Patent Publication Number: US-9404326-B2

Title: Downhole tool for use in a drill string

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 61/623,786, filed Apr. 13, 2012, the full disclosure of which is hereby incorporated by reference herein for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to operations in a wellbore. More specifically, the invention relates to a system and method for mitigating hazards associated with use of a drill string. 
     2. Description of the Related Art 
     Hydrocarbon producing wellbores extend subsurface and intersect subterranean formations where hydrocarbons are trapped. The wellbores generally are created by drill bits that are on the end of a drill string, where a drive system above the opening to the wellbore rotates the drill string and bit. Cutting elements are usually provided on the drill bit that scrape the bottom of the wellbore as the bit is rotated and excavate material thereby deepening the wellbore. Drilling fluid is typically pumped down the drill string and directed from the drill bit into the wellbore. The drilling fluid flows back up the wellbore in an annulus between the drill string and walls of the wellbore. Cuttings produced while excavating are carried up the wellbore with the circulating drilling fluid. Drill strings are typically made up of tubular sections attached by engaging threads on ends of adjacent sections to form threaded connections. New tubular sections are attached to the upper end of the drill string as the wellbore deepens and receives more of the drill string therein. Drill string rotation is temporarily suspended each time a tubular section is added to the drill string. 
     To overcome dynamic losses in the drill string while drilling, sometimes high solids mud and or large amounts of loss circulation material (LCM) are pumped downhole. These solids can plug the drill string thus preventing fluid from flowing through the drill bit. If the well starts to produce while the drill string is plugged, flow cannot be circulated through the drill string to kill the well, thereby introducing the possibility of a blowout. Another undesirable situation resulting from a plugged drill string is that the drill string can become stuck against the wellbore wall. 
     SUMMARY OF THE INVENTION 
     Described herein is an example of a downhole device that selectively couples with a drill string, and which can mitigate hazards of a blockage in an annulus of the drill string. In an example embodiment disclosed is a downhole sub that is selectively coupled in series with a drill string, where the downhole sub includes a bypass sub having a housing with an outer surface, an annulus axially disposed in the housing, a relief valve assembly in a side wall of the housing that is selectively moveable from a closed position with the outer surface isolated from the annulus to an open position with the fluid communication between the annulus and outer surface, and a passage in the side wall of the housing having an end in communication with the annulus and a distal end in communication with the relief valve assembly. The relief valve assembly can include an annular space formed axially in the side wall of the housing, a sleeve axially moveable in an annular space formed axially in the side wall of the housing, an opening radially formed through a side wall of the sleeve, and a port formed radially through the housing that registers with the opening when the valve assembly is in the open position. In this example, the relief valve assembly can also include a poppet valve in the passage that is selectively moveable to an open position when pressure in the annulus exceeds a designated value. Further in this example is that the relief valve can include a piston head on an end of the sleeve that has a high pressure side in pressure communication with the passage, and a spring on a side of the piston distal from the high pressure side to bias the piston and sleeve into the closed position. In an alternate example, the annulus has diameter with a magnitude that remains substantially the same along a length of the annulus. The downhole sub may further include a disconnect sub having upper and lower members that are selectively coupled by a latch assembly. This example may also include a motion detector and a controller for actuating the latch assembly, and further optionally include a piston movable in a cylinder that is axially formed within the disconnect sub and having a low pressure side in communication with the latch assembly, a pressure vent in communication with fluid ambient to the sub system and having an end intersecting a high pressure end of the cylinder, a control valve for controlling flow through the pressure vent, and a controller for controlling operation of the control valve and that is in communication with the motion detector, so that when the motion detector detects a period of time that the sub system is motionless which exceeds a designated period of time, the controller directs the control valve to open, which pressurizes the cylinder and actuates the latch assembly. In an example of the downhole sub of claim  8 , the latch assembly is made up of a latch rod that selectively moves from within interfering contact between the upper and lower members into a one of the upper or lower members. In an alternative, the lower member has elongated clutch members that project axially into slots on the upper segment and wherein the latch rod extends from within a chamber in each of the clutch members and into a chamber in each of the slots when the upper and lower members are connected to one another, and where the latch rod is withdrawn from one of the chambers when the upper and lower members are separable. 
     Also disclosed herein is an alternative embodiment of a downhole sub for use in a borehole, where the downhole sub has an end connected with a length of a tubular and an opposite end connected with a length of a tubular to define a drill string, a bypass sub for selectively diverting fluid from within the drill string to the borehole, and a disconnect sub having upper and lower members that selectively decouple when the drill string remains motionless for more than a designated period of time. Optionally, a flow path is provided that projects axially through the bypass sub having a diameter that remains substantially the same along an axial length of the bypass sub. In an embodiment, a relief valve assembly is provided in a side wall of the bypass sub, so that when fluid in the bypass sub exceeds a designated value, the fluid in the bypass sub is selectively diverted from within the drill string to the borehole. The upper and lower members can be coupled by a coupling assembly that includes castellated elements on both the upper and lower members that insert into slots formed between the castellated elements. In this example, the coupling assembly further has chambers formed laterally in the castellated elements, and a latch rod that selectively moves within chambers in the castellated elements, wherein the latch rod is hydraulically actuated. In one example embodiment, fluid in the borehole provides a pressure source for operating the bypass sub and the disconnect sub. 
     Another example embodiment of a downhole sub is disclosed that selectively couples in series with a drill string. In this example the downhole sub is made up of a bypass sub having a housing with an outer surface, an annulus axially disposed in the housing, a relief valve assembly in a side wall of the housing that is selectively moveable from a closed position with the outer surface isolated from the annulus to an open position with the fluid communication between the annulus and outer surface, a disconnect sub having upper and lower members selectively coupled by a latch assembly, an actuation system in communication with the latch assembly and in communication with fluid ambient to the downhole sub, a motion detector, and a controller in communication with the motion detector and the actuation system, so that when the motion detector senses a designated period of motionless, a signal is sent to the controller to decouple the upper and lower members. In this embodiment, a bit can be mounted on a lower terminal end of the drill string, and a downhole tool is between the downhole sub and the bit. In an alternative, a downhole tool is mounted in a portion of the drill string between the downhole sub and an opening of a wellbore in which the drill string is inserted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features, aspects and advantages of the invention, as well as others that will become apparent, are attained and can be understood in detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings that form a part of this specification. It is to be noted, however, that the appended drawings illustrate only preferred embodiments of the invention and are, therefore, not to be considered limiting of the invention&#39;s scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a side view of an example embodiment of a downhole tool for use in a drill string in accordance with the present invention. 
         FIG. 2A  is a side sectional view of an example of a circulation sub in the downhole tool of  FIG. 1  in a closed position and in accordance with the present invention. 
         FIG. 2B  is a side sectional view of an example of a circulation sub in the downhole tool of  FIG. 1  in an open position and in accordance with the present invention. 
         FIG. 3A  is an axial sectional view of the circulation sub of  FIG. 2A  taken along lines  3 A- 3 A and in accordance with the present invention. 
         FIG. 3B  is an axial sectional view of the circulation sub of  FIG. 2B  taken along lines  3 B- 3 B and in accordance with the present invention. 
         FIG. 4A  is an axial sectional view of the circulation sub of  FIG. 2A  taken along lines  4 A- 4 A and in accordance with the present invention. 
         FIG. 4B  is an alternate embodiment of the circulation sub of  FIG. 4A  in accordance with the present invention. 
         FIG. 5A  is an axial sectional view of the circulation sub of  FIG. 2A  taken along lines  5 A- 5 A and in accordance with the present invention. 
         FIG. 5B  is an axial sectional view of the circulation sub of  FIG. 2A  taken along lines  5 B- 5 B and in accordance with the present invention. 
         FIG. 6A  is a side sectional view of an example of a disconnect sub in the downhole tool of  FIG. 1  in a latched configuration and in accordance with the present invention. 
         FIG. 6B  is a side sectional view of an example of the disconnect sub of  FIG. 6A  changing from a latched configuration to an unlatched configuration and in accordance with the present invention. 
         FIG. 6C  is a side sectional view of an example of the disconnect sub of  FIG. 6A  in an unlatched configuration and in accordance with the present invention. 
         FIG. 7A  is an axial sectional view of the circulation sub of  FIG. 6A  taken along lines  7 A- 7 A and in accordance with the present invention. 
         FIG. 7B  is an axial sectional view of the circulation sub of  FIG. 6A  taken along lines  7 B- 7 B and in accordance with the present invention. 
         FIG. 7C  is an axial sectional view of the circulation sub of  FIG. 6A  taken along lines  7 C- 7 C and in accordance with the present invention. 
         FIG. 8  is an axial sectional view of the circulation sub of  FIG. 6A  taken along lines  8 - 8  and in accordance with the present invention. 
         FIG. 9A  is a side sectional view of the circulation sub of  FIG. 6A  taken along lines  9 A- 9 A and in accordance with the present invention. 
         FIG. 9B  is a side sectional view of the circulation sub of  FIG. 6B  taken along lines  9 B- 9 B and in accordance with the present invention. 
         FIG. 9C  is a side sectional view of the circulation sub of  FIG. 6C  taken along lines  9 C- 9 C and in accordance with the present invention. 
         FIG. 10  is a side partial sectional view of a drill string recirculating fluid through an embodiment of a downhole sub in accordance with the present invention. 
         FIG. 11  is a side partial sectional view of a drill string having a downhole sub with a disconnecting portion in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Shown in  FIG. 1  is a side view of an elongated downhole tool  10  for use in a wellbore and for mitigating hazards that may occur during drilling. In one example embodiment, the downhole tool  10  is integrally included within a drill string  11 . Included with the downhole tool  10  of  FIG. 1  is a disconnect sub  12  shown having an upper member  14  and lower member  16 , where upper member  14  selectively connects and disconnects from lower member  16 . In the example of  FIG. 1 , the upper and lower members  14 ,  16  are generally annular and having a substantially circular outer surface. Clutch members  18  are provided on an upper end of the lower member  16  and are shown projecting into slots  20  formed on a lower end of the upper member  14 . The clutch members  18  and slots  20  respectively circumscribe the lower member  16  and upper member  14 . As the clutch members  18  and slots  20  are within the outer surface of the tool  10 , they are illustrated by a dashed line. The rectangular outer periphery of the clutch members  18  and slots  20  create a castellated profile along their interface. The downhole tool  10  also includes a bypass sub  22  shown above the disconnect sub  12 . In the example of  FIG. 1 , the bypass sub  22  has a substantially circular outer periphery. Ports  24  extend through the side wall of the bypass sub  22  along a path that circumscribes its outer surface at an axial location. 
       FIGS. 2A and 2B  illustrate in side sectional view examples of the bypass sub  22  respectively in a closed and open position. In the closed position depicted in  FIG. 2A , the bypass sub  22  is shown having a sidewall  26 , where a bore  28  extends radially through the sidewall  26 . A spring valve  30  is set within the bore  28 , and a plug  32  inserted in the bore  28  on an outer surface of the sidewall  26  retains the spring valve  30  within bore  28 . Embodiments of the spring valve  30  include stacked Belleville washers/springs and a coil spring with a piston like disk on the end facing inlet  34  that seals against the walls of the bore  28 . Proximate an inner radius of the sidewall  26 , the diameter of the bore  28  is reduced and defines an inlet  34  to the bore  28  from an annulus  36  shown extending axially through the bypass sub  22 . An axial passage  38  is formed axially in the sidewall  26  and has an end that intersects the bore. Distal from the bore  28 , the passage  38  projects radially redirected radially outward and intersects with an annular chamber  40  formed in the sidewall  26 . The annular chamber  40  has an elongate side disposed substantially parallel with an axis A X  of the bypass sub  22  and extends downward past a lower end of passage  38  and axially upward towards bore  28 . A transition  42  in the chamber  40  defines a change in its radial diameter. Above the transition  42  a radius of the chamber  40  is greater than the radius of the chamber  40  below transition  42 . For the purposes of discussion herein, the spring valve  30  can be referred to as a poppet valve for selectively allowing flow from the annulus  36  to the passage  38 . 
     An annular sleeve  44  is shown disposed within the chamber  40  and having a portion extending below and above transition  42 . Mounted on an upper end of the example of the sleeve  44  of  FIG. 2A  is a piston head  46  whose radial thickness substantially matches the radial thickness of the chamber  40  above transition  42 . In one example, the piston head  46  sealingly contacts the walls of the annular chamber  40  to form a pressure barrier in the chamber  40  along the region of contact. A spring  48  is shown set within the annular chamber  40  on an upper axial surface of the piston head  46  for downwardly biasing piston head  46  and sleeve  44 . In the example of  FIG. 2A , a shear pin  50  extends radially outward from the sleeve  44  and through a radial bore in the sidewall  26 , thereby retaining sleeve  44  in the position of  FIG. 2A . Below the transition  42 , a port  24  extends radially through the sidewall  26  from the annulus  36  and to an outer circumference of the bypass sub  22 . Further illustrated in  FIG. 2A  is an opening  54  formed radially through the sleeve  44 , but at an axially location offset from port  24 . Thus in the example of  FIG. 2A , a solid portion of the sleeve  44  intersects the port  24  and blocks flow from the annulus  36  into the outer surface of the bypass sub  22 . 
     Referring now to  FIG. 2B , a plug  56  is schematically represented in the annulus  36  past a terminal end of the chamber  40  distal from the bore  28 . The plug  56  is to block flow axially through the annulus  36 ; as described above, the plug  56  may introduce a hazard if flow through the drill string  11  ( FIG. 1 ) is not allowed to circulate back to surface. In this example, the presence of the plug  56  increases fluid pressure in the annulus  36 , that communicates through inlet  34  to spring valve  30 . Above a threshold value, the pressure in the annulus  36  compresses spring valve  30  radially outward and away from inlet  34 . Continued application of pressure to the spring valve  30  further compresses it so its radial inward end is urged outward past the passage  38 ; which allows fluid  58  from annulus  36  to flow through the passage  38  and into the annular chamber  40 . Introducing the pressurized fluid  58  into the chamber  40  exerts an upward force on the sleeve  44  as the fluid  58  contacts a lower facing surface of the piston head  46 . With sufficient force on the piston head  46 , the biasing force of the spring  48  is overcome so that the spring  48  is compressed as the sleeve  44  is moved upward. Ultimately, the opening  54  in sleeve  44  registers with port  24  thereby providing a fluid flow path from annulus  36  to outside of the bypass sub  22 . As such, fluid flowing downward through drill string  11  ( FIG. 1 ) from surface can be bypassed from the drill string  11 , to an outer annulus between the drill string  11 . Optionally, fluid flow can be between downhole tool  10  ( FIG. 1 ) and wellbore wall (not shown), and back to surface. Further shown in the example of  FIG. 2B  is that the shear pin  50 A has been sheared after the upward force supplied to the piston head  46  overcomes the shear strength within the shear pin  50 . As the sleeve  44  in piston head  46  moves upward within the annular chamber  40 , any fluid in the chamber  40  above piston head  46  can escape from the bypass sub  22  from pressure vents  60  that extend radially outward through the side wall  26  from the annular chamber  40  and intersect with an outer surface of the bypass sub  22 . For the purposes of discussion herein, one or more of the sleeve  44 , piston head  46 , spring  48 , and poppet valve can be referred to as a relief valve assembly. 
       FIGS. 3A and 3B  are axial sectional views of the bypass sub  22  respectively taken along lines  3 A- 3 A of  FIG. 2A and 3B-3B  of  FIG. 2B . More specifically, as shown in  FIG. 3A , the solid portion of the sleeve  44  is intersecting the ports  24  thereby blocking any fluid flow from annulus  36  to outside of the bypass sub  22 . In  FIG. 3B , the sleeve  44  has moved axially in response to fluid  58  impinging on the piston head  46  ( FIG. 2B ) so that openings  54  register with ports  24 ; which allows flow in annulus  36  to escape outside of the bypass sub  22 . In the embodiment of  FIGS. 3A and 3B  ports  24  and openings  54  are shown strategically oriented at selected angular positions around the circumference of the sleeve  44  and the sidewall  26 . Moreover, while the example of  FIGS. 3A and 3B  depicts four ports  24  and openings  54 , embodiments exist having a fewer or greater number of ports  24  and openings  54 . 
       FIG. 4A  illustrates one example in an axial sectional view of the bypass sub  22  and taken along lines  4 A- 4 A of  FIG. 2A . In this example, two shear pins  50  intersect the sleeve  44  and sidewall  26  to retain sleeve in its position of  FIG. 2A . Optionally, as shown in  FIG. 4B , up to four shear pins  50  are utilized for retaining the sleeve  44  in place.  FIG. 5A  is an axial sectional view of the bypass sub  22  taken along lines  5 A- 5 A, wherein the spring  48  is shown set in the annular chamber  40  within sidewall  26 .  FIG. 5B  illustrates an axial sectional view of the bypass sub  22  taken along lines  5 B- 5 B, wherein the spring valves  30  are in bores  28  and each has an inner radial portion facing the inlet  34  and blocking flow from annulus  36  and into passage  38  ( FIG. 2A ). Plugs  32  on the outer radial end of the spring valves  30  retain the spring valves  30  in the bores  28 . 
       FIG. 6A  is a side sectional view of a portion of the disconnect sub  12  with its upper and lower members  14 ,  16  in a connected configuration. Further in the example of  FIG. 6A , a housing  61  covers the upper and lower members  14 ,  16 . Radially inward from the housing  61  the upper sub  14  is made up of an elongated body  62  having a generally cylindrical outer surface, and an bore  63  formed along its axis A X . In an example, the bore  63  has a generally circular cross section. A skirt member  64  depends axially from a lower end of the body  62 , and whose radial cross section is thinner than that of the body  62 . In the illustrated embodiment, the outer radius of the skirt  64  is less than the outer radius less of the body  62 , thereby defining an inner radial surface of the slot  20  where the skirt  64  is set radially inward from clutch member  18 . The skirt  64  is generally annular and has a rectangular cross section as shown. Depending axially from the skirt  64  is a wedge portion  66  that as shown, is a generally annular portion having a wedge shaped cross section with inner and outer radial sides that angle towards one another and form a point at an end of wedge portion  66  distal from the skirt  64 . The upper end of the wedge section  66 , which is proximate the skirt  64 , has an outer radius substantially similar to an outer radius of the skirt section  64 , but has an inner radius set radially outward from an inner radius of skirt section  64 . Wedge section  66  inserts within a correspondingly shaped chamber  67  formed in the body of the lower member  16  and with an open end facing towards skirt  64 . 
     Still referring to  FIG. 6A , an inlet line  68  is shown passing radially inward through the housing  61  and into the body  62 . Within the body  62 , the inlet line  68  courses into an axial direction and terminates at, and into communication with, an upper end of a cylinder  70 . The cylinder  70  is formed within the body  62  of  FIG. 6A  and has an elongate side shown extending generally parallel with an axis A X  of the downhole tool  10 . In one example the cylinder  70  can be a single cylindrically shaped cylinder formed through the body  62 . Optionally, the cylinder  70  can be an annular space in the body  62 , or a number of separate and distinct cylinders  72  formed in the body  62  at circumferential locations within the body  62 . A selectively open and closed valve  72  is shown set within inlet line  68  for controlling flow through inlet line  68 . In the example of  FIG. 6A , a controller  74  is provided within body  62  that provides a means for controlling the selective opening and closing of valve  72 . In the embodiment of  FIG. 6A , the controller  74  is coupled with a motion detector  76  that may detect motion of the downhole tool  10  and generate signals sent to a processor (not shown) within the controller  74 . Depending on an amount of time detected in the controller  74  between successive episodes of movement, a signal may be delivered to the valve  72  via control line  77  for selectively opening and closing valve  72 . In one example of operation, the motion detector  76  collects tool motion data about every 30 minutes. Examples of time periods where no motion is detected that would trigger the controller  74  to open the valve  72  include 8, 10, 12, or more hours. 
     When the valve  72  is in an open position, fluid ambient in a wellbore may flow through inlet line  68  and into an upper end of cylinder  70 . A piston  78  is within cylinder  70 , and depending on the flow of fluid into the cylinder  70 , the piston  78  can be moved axially within the cylinder  70  in a direction away from inlet line  68 . Fluid resident in cylinder  70  and below piston  78  can be urged from the cylinder  70  by movement of piston  78 . The fluid urged out of the cylinder  70  flows into an outlet line  80  shown connected to an end of the cylinder  70  distal from where inlet line  68  connects to cylinder  70 . As will be described in more detail below, urging fluid at a designated pressure through the outline line  80  actuates a latch rod  82  that couples clutch member within slot  20 . In the example of  FIG. 6A , the slot  20  defines an area within body  62  profiled at a radius set within housing  61  and along an axial distance to define an opening that receives the clutch member  18  therein. 
     Referring now to  FIG. 6B , in this example embodiment the motion detector  76  has sensed no motion of the downhole tool  10  and generated and sent signals to the controller  78  representing the motionless downhole tool  10 . After receiving a successive string of “motionless” signals from the motion detector  76  indicating the downhole tool  10  has remained stationary for at least a designated time period; the controller  78  generates a signal and sends the signal through the control line  77  to open valve  72 . Opening the valve  72  allows fluid in the wellbore to flow into cylinder  70  and urge piston  78  away from inlet line  68 .  FIG. 6C  illustrates how the upper and lower members  14 ,  16  of the disconnect sub  12  of  FIG. 6B  can be decoupled from one another by manipulating the position of the latch rod  82 . 
     A detailed example of an interface between the clutch member  18  and slot  20  is shown in a side sectional view in  FIG. 9A . In the example embodiment of  FIG. 9A , the upper and lower members  14 ,  16  are illustrated coupled together by the latch rod  82 . Chamber  86  is shown in the body  16  of upper member  14  that registers with a chamber  88  in the clutch member  18 ; where the latch rod  82  projects laterally into both chambers  86 ,  88 . The presence of the latch rod  82  in the chambers  86 ,  88  retains the clutch member  18  in the slot  20 , thereby coupling the upper and lower members  14 ,  16 . Further illustrated in  FIG. 9A  is that the outlet line  80  terminates at an interface between the lower end of slot  20  and upper end of clutch member  18  and registers with a manifold port  89  shown formed within the clutch member  18 . The manifold port  89  extends axially through a portion of the clutch member  18 , splits into two laterally directed branches that intersect with ends of the chambers  88  formed laterally through the clutch member  18 . Springs  90  are shown set within chamber  86  for biasing the latch rod  82  in a position within both chamber  86  and chamber  88  for coupling upper and lower members  14 ,  16 . 
       FIG. 9B , taken along line  9 B- 9 B of  FIG. 6B , illustrates a side sectional view of the example of  FIG. 9A  where fluid  92  being forced from cylinder  70  by piston  78  ( FIG. 6B ) flows through outlet line  80 , into manifold port  89 , and urges the latch rods  82  laterally outward from within chambers  88  solely into chambers  86 , and compressing springs  90 . Realigning the latch rod  82  so it no longer extends into both chambers  86 ,  88  decouples the clutch member  18  and slot  20 . Thus, as shown in  FIG. 9C , the upper and lower members  14 ,  16  can be separated from one another as the clutch member  18  is allowed to pull axially from within slot  20 .  FIG. 9C , taken along lines  9 C- 9 C of  FIG. 6C , illustrates an embodiment where a portion of the latch rod  82  defines a sealing piston  94  that shears from the latch rod  82  and remains in chamber  88 . Decoupling the upper and lower members  14 , 16  so that the clutch member  18  pulls out from slot  20  allows springs to bias latch rod  82  into the space in the slot  20  formerly occupied by clutch member  18 . In an example, one or more of the latch rods  82 , springs  90 , outlet line  80 , and chambers  86 ,  88  can be collectively referred to as a latch assembly. 
       FIGS. 7A through 7C  are axial sectional views of the downhole tool  10  of  FIG. 6A  taken respectively along lines  7 A- 7 A,  7 B- 7 B, and  7 C- 7 C. As shown, in  FIG. 7A , the wedge section  66  is within chamber  67  formed through the body of the lower member  16 .  FIG. 7B  illustrates how the inner diameter of the skirt  64  interfaces within outer circumference of annulus  84 . In  FIG. 7C  an axial view illustrates how a portion of the clutch member  18  inserts within the slots  20  that extend axially through the body  62  of the upper member  14 . In the example of  FIG. 7C , the lateral and inward facing surfaces of the clutch members  18  are substantially linear, whereas the radially outward facing surfaces of each clutch member  18  are curved and extend substantially to the outer radial thickness of the body  62 . Referring now to  FIG. 8 , an axial view of the disconnect sub  12  is shown and taken along line  8 - 8  wherein the cylinders  70  are shown spaced angularly apart at locations within the body  62  of the upper member  14 . In the example of  FIG. 8  also the outer periphery of the cylinder  70  is shown having a substantially rectangular shape. Optionally, the cylinder  70  can have a circular or other curved shape. 
       FIG. 10  is a partial side sectional view illustrating that the downhole tool  22  and drill string  11  are part of a drilling system  96  for forming a wellbore  98  through a subterranean formation  100 . The drilling system  96  further includes a bit  102  on a lower end of the string  11  for excavating the wellbore  98 . A drive assembly  104  is shown on surface  106  for rotating the string  11 . A fluid supply system  108  provides pressurized fluid to the drill string  11  that exits the bit  102  and flows back to surface  106  in the annular space between the walls of the wellbore  98  and outer surface of the drill string  11 . In one example of operation, the fluid supply system  108  delivers pressurized fluid  58  into the drill string  11 ; where the pressurized fluid  58  is shown exiting from ports  24  on the bypass sub  22 . In the illustrated example a blockage in the string  11  downstream of the bypass sub  22  increases pressure within the annulus  36  ( FIGS. 2A and 2B ) to above a threshold value that moves the sleeve  44  into its position of  FIG. 2B  thereby providing communication between the annulus  36  and wellbore  98 ; which allows the pressurized fluid  58  to exit the ports  24 . Still referring to  FIG. 2B , it should be pointed out that when pressure in the annulus  36  drops below the designated set pressure for actuating the sleeve  44 , potential energy stored in the springs  48  can bias the piston head  46  and sleeve  44  back to their position of  FIG. 2A . In the configuration of  FIG. 2A , the fluid  58  is blocked from exiting ports  24  and instead resumes its flow through the drill string  11  where it can be directed out from the bit  102 . Referring back to  FIG. 10 , a downhole tool  110  is shown included with the drill string  11  in a space between the disconnect sub  12  and drill bit  102 . Examples of the downhole tool  110  can include imaging tools for use in logging while drilling (LWD), such as a nuclear source density tool, gamma ray tools, resistivity tools, and the like. An advantage of the bypass sub  22  is that recirculation of the pressurized fluid  58  is activated by a value of the pressure of the pressurized fluid  58 , rather than introducing a pressure drop in the flow of the fluid  58 . Activating the bypass sub  22  on pressure rather than flow rate provides for continued fluid circulation into the wellbore  98  which maintains hydrostatic pressure at the bottom of the wellbore  98  and prevents an underbalanced condition. Moreover, known systems that induce a pressure drop in the string to activate a bypass flow can reduce operability of the drilling system as a whole. 
       FIG. 11  provides a side partial sectional view of an example of the upper and lower members  14 ,  16  of the disconnect sub  12  being separated after being decoupled from one another. In the example of  FIG. 11 , upper and lower members  14 ,  16  are separated by pulling the string  11  upward from the wellbore  98 . One manner of decoupling upper and lower members  14 ,  16  is described above and depicted in the examples of  FIGS. 6A-6C and 9A-9C . In the example of  FIG. 11 , the downhole tool  110  is above the disconnect sub  12  and can be retrieved along with the portion of the string  11  being removed from the wellbore  98 . Thus the option exists to position the downhole tool  110  above or below the disconnect sub  12 , without affecting operation of the disconnect sub  12 . An advantage of multiple positioning of the downhole tool  110  is that imaging results may dictate positioning, or that a desire may exist to not leave the downhole tool  110  in the wellbore  98  when removing an unstuck portion of the drill string  11 , but instead to bring the downhole tool  110  to surface  106  for data analysis, repair, inspection, or other operational purposes. 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.