be removed is identified and removed.

(36) Although the above description refers to removing casing diameters of 9⅝ inches and 13⅜ inches, the method and apparatus may be used with other casing diameters.

(37) Referring to FIG. 7 there is disclosed an alternative downhole tool assembly 30a for removing a casing from a well comprising: a downhole pull tool; a spear tool; and a cutting device; wherein the downhole pull tool is configured to provide through rotation capability so that the cutting device can be rotated from surface. Accordingly this would provide a method of removing a casing from a well comprising providing: a downhole tool assembly 30a, the downhole tool assembly comprising: a downhole pull tool 42a with through rotation capability, a spear tool 40a and a cutting device 36a; lowering the downhole tool assembly into the well; cutting a casing; gripping the casing; and pulling the cut casing to dislodge the cut casing.

(38) The spear tool 40a and cutting device 36a are as described with reference to FIGS. 2 to 6. The downhole pull tool 42a may be as described herein before with reference to FIGS. 2 to 6 with the addition of a rotational mechanism 50. Such a rotational mechanism will allow an outer body 52 of the downhole pull tool, anchored to the casing, to be held stationary while an inner body 54, typically a mandrel connected in the work string, can rotate. In this way the work string can rotate through the downhole pull tool. The motor unit is therefore not required as the casing cutter 36a can be operated to rotate and cut the casing by rotation of the work string 34 at surface. The downhole pull tool 42a may contain a bearing 56 in the rotation mechanism 50 to provide the through rotation capability.

(39) It will be realised that during cutting only the anchor on the downhole pull tool 42a will be set and the spear tool 40a now needs to be unset. The assembly 30a will be run in the well until the spear casing cutter 36a is in the lower casing string 18. The downhole pull tool 42a will be set in the upper casing string 14. By rotation of the work string 34 through the downhole pull tool 42a, the casing cutter 36a will cut the casing 18 separating it into an upper 18a and lower 18b portion. Once cutting is complete, the spear tool 40a is actuated to grip the cut casing section 18a. The assembly may be repositioned in the wellbore to achieve this as it is preferred that the spear tool 40a is positioned at the upper end of the cut casing section 18b. With the spear tool 40a engaged, the work string 34 can be attempted to be lifted from surface. If the cut casing section 18a will not move and is stuck, the downhole pull tool 42a is actuated to anchor the tool 42a to the wall of the upper casing 14. The downhole pull tool 42a is further actuated to raise the work string 34 under a high load to jack the cut casing section 18a upwards. Pressure through the downhole pull tool 42a at surface will indicated if the cut casing section has not, partly or entirely dislodged. If entirely free the cut casing section 18a and downhole assembly can be raised to surface if the rig to which it is attached has sufficient pulling capacity. Alternatively, the downhole pull tool 42a is unset and the outer body raised to a higher position in the wellbore and the anchor set again. The downhole pull tool 42a is further actuated to raise the work string 34 under a high load to jack the cut casing section 18a upwards with the downhole assembly 30a. these steps can be repeated until the cut casing section 18a is dislodged and free, and the rig has sufficient pulling capacity to raise the work string to surface with the downhole assembly 30a and the cut casing section 18a. As for the embodiment shown in FIGS. 2 to 6, this provides a single trip can and pull system in which stuck casing can be dislodged so that longer lengths of casing can be recovered as compared to casing and pull systems which just comprise the spear tool and the casing cutter.

(40) The downhole tool assembly is described in use in a well borehole lined with a well casing. It will be appreciated that this is only one example use. The tool may be used in other applications in gripping, cutting and removing tubular structures. It will also be appreciated that the downhole tool assembly may be used in other applications in gripping and removing downhole fish.

(41) Throughout the specification, unless the context demands otherwise, the terms ‘comprise’ or ‘include’, or variations such as ‘comprises’ or ‘comprising’, ‘includes’ or ‘including’ will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. Furthermore, relative terms such as”, “lower”, “upper, upward, downward, “up” “down” and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations.

(42) The invention provides a method of removing a casing from a well. The method comprises providing a downhole tool assembly. The downhole tool assembly comprises a downhole pull tool, a spear tool, a cutting device, and a motor unit. The method comprises lowering the downhole tool assembly into the well and cutting a casing. The method also comprises gripping the casing and pull the cut casing section to dislodge the cut casing.

(43) The present invention obviates or at least mitigates disadvantages of prior art methods of removing casing from a well and reliable, quick and cost efficient method of removing a casing from a wellbore. The invention enables the maximum length of casing to be cut and removed in a single trip.

(44) The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the Invention herein intended