Patent Publication Number: US-8967300-B2

Title: Pressure activated flow switch for a downhole tool

Description:
BACKGROUND 
     Downhole drilling operations commonly require a downhole tool to be actuated after the tool has been deployed in the borehole. For example, underreamers are commonly tripped into the borehole in a collapsed state (i.e., with the cutting structures retracted into the underreamer tool body). At some desired depth (or location), the underreamer is actuated such that the cutting structures expand radially outward from the tool body thereby engaging the borehole wall. Hydraulic actuation mechanisms are well known in oilfield services operations and are commonly employed, and even desirable, in such operations. 
     For example, one well-known hydraulic actuation methodology involves wireline retrieval of a plug (or “dart”) through the interior of the drill string to create differential pressure to actuate an underreamer. Upon completion of the reaming operation, the underreamer may be deactuated by redeploying the dart. While commercially serviceable, such wireline actuation and deactuation mechanisms are both expensive and time-consuming in that they require concurrent use of wireline or slick line assemblies. 
     Another commonly used hydraulic actuation methodology makes use of shear pins designed to shear at or above a specific differential pressure (or in a predetermined range of pressures). Ball drop mechanisms are also known in the art, in which a ball is dropped down through the drill string to a ball seat. Engagement of the ball with the seat typically causes an increase in differential pressure which in turn actuates the downhole tool. The tool may be deactuated by increasing the pressure beyond a predetermined threshold such that the ball is urged through the seat. While such shear pin and ball drop mechanisms are also commercially serviceable, they are generally one-time or one-cycle mechanisms and do not typically allow for repeated actuation and deactuation of a downhole tool. Moreover, ball drop mechanisms generally require that the drill string have an unobstructed through bore extending from the surface to the ball seat. As such, ball drop mechanisms are not typically suitable for near bit tool deployments (e.g., tool deployments that are below measurement while drilling “MWD” and logging while drilling “LWD” tools). 
     There remains a need in the art for a hydraulic actuation assembly that enables a downhole tool, such as an underreamer or a stabilizer, to be actuated and deactuated substantially any number of times during a drilling operation without breaking the tool string and/or tripping the tool out of the borehole. 
     SUMMARY 
     A downhole tool including a pressure activated flow switch is disclosed. One or more disclosed tool embodiments include a block assembly (e.g., a reaming block) deployed in an axial recess of a tool body. The block assembly is configured to translate between radially retracted and radially extended positions in response to differential pressure. The flow switch is deployed external to the flow bore in an annular region between the tool body and a tool mandrel. The flow switch includes a flow piston configured to reciprocate between axially opposed open and closed positions in the annular region such that the block assembly is radially extended when the flow piston is in the open position and radially retracted when the flow piston is in the closed position. The flow piston is configured to translate from the closed position to the open position when a differential pressure between the flow bore of the downhole tool and a chamber of the downhole tool exceeds a predetermined threshold. The flow piston may be further configured to remain in the open position at differential pressures less than the threshold. 
     The disclosed embodiments may provide one or more technical advantages. For example, in the disclosed embodiments the flow switch is deployed entirely external to the central flow bore of the downhole tool. Such deployment tends to advantageously preserve the cross sectional area of the flow bore thereby providing no obstruction to drilling fluid flowing towards the drill bit. This acts to minimize both the pressure drop through the tool and erosion of internal tool components during use. Moreover, external deployment of the flow switch enables the downhole tool to be deployed low in the BHA (e.g., just above the drill bit). 
     The disclosed embodiments further enable a downhole tool to be selectively and repeatedly actuated and deactuated substantially any number of times without breaking the drill string and/or or tripping the tool out of the borehole. The disclosed embodiments further obviate the need for physical actuation and deactuation (e.g., including the use of darts, ball drops, and the like). 
     One or more embodiments of the invention may further make use of upper and lower thresholds thereby enabling the downhole tool to remain either actuated or deactuated over a wide range of operating pressures. This feature of the disclosed embodiments may enhance operational certainty as it tends to eliminate inadvertent actuation and deactuation. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed subject matter, and advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts one example of how a downhole tool employing a pressure activated flow switch may be utilized in a conventional drilling rig. 
         FIGS. 2A and 2B  (collectively  FIG. 2 ) depict longitudinal cross sectional views of a disclosed underreamer in retracted ( FIG. 2A ) and extended ( FIG. 2B ) configurations. 
         FIGS. 3A and 3B  (collectively  FIG. 3 ) depict detailed views of a flow switch embodiment of the underreamer shown on  FIGS. 2A and 2B , respectively. 
         FIG. 4  depicts a plot of the flow piston axial position as a function of the differential pressure in the underreamer embodiment shown on  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts one example of an offshore drilling assembly, generally denoted  10 , on which a downhole tool employing a disclosed pressure activated flow switch may be used. A semisubmersible drilling platform  12  is positioned over an oil or gas formation disposed below the sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to a wellhead installation  22 . The platform may include a derrick and a hoisting apparatus for raising and lowering the drill string  30 , which, as shown, extends into borehole  40  and includes drill bit  32  and an actuatable downhole tool such as underreamer  100  deployed above the bit  32 . The drill string  30  may optionally further include substantially any number of other downhole tools including, for example, measurement while drilling (MWD) or logging while drilling (LWD) tools, stabilizers, a drilling jar, a rotary steerable tool, and/or a downhole drilling motor. The underreamer  100  may be deployed at substantially any location along the string, for example, just above the bit  32  or further uphole above various MWD and LWD tools. 
     During a typical drilling operation, drilling fluid (commonly referred to as “mud” in the art) is pumped downward through the drill string  30  and the bottom hole assembly (BHA) where it emerges at or near the drill bit  32  at the bottom of the borehole  40 . The mud serves several purposes, for example, including cooling and lubricating the drill bit, clearing cuttings away from the drill bit and transporting them to the surface, and stabilizing and sealing the formation(s) through which the borehole  40  traverses. The discharged mud, along with the borehole cuttings and sometimes other borehole fluids, then flow upwards through the borehole annulus  42  (the space between the drill string  30  and the borehole wall) to the surface. In the disclosed exemplary embodiments, the downhole tool uses differential pressure, e.g., between an internal flow channel and the annulus, to selectively actuate and deactuate certain tool functionality (e.g., the radial extension of a cutting structure or a stabilizer blade outward from a tool body). 
     It will be understood by those of ordinary skill in the art that the deployment illustrated on  FIG. 1  is merely an example. It will be further understood that the disclosed embodiments are not limited to use with a semisubmersible platform as illustrated on  FIG. 1 . The disclosed embodiments are equally well suited for use with any kind of subterranean drilling operation, either offshore or onshore. 
       FIGS. 2A and 2B  depict longitudinal cross sectional views of an underreamer  100  including a pressure activated flow switch  200 . In  FIG. 2A  the underreamer  100  is depicted in a collapsed configuration in which the reaming block  150  is fully retracted into the tool body  110 . In  FIG. 2B  the underreamer  100  is depicted in an expanded configuration in which the reaming block  150  is fully extended radially outward from the tool body  110 . The reaming block  150  is deployed in a corresponding axial recess  115  in the tool body  110  and is disposed to reciprocate between the radially retracted and radially extended positions depicted on  FIGS. 2A and 2B . While underreamer  100  is described with respect to a single reaming block  150 , it will be understood that the disclosed embodiments are not limited in regard to the number of reaming blocks. Embodiments of underreamer  100  may include substantially any number of reaming blocks (e.g., three). 
     In one or more of the disclosed embodiments, the reaming block  150  includes a plurality of splines (not shown) on the lateral sides thereof. The splines are sized and shaped to engage corresponding splines (not shown) on the lateral tool body sides of the recess  115 . Interconnection between these sets of splines may advantageously increase the surface area of contact between the reaming block  150  and the tool body  110  thereby providing a robust structure suitable for downhole operations (e.g., downhole reaming or stabilizing operations). The splines are angled such that they are non-parallel with respect to a longitudinal axis  102  of the underreamer  100 . Thus, relative axial motion between the reaming block  150  and the tool body  110  causes a corresponding radial extension or retraction of the reaming block  150 . In the depicted embodiment the splines are angled such that the reaming block  150  is radially extended via uphole axial motion thereof with respect to the tool body  110 , although the disclosed embodiments are not limited in regard to the spline configuration. Commonly assigned U.S. Pat. No. 6,732,817, which is incorporated by reference in its entirety herein, discloses suitable reaming block configurations. 
     The radially facing outer surface (also referred to in the art as the gauge surface) of the reaming block  150  may optionally be fitted with various cutting elements. Substantially any cutting elements suitable for downhole reaming operations may be utilized, for example, including polycrystalline diamond cutter (PDC) inserts, thermally stabilized polycrystalline (TSP) inserts, diamond inserts, boron nitride inserts, abrasive materials, and the like. The reaming block  150  may alternatively or additionally include various wear protection measures deployed thereon, for example, including the use of wear buttons, hardfacing materials, or various other wear resistant coatings. The reaming block  150  may also include wear resistant stabilizer pads. It will be understood that the disclosed embodiments are not limited to any particular cutting element configuration or wear protection measures. 
     Extension and retraction of the reaming block  150  is now described in more detail. In the depicted embodiment, the reaming block  150  is deployed axially between spring biasing  130  and hydraulic actuation  140  mechanisms that are in turn deployed in the tool body  110 . An internal mandrel  120  is deployed in the tool body  110  internal to the spring biasing mechanism  130  and the reaming block  150 . The mandrel  120  includes a central through bore  122  that provides a channel for the flow of drilling fluid through the tool  100 . The depicted spring biasing mechanism  130  includes a compression spring  132  deployed about the mandrel  120  in a spring retainer  133  and axially between an upper cap  135  and a stop ring  137 . The upper cap is rigidly connected with the tool body  110  such that the compression spring  132  is configured to bias the reaming block  150  in the downhole direction. The spring bias also urges the reaming block  150  radially inward (due to the configuration of the angled splines described above). 
     The hydraulic actuation mechanism  140  is configured to urge the reaming block  150  in the uphole direction against the spring bias when a differential pressure between a chamber of tool  100  and the bore  122  of tool  100  (i.e., pressure from the flow bore  122 ) is greater than a predetermined threshold. The depicted embodiment includes an axial piston  142  sealingly engaged with an inner surface  111  of the tool body  110  and an outer surface  123  of the mandrel  120 . Differential pressure acts on an axial face  143  of the piston  142  when flow switch  200  is open thereby urging the piston  142  in the uphole direction. The piston engages drive ring  145  and retainer  146  which in turn engages the reaming block  150  such that translation of the piston  142  causes a corresponding translation and extension of the reaming block  150 , as best shown in  FIG. 2B . 
     A flow switch embodiment  200  is now described in more detail with respect to  FIGS. 3A and 3B . Flow switch  200  includes a flow piston  210  deployed in an annular chamber  220  located between a lower mandrel  125  at the inner diameter and axial piston  142  and lower cap  144  at the outer diameter. The flow piston  210  is sealingly engaged with an outer surface of the lower mandrel  125  via at least a first (inner) sealing member/element, e.g., a seal,  215  and an inner surface of the lower cap  144  via at least a second (outer) sealing member/element, e.g., a seal,  217  and thus divides the annular chamber into first and second upper and lower chambers  222  and  224 . The flow piston  210  is arranged and designed to reciprocate axially between first and second closed and open positions. Lower chamber  224  is vented at  229  through the tool body  110  to the borehole annulus  42  ( FIG. 1 ) to provide pressure equalization between the lower chamber  224  and the borehole annulus  42  ( FIG. 1 ). Substantially any suitable vent, jet or port may be utilized. 
     A compression spring  226  is deployed in the lower chamber  224  between an end cap  228  and a shoulder portion  212  of the flow piston  210 . The spring  226  is configured to bias the flow piston  210  in the uphole direction towards the first position such that sleeve  231  engages seat  232  thereby creating a solid contact seal  230 . The solid contact seal  230  closes a flow channel  234  ( FIG. 3B ) between a central flow bore  126  of the lower mandrel  125  and the upper chamber  222 . In the depicted embodiment, a retaining ring  236  secures the sleeve  231  to an uphole end of the flow piston  210 . While the disclosed embodiments are not limited in this regard, the sleeve  231  and seat  232  may be fabricated from a hard, wear resistant material such as tungsten carbide to prevent wear and/or erosion thereof during service. 
     Flow switch  200  is configured to open flow channel  234  ( FIG. 3B ) when a differential pressure between bore  126  and chamber  224  exceeds a predetermined upper threshold (e.g., via increased flow rate through bore  126 ). At least one radial port  128  (four in the depicted embodiment) in lower mandrel  125  provides fluid communication between the bore  126  and the flow piston  210 . When the flow piston  210  is in the closed position ( FIG. 3A ), bore  126  is in fluid communication with seal  215  (near face  214 ) and solid contact seal  230 . The solid contact seal  230  has a diameter that is slightly larger than the diameter of seal  215 . Owing to the difference in seal area between solid contact seal  230  and seal  215  (such seal area between solid contact seal  230  and seal  215  being defined as the inner seal area), a differential pressure between bore  126  and lower chamber  224  provides a force that acts on the inner seal area to oppose the bias of spring  226 . The flow piston  210  remains in the closed position until the differential pressure exceeds the predetermined upper threshold at which point the fluid force begins to overcome the spring force. The predetermined upper threshold is influenced by the configuration of spring  226  and the difference in seal area between the solid contact seal  230  and seal  215 . This difference in seal area is about one square inch in the depicted embodiment. 
     When the differential pressure between bore  126  and chamber  224  exceeds the predetermined upper threshold, the flow piston  210  begins to move in the downhole direction against the bias of the spring  226  and towards the second position. Movement of the flow piston  210  breaks the solid contact seal  230  and thereby begins to open flow channel  234 , which allows drilling fluid to enter upper chamber  222  and act on face  216  of flow piston  210  and face  237  of retaining ring  236 . High pressure drilling fluid in upper chamber  222  easily overcomes the biasing force of spring  226  (due to the fluid acting on the full annular seal area of the flow piston—i.e., the annular/upper chamber  222  area between seals  215  and  217 ). The flow piston  210  thus moves rapidly to the open position until it abuts end cap  228  as depicted at  229  in  FIG. 3B . 
     Movement of the flow piston  210  to the open position provides full fluid communication between central bore  226  and upper chamber  222 . As described above with respect to  FIG. 2 , fluid communication between central bore  126  and upper chamber  222  also enables the drilling fluid to act on piston  142 , which causes the reaming block  150  to translate axially uphole and radially outward against the spring bias. In the depicted embodiment, drilling fluid is also routed to fluid jets  165  where it is vented from the tool so as to lubricate and cool the reaming block during a reaming operation. 
       FIG. 4  depicts a plot of the axial position of the flow piston  210  versus differential pressure between bore  126  and lower chamber  224  (i.e., the effect of fluid flow rate through bore  126 ) for the flow switch depicted on  FIGS. 3A and 3B . As the flow rate increases at  252 , the flow piston  210  ( FIG. 3A ) remains in the first closed position under the bias of spring  226  with sleeve  231  engaging seat  232 . When the differential pressure reaches the upper threshold, the flow piston  210  ( FIG. 3B ) translates  254  in the downhole direction to the second open position where it contacts the end cap  228  as described above. The pressure may be increased above the upper threshold without further translating the flow piston  210  as indicated at  256 . Since the annular seal area (i.e., upper chamber  222  between seals  215 ,  217 ) of the flow piston  210  is greater than the difference in seal area between the solid contact seal  230  and seal  215  (i.e., inner seal area), the flow piston  210  remains in the open position when the pressure is lowered below the upper threshold at  258 . When the pressure reaches a lower threshold the flow piston translates  259  in the downhole direction to the closed position such that the sleeve  231  engages seat  232 . 
     It will be understood that the upper threshold is related to the configuration of spring  226  (e.g., the spring force) and the difference in seal area between the solid contact seal  230  and seal  215 , while the lower threshold is related to the configuration of spring  226  and the annular seal area of the flow piston  210 . In the depicted embodiment, the difference in seal area between the solid contact seal  230  and seal  215  is about one square inch while the annular seal area of the flow piston  210  is about 14 square inches, thereby resulting in an upper threshold to lower threshold ratio of about 14. While the disclosed embodiments are of course not limited in this regard, it may be advantageous in certain applications to configure the downhole tool such that it has an upper threshold to lower threshold ratio in the range from about 5 to about 25. Ratios greater than about 5 tend to advantageously provide a wide differential pressure (or bore flow rate) window in which the flow switch  200  ( FIG. 3B ) remains open as indicated at  258  in  FIG. 4 . Moreover, these ratios tend to provide a strong hydraulic force to the flow piston  210  ensuring that it remains open during reaming operations at pressures above the lower threshold. Ratios less than about 25 enable the difference in seal area between the solid contact seal  230  and seal  215  to remain sufficiently large for actuation of the flow piston  210  from the closed position to the open position. 
     With reference again to  FIGS. 3A and 3B , the disclosed embodiments of pressure activated flow switch  200  are advantageously deployed external to the central flow bore  126 . No component of the flow switch  200  is deployed in the central flow bore  126 . In the depicted embodiments, the flow switch  200 , including the flow piston  210 , the compression spring  226 , the ring member  236 , and the seat member  232  are deployed in the annular region  220  between the tool body  110  and the lower mandrel  125 . The disclosed flow switch configuration thus advantageously preserves the cross sectional area of the flow bore thereby providing no obstruction (or diameter shrinkage) for drilling fluid flowing towards the drill bit. 
     While one or more embodiments of the pressure activated flow switch are described with respect to underreamer embodiments depicted on  FIGS. 2 and 3 , it will be under that the disclosure is not so limited. The disclosed pressure activated flow switch may be utilized to actuate substantially any downhole tool for which repeated hydraulic actuation and deactuation may be advantageous. Such tools may include, for example, hydraulically actuated stabilizers, expanding milling and pipe cutting tools, packers, impact tools, and the like. 
     Although one or more pressure activated flow switch embodiments and their advantageous deployment in downhole drilling tools have been disclosed, it should be understood to those of ordinary skill in the art that various changes, substitutions, and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.