Abstract:
A downhole tool for circulating fluid in a well bore. The tool includes an axial inlet and outlet with radial second outlets. A sleeve moves over the second outlets to control circulation of fluid. The sleeve can be selectively locked in an opened or closed configuration while the tool is in tension or compression. Variation of fluid pressure in the work string and stroking the tool move the sleeve between the operating positions. Cyclic operation of the tool is also described.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from PCT/GB2004/002806, having an international filing date of 30 Jun. 2004, and a priority date of 1 Jul. 2003. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
   Not Applicable 
   INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a downhole tool for circulating fluid in a well bore and in particular, though not exclusively, to a circulation tool which can be selectively locked in an opened or closed configuration while in tension or compression. 
   At various times during the drilling, completion and production of an oil or gas well, it may be necessary to circulate fluid within the well bore. This is typically done by running a tool on a workstring, the tool having a cylindrical body with radial ports, through which fluid from the bore of the workstring can pass. The procedure can provide a cleaning action and/or provide a transport system to carry debris and other materials from the well bore to the surface in the circulating fluid. 
   A known circulating tool is that disclosed in GB 2272923. This tool for circulating fluid in a well bore comprises a body member having a radial fluid outlet. An isolation sleeve is movably mounted on the body member for movement between an open position in which fluid may flow out of the outlet and a closed position. The isolation sleeve is moved to its open position against the action of spring by engaging a shoulder with the top of a liner and setting down on the tubing string. Alternatively, the outlet is opened when the lower end of the tubing string engages the bottom of the well bore. 
   This tool has a number of disadvantages. The tool can operate only by contacting a formation in the well bore e.g. a liner top or bottom of the well, and thus cannot be operated at any desired location in the well bore. In contacting a formation the tool is held in compression which limits other functions which can be performed from the work string when fluid is circulated through the tool. Further any spurious debris in the well bore, or indeed sudden pressure changes within the well bore can cause the tool to operate prematurely. 
   U.S. Pat. No. 6,152,228 provides a circulation tool which overcomes the problem of premature operation. The tool comprises a tubular assembly which has an axial through passage between a fluid inlet and first fluid outlet. The fluid inlet and the first fluid outlet are connected in a work string which is supported from the surface above the well bore. There is a second outlet which extends generally transversely of the assembly. An obturating member is moveable between a first position in which the second fluid outlet is closed and a second position which permits fluid flow through the second outlet. An engagement mechanism is moveable between an engaged configuration in which the obturating member is maintained in one of the first and second positions, and a disengaged configuration in which the obturating member is in the other of the first and second positions. The tubular assembly is coupled to a shoulder which is engageable with the formation in the well bore to engage or disengage the engagement mechanism. Setting down weight on the work string causes a formation of the well bore to exert a force on the shoulder which results in the second outlet being opened. 
   As the engagement mechanism allow the tool to be maintained in either the open or closed configuration, the tool cannot be prematurely set. However, the major disadvantage of this tool is that its use is limited to locations within the well bore where a formation exists so that the tool must be placed in compression to switch configuration. 
   It is an object of the present invention to provide a circulation tool which can be selectively opened and closed without the need to set down weight on the tool or contact a formation in the well bore. 
   It is a further object of at least one embodiment of the present invention to provide a circulation tool which can be locked in an open or closed configuration to operate the tool in tension or compression. 
   It is a still further object of at least one embodiment of the present invention to provide a method of operating a circulation tool by varying fluid pressure through the tool from pumps located above the tool. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention there is provided a tool for circulating fluid in a well bore, the tool comprising a tubular assembly having a through passage between an inlet and a first outlet, the inlet and first outlet being adapted for connection in a work string, a second outlet extending generally transversely of the tubular assembly of the tubular assembly; 
   an obturating member moveable between a first position closing the second outlet and a second position permitting fluid flow through the second outlet, the obturating member including restraining means to actively retain the obturating member independently in the first and the second positions; 
   an engagement mechanism actuable between an engaged configuration, in which the obturating member is locked in one of the first or second positions; and a disengaged configuration in which the obturating member can move to the other of the first and second positions; 
   a fluid pressure actuation surface coupled to the engagement mechanism and biased by a spring located between the tubular assembly and the engagement mechanism; 
   wherein variation of fluid pressure on the actuation surface controls actuation of the engagement mechanism and stroking the tool in the disengaged configuration moves the obturating member. 
   Preferably the obturating member comprises a sleeve axially slidable within the tubular assembly. Preferably the restraining means is a collet. The collet may be retainable in a plurality of recesses on the tubular assembly. 
   Preferably the fluid pressure actuation surface is located on an actuator sleeve axially slidable within the tubular assembly. More preferably a portion of the actuator sleeve can locate across the collet. 
   Preferably the engagement mechanism comprises mutually engageable formations on each of the actuator sleeve and the tubular assembly. More preferably the formations comprise a pin and a groove. Advantageously the groove is continuous so that the pin can travel in a continuous cycle around the groove. Preferably the groove comprises a plurality of apexes and bases such that the pin moves longitudinally to the tubular assembly. The distance of longitudinal travel will determine whether the engagement mechanism is in the locked or disengaged position. 
   Preferably also the second outlet comprises a plurality of ports in the tubular assembly which communicate with the inlet. Typically the ports may be distributed circumferentially around the outer surface of the tubular assembly. 
   Typically the cross-sectional area of the first outlet is greater than the cross-sectional area of the second outlet. 
   The ports may be designed to direct the fluid exiting the second outlet in an uphole or downhole direction into the well bore. 
   According to a second aspect of the present invention there is provided a method for circulating fluid in a well bore, the method comprises the steps:
     (a) inserting a work string into the well bore, the work string having a fluid inlet, a first fluid outlet and a second fluid outlet, an obturating member which is moveable between a first and second position to respectively close and open the second fluid outlet, and an engagement mechanism which when engaged locks the obturating member in one of the first or second positions;   (a) varying the fluid pressure through the work string to move the engagement mechanism between locked and unlocked configurations; and   (b) stroking the work string to move the obturating member between the first and second positions.   

   Preferably varying the fluid pressure through the work string is achieved by pumping fluid through the work string. 
   Preferably the method includes the step of running the work string in a closed and locked configuration with the pumps turned off. 
   Preferably the method includes the step of drilling with the work string in a closed and locked configuration and in compression while pumping fluid. 
   Preferably the method includes the step of back reaming with the work string in a closed and unlocked configuration and in tension while pumping fluid. 
   Preferably also the method includes the step of opening the second outlet with the work string in tension with the pumps off. 
   Preferably also the method includes the step of stroking the work string in a locked and open configuration while pumping fluid. 
   Preferably also the method includes the step of stroking the work string in a locked and open configuration with the pumps off. 
   Preferably the method includes operating the work string in a cyclic manner through the following configurations:
     (a) locked closed;   (b) unlocked closed;   (c) unlocked open;   (d) locked open;   (e) unlocked open; and   (f) unlocked closed.   

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described, by way of example only, with reference to the following drawings of which: 
       FIG. 1  is a part cross-sectional view of a tool for circulating fluid in a well bore according to an embodiment of the present invention; 
       FIG. 2  is a schematic view of the profile of the groove in the index sleeve of the tool of  FIG. 1 ; 
       FIG. 3  is a view through the section line A-A′ of  FIG. 1 ; and 
       FIG. 4  is a part view through the section line B-B′ of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference is initially made to  FIG. 1  of the drawings which illustrates a tool, generally indicated by reference numeral  10 , for circulating fluid in a well bore. Tool  10  has an upper end  12  comprising a top sub  14  being a cylindrical body and including a box section  16  for connecting the tool  10  to a work string or drill string. Located below the top sub  14  and connected thereto is a spring housing  18 . Spring housing  18  is a substantially cylindrical body whose inner surface  20  includes a shoulder  22  against which a spring  24  is located. A radial port  26  is arranged through the spring housing  18  through which an index pin  28  is located. Though only a single index pin  28  is shown, more than one index pin may be used. In the preferred embodiment two index pins  28  are arranged opposite each other. 
   Located below the spring housing  18  and connected thereto is a collet housing  30 . Collet housing  30  comprises a tubular body with an inner surface  32 . Arranged on inner surface  32  are two concentric recesses  34 , 36 . Arranged through the body are radial ports  38 . In the preferred embodiment there are four radial ports arranged equidistantly around the housing body. A further access port  40  is provided in the housing  30  through which a plug and grease nipple arrangement  42  is positioned. 
   Located below the collet housing and connected thereto is a hex drive  44 . Hex drive  44  comprises a cylindrical body having an inner surface  46  of which a portion  48  is hexagonal. At an upper end of the portion  48  is located a ledge  50 . The hex drive  44  is positioned over a bottom sub  52  which extends therefrom. Bottom sub  52  includes a pin section  54  at a lower end for connection into a work string or drill string. A shoulder  62  is located to engage the ledge  50 . The sub  52  also includes a hexagonal mating portion  56  to match the portion  48  on the hex drive  44 . This is shown with the aid of  FIG. 3  which demonstrates the hex profile matching between the hex drive  44  and the bottom sub  52 . In this way rotation of the hex drive  44  will be transmitted to the bottom sub  52 . 
   The top sub  14 , spring housing  18 , collet housing  30 , hex drive  44  and bottom sub  52  provide an outer surface  58  to the tool  10  while principally defining a central bore  60  through the tool for fluid communication with the work string. Rotation of the work string will be transmitted through the entire assembly regardless of whether fluid is being circulated out of the tool. 
   Arranged within the central bore  60  against the collet housing  30  is a collet assembly  64 . Assembly  64  is substantially cylindrical to allow the passage of fluid through the central bore  60 . The assembly includes, at its upper end eight sprung pins  66  which are biased in an outwardly radial direction. These pins  66  are shown in cross-section in  FIG. 4 , illustrating the bulbous heads which are sized to fit within recess  34  or recess  36  on the collet housing  30 . Assembly  64  includes radial ports  68  arranged equidistantly around and through the assembly  64 . Preferably there are four ports  68  to match the four ports  38  on the collet housing  30 . The collet assembly  64  is located against the housing  30  to provide a channel  70  around the ports  68 . The channel is sealed via a wear ring  72  and o-rings  74  located at each end of the channel  70 . The channel  70  allows the ports  68 ,  38  to be near alignment for fluid to flow from the central bore  60  to the outer surface  58  of the tool  10 . A further set of o-rings  76  are located between a lower end of the assembly  64  and the housing  30  such that, when the ports  68 ,  38  are sufficiently misaligned and the passage for fluid is blocked, the ports  38  on the housing  30  are sealed to prevent the ingress of fluid between the housing  30  and the assembly  64 . 
   Also located within the bore  60  is a collet support sleeve  78 . Sleeve  78  is sized to locate over the sprung pins  66  of the collet assembly  64  and hold them in place within recess  34  or recess  36  as desired. The sleeve  78  can also locate above the collet assembly  64  leaving the pins  66  free to move within the central bore  60  against the inner surface  32  of the collet housing  30 . An upper end  80  of sleeve  78  is connected to an actuator sleeve  82 . The connection includes a bearing ring. Thus sleeve  78  is moved by virtue of actuation of the actuator sleeve  82 . Actuator sleeve  82  has an inner surface  84  located against the central bore  60 . At an upper end  86  of the sleeve  82  is a conical surface  88 . Surface  88  is a fluid pressure actuated surface. At the base of the surface  88  is located a choke ring  90 . Surface  88  and choke ring  90  together ensure that variations in fluid pressure through the central bore  60  can cause movement of the actuator sleeve  82 . At the upper end  86  facing the inner surface  20  of the spring housing  18  is a shoulder  92 . Shoulder  92  is oppositely opposed to shoulder  22  of the spring housing  18 . Between the shoulders  22 , 92  is arranged the spring  24 . The shoulder  22  is fixed and thus movement of the actuator sleeve  82  downward is against the bias of the spring  24 . 
   Adjacent the spring  24 , between the actuator sleeve  84  and the spring housing  18  is located a cylinder sleeve  94 . O-rings  96  seal the cylinder sleeve  94  against the actuator sleeve  84  but they do not prevent relative movement occurring between the sleeves. Cylinder sleeve  94  is held in position by virtue of the index pin  28  located through the access port  26  on the spring housing  18 . Pin  28  locates through the cylinder sleeve  94  and into an index sleeve  98 . Index sleeve  98  is located in a recess  100  of the actuator sleeve  84  with bearing rings located at each end thereof. Thus movement of the actuator sleeve  84  can move the index sleeve  98  and likewise arrest of the index sleeve  98  can prevent movement of the actuator sleeve  84 . Additionally the index sleeve  98  can rotate without the rotating the actuator sleeve  84 . 
   On an inner surface  102  of the index sleeve  98  is located a groove or profile  104 . This is best seen with the aid of  FIG. 2  which shows the developed circumference of the index sleeve  98 . In the Figure shown there are two index pins  28  making an identical path through the profile  104 . The index pins  28  are shown located in a small apex  106 . Actuation on the sleeve  98  will cause the pins to move to a first base  108 . The bias on spring  24  will move the pins  28  to a high apex  110  providing the greatest longitudinal movement of the sleeve  98 . On return the pins will locate in a second base  112 . As will be appreciated the pins  28  can cycle continuously around the sleeve  98  and consequently the movement of the actuator sleeve  84  can be controlled. When the pins  28  are located in the small apex the actuator sleeve  84  is effectively locked in position. A longitudinal wall on the first base side prevents accidental movement into the high apex  110 , and movement in the opposite direction causes the pin  28  to fall into the second base  112 . 
   In use, the tool is inserted into a drill string and connected thereto by use of the box section  16  and the pin section  54 . We will describe the operation of the tool cycling from a closed and locked position to an identical position. It will be understood that the tool can be cycled from any starting position in the cycle and thus the tool run into a well bore in any configuration and pulled from the well bore in any configuration. 
   Additionally it will be appreciated that although the description has referred to terms such as upper, lower, above, below, these are all relative. The tool of the present invention finds equal application in non-vertical wells such as those that are inclined or horizontal. 
   The tool  10  is run on the drill string into the well bore in a locked closed configuration. In this configuration the index pins  28  are located in the small apex  106  of the profile  104  on the index sleeve  98 . This ‘locks’ the index sleeve  98  in position and with it the actuator sleeve  84  and the collet support sleeve  78 . Collet support sleeve  78  extends over the sprung pins  66  of the collet assembly  64  and thus holds the sprung pins  66  in the upper recess  34 . Radial ports  68  and  38  are thus misaligned and the tool is ‘closed’. Fluid low is only through the central bore  60 . 
   In order for drilling to take place from the end of the drill string, fluid is required to be pumped through the central bore. The drilling action compresses the drill string and thus the tool  10  is in compression. Fluid pressure on the pressure surface  88  causes movement of the actuator sleeve and with it the index sleeve  98 . Index pin  28  moves to the first base  108  and the compression prevents it from moving into the high apex  112 . Loading within the tool is on the shoulder  62 . This effectively is a downstroke. The tool remains locked and closed. On the upstroke, occurring when drilling stops and back reaming for instance starts, the drag forces created by the weight of tools on the string below tool  10  causes tool  10  to go into tension. The index pin  28  remains in the first base  108  and the tool is still in the locked and closed position. Loading, however, has shifted from shoulder  62  to the sprung pins  66  against the recess  34 . 
   Turning the pumps off to lower fluid pressure in the tool  10  and again stroking the tool, causes the collet support sleeve  78  to raise and clear the sprung pins  66  on the downstroke and move the sprung pins  66  to the lower recess  36  on the upstroke. The index pin  28  is now located in the high apex  110 . Movement of the sprung pins  66  to the lower recess  36  causes lowering of the collet assembly  64  within the tool  10 . Channel  70  now locates across the radial ports  38  and fluid can thus circulate from the bore  60  through the ports  68  and out of the tool  10  to the outer surface  58  via ports  38 . The tool  10  is ‘open’. 
   To ‘lock’ the tool ‘open’ the pumps are turned on and pumping is maintained at a sufficiently high rate to cause movement of the actuator sleeve  84  against the spring  24  by fluid pressure on the pressure surface  88 . The collet support sleeve  78  moves across the sprung pins  66  to hold them in the lower recess  36 . Index pin  28  is moved to the second base  112 . The ports will remain open in this configuration even if the tool  10  is moved up and down in a well bore or back and forth in an inclined well bore. Stroking the tool merely switches loading between the sprung pins  66  on the recess  36  and the top of the hex drive  44 . 
   When the pumps are turned off in this configuration the tool  10  will remain ‘open’ and ‘locked’ as the only movement occurring is the index pin  28  moving into the small apex  106 . 
   To reset, the tool  10  is placed in tension and picked-up on the upstroke. This releases the collet support sleeve  78  from the sprung pins  66  and allows them to move back to recess  34 . Switching on and off of the pumps with a downstroke will return the tool  10  to the ‘locked’ and ‘closed’ configuration. The cycle can be resumed from this point whenever fluid circulation from the tool  10  is required. Alternatively the tool can be pulled out of the well bore on the string. 
   The principal advantage of the present invention is that it provides a tool for circulating fluid in a well bore which can be operated without the need to land the tool on a formation. This allows the tool to be operated in inclined or horizontal well bores. This provides the further advantage that the tool can be operated on a drill string so that circulation can be used to sweep cuttings from the bit back to the surface of the well. Jetting fluid from the tool can also held clear blockages in the well bore. 
   A further advantage of the present invention is that it provides a tool which can be locked in the open or closed position whether the tool is placed in tension or compression. Additionally the hex drive allows other tools to be operated below the tool regardless of the configuration of the tool. 
   Further modifications may be made to the invention hereindescribed without departing from the scope thereof. For example, The actuator sleeve and the index sleeve could be a unitary piece. The collet assembly could comprise two sleeves, the first including the sprung pins and the second including the radial ports, with the first sleeve acting on the second to open the ports.