Abstract:
Some embodiments of the present invention generally provide an apparatus that may be used in a coiled tubing drillstring and that can switch between effectively straight drilling and curved drilling without halting drilling. Methods for steering a coiled tubing drillstring are also provided. In one embodiment, an apparatus for use in drilling a wellbore is provided. The apparatus includes a mud motor; a housing; an output shaft; and a clutch actuatable between two positions. The clutch is configured to rotationally couple the mud motor to the output shaft when the clutch is in a first position as a result of fluid being injected through the clutch at a first flow rate, and rotationally couple the output shaft to the housing when the clutch is in a second position as a result of fluid being injected through the clutch at a second flow rate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of U.S. Provisional Patent Application No. 60/680,731, filed May 13, 2005, which is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention generally relate to directional drilling in a wellbore. 
   2. Description of the Related Art 
   Conventional directional drilling with jointed pipe is accomplished through use of a Bottom Hole Assembly (BHA) consisting of a bent housing directional drilling motor and directional Measurement While Drilling (MWD) tool in the following fashion. 
   To drill a curved wellbore section, the drillstring is held rotationally fixed at the surface and the drilling motor will drill a curved wellbore in the direction of the bend in its outer housing. This is termed “slide” drilling because the entire drillstring slides along the wellbore as drilling progresses. The wellbore trajectory is controlled by orienting the BHA in the desired direction by rotating the drillstring the appropriate amount at the surface. 
   To drill a straight wellbore section, the drillstring is rotated at the surface with the rotary table or top-drive mechanism at some nominal rate, typically 60 to 90 rpm. This is termed “rotating” drilling. In so doing, the tendency of the bent housing motor to drill in a particular direction is overridden by the superimposed drillstring rotation causing the drilling assembly to effectively drill straight ahead. 
   When drilling with coiled tubing neither “rotating” drilling nor rotational orientation of the BHA can be accomplished without the addition to the BHA of a special rotating device to orient the BHA since coiled tubing cannot be rotated at the surface in the wellbore. One such rotational device, or orienter, operates by rotating in even angular increments, for example 30°, each time the surface pumps are stopped and then re-started. After each pump cycle, the orienter locks into and maintains its rotational position. This “ratcheting” device allows the directional driller to position the directional assembly closely enough to the desired toolface orientation to allow the wellbore to be drilled in a particular direction. 
   One significant drawback to directional drilling with the ratcheting orienter described above is the fact that drilling must be stopped each time the orienter is actuated. For example, if a rotational change of 210° is needed, drilling is stopped, the BHA is lifted off-bottom, and the pumps must be cycled 7 times to rotate the BHA by the required amount. This non-productive time is significant and has an adverse affect on the average drilling rate. In the case in many Canadian wells, an entire well is drilled in a matter of 6 to 8 hours. The time spent orienting can become a significant portion of the total drilling time. 
   A second drawback to directional drilling with the ratcheting orienter relates to its inability to drill an effective straight wellbore section. As described above, in conventional directional drilling, continuous drillstring rotation is used to wash-out the directional tendency of a bent-housing motor. This produces a very straight trajectory. When drilling with coiled tubing and a ratcheting orienter, continuous rotation is not possible. Thus the driller is forced to orient slightly left of the desired path and drill some distance ahead. Then after stopping to re-orient right of the desired path, the driller drills ahead again. This process is repeated until the “straight” section is completed. The resulting left-right-left or “wig-wag” wellbore trajectory roughly approximates the desired straight path. 
   Therefore, there exists a need in the art for an orienter that may be used in a coiled tubing drillstring and that can switch between effectively straight drilling and curved drilling without halting drilling. 
   SUMMARY OF THE INVENTION 
   Some embodiments of the present invention generally provide an apparatus that may be used in a coiled tubing drillstring and that can switch between effectively straight drilling and curved drilling without halting drilling. Methods for steering a coiled tubing drillstring are also provided. 
   In one embodiment, an apparatus for use in drilling a wellbore is provided. The apparatus includes a mud motor; a housing; an output shaft; and a clutch. The clutch is operable to rotationally couple the output shaft to the housing when the clutch is in a first position, rotationally couple the motor to the output shaft when the clutch is in a second position, and actuate from one of the positions to the other of the positions as a result of fluid being injected through the clutch at a flow rate which is greater than or equal to a predetermined threshold flow rate. 
   In another embodiment, an apparatus for use in drilling a wellbore is provided. The apparatus includes a housing having a splined portion for mating with a second splined portion of a locking sleeve; an input shaft having a splined portion for mating with a first splined portion of the locking sleeve; the locking sleeve having a flow bore therethrough, and a third splined portion rotationally coupling the locking sleeve to a splined portion of an output shaft. The locking sleeve is actuatable between a first axial position and a second axial position by choking of fluid through the flow bore. The locking sleeve mates with the splined portion of the housing in the first axial position and the splined portion of the input shaft in the second axial position. The apparatus further includes the output shaft; and a spring disposed between the output shaft and the locking sleeve, the spring biasing the locking sleeve towards one of the axial positions. 
   In another embodiment, a method for drilling a wellbore is provided. The method includes drilling in a first direction while injecting fluid through a drilistring at a first flow rate; and changing the flow rate to a second flow rate, wherein an orienter changes the direction of drilling to a second direction, and drilling remains continuous while changing the flow rate. In one aspect, the first direction is a substantially straight direction and the second direction is a curved direction. In another aspect, the first direction is a curved direction and the second direction is a substantially straight direction. 
   In another embodiment, a method for drilling a wellbore is provided. The method includes providing a drillstring. The drillstring includes a run-in string and an orienter. The orienter includes a motor; a housing coupled to the run-in string; an output shaft; and a clutch, the clutch operable to rotationally couple the output shaft to the housing when the clutch is in a first position, rotationally couple the motor to the output shaft when the clutch is in a second position, and actuate from one of the positions to the other of the positions as a result of fluid being injected through the clutch at a flow rate which is greater than or equal to a predetermined threshold flow rate. The drill string further includes a bent sub rotationally coupled to the output shaft; and a drill bit coupled to the bent sub. The method further includes drilling in a first curved direction, due to the bent sub being at a first orientation, while injecting fluid through the drillstring at a first flow rate; injecting the fluid through the drillstring at a second flow rate, wherein the orienter will rotate the bent sub from the first orientation to a second orientation; and drilling in a second curved direction due to the bent sub being at the second orientation, while injecting fluid through the drillstring at the first flow rate. 
   In another embodiment, a method for forming a window in a wellbore is provided. The method includes assembling a drillstring. The drillstring includes a run-in string and an orienter. The orienter includes a motor; a housing coupled to the run-in string; an output shaft; and a clutch, the clutch operable to rotationally couple the output shaft to the housing when the clutch is in a first position, rotationally couple the motor to the output shaft when the clutch is in a second position, and actuate from one of the positions to the other of the positions as a result of fluid being injected through the clutch at a flow rate which is greater than or equal to a predetermined threshold flow rate. The drillstring further includes a cutting tool rotationally coupled to the output shaft; a whipstock; and an anchor coupled to the whipstock. The method further includes orienting the whipstock while the clutch is in the first position; and setting the anchor while the clutch is in the first position; actuating the clutch to the second position, wherein the motor rotates the cutting tool; and forming the window. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1  is a diagram of a coiled tubing Bottom Hole Assembly (BHA), according to one embodiment of the present invention. 
       FIG. 2  is a more detailed schematic of the orienter of  FIG. 1 . 
       FIGS. 3A and 3B  are sectional views of the clutch of  FIG. 2  in an engaged and disengaged position, respectively. 
       FIG. 4A  is a sectional view of a drillstring run into a wellbore, according to another embodiment of the present invention.  FIG. 4B  is a sectional view of the drillstring of  FIG. 4A  with an anchor set in position.  FIG. 4C  is a sectional view of the drillstring of  FIG. 4A  with a mill cutting an window through the casing. 
       FIG. 5  is a sectional view of the orienter of  FIGS. 4A-4C . 
   

   DETAILED DESCRIPTION 
   The term “coupled” as used herein includes at least two components directly coupled together or indirectly coupled together with intervening components coupled therebetween. 
     FIG. 1  is a diagram of a coiled tubing Bottom Hole Assembly (BHA)  100 , according to one embodiment of the present invention. The coiled tubing BHA  100  includes: a drill bit  5 , a bent-housing drilling motor  10 , Measurement While Drilling (MWD) module  15 , orienter  200 , and connector  25 . As discussed above, bent-housing drilling motor  10  will cause drilling in a curved direction provided that the drillstring is rotationally fixed. Alternatively, a bent sub and a straight-housing motor could be used instead of the bent-housing motor  10 . The bent-housing motor  10  is a mud motor, which harnesses energy from drilling fluid by channeling it between a profiled rotor and stator, thereby imparting the energy into rotational motion of the rotor. The drill bit  5  is coupled to the rotor of the motor  10 . 
   MWD module  15  may incorporate, for example, magnetometers and accelerometers to measure and transmit to the surface data indicative of borehole inclination and direction. The connector  25  couples the BHA  100  to a string of coiled tubing  30 . The connector  25  is also coupled to the orienter  200 . Discussed in more detail below, the orienter  200  contains a device which converts fluid energy into rotational energy, such as a mud motor, which is selectively rotationally coupled to the MWD module  15 , the bent-housing drilling motor  10 , and the drill bit  5 . When rotationally coupled, the orienter  200  effects drilling in an overall straight direction (analogous to a corkscrew) and, when not, allows drilling in a curved direction. 
     FIG. 2  is a more detailed schematic of the orienter  200  of  FIG. 1 . The orienter  200  includes a housing  270 . Disposed in the housing  270  is stator  265 . The stator  265  corresponds with a rotor  260 . The rotor  260  and stator  265  transform fluid energy into mechanical energy, resulting in the rotation of the rotor. The rotor  260  is rotationally coupled through a transmission  255  and a speed reducer  250  to an input shaft  320  (see  FIG. 3 ) of a clutch  300 . The clutch  300  selectively rotationally couples the input shaft  320  to an output shaft  235 . The output shaft  235  is supported for rotation relative to the housing  270  by two sets  240   a,b  of bearings 
     FIGS. 3A and 3B  are sectional views of the clutch  300  of  FIG. 2  in an engaged and disengaged position, respectively. The clutch  300  has an axial flow bore therethrough. The clutch includes the input shaft  320  which has radial fluid channels therethrough (two shown). Flow of fluid through the clutch is denoted by arrows  325 . The input shaft  320  is supported for rotation relative to the housing  270  by a bearing  330 . The input shaft  320  is selectively rotationally coupled to a locking sleeve  305 . This coupling is achieved by a splined portion  320   a  of the input shaft  320  which corresponds with a splined portion  305   a  of the locking sleeve  305 , thereby rotationally coupling the two portions together when the locking sleeve  305  is moved axially into engagement with the input shaft  320 . 
   The locking sleeve  305  is selectively rotationally coupled to the housing  270 . This coupling is achieved by a second splined portion  305   b  of the locking sleeve  305  which corresponds with a splined portion  270   a  of the housing  270 , thereby rotationally coupling the two portions together when the locking sleeve  305  is moved axially into engagement with the housing  270 . The locking sleeve  305  is rotationally coupled to the output shaft  235  but is free to move axially relative to the output shaft. This coupling is achieved by a third splined portion  305   c  of the locking sleeve  305  which corresponds with a splined portion  235   a  of the output shaft which extends axially along a travel path of the locking sleeve  305 , thereby rotationally coupling the two portions together regardless of the axial position of the locking sleeve  305  relative to the output shaft  235 . 
   The locking sleeve  305  is axially biased away from the output shaft  235  by biasing member, such as spring  315 , which is disposed between two facing shoulders of the two parts. A nozzle  310  is received in a recess formed in the locking sleeve  305  and is exposed to the fluid path  325 . The nozzle  310  is disposed between a first portion  306   a  of a flow bore  306  of the locking sleeve  305  and a second portion  306   b  of the bore  306 . The nozzle  310  enables the locking sleeve  305  to act as a dynamic flow piston. Flow is choked through the nozzle  310 , resulting in a pressure drop across the nozzle and creating an actuation force which counters the biasing force acting on the locking sleeve  305  provided by the spring  315 . In this manner, the axial position of the locking sleeve  305  may be controlled by the injection rate of fluid through the clutch  300 . Optionally, a first sealing element  335   a  is disposed between the locking sleeve  305  and the housing  270  and a second sealing element  335   b  is disposed between the locking sleeve and the output shaft  235 . The optional sealing elements  335   a,b  prevent excess leakage from the flow path  325 . 
   Operation of the orienter  200  is as follows. Rotation of the orienter  200  is powered by the flow of drilling fluid provided by the surface pumps (not shown). In the engaged operating mode ( FIG. 3A ), the orienter  200  rotates the bent-housing motor  10  and MWD module  15  at a slow, but continuous speed, for example between about 2 and about 5 rpm, thus facilitating the “straight” drilling capability similar to that accomplished by the rotational technique employed when drilling with jointed pipe, discussed above. In this mode, the surface pumps are injecting fluid through the orienter  200  at a flow rate greater than or equal to a predetermined threshold flow rate so the actuation force from the pressure acting on the locking sleeve  305  is sufficient to compress the spring  315 , thereby holding the locking sleeve  305  in a position to engage the splined portions  305   a,    320   a.  Engagement of the splined portions means that the input shaft  325  is rotationally coupled to the locking sleeve  305  which is rotationally coupled to the output shaft  235 . Alternatively, the clutch  300  could be configured so that the locking sleeve  305  is rotationally coupled to the housing  270  in the engaged position and rotationally coupled to the input shaft  320  in the disengaged position. 
   When it is desired to change from straight ahead drilling to oriented directional drilling, the flow rate of the surface pumps is decreased by a pre-selected amount to a flow rate that is less than the predetermined threshold flow rate, thereby decreasing the pressure acting on the locking sleeve  305 . The spring  315  will then move the locking sleeve  305  out of engagement with the input shaft  320  and into a position where the splined portions  270   a,    305   b  are engaged ( FIG. 3B ). The locking sleeve  305 , which is rotationally coupled to the output shaft  235 , is now rotationally coupled to the housing  270 , which is stationary. In this mode, drilling will proceed in the direction determined by the rotational orientation of the bent-housing motor  10 . It is not necessary to stop drilling ahead to change from straight-ahead directional drilling to oriented drilling. When it is desired to change from oriented drilling to straight ahead drilling, the flow rate of the pumps is increased to a flow rate which is greater than or equal to the predetermined flow rate, thereby moving the locking sleeve  305  into engagement with the input shaft  320  and rotationally coupling the input shaft  320  to the output shaft  235 . 
   In addition to changing between straight ahead and directional drilling, the orienter  200  may be used to adjust an orientation of the directional drilling. In order to accomplish this, the clutch  300  is engaged for a relatively short time to rotate the bent sub  10  from a first orientation to a desired second orientation. 
   Some advantages of the orienter  200  over the prior art are as follows. No electric line is required in the coiled tubing  30  to provide power to the orienting device. This means that the system can be used with any coiled tubing drilling rig. A second difference from most prior art systems is that the orienter  200 , when engaged, provides continuous rotation of the bit  5 , motor  10 , and MWD module  15 . A third difference is that unlike some prior art systems, drilling need not stop to adjust BHA orientation. Finally, unlike any of the electrically powered systems which are very complex electro-hydraulic systems, the orienter  200  is a purely mechanical tool much less susceptible to failure in a wellbore. 
     FIG. 4A  is a cross sectional view of a drillstring  415  inserted into a wellbore  410 , according to another embodiment of the present invention. The wellbore  410  is drilled from a surface  411 , which may be either a surface of land or sea. Typically, the wellbore  410  is cased with a casing  414 . An annulus  412  between the drilled wellbore and the casing  414  is sealed with a solidifying aggregate such as concrete. The drillstring  415  includes a run-in string  416 , such as coiled tubing or a string of drill pipe. Various components can be assembled as part of the drillstring  415 . For example, beginning at the lower end of the arrangement, an anchor  438 , such as a bridge plug, packer, or other setting device, is releasably coupled to the drillstring  415  generally on a lower end of the arrangement. Preferably, the anchor  438  is hydraulically set so that the anchor  438  can be actuated remotely and thus does not require a separate trip. The hydraulic anchor  438  may be set with a hydraulic fluid flowing through a tube (not shown). The drillstring  415  shown in  FIGS. 4A-4C  can be used to set the anchor  438  and the whipstock  420  and begin cutting a window  436  (see  FIG. 4C ) in the wellbore  410  in a single trip. 
   A whipstock  420  is attached to the anchor  418  and includes an elongated tapered surface that guides a cutting tool, such as a mill  422 , outwardly toward casing  414 . The mill  422  is releasably coupled to the whipstock  420  with a connection member  424 , for example a shear pin, that may be later sheared downhole by an actuation force, such as by rotation of mill  422 , by pulling on the run-in string  416 , or otherwise. A spacer or watermelon mill  426  may also be coupled to the mill  422 . The spacer mill  426  typically is a mill used to further define the hole or window created by the mill  422 . In other embodiments, other types of cutting tools may be employed, such as hybrid bits that are capable of milling a window and continuing to drill into the formation. An exemplary hybrid bit is disclosed in U.S. Pat. No. 5,887,668 and is incorporated by reference herein. 
   In some arrangements, a stabilizer sub  428  is assembled as part of the drillstring  415 . The stabilizer sub  428  has extensions protruding from the exterior surface to assist in concentrically retaining the drillstring  415  in the wellbore  410 . A clutched mud motor  400  can be assembled with the drillstring  415  above the mills  422 , 426 . The clutched mud motor  400  may be similar to the orienter  200  except that the rotor  260 , stator  265 , speed reducer  250 , and transmission  255  may be replaced by a mud motor. When the clutch  300  is engaged, the mud motor  400  rotates the mills  422 , 426  while the drillstring  415  remains rotationally stationary (if the run-in string  416  is drill pipe, the drill pipe may be rotated in tandem with the mills  422 , 426  or held rotationally stationary). A position measuring member, such as an MWD tool  432 , is coupled above the motor  400 . The MWD tool  432  may require a certain level of flow Fm to activate and provide feedback to equipment located at the surface  411 . 
   When the run-in string  416  is coiled tubing, an orienter  434  (see also  FIG. 5 ) is assembled as part of the drillstring  415  above the MWD tool  432 . When the run-in string  416  is drill pipe, the whipstock  420  may be oriented by turning the drill pipe from the surface  411  and the orienter  434  is not needed. The orienter  434  includes housing elements  502 - 505  connected to one another, has a passage for, fluid such as drilling fluid, and may be activated for rotation of the whipstock  420 , so that the whipstock  420  may be properly oriented. Referring to  FIG. 5 , the orienter  434  includes an actuator valve  521  arranged to choke the passage, so that the orienter  434  can be activated for the rotation, a piston  518  adapted for providing the rotation after the through passage has been choked, and sets of co-operating guides, preferably twisted splines  526 ,  527 , adapted for causing the piston  518  to rotate relative to the housing  502 - 505 . The splines  526 , 527  are formed in an inner surface of the housing element  503  and an outer surface of the piston  518 . Thus, the orienter  434  can rotate the whipstock  420  to a desired orientation within the wellbore  410 , while the MWD tool  432  provides feedback to determine the orientation. A more detailed discussion of the principles and operation of the orienter  434  may be found in U.S. Pat. No. 6,955,231, entitled “Tool for Changing the Drilling Direction while Drilling,” which is hereby incorporated by reference in its entirety. 
   The flow rate Fo required to actuate the orienter  434  may be set above the flow rate required to activate the MWD tool  432 , below the flow rate Fa required to set the anchor  438 , and below the flow rate required to engage the clutch  300  of the clutched motor  400  Fc. The flow rate Fa required to set the anchor may be set below the flow rate Fc required to engage the clutch  300  of the clutched motor  400 . To summarize, preferably, Fc&gt;Fa&gt;Fo&gt;Fm. In the case that the run-in string  416  is drill pipe, a similar relation may be used with the exception that Fo would be omitted. In light of this relation, it may be observed that when setting the anchor, some unintended actuation of the orienter  434  may occur. To reduce this, the orienter is equipped with a choke valve  541  which controls the speed of the orienter  434 . The choke valve  541  may be configured to slow the orienter sufficiently such that the unintended actuation is negligible. Further, the orienter  434  may be configured with a relatively short stroke and/or a gradual twist in the splines to further reduce the unintended actuation. Alternatively, or in addition to, the unintended actuation may be measured or estimated and the MWD tool configured with an offset to compensate for the unintended actuation. Alternatively, the offset may be manually performed at the surface. 
     FIG. 4B  is a sectional view of the drillstring  415  with an anchor  438  set in position. The whipstock  420  is oriented using the orienter  434  to a desired position indicated by the MWD tool  432 , while the clutch  300  allows flow through the motor  400  without engagement of the motor. The hydraulic anchor  438  is set to fix the whipstock  420  at the desired orientation. 
     FIG. 4C  is a cross sectional view of the whipstock  420  set in position and the mill  422  cutting a window  436  through the casing  414  at an angle to the wellbore  410 . In one aspect, the connection member is sheared by pulling on the run-in string  416 . As the flow rate and/or pressure of fluid within the drillstring  415  increases, the clutch  300  engages the motor  400  which turns the mill  422 . In another aspect, sufficient torque created by the motor  400  shears the connection member  424  between the whipstock  420  and the cutting tool  422 . The mill  422  begins to turn and is guided at an angle to the wellbore  410  by the whipstock  420 . As the drillstring  415  is further lowered downhole, the mill  422  cuts at an angle through the casing  414  and creates an angled window  436  therethrough. In some embodiments, the casing  414  may not be placed in a wellbore  410 . It is to be understood that the arrangements described herein for cutting an angled window apply regardless of whether the casing  414  is placed in the wellbore. Actuation of the orienter  434  during this process does not affect the ability of the motor  400  to operate the mill  422  nor the direction of the mill  422  because the mill is guided by the whipstock  420 . 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.