GB2410042A

GB2410042A - A shielded hydraulic actuator for a drilling tool

Info

Publication number: GB2410042A
Application number: GB0400823A
Authority: GB
Inventors: Christian Menger
Original assignee: Schlumberger Holdings Ltd
Current assignee: Schlumberger Holdings Ltd
Priority date: 2004-01-15
Filing date: 2004-01-15
Publication date: 2005-07-20
Anticipated expiration: 2024-01-15
Also published as: GB0400823D0; GB2410042B

Abstract

A shielded actuator for a drilling tool, with a piston (14) moved by the pressure difference between a high- (20) and a low pressure side (18). The piston with its seal (16) is shielded from operating in abrasive conditions by a first membrane (66) on the high side and a second membrane (56) on the low side. The membranes connect the piston with the actuator body (10), creating cavities which are filled with clean lubricating fluid. The cavities communicate with high- (54) and low pressure balance reservoir (52) through ports (28,26) respectively. The reservoirs having compensators (44,42). The pressure compensator chambers high/low (24,22) communicates through bores (38,36) with the high/low pressure respectively. The figure shows the actuator body (10) integral to a main body of a drilling tool, having a through bore (83) for a downward flow (high pres.) of a drilling fluid and a space (90) for an upward flow. The actuator is in the context of a kick pad tool, with a pad (102) displaceable by the actuator piston.

Description

24 1 0042

COMPENSATED SHIELDED ACTUATOR APPARATUS AND METHOD

BACKGROUND OF INVENTION

1] This invention generally relates to actuator assemblies for downhole drilling tools.

More particularly, the invention relates to shielding elements for pistonactuated steerable downhole drilling tools to minimize ingress of abrasive materials into contact with the piston actuator assemblies and associated components. More particularly still, the invention relates to increasing the service life of downhole actuator assemblies.

[00021 In drilling systems, various downhole apparatuses are used to bias or align downhole tools (for example, drill bit assemblies) relative to the center of the wellbore. Biasing a drill bit deviates the borehole and thereby helps steer the well in a desired direction. An actuator can be used to selectively retain a bearing surface such as a pressure pad against a borehole wall, tool wall, or an interior wall of a well casing. Force transferred from the pad through the actuator deflects a bottom end of the drill string to effect the steering bias.

3] One form of apparatus frequently used in directional drilling provides a plurality of piston-driven hydraulic actuators spaced apart around the periphery of the apparatus, each actuator having moveable thrust members that displace outwardly to engage the borehole or casing wall. Such apparatus typically uses a drilling fluid as hydraulic drive fluid for the actuators. Typical drilling fluids are slurry mixtures containing high percentages of very fine, suspended solids. These solids, while necessary to impart preferred drilling fluid properties, can be extremely abrasive and can be extremely erosive at high pressures and flow rates and can erode sensitive sealing surfaces that require high dimensional tolerances to properly function.

4] Dynamic, reciprocating piston seals in downhole actuators are customized to provide a large footprint for effective sealing at high pressure differentials, and typically have a scraper lip for selfcleaning on the low-pressure side. In spite of these design measures, however, components of typical drilling fluids can cause high rates of abrasion damage and plugging the piston seals of steering actuator components. This damage can often result in significantly reduced service life cycles and costly maintenance delays in drilling operations.

5] Forms of pressure seals that may resist invasive and damaging components of drilling fluids, for example rolling diaphragms, are not viable at high pressure differentials.

Diaphragm thicknesses required at high differentials will lead to high diaphragm failure rates due to fatigue caused by large piston travel. Similarly, downhole constraints of geometry typically preclude the effective use of bellows seals in steering systems' piston actuators.

SUMMARY OF THE INVENTION

100061 An embodiment of the present invention provides a shielded and compensated hydraulic actuator to be used on a drilling tool in a borehole in the presence of drilling fluids.

The actuator comprises a piston slideably engaged within a piston bore, the piston characterized by a high-pressure side and a low-pressure side. A first membrane creates a first clean reservoir between the piston and the piston bore on the high pressure side. The first clean reservoir is in communication with a first pressure compensator. A second membrane creates a second clean reservoir between the piston and the piston bore on the low pressure side. The second clean reservoir is in communication with a second pressure compensator. The first and second pressure compensators are configured to isolate the first and the second clean reservoirs from contamination with the drilling fluids. The first pressure compensator is in fluid communication with drilling fluids on the high-pressure side ofthe piston. The second pressure compensator is in fluid communication with the drilling fluids on the low-pressure side of the piston.

7] Another embodiment of the present invention provides a directional drilling tool to be run in a borehole in the presence of drilling fluids. The drilling tool comprises a central through-bore through which the drilling fluids are delivered. An annulus exists between the directional drilling tool and the borehole through which the drilling fluids are returned. A piston is slidably engaged within a piston bore. The piston is characterized by a high pressure side and a low pressure side. A first membrane creates a first clean reservoir between the piston and the piston bore on the high pressure side. A first clean reservoir is in communication with a first pressure compensator. A second membrane creates a second clean reservoir between the piston and the bore on the low pressure side. The second clean reservoir is in communication with the second pressure compensator. The first and the second pressure compensators are configured to isolate the first and the second clean reservoirs from contamination with the drilling fluids. The first pressure compensator is in fluid communication with drilling fluids on the high-pressure side of the piston. The second pressure compensator is in fluid communication with drilling fluids on the low-pressure side of the piston. The low-pressure side of the piston is connected to a pressure pad, the pressure pad configured to bias the directional drilling tool in a desired position relative to the borehole when the pressure pad is engaged with the borehole.

8] Another embodiment of the present invention provides a method to actuate a pressure pad of a drilling apparatus with drilling fluids in a subterranean borehole. The method comprises; (a) slideably engaging a piston within a piston bore of the drilling apparatus, the piston configured to slide between a high pressure zone and a low pressure zone; (b) installing a first membrane between the piston and the piston bore in the high pressure zone to create a first clean reservoir wherein the first clean reservoir is in communication with a first hydraulic compensator; (c) installing a second membrane between the piston and the piston bore in the low pressure zone to create a second clean reservoir wherein the second clean reservoir is in communication with a second hydraulic compensator; (d) communicating the first hydraulic compensator with the high pressure zone such that the first clean reservoir is isolated from any drilling fluids in the high pressure zone; (e) communicating the second hydraulic compensator with the low pressure zone, such that the first clean reservoir is isolated from any drilling fluids in the low pressure zone; (f) mounting the pressure pad upon the drilling apparatus, the pressure pad configured to be engaged by the piston when actuated in the direction of the low pressure zone; and (g) increasing the pressure of the high pressure zone to engage the pressure pad to bias the drilling apparatus in a desired position.

9] Another embodiment of the present invention provides an apparatus to be used in a directional drilling system. The apparatus comprises one or more actuators having a dynamic seal slideably carried in a lateral bore of a tool and moveably responsive to changes in the pressure of a drilling fluid. A high-pressure clean reservoir is provided for the retention of a lubricating fluid formed by a first membrane contiguous between an interior edge of the lateral bore and an interior surface of the actuator in fluid communication with a high-pressure compensator responsive to changes in a high-pressure drilling fluid on an interior longitudinal passage of the tool. A low-pressure clean reservoir is provided for the retention of a lubricating fluid formed by a second membrane contiguous between an exterior edge of the lateral bore and an exterior surface of the actuator in fluid communication with a lowpressure compensator responsive to changes in the low-pressure drilling fluid on the exterior of the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

0] Fig. 1 is a plan view schematic of a compensated actuator in accordance with the present invention.

1] Fig. 2 is an elevation view schematic of the compensated, actuator of Fig. 1.

2] Fig. 3 is a cross-sectional schematic view of a double-shielded actuator piston in accordance with the present invention.

[00131 Fig. 4 is a cross-sectional perspective view drawing of a compensated, double- shielded actuator piston in accordance with a preferred embodiment of the present invention.

4] Fig. 5 is a cross-sectional perspective view drawing of the compensated, double shielded actuator of Fig. 4 in the context of a kick pad tool.

DESCRIPTION OF A PREFERRED EMBODIMENT

5] Referring initially to Figs. 1-2, plan and elevation view schematics of a compensated actuator body 10 are shown respectively. An actuator piston 14 is configured to reciprocate within a seal bore 12 of actuator body 10 between a high- pressure zone 20 and a low- pressure zone 18. At least one dynamic seal 16 is preferably located upon piston 14 and is used to isolate the high and low-pressure zones 20, 18 from one another. While seal 16 is shown schematically as a single o-ring, it should be understood by one of ordinary skill in the art that seal 16 may comprise any number of seal devices, including, but not limited to, orings, backup rings, spacers, and wipers. The particular configuration of seal 16 is not important, so long as seal 16 is designed to handle the reciprocal movement of piston 14 within bore 12 at the temperatures and pressures experienced by actuator 10.

[00161 Actuator body 10 has an interior, low-pressure compensator chamber 22 and an interior, high-pressure compensator chamber 24 adjacent the at least one lateral opening 12.

Low-pressure compensator chamber 22 communicates with lateral opening 12 in low-pressure zone 18 via a low-pressure balance port 26. Similarly, high-pressure compensator chamber 24 communicates to lateral opening 12 in high-pressure zone 20 via a high-pressure balance port 28.

Compensator chambers 22, 24 are each closed by respective low-pressure and high-pressure s compensator end caps 32, 34. Low-pressure compensator end cap 32 has a low-pressure equalization bore 36 to equalize low-pressure compensator chamber pressure with the low- pressure zone 18. High-pressure compensator chamber 24 is fed by a first high-pressure equalization bore 38 in communication with a high-pressure source (not shown).

IoOI7] The disclosed embodiment provides both a low-pressure and a highpressure compensator chamber 22, 24, respectively, which retain lowpressure and high-pressure compensators 42, 44. In Figs. 1-2, the low/high-pressure compensators 42, 44 are shown as pistons with dual sliding mechanical seals 45, 46 respectively. Compensators 42, 44 respectively shield a low-pressure balance reservoir 52 and a highpressure balance reservoir 54 in communication with the respective pressure balance ports 26, 28. Balance reservoirs 52, 54 confine a clean lubricating fluid, and sealed compensators 42, 44 eliminate or minimize intrusion by hydraulic drive fluids or solids into the reservoirs 52, 54. High-pressure compensator 44 can be stopped or pinned (not shown) to prevent blocking or movement over or past the equalization bore 38, thereby preventing contamination of the clean side of the compensator chamber 24 with drilling fluid.

[00181 Compensators 42, 44 are shown as piston-type assemblies, but can be of any form known to one skilled in the art. For example, compensators 42, 44 may optionally be constructed as expansion bladders connected to the respective balance ports 26, 28. The bladder materials can be impermeable, permeable, or semi-permeable, selected for properties that preferentially minimize drilling fluid and particulate intrusion into the reservoirs 52, 54 while maximizing flexibility and tear resistance.

9] Referring now to Fig. 3, a double-shielded actuator piston is shown providing flexible shield membranes 56,66 connected to actuator piston 14. In low-pressure zone 18, an exterior shield membrane 56 connects a low-pressure face of the actuator piston 14 to the actuator body 10. The exterior shield connections form a first exterior seal along an outer seal ring 58 of actuator piston 14, and a second exterior seal along an outer seal lip 59 of lateral opening 12. In high-pressure zone 20, an interior shield membrane 66 connects a high-pressure face of the actuator piston 14 to the actuator body 10. The interior shield connections form a first interior seal along an inner seal ring 68 of actuator piston 14, and a second interior seal along an inner seal lip 69 of lateral opening 12. Shield membranes 56, 66 are illustrated in a form similar to a rolling diaphragm. Furthermore, while diaphragm membranes are shown, it should be understood by one of ordinary skill in the art that other structures, including, but not limited to, bellows may be used without departing from the spirit ofthe invention.

0] Shield membranes 56, 66 define low-pressure and high-pressure clean cavities 72, 74 in the respective low- and high-pressure zones 18, 20. Clean cavities 72, 74 are additionally bounded by a wall 76 of the lateral opening 12. Low-pressure clean cavity 72 is lastly bounded by an exterior peripheral surface 78 of the actuator piston 14, while the high-pressure clean cavity is lastly bounded by an interior peripheral surface 80 of the actuator piston 14. Actuator seal 16 minimizes fluid communication between the low-pressure and high-pressure clean cavities 72, 74. Clean cavities 72, 74 are filled with clean lubricating fluid via hydraulic communication with the respective low/high-pressure balance reservoirs 52, 54 through the low/high-pressure balance ports 26, 28. Thus, dynamic pressure seal 16 of actuator piston 14 resides in a clean fluid environment maintained by double shielding provided by the compensators 42, 44 and the flexible shield membranes 56, 66.

1] Referring now to Fig. 4, a cross sectional perspective view drawing of a compensated, double-shielded actuator is shown integral to a main body 82 of a drilling tool.

Drilling tool 82 can be a drilling bit body, a rotary steerable system, or any other drilling tool in which a robust actuator assembly 10 may be useful. Main body 82 is shown having a through bore 83 with a centerline 84 for a downward flow 86 of drilling fluid therethrough at a relatively higher pressure. Main body 82, when suspended in a well casing or borehole 88, is surrounded by an annular space 90 for an upward flow 92 of drilling fluid, possibly mixed with produced fluids, at a relatively lower pressure. For downhole steering of main body 82, a plurality of actuator bodies 10 with associated elements as described above, can be advantageously disposed around a periphery of main body 82. Additionally, peripheral actuator bodies, similar to actuator 10, can be situated along the main body 82, aligned parallel to the centerline 84.

10022] Each actuator piston 14 is adjacent a piston well 94, and a fluid feed bore 96 connects the piston well 94 with a supply (not shown) of high-pressure drive fluid to energize actuator piston 14. Feed bore 96 connects to the first high-pressure compensator equalization bore 38 by an extension that is a second high-pressure compensator equalization bore 98 in main body 82. Typically the drive fluid is provided from the flow 86 of drilling fluid inside tool body 82, using systems of control valves (not shown) well known in the art to sequentially energize and de-energize peripheral actuator pistons 14 so that main body 82 is more or less fixedly biased relative to a spatial orientation as it rotates axially in the rotary drilling operation.

3] The structure shown in Fig. 4 can also be fabricated as a first sub-assembly comprising actuator body 10 and its internal components described above, and a second sub- assembly comprising main body 82, including piston well 94 plus feed bore 96 and second high- pressure equalization bore 98. A logical physical junction between the two sub-assemblies can be made advantageously along dashed lines in Fig. 4 tracing a path 4A/4B/4C.

10024] Referring finally to Fig. 5, a cross-sectional drawing of a compensated, double shielded actuator is shown in the context of a kick pad tool. The figure depicts the invention implemented in a biasing actuator tool assembly, including a flexible connection 100 attached to actuator body 10 and a displaceable pressure pad (or kickoff pad) 102 attached to the flexible connection 100. Fig. 5 exemplifies a configuration of main body 82 for use in a downhole tool for directional drilling. Flexible connection 100 is shown as hinged for attaching the pressure pad 102 to actuator body 10. The flexible connection 100 can optionally include a spring or other biasing element to effectuate the retraction (if desired) of pressure pad 102. As shown in Fig. 5, actuator piston 14 addresses pressure pad 102 on a posterior surface moving the anterior face of pad 102 into engagement with the bore (not shown).

5] As described above, dynamic pressure seal 16 of actuator piston 14 resides in a clean, lubricating fluid environment maintained by double shielding provided by sliding compensators 42, 44 and flexible shield membranes 56, 66. Actuator seal 16 constrains substantially the entire pressure difference between the low-pressure and high-pressure zones 18, 20, while shield membranes 56, 66 experience only minimal, transient pressure differentials.

This is possible because the low- and high-pressure compensators 42, 44 are externally pressurized by the low-pressure and high-pressure zones 18, 20 via the respective equalization bores 36 and 38/98. Compensators 42, 44 transmit the respective low and high pressures to the corresponding pressure balance reservoirs 52, 54 which, in turn, communicate the low and high pressures to the clean cavities 72, 74 via the balance ports 26, 28. This pressure balance maintains the clean cavities 72, 74 at pressures equalized with respective pressures in the low- pressure and high-pressure zones 18, 20. Also, the compensators absorb differential thermal expansion of the lubricant in the balance reservoirs 52, 54 and clean cavities 72, 74, and the compensators adjust to minor leakage of lubricant across the actuator seal 16.

6] Accordingly, membranes 56, 66 can be designed using light gauge materials to reducing operating bending stresses as membranes 56, 66 flex (or roll) with movement of the actuator piston 14. Furthermore, the if membranes 56, 66 are constructed as bellows, clean reservoirs 72, 74 can be maintained at substantially constant volumes regardless of position of piston 14.

[00271 Finally, having durable shielding in place to protect mechanical actuator seal 16 in clean lubricant, actuator seal 16 and actuator piston 14 are spared from operating in highly abrasive conditions that are common in existing technology. In an exemplary application, systems of control valves in downhole apparatus well known in the art (not shown) sequentially energize and de-energize actuator pistons 14 with each rotation of a drill string. Hydraulic actuators with pressure pads 102, as in Fig. 5, can bias a tool having main body 82 relative to a spatial orientation by successively extending and retracting as tool body 82 rotates axially in the rotary drilling operation. In a one-day period of operation, a single hydraulic actuator can hypothetically experience on the order of 105 cycles of actuation. Absent the abrasive influence of drilling fluid 86 directly contacting actuator seal 16, as made possible with this invention, actuator integrity can be substantially prolonged at such high frequencies of use.

8] The invention is described above with reference to non-limiting examples provided for illustrative purposes only. Various modifications and changes will become apparent to the skilled artisan in view thereof. It is intended that all such changes, modifications, and respective applications are within the scope and spirit of the appended claims and shall be embraced thereby.

Claims

What is claimed: I. A shielded and compensated hydraulic actuator to be used on a drilling tool in a borehole in the presence of drilling fluids, the actuator comprising: a piston slideably engaged within a piston bore, said piston characterized by a high pressure side and a low-pressure side; a first membrane to create a first clean reservoir between said piston and said piston bore on said high pressure side, said first clean reservoir in communication with a first pressure compensator; a second membrane to create a second clean reservoir between said piston and said piston bore on said low pressure side, said second clean reservoir in communication with a second pressure compensator; said first and said second pressure compensators configured to isolate said first and said second clean reservoirs from contamination with the drilling fluids; said first pressure compensator in fluid communication with drilling fluids on said high pressure side of said piston; and said second pressure compensator in fluid communication with drilling fluids on said low- pressure side of said piston.
2. The hydraulic actuator of claim I wherein said high-pressure side of said piston is in communication with drilling fluids pressurized in a through-bore of the drilling tool.
3. The hydraulic actuator of claim 1 wherein said low pressure side of said piston is in communication with drilling fluids pressurized in an annulus between the drilling tool and the borehole.
4. The hydraulic actuator of claim 1 wherein a pressure pad corresponds with said low pressure side of said piston, said pressure pad configured to engage the borehole when said piston moves from said high pressure side to said low pressure side.
5. The hydraulic actuator of claim 1 wherein the piston bore is a lateral bore.
6. The hydraulic actuator of claim 1 wherein said first and said second clean reservoirs contain hydraulic fluid, said hydraulic fluid configured to protect and maintain the integrity of a dynamic seal isolating said first side of said piston from said second side of said piston.
7. The hydraulic actuator of claim 6 wherein said dynamic seal includes an o-ring.
8. The hydraulic actuator of claim 6 wherein said dynamic seal includes backup rings.
9. The hydraulic actuator of claim 6 wherein said dynamic seal includes a wiper.
10. The hydraulic actuator of claim 1 wherein said first and said second membranes are constructed as bellows.
The hydraulic actuator of claim I wherein said first and said second membranes are constructed as impermeable membranes.
12. The hydraulic actuator of claim I wherein said first and said second membranes are constructed as permeable membranes.
13. The hydraulic actuator of claim I wherein said first and said second membranes are constructed as semi-permeable membranes.
14. The hydraulic actuator of claim 1 wherein said first and said second membranes are constructed using light gauge materials to reduce operating stresses of said membranes.
15. The hydraulic actuator of claim I wherein said first and said second pressure compensators include internal pistons to isolate said first and said second clean reservoirs from the drilling fluids.
16. The hydraulic actuator of claim I wherein said first and said second pressure compensators include expansion bladders to isolate said first and said second clean reservoirs from the drilling fluids.
17. A directional drilling tool to be run in a borehole in the presence of drilling fluids, the drilling tool comprising: a central through-bore through which the drilling fluids are delivered; an annulus between the directional drilling tool and the borehole through which the drilling fluids are returned; a piston slidably engaged within a piston bore, said piston characterized by a high pressure side and a low pressure side; a first membrane to create a first clean reservoir between said piston and said piston bore on said high pressure side, said first clean reservoir in communication with a first pressure compensator; a second membrane to create a second clean reservoir between said piston and said bore on said low pressure side, said second clean reservoir in communication with a second pressure compensator; said first and said second pressure compensators configured to isolate said first and said second clean reservoirs from contamination with the drilling fluids; said first pressure compensator in fluid communication with drilling fluids on said high pressure side of said piston; said second pressure compensator in fluid communication with drilling fluids on said low-pressure side of said piston; and said low-pressure side of said piston connected to a pressure pad, said pressure pad configured to bias the directional drilling tool in a desired position relative to the borehole when said pressure pad is engaged with the borehole.
18. The directional drilling tool of claim 17 wherein said central through-bore is in communication with said high-pressure side of said piston.
19. The directional drilling tool of claim 17 wherein said annulus is in communication with said low-pressure side of said piston.
20. The directional drilling tool of claim 17 wherein said first and said second clean reservoirs contain hydraulic fluid, said hydraulic fluid configured to protect and maintain the integrity of a dynamic seal isolating said high pressure side of said piston from said low pressure side of said piston.
21. The directional drilling tool of claim 17 wherein said first and said second pressure compensators include internal pistons to isolate said first and said second clean reservoirs from the drilling fluids.
22. The directional drilling tool of claim 17 wherein said first and said second pressure compensators include expansion bladders to isolate said first and said second clean reservoirs from the drilling fluids.
23. A method to actuate a pressure pad of a drilling apparatus with drilling fluids in a subterranean borehole, the method comprising: slideably engaging a piston within a piston bore of the drilling apparatus, the piston configured to slide between a high pressure zone and a low pressure zone; installing a first membrane between the piston and the piston bore in the high pressure zone to create a first clean reservoir wherein the first clean reservoir is in communication with a first hydraulic compensator; installing a second membrane between the piston and the piston bore in the low pressure zone to create a second clean reservoir wherein the second clean reservoir is in communication with a second hydraulic compensator; communicating the first hydraulic compensator with the high pressure zone such that the first clean reservoir is isolated from any drilling fluids in the high pressure zone; communicating the second hydraulic compensator with the low pressure zone, such that the first clean reservoir is isolated from any drilling fluids in the low pressure zone; mounting the pressure pad upon the drilling apparatus, the pressure pad configured to be engaged by the piston when actuated in the direction of the low pressure zone; and increasing the pressure of the high pressure zone to engage the pressure pad to bias the drilling apparatus in a desired position.
24. The method of claim 23 further comprising communicating the highpressure zone with a central through-bore of the drilling apparatus.

IS I r
25. The method of claim 23 further comprising communicating the lowpressure zone with an annulus formed between the drilling apparatus and the borehole.
26. An apparatus to be used in a directional drilling system, the apparatus comprising: one or more actuators having a dynamic seal slideably carried in a lateral bore of a tool and moveably responsive to changes in the pressure of a drilling fluid; a high-pressure clean reservoir for the retention of a lubricating fluid formed by a first membrane contiguous between an interior edge of the lateral bore and an interior surface of the actuator in fluid communication with a highpressure compensator responsive to changes in a high-pressure drilling fluid on an interior longitudinal passage of the tool; and a low-pressure clean reservoir for the retention of a lubricating fluid formed by a second membrane contiguous between an exterior edge of the lateral bore and an exterior surface of the actuator in fluid communication with a lowpressure compensator responsive to changes in the low-pressure drilling fluid on the exterior of the tool.