CA2875568C

CA2875568C - Hydraulic ram for shearing shear couplings

Info

Publication number: CA2875568C
Application number: CA2875568A
Authority: CA
Inventors: James B. Tom
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-12-19
Filing date: 2014-12-19
Publication date: 2020-05-05
Anticipated expiration: 2034-12-19
Also published as: CA2875568A1

Abstract

There is provided a hydraulic ram for shearing a downhole shear coupling, having a piston chamber with an upper fluid port, a lower fluid port, and a mounting structure carried by the piston chamber for mounting the piston chamber in a fixed position relative to a downhole well, a piston positioned within the piston chamber between the upper fluid port and the lower fluid port, the piston chamber being filled with hydraulic liquid above and below the piston, a connector for connecting to an elongate downhole string of the downhole well, and a pump connected to pump fluid into the lower fluid port, the pump applying sufficient fluid pressure to the piston to move the piston from a lower position to a raised position and cause the connector to apply a shearing force to the elongate downhole string.

Description

HYDRAULIC RAM FOR SHEARING SHEAR COUPLINGS
TECHNICAL FIELD
[0001] This relates to a method and apparatus for shearing a shear coupling using a hydraulic ram.
BACKGROUND

[0002] Shear couplings are used in downhole tools to disconnect a tubing or rod string from a downhole tool, such as a downhole pump, that cannot be easily retrieved. One example of a shear coupling is shown in US pre-grant publication no.
2004/0202521 (Bostik) entitled "Shear coupling", although other types of shear couplings are known.
Most shear couplings are designed to shear and release when a sufficient upward force is applied to the tubing or rod string at surface.
SUMMARY

[0003] According to an aspect, there is provided a hydraulic ram for shearing a downhole shear coupling, comprising a piston chamber comprising an upper fluid port, a lower fluid port, and a mounting structure carried by the piston chamber for mounting the piston chamber in a fixed position relative to a downhole well, a piston positioned within the piston chamber between the upper fluid port and the lower fluid port, the piston chamber being filled with hydraulic liquid above and below the piston, a connector for connecting to an elongate downhole string of the downhole well, and a pump connected to pump fluid into the lower fluid port, the pump applying sufficient fluid pressure to the piston to move the piston from a lower position to a raised position and cause the connector to apply a shearing force to the elongate downhole string.

[0004] According to another aspect, the connector may further comprise an elongate passage that extends through the piston and the piston chamber, the connector engaging the downhole string above the piston chamber.

[0005] According to another aspect, the connector rod may be attached to the piston by a threaded connection.

[0006] According to another aspect, the hydraulic ram may further comprise a seal carried by the piston chamber that seals around the connector rod.

[0007] According to another aspect, the connector of the connector rod may be a rod string connector.

[0008] According to another aspect, the upper fluid port may be connected to the pump in a closed loop.

[0009] According to another aspect, the fluid in the piston chamber above the piston may act as a cushion against a reactive force applied to the piston by the elongate downhole string after a shearing event.

[0010] According to another aspect, the mounting structure may comprise a wellhead connector adjacent to the lower fluid port for connecting to a wellhead of the downhole well.

[0011] According to an aspect, there is provided a method of shearing a downhole shear coupling in an elongate downhole string positioned in a downhole well having a wellhead, the method comprising the steps of exposing an upper portion of the elongate downhole string, attaching a connector to the elongate downhole string, the connector being carried by a piston in a piston chamber, the piston chamber having an upper fluid port, a lower fluid port, and a mounting structure carried by the piston chamber, using the mounting structure, mounting the piston chamber in a fixed position relative to the downhole well, pumping hydraulic fluid through the lower fluid port into the piston chamber to cause the shear actuator to apply a shearing force to the elongate downhole string, the shearing force being sufficient to cause the downhole shear coupling to shear, and permitting the hydraulic fluid in the piston chamber above the piston to act as a cushion to a reactive force from the elongate downhole string after the shear coupling shears.

[0012] According to another aspect, the connector may comprise an elongate passage that extends through the piston and the piston chamber, and attaching the connector to the downhole string may comprise inserting the downhole string through the elongate passage and engaging the downhole string above the piston chamber.

[0013] According to another aspect, the connector rod may be attached to the piston by a threaded connection.

[0014] According to another aspect, the connector rod may be sealed by a seal carried by the piston chamber.

[0015] According to another aspect, the connector of the connector rod may be a rod string connector.

[0016] According to another aspect, the upper fluid port may be connected to a pump that pumps hydraulic fluid through the lower fluid port.

[0017] According to another aspect, the fluid in the piston chamber above the piston may act as a cushion against a reactive force applied to the piston by the elongate downhole string after a shearing event.

[0018] According to another aspect, the mounting structure may comprise a wellhead connector adjacent to the lower fluid port that connects to a wellhead of the downhole well.
BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein:
FIG. 1 is a schematic view of a hydraulic ram connected to an elongate downhole string.
FIG. 2 is a side elevation view in section of the hydraulic ram of FIG. 1 DETAILED DESCRIPTION

[0020] Referring to FIG. 1, there is shown a hydraulic ram 10 that is designed to shear a shear coupling 12 that connects an elongate downhole string 14 to a downhole tool 16. When it is necessary to separate shear coupling 12 from downhole tool 16, some or all of the wellhead equipment (not shown) that would normally be mounted to wellhead 18 is removed, an upper portion of the elongate downhole string 14 is exposed, and hydraulic ram 10 is attached to wellhead 18 and to elongate downhole string 14, as will be described below.

[0021] Referring to FIG. 2, hydraulic ram 10 is shown in greater detail.
As depicted, hydraulic ram 10 is designed to connect to a sucker rod string, although it will be understood that hydraulic ram may be designed to suit other types of elongate downhole strings.
Hydraulic ram 10 has a piston chamber 20 that has an upper fluid port 22 and a lower fluid port 24 through which fluid is pumped using a hydraulic pump 26 (shown in FIG.
1). A
piston 28 is positioned within piston chamber 20 between upper fluid port 22 and lower fluid port 24. Piston chamber 20 is filled with hydraulic liquid above and below piston 28 such that the position of piston 28 may be controlled by hydraulic pump 26 as it pumps fluid through the desired port 22 and 24. Preferably, hydraulic pump 26 is connected to a closed loop that uses valves to control the flow of hydraulic fluid as is known in the art. It will be understood that other arrangements may also be made, such as only connecting pump 26 to lower fluid port 24, or not providing a closed loop. Those of ordinary skill will be able to provide a suitable arrangement and control of the flow of hydraulic fluid based on the preferences of the user in order to accomplish the purposes discussed below.

[0022] As shown, piston 28 carries a shaft, preferably a shaft with an upper portion 30 and a lower portion 32, that extends above and below piston 28 and out of piston chamber 20.
The upper and lower portions of the shaft 30 and 32 are sized to receive the downhole string 14. Piston 28 has a connection that connects to the elongate downhole string 14. As shown, this connection includes an elongate passage 33 defined by upper and lower portions 30 and 32 of the shaft such that passage 33 extends through piston 28 and piston chamber 20. Upper portion 30 has an engagement 34 that is designed to secure the sucker rod to piston 28 above the piston chamber 20 via upper portion 30 of shaft. . As shown, engagement 34 is formed by slips, however, it will be understood that the downhole string 14 may be engaged using slips, a clamp, or other known devices that engage a downhole string. While other designs may be used, providing engagement 34 above piston chamber 20 allows hydraulic ram 10 to be installed while still allowing workers to connect downhole string 14 to the movable portion of 5 hydraulic ram 10. Upper portion 30 may also be used to provide a connection point on the top of hydraulic ram 10 and a visual indicator of the operation of hydraulic ram 10. In the depicted embodiment, both upper and lower portions 30 and 32 are threaded into piston 28 in order to provide a strong connection and withstand the forces that may be encountered.

[0023] As can be seen, seals 35 are provided where shear actuator 32 exits the bottom of piston chamber 20, around piston 28, and where upper portion 30 exits the top of piston chamber 20. Seals 35 will be designed or selected as is known in the art to withstand the anticipated hydraulic pressures that will be applied within piston chamber 20, according to their position and purpose. By sealing against upper and lower portions 30 and 32, piston chamber 20 is able to have a more reliable, robust seal when compared to having to seal around downhole string 14 each time hydraulic ram 10 is installed.

[0024] A mounting structure 36 is carried by the piston chamber 20 for mounting the piston chamber 20 in a fixed position relative to wellhead 18. Mounting structure 36 may be positioned adjacent to lower fluid port 24 for connecting to the wellhead 18.

[0025] Referring again to FIG. 1, during use, pump 26 is connected to pump fluid into lower fluid port 24 of piston chamber 20, and preferably to also receive fluid from upper fluid port 22. Pump 26 applies sufficient fluid pressure to piston 28, which in turn applies a lifting force to connector rod 32 and thus to apply a sufficient force to move the piston 28 from a lower position to a raised position and cause shear coupling 12 to shear, releasing string 14 from downhole tool 16. In some examples, hydraulic ram 10 may be capable of providing at least 30,000 pounds of lift to rod string 14. Preferably, hydraulic ram 10 is capable of providing at least 40,000 pounds of lift, or more preferably, 60,000 pounds of upward force in order to separate shear coupling 12. Alternatively, hydraulic ram 10 may be designed to apply a force that meets or exceeds the rating of the connections in rod string 12 (or other type of downhole string, as the case may be). It will be understood that the pressure rating of pump 26 will be determined based on the dimensions of piston chamber 20 and piston 28 in order to apply sufficient pressure to piston 28 to provide the necessary lifting force to connector rod 32.

[0026] The height of piston chamber 20 is sufficient to provide the necessary travel in order to separate shear coupling 12. As there will be some elastic force built up in rod string 14 that will be released after a shearing event, some additional height may be required in piston chamber 20 in order to provide for some movement as the fluid above piston 28 acts as a type of cushion against this reactive force. In one embodiment, with a piston height of about 4 inches, a height of around 30 inches was found to be sufficient, although the height may be as low as 24 inches or 27 inches, and may be increased to 33 or 36 inches, with a similar size of piston.

[0027] It will be understood that, after the shearing event, the upward movement will be minimized as hydraulic fluid is incompressible. Instead, the reactive force will be transferred through wellhead connector 36 to wellhead 18 and ultimately casing (not shown). As a result, the amount of backlash will be reduced, particularly when compared with a crane or other equipment that may apply the lifting force to separate shear coupling 12.

[0028] In this patent document, the word "comprising" is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements.

[0029] The scope of the following claims should not be limited by the preferred embodiments set forth in the examples above and in the drawings, but should be given the broadest interpretation consistent with the description as a whole.

Claims

What is claimed is:

1. A hydraulic ram for shearing a downhole shear coupling, comprising:
a piston chamber comprising an upper fluid port, a lower fluid port, and a mounting structure carried by the piston chamber for mounting the piston chamber in a fixed position relative to a downhole well;
a piston positioned within the piston chamber between the upper fluid port and the lower fluid port, the piston chamber being filled with hydraulic liquid above and below the piston;
a connector for connecting to an elongate downhole string of the downhole well; and a pump connected to pump fluid into the lower fluid port, the pump applying sufficient fluid pressure to the piston to move the piston from a lower position to a raised position and cause the connector to apply a shearing force to the elongate downhole string.

2. The hydraulic ram of claim 1, wherein the connector comprises an elongate passage that extends through the piston and the piston chamber, the connector engaging the downhole string above the piston chamber.

3. The hydraulic ram of claim 1, wherein the connector rod is attached to the piston by a threaded connection.

4. The hydraulic ram of claim 1, further comprising a seal carried by the piston chamber that seals around the connector rod.

5. The hydraulic ram of claim 1, wherein the connector of the connector rod is a rod string connector.

6. The hydraulic ram of claim 1, wherein the upper fluid port is connected to the pump in a closed loop.

7. The hydraulic ram of claim 1, wherein the fluid in the piston chamber above the piston acts as a cushion against a reactive force applied to the piston by the elongate downhole string after a shearing event.

8. The hydraulic ram of claim 1, wherein the mounting structure comprises a wellhead connector adjacent to the lower fluid port for connecting to a wellhead of the downhole well.

9. A method of shearing a downhole shear coupling in an elongate downhole string positioned in a downhole well having a wellhead, the method comprising the steps of:
exposing an upper portion of the elongate downhole string;
attaching a connector to the elongate downhole string, the connector being carried by a piston in a piston chamber, the piston chamber having an upper fluid port, a lower fluid port, and a mounting structure carried by the piston chamber;
using the mounting structure, mounting the piston chamber in a fixed position relative to the downhole well;
pumping hydraulic fluid through the lower fluid port into the piston chamber to cause the shear actuator to apply a shearing force to the elongate downhole string, the shearing force being sufficient to cause the downhole shear coupling to shear; and permitting the hydraulic fluid in the piston chamber above the piston to act as a cushion to a reactive force from the elongate downhole string after the shear coupling shears.

10. The method of claim 9, wherein the connector comprises an elongate passage that extends through the piston and the piston chamber, and wherein attaching the connector to the downhole string comprises inserting the downhole string through the elongate passage and engaging the downhole string above the piston chamber.

11. The method of claim 9, wherein the connector rod is attached to the piston by a threaded connection.

12. The method of claim 9, wherein the connector rod is sealed by a seal carried by the piston chamber.

13. The method of claim 9, wherein the connector of the connector rod is a rod string connector.

14. The method of claim 9, wherein the upper fluid port is connected to a pump that pumps hydraulic fluid through the lower fluid port.

15. The method of claim 9, wherein the fluid in the piston chamber above the piston acts as a cushion against a reactive force applied to the piston by the elongate downhole string after a shearing event.

16. The method of claim 9, wherein the mounting structure comprises a wellhead connector adjacent to the lower fluid port that connects to a wellhead of the downhole well.