WO2013082376A1

WO2013082376A1 - Pressure actuated centralizer

Info

Publication number: WO2013082376A1
Application number: PCT/US2012/067219
Authority: WO
Inventors: Jeremy Murphy
Original assignee: Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Technology Corp; Schlumberger Holdings Ltd; Prad Research and Development Ltd
Current assignee: Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Technology Corp; Schlumberger Holdings Ltd; Prad Research and Development Ltd
Priority date: 2011-12-02
Filing date: 2012-11-30
Publication date: 2013-06-06
Anticipated expiration: 2014-06-02

Abstract

A system includes a pressure actuated centralizer configured to be disposed about a downhole tool module. The pressure actuated centralizer includes a central body, a plurality of blades extending radially outward from the central body, and a plurality of piston assemblies. Each piston assembly is disposed in a respective blade, where a portion of each piston assembly may extend radially outward from the central body when exposed to pressure within the downhole tool module.

Description

PRESSURE ACTUATED CENTRALIZER

BACKGROUND

[0001] The present disclosure relates generally to drilling systems and, more particularly, to downhole drilling tools.

[0002] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0003] Wells are generally drilled into the ground or ocean bed to recover natural deposits of oil and gas, as well as other desirable materials that are trapped in geological formations in the Earth's crust. A well may be drilled using a drill bit attached to the lower end of a "drill string." Drilling fluid, or "mud," may be pumped down through the drill string to the drill bit. The drilling fluid lubricates and cools the drill bit, and it carries drill cuttings back to the surface in an annulus between the drill string and the borehole wall.

[0004] For successful oil and gas exploration, it is beneficial to have information about the subsurface formations that are penetrated by a borehole. For example, one aspect of standard formation evaluation relates to measurements of the formation pressure and formation permeability. These measurements may be used for predicting the production capacity and production lifetime of a subsurface formation. [0005] One technique for measuring formation properties includes lowering a "wireline" tool into the well to measure formation properties. A wireline tool is a measurement tool that is suspended from a wire as it is lowered into a well so that it can measure formation properties at desired depths. A wireline tool may include a probe or packer inlet that may be pressed against the borehole wall to establish fluid communication with the formation. This type of wireline tool is often called a "formation tester." A formation tester measures the pressure of the formation fluids and generates a pressure pulse, which is used to determine the formation permeability. The formation tester tool may also withdraw a sample of the formation fluid for later analysis.

[0006] In order to use a wireline tool, whether the tool is a resistivity, sampling, porosity, or formation testing tool, the drill string is removed from the well so that the tool can be lowered into the well. This is called a "trip" downhole. Further, wireline tools are lowered to the zone of interest, generally at or near the bottom of the hole. A combination of removing the drill string and lowering the wireline tools downhole are time-consuming measures and can take up to several hours, depending upon the depth of the borehole. Because of the expense and rig time involved to "trip" the drill pipe and lower the wireline tools down the borehole, wireline tools are generally used when the information is greatly desired, or when the drill string is tripped for another reason, such as changing the drill bit.

[0007] As an improvement to wireline technology, techniques for measuring formation properties using tools and devices that are positioned near the drill bit in a drilling system have been developed. Thus, formation measurements are made during the drilling process, and the terminology generally used in the art is "MWD" (measurement-while-drilling) and "LWD" (logging-while-drilling). MWD refers to measuring the drill bit trajectory, as well as borehole temperature and pressure, while LWD refers to measuring formation parameters or properties, such as resistivity, porosity, permeability, and sonic velocity, among others. Real-time data, such as the formation pressure, allows the drilling entity to make decisions about drilling mud weight and composition, as well as decisions about drilling rate and weight-on-bit, during the drilling process.

[0008] Multiple moving parts involved in a formation testing tool, such as MWD and LWD tools, can result in less than optimal performance. Further, at greater depths, substantial hydrostatic pressure and high temperatures are experienced, thereby further complicating matters. Still further, formation testing tools are operated under a wide variety of conditions and parameters that are related to both the formation and the drilling conditions. Therefore, there is a need for improved downhole formation evaluation tools and improved techniques for operating and controlling downhole formation evaluation tools so that these tools are more reliable, efficient, and adaptable to formation and mud circulation conditions.

SUMMARY

[0009] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0010] In a first embodiment, a system a centralizer to be disposed about a downhole tool module. The downhole tool module includes a central body, a plurality of blades extending radially outward from the central body, and a plurality of piston assemblies. Each piston assembly is disposed in a respective blade, and a portion of each piston assembly may extend radially outward from the central body when exposed to pressure within the downhole tool module.

[0011] In another embodiment, a centralizer includes a central body defining an interior passage configured to receive a tool and a plurality of blades extending radially outward from the central body. Each blade includes a piston assembly, and each piston assembly includes a piston disposed within the respective blade, where the piston is exposed to the interior passage of the central body, a piston retaining cap configured to retain the piston within the respective blade, and a plurality of seals at least partially defining a pressurized volume within the piston assembly.

[0012] In a further embodiment, a system includes a downhole tool module having a flow passage and a pressure actuated centralizer. The pressure actuated centralizer includes a central body defining an annular passage that may receive the downhole tool module and a plurality of blades extending radially outward from the central body and spaced substantially equidistantly about the central body. Each blade includes a piston assembly. Each piston assembly includes a piston disposed within the respective blade, where the piston is exposed to the flow passage of the downhole tool module. Additionally, each piston assembly includes a piston retaining cap for retaining the piston within the respective blade,_a first seal assembly disposed between the piston and an interior wall of the respective blade, a second seal assembly disposed between the piston and an interior wall of the piston retaining cap, and an outer seal disposed between the piston retaining cap and the interior wall of the respective blade. [0013] Various refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0015] FIG. 1 is a partial cross sectional view of an embodiment of a drilling system used to drill a well through subsurface formations;

[0016] FIG. 2 is a perspective view of a hydraulic extender including a pressure actuated centralizer;

[0017] FIG. 3 is a perspective view of a pressure actuated centralizer; and [0018] FIG. 4 is a cross sectional axial view of a pressure actuated centralizer. DETAILED DESCRIPTION

[0019] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation- specific decisions may be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a

development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0020] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0021] Present embodiments are directed to a pressure actuated centralizer for a downhole drilling tool. In certain embodiments, the pressure actuated centralizer includes a plurality of blades, which may be spaced substantially equidistantly about a central body and may extend radially outward from the central body. Furthermore, each blade includes a piston assembly. In the manner described in detail below, each piston assembly is configured to be actuated by a pressure within the tool, such as a hydrostatic pressure created by a fluid column (e.g., a drilling mud or formation fluid column extending above the pressure actuated centralizer). In particular, a piston of each piston assembly may be exposed to a flow passage of the tool and may extend radially outward from the piston assembly and/or the respective blade as the pressure within the flow passage increases and acts on the piston. As each piston extends radially outward from the respective blade, the piston may contact an inner wall of a drill collar, borehole, or other volume in which the pressure actuated centralizer is disposed. As the pistons contact the inner wall of the drill collar, borehole or other volume, the pistons may act to centralize the pressure actuated centralizer and the tool to which the pressure actuated centralizer is attached within the drill collar, borehole, or other volume.

[0022] FIG. 1 illustrates a drilling system 10 used to drill a well through subsurface formations 12. A drilling rig 14 at the surface 16 is used to rotate a drill string 18 that includes a drill bit 20 at its lower end. As the drill bit 20 is rotated, a "mud" pump 22 is used to pump drilling fluid, commonly referred to as "mud" or "drilling mud," downward through the drill string 18 in the direction of the arrow 24 to the drill bit 20. The mud, which is used to cool and lubricate the drill bit 20, exits the drill string 18 through ports (not shown) in the drill bit 20. The mud then carries drill cuttings away from the bottom of the borehole 26 as it flows back to the surface 16, as shown by the arrows 28, through the annulus 30 between the drill string 18 and the formation 12. While a drill string 18 is illustrated in FIG. 1, it will be understood that the embodiments described herein are applicable to work strings and pipe strings as well. At the surface 16, the return mud is filtered and conveyed back to a mud pit 32 for reuse. [0023] As illustrated in FIG. 1, the lower end of the drill string 18 includes a bottom-hole assembly ("BHA") 34 that includes the drill bit 20, as well as a plurality of drill collars 36, 38 that may include various instruments, subassemblies, and tools 40 such as sample -while-drilling ("SWD") tools that include sensors, telemetry equipment, pumps, sample chambers, and so forth. For example, the drill collars 36, 38 may include logging-while-drilling ("LWD") modules 42 and/or measurement- while drilling ("MWD") modules 44. The LWD modules 42 of FIG. 1 are each housed in a special type of drill collar 36, 38, and each contain any number of logging tools and/or fluid sampling devices. The LWD modules 42 include capabilities for measuring, processing and/or storing information, as well as for communicating with the MWD modules 44 and/or directly with the surface equipment such as a logging and control computer. The BHA 34 may also include a hydraulic extender or connector 46. The hydraulic extender 46 extends between two tools 40 (e.g., LWD modules 42 and/or MWD modules 44) and couples auxiliary flow lines that extend through the two tools 40. Additionally, in certain embodiments, the hydraulic extender 46 may include electrical connections for transmitting electrical

communications between the two tools 40 connected by the hydraulic extender 46.

[0024] In certain embodiments, the tools (e.g., LWD modules 42, MWD modules 44, and/or hydraulic extenders 46) may also include or be disposed within a centralizer or stabilizer 48. For example, the centralizer 48 may include blades that are in contact with the borehole wall 50 as shown in FIG. 1 to limit "wobble" of the drill bit 20. In other embodiments, the blades of the centralizer 48 may be in contact with an interior surface of the drill collars 36, 38. "Wobble" is the tendency of the drill string 18, as it rotates, to deviate from the vertical axis of the borehole 26 and cause the drill bit 20 to change direction. Because the centralizer 48 is already in contact with the drill collars 36, 38 or the borehole wall 50, a probe is extended a relatively small distance from the tool to establish fluid communication with the formation 12. It will be understood that a formation probe may be disposed in locations other than in the centralizer 48 without departing from the scope of the presently disclosed embodiments.

[0025] As discussed in detail below, the centralizer 48 may be a pressure actuated centralizer 48. More specifically, blades which extend from a central body of the centralizer 48 may include one or more pistons slidably disposed therein which may be actuated by a hydrostatic pressure or other pressure within the central body of the centralizer 48 or a flow passage of the tool 40 having the centralizer 48. In other words, a hydrostatic pressure within the central body of the centralizer 48 or a flow passage of the tool 40, which may be created by a fluid, such as drilling mud, flowing through the centralizer 48 or the tool 40, may urge the pistons within the blades radially outward. In particular, distal ends of the pistons may extend beyond a distal surface of the blades and engage with the drill collars 36, 38 or borehole wall 50. By engaging with the interior surface of the drill collars 36, 38 or borehole wall 50, the pistons will cause the centralizer 48 to be centralized within the drill collars 36, 38 or borehole 26.

[0026] FIG. 2 is a perspective view of an embodiment of the hydraulic extender 46 including a pressure actuated centralizer 60 disposed thereon. As mentioned above with respect to FIG. 1, the hydraulic extender 46 is configured to join two tools 40 of the BHA 34 or drill string 18. For example, the hydraulic extender 46 may couple to one tool 40 at a first end 62 of the hydraulic extender 46, and the hydraulic extender 46 may couple to another tool 40 at a second end 64 of the hydraulic extender 46. As will be appreciated, the first end 62 and the second end 64 of the hydraulic extender 46 may each include a coupling mechanism configured to couple the respective tool 40 to the end 62, 64 of the hydraulic extender 46. [0027] In the illustrated embodiment, the hydraulic extender 46 includes a body 66, which generally defines a flow passage 68. When the hydraulic extender 46 joins two tools 40, the flow passage 68 of the hydraulic extender 46 may fluidly couple respective internal flow lines of the tools 40. As a result, a fluid flow may be transferred from one tool 40 to another tool 40 through the flow passage 68 of the hydraulic extender 46. Additionally, as mentioned above, the hydraulic extender 46 may include electrical connections (e.g., conductive pathways) for conducting electrical signals between the two tools 40 joined by the hydraulic extender 46. Moreover, certain embodiments of the hydraulic extender 46 may include multiple flow passages 68, and one or more flow passages 68 may be used to actuate the pressure actuated centralizer 60 in the manner described below.

[0028] Furthermore, in certain embodiments, the hydraulic extender 46 includes a length- adjusting assembly 70. The length-adjusting assembly 70 may be used to adjust the length of the body 66 of the hydraulic extender 46. As a result, the hydraulic extender 46 may be configured to accommodate various distances between the two tools 40 that are coupled together by the hydraulic extender 46. In certain embodiments, the length-adjusting assembly 70 may include sleeves, threaded connections, or other components configured to move (e.g., axially) relative to one another.

[0029] As mentioned above, the pressure actuated centralizer 60 is disposed about and coupled to the hydraulic extender 46. More specifically, the pressure actuated centralizer 60 is coupled to the body 66 of the hydraulic extender 46. In the manner described in detail below, the pressure actuated centralizer 60 functions to center the hydraulic extender 46 within the drill collars 36, 38 or the borehole 26. In certain embodiments, a portion of the pressure actuated centralizer 60 may be exposed to the flow passage 68 of the hydraulic extender 46 through ports or other passages. As mentioned above and explained in detail below, a hydrostatic pressure within the flow passage 68 of the hydraulic extender 46 may be used to actuate pistons of the pressure actuated centralizer 60. In particular, hydrostatic pressure within the flow passage 68 of the hydraulic extender 46 may force the pistons of the pressure actuated centralizer 60 radially outward to extend beyond the outer periphery of the centralizer body, thereby causing the pistons to engage with an interior wall of the drill collars 36, 38 or the borehole wall 50. As the pistons engage with the interior wall of the drill collars 36, 38 or the borehole wall 50, the pressure actuated centralizer 60 acts to centralize the hydraulic extender 46 within the drill collar 36, 38 or borehole 26. Furthermore, while the illustrated embodiment shows the pressure actuated centralizer 60 disposed about the hydraulic extender 46, it will be appreciated that the pressure actuated centralizer 60 may be disposed about and used to centralize any of a variety of downhole tools, such as LWD modules 42, MWD modules 44, mandrel assemblies, housings, or other tools disposed within the drill collars 36, 38 or borehole 26.

[0030] FIG. 3 is a perspective view an embodiment of the pressure actuated centralizer 60. In the illustrated embodiment, the pressure actuated centralizer 60 includes a central body 100 with blades 102 extending radially outward from the central body 100. The central body 100 is a generally annular configuration and defines an interior passage 104. When the pressure actuated centralizer 60 is installed, the tool 40 on which the pressure actuated centralizer 60 is positioned (e.g., the hydraulic extender 46 shown in FIG. 2) may extend through the interior passage 104 of the pressure actuated centralizer 60. [0031] As mentioned above, the blades 102 extend radially outward from the central body 100. Additionally, the blades 102 are spaced substantially equidistantly about a circumference of the central body 100 of the pressure actuated centralizer 60. For example, in an embodiment of the pressure actuated centralizer 60 having three blades 102, the blades 102 may be spaced about a circumference of the central body 100 such that a central axis of each blade 102 is approximately 120 degrees from a central axis of adjacent blades, within a tolerance of approximately 1 to 5 degrees. Moreover, while the illustrated embodiment includes three blades 102, other embodiments of the pressure actuated centralizer 60 may include other suitable numbers of blades 102, such as four or five blades 102, which also may be spaced substantially equidistantly about a circumference of the central body 100 of the pressure actuated centralizer 60.

[0032] Additionally, each of the blades 102 extending from the body 100 includes a piston assembly 106. In the manner described below, each piston assembly 106 may be actuated by a hydrostatic pressure or other pressure within the tool 40 disposed within the interior passage 104 of the pressure actuated centralizer 50. While each blade 102 of the pressure actuated centralizer 60 includes one piston assembly 106 in the illustrated embodiment, other embodiments may includes blades 102 having two or more piston assemblies 106. As shown, each piston assembly 106 includes a piston 108 which is positioned within its respective blade 102. More specifically, each piston 108 is held and retained within the blade 102 by a respective piston retaining cap 110. In certain embodiments, the piston retaining cap 110 may couple to its respective blade 102 with a threaded connection. [0033] Furthermore, in the illustrated embodiment, the pressure actuated centralizer 60 has a multi-piece configuration. As shown, three pieces 112 are joined to form the central body 100 and the blades 102 of the pressure actuated centralizer 60. More specifically, each piece 112 forms approximately a one third portion of the central body 100, and each piece 112 includes at least one portion of two different blades 112. As such, each blade 102 is formed by portions of two different pieces 112. Collectively, the three pieces 112 are joined to form the central body 100 and the three blades 102. As shown, the multiple pieces 112 are coupled together with bolts 114, which may couple to the pressure actuated centralizer 60 with a threaded connection.

Furthermore, each bolt 114 includes a retaining plate 116 to retain the respective bolt 114 within the pressure actuated centralizer 60. For example, the retaining plate 116 may block the respective bolt 114 from unthreading from the pressure actuated centralizer 60. Moreover, while the illustrated embodiment of the central body 100 and the blades 102 has a multi-piece configuration, other embodiments may include a single piece that forms the central body 100 and the blades 102 of the pressure actuated centralizer 60.

[0034] FIG. 4 is a cross-sectional schematic of the pressure actuated centralizer 60 disposed about the hydraulic extender 46 and within the drill collar 36, 38. As mentioned above, the piston assemblies 106 are exposed to a hydrostatic pressure or other pressure within the hydraulic extender 46 (or other tool 40). In the illustrated embodiment, each piston assembly 106 (e.g., the piston 108 of each piston assembly 106) abuts a respective pressure port 120 formed in the central body 100 of the pressure actuated centralizer 60. Additionally, each pressure port 120 of the central body 100 is fluidly coupled to (and aligns with) a respective pressure port 122 formed in the hydraulic extender 46. Specifically, the pressure ports 122 extend radially through the body 66 of the hydraulic extender 46. Therefore, each piston assembly 106 is exposed to the flow passage 68 of the hydraulic extender 46. As such, the piston 108 of each piston assembly 106 is exposed to a pressure (e.g., a hydrostatic pressure) within the flow passage 68 of the hydraulic extender 46. As will be appreciated, in applications where the pressure actuated centralizer 60 is disposed about other tools 40, the other tools 40 may have similar pressure ports 122 exposing each piston 108 to an internal pressure within the tool 40.

[0035] Each piston assembly 106 includes various seals to enable the functionality of the pressure actuated centralizer 60. For example, each piston assembly 106 includes a first seal assembly 124 disposed between the piston 106 and an interior wall 126 of the respective blade 102. As shown, each first seal assembly 124 includes a main seal 128 and backup seals 130 disposed on opposite sides of the main seal 128. In certain embodiments, the seals 128 and 130 may be O-rings or T-seals. Additionally, the main seals 128 and the backup seals 130 may be formed from a thermoplastic, such as polyetheretherketone (PEEK), or an elastomer. Each piston assembly 106 further includes a second seal assembly 132 disposed between the piston 108 and an interior wall 134 of the piston retaining cap 110. As similarly described with respect to the first seal assemblies 124, each second seal assembly 132 includes a main seal 136 and backup seals 138 disposed on opposite sides of the main seal 136. Likewise, the seals 136 and 138 may be O-rings or T-seals and may be formed from a thermoplastic, such as

polyetheretherketone (PEEK), or an elastomer. Each piston assembly 106 also includes an outer seal 140, which may be a seal similar to those described above, disposed between the interior wall 126 of the respective blade 102 and the piston retaining cap 110. [0036] For each piston assembly 106, the first seal assembly 124, the second seal assembly 132, and the outer seal 140 collectively seal a volume 141 defined by the piston 108, the piston retaining cap 1 10, and the interior wall 126 of the respective blade 102. When these various components of the pressure actuated centralizer 60 are assembled (e.g., in a factory or at the surface 16), an atmospheric pressure may be contained within the volume 141. In particular, the atmospheric pressure may be maintained within the volume 141 when the pressure actuated centralizer 60 is disposed within the drill collar 36, 38 or the wellbore 26. As such, in the illustrated embodiment, when a pressure (e.g., a hydrostatic pressure) within the flow passage 68 of the hydraulic extender 46 is greater than the atmospheric pressure within the volume 140 of each piston assembly 106, the respective piston 108 of each piston assembly 106 may be forced radially outward, as indicated by arrows 142. More specifically, as a pressure within the flow passage 68 increases, the pressure may be exposed to each piston 106 through the respective pressure ports 120 and 122. When the pressure within the flow passage 68 exceeds the atmospheric pressure within the volume 140 of the respective piston assembly 106, the respective piston 108 is pushed radially outward in the respective direction 142. As mentioned above, the pressure within the flow passage 68 may be a hydrostatic pressure. For example, the hydrostatic pressure may be created by drilling mud or a formation fluid flowing through the flow passage 68 of the hydraulic extender 46.

[0037] As the piston 108 of each piston assembly 106 is pushed radially outward in the respective direction 142, each piston 108 may contact and engage with an inner wall 144 of the drill collar 36, 38. That is, a distal end 146 of each piston 108 may extend beyond an outer periphery of a respective blade 102 to contact and engage with the inner wall 144 of the drill collar 36, 38. As a result, the pistons 108 may operate to centralize the pressure actuated centralizer 60 and the hydraulic extender 46 within the drill collar 36, 38. As will be appreciated, the pistons 108 may each extend radially outward by substantially the same amount as each piston 108 is exposed to the same pressure within the flow passage 68, thereby enabling the pistons 108 to centralize the pressure actuated centralizer 60 and the hydraulic extender 46 within the drill collar 36, 38. Furthermore, when the pressure within the flow passage 68 subsequently decreases below the atmospheric pressure within the volume 140 of each piston assembly 106, the respective piston 108 may be forced back to its original position within its respective blade 102 (e.g., by contact with the inner wall 144 of the drill collar 36, 38).

[0038] Embodiments of the present disclosure include the pressure actuated centralizer 60 for a downhole drilling tool (e.g., tool 40). For example, the pressure actuated centralizer 60 may be disposed about the LWD tool 42, the MWD tool 44, or the hydraulic extender 46. The pressure actuated centralizer 60 includes a plurality of blades 102 spaced substantially equidistantly about a circumference of the central body 100 and extending radially outward from the central body 100. Furthermore, each blade 102 includes the piston assembly 106. In the manner described in detail above, each piston assembly 106 is configured to be actuated by a pressure within the tool 40, such as a hydrostatic pressure created by a fluid flow (e.g., a drilling mud or formation fluid flow). In particular, the piston 108 of each piston assembly 106 is exposed to a flow passage 68 of the tool 40 and may extend radially outward from the piston assembly 106 and/or the blade 102 as the pressure within the flow passage 68 increases and acts on the piston 108. As each piston 108 extends radially outward from the respective blade 102, the piston 108 may contact the inner wall (e.g., 144) of the drill collar 36, 38 or borehole 26 in which the pressure actuated centralizer 60 is disposed. As the pistons 108 contact the inner wall of the drill collar 36, 38 or borehole 26, the pistons 108 may act to centralize the pressure actuated centralizer 60 and the tool 40 to which the pressure actuated centralizer 60 is attached within the drill collar 36, 38 or borehole 26.

[0039] The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Claims

CLAIMS What is claimed is:

1. A system, comprising:

a centralizer configured to be disposed about a downhole tool module, comprising:

a central body;

a plurality of blades extending radially outward from the central body; and a plurality of piston assemblies, each piston assembly disposed in a respective blade, wherein a portion of each piston assembly is configured to extend radially outward from the central body when exposed to pressure within the downhole tool module.

2. The system of claim 1, wherein each piston assembly comprises a piston configured to extend past the respective blade to an extended position when exposed to the pressure within the downhole tool and to retract within the respective blade to a retracted position when the pressure within the downhole tool decreases.

3. The system of claim 1, wherein each piston assembly comprises a piston disposed within the respective blade, wherein the piston is exposed to a flow passage of the downhole tool module by one or more pressure ports formed in the downhole tool module and the central body.

4. The system of claim 3, wherein each piston assembly comprises a piston retaining cap coupled to the respective blade, wherein each piston retaining cap at least partially retains the piston within the respective blade, wherein each piston assembly comprises a first seal assembly disposed between the piston and an interior wall of the respective blade, and a second seal assembly disposed between the piston and an interior wall of the piston retaining cap, and wherein the first and second seal assemblies define a sealed volume..

5. The system of claim 4, wherein the sealed volume comprises an atmospheric pressure.

6. The system of claim 4, wherein each of the first and second seal assemblies comprises at least one O-ring seal and at least one backup seal.

7. The system of claim 1, wherein the plurality of blades comprises three blades spaced substantially equally about the central body.

8. The system of claim 1, wherein the pressure is a hydrostatic pressure created by a drilling mud flow within the downhole tool module.

9. The system of claim 1, wherein the central body and the plurality of blades have a multi- piece configuration.

10. The system of claim 1, comprising the downhole tool module, wherein the downhole tool module comprises a logging-while-drilling tool, a measurement-while-drilling tool, or a hydraulic extender.

11. A centralizer, comprising:

a central body defining an interior passage configured to receive a tool; a plurality of blades extending radially outward from the central body, each blade comprising a piston assembly, wherein each piston assembly comprises:

a piston disposed within the respective blade, wherein the piston is exposed to the interior passage of the central body;

a piston retaining cap configured to retain the piston within the respective blade; and

a plurality of seals at least partially defining a pressurized volume within the piston assembly, wherein the pressurized volume has a first pressure.

12. The system of claim 11, wherein the plurality of seals comprises an outer seal disposed between the piston retaining cap and an interior wall of the respective blade, a first seal assembly disposed between the piston and the interior wall of the respective blade and a second seal assembly disposed between the piston and an interior wall of the piston retaining cap.

13. The system of claim 11, wherein the piston retaining cap is retained within the respective blade by a threaded connection.

14. The system of claim 11, wherein the first pressure comprises an atmospheric pressure.

15. The system of claim 11, wherein the piston is exposed to a flow passage of the tool, and the flow passage of the tool is configured to flow a fluid.

16. The system of claim 15, wherein the piston is configured to extend at least partially radially outward from the respective blade when a second pressure within the flow passage exceeds the first pressure within the pressurized volume.

17. The system of claim 11, wherein the plurality of blades are spaced substantially equidistantly about a circumference of the central body.

18. A system, comprising :

a downhole tool module comprising a flow passage; and

a pressure actuated centralizer, comprising:

a central body defining an annular passage configured to receive the downhole tool module;

a plurality of blades extending radially outward from the central body and spaced substantially equidistantly about the central body, each blade comprising a piston assembly, wherein each piston assembly comprises:

a piston disposed within the respective blade, wherein the piston is exposed to the flow passage of the downhole tool module;

a piston retaining cap configured to retain the piston within the respective blade;

a first seal assembly disposed between the piston and an interior wall of the respective blade;

a second seal assembly disposed between the piston and an interior wall of the piston retaining cap; and an outer seal disposed between the piston retaining cap and the interior wall of the respective blade.

19. The system of claim 18, wherein the downhole tool module comprises a logging-while- drilling tool, a measurement-while drilling tool, or a hydraulic extender.

20. The system of claim 18, wherein the first seal assembly, the second seal assembly, and the outer seal at least partially define a sealed volume, and the sealed volume comprises an atmospheric pressure.