Abstract:
An assembly for use in drilling in earth borehole using a drill string including a drill bit comprising a first downhole motor having a rotor operatively connected to said drill bit, a second downhole motor distal said first downhole motor, said second downhole motor having a rotor with a passageway therethrough and a bypass valve operatively connected to the second downhole motor, the bypass valve having a first position permitting drilling fluid to flow through said passageway and a second position wherein drilling fluid is prevented from flowing through said passageway.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of U.S. Provisional Application No. 60/899,531 filed on Feb. 5, 2007, the disclosure of which is incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to drilling earth boreholes and, more particularly, to an assembly for effecting directional drilling of earth boreholes using either coiled tubing rigs or jointed pipe rigs. 
         [0004]    2. Description of Prior Art 
         [0005]    Directional drilling is widely used in the oil and gas industry whether the drilling be accomplished using coiled tubing rigs or conventional, jointed pipe rigs. As is well known to those skilled in the art, a typical directional drilling system has a drill bit at its bottom end which is rotated by a drill motor, commonly referred to as a “mud motor.” In addition to the drill bit and the mud motor, a typical directional drilling assembly can include an orienting or steering tool, an MWD or LWD tool, drill collars, and a bent sub which can comprise a portion of the housing of the mud motor. 
         [0006]    Typically, prior art directional drilling assemblies have comprised a single mud motor, the mud motor supplying, as well known to those skilled in the art, the power to rotate the drill bit. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the present invention provides an assembly for use in drilling an earth borehole employing a drill string including a drill bit. The assembly can include a first downhole motor having an upper end and a lower end, a first rotor and a first stator, the lower end of the first downhole motor being proximal and operatively connected to the drill bit. 
         [0008]    There is also a second downhole motor having an upper end and a lower end, a second rotor and a second stator, the second rotor having a passageway there through and being distal the drill bit. There is a bypass valve operatively connected to the upper end of the second downhole motor, the bypass valve including a valve element which is selectively movable from a first position wherein a drilling fluid flowing through the drill string can flow through the passageway in the second rotor to a second position wherein the drilling fluid is prevented from flowing through the passageway in the second rotor. 
         [0009]    In another aspect of the present invention, there is a orienter subassembly forming part of the drill string which can include a bent housing separate from or forming part of the first motor. The second downhole motor, in conjunction with the bypass valve, can be used to induce or stop rotation of at least a portion of the orienter subassembly as required. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view of one embodiment of the assembly of the present invention. 
           [0011]      FIG. 2  is a schematic, elevational view of a bypass valve used in conjunction with the first or lower motor; and 
           [0012]      FIG. 3  is a cross-sectional view taken along the lines  3 - 3  of  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    Referring to  FIG. 1 , the assembly of the present invention is shown generally as  10 . Assembly  10  is comprised of a bypass valve assembly  12  which would be connected in a suitable manner to coiled tubing or jointed drill pipe, neither of which are shown, which would extend to the surface and be operated either by a coiled tubing injector in the case of coil tubing, or a top drive, rotary table or the like in the case of jointed pipe. Connected to and below bypass valve assembly  12  is the upper mud motor  14  described more fully hereafter. A gear reduction assembly  16  incorporating an anti-torque unit, or a rotary brake unit is connected to the rotor  32  of the motor  14  (see  FIG. 2 ). A tool joint  18  is connected to the gear reduction assembly  16 . Connected to tool joint  18  is a bottom hole assembly (BHA)  20  which can comprise suitable drill collars and non-magnetic isolation collars if needed. An MWD logging tool  22  or other formation parameter measuring tool is connected to the BHA  20 , an orientation sub  24  being connected to the MWD tool  22 . The first or lower motor  26  is connected to the orientation sub  24 . As seen, motor  26  has a bent housing as is well known to those skilled in the art. The output of lower motor  26  is operatively connected to a drill bit  28  to effect rotation. 
         [0014]    As noted above, the assembly  10  of the present invention is comprised of two mud motors of the positive displacement type. Upper motor  14 , as is in the case with most mud motors and as shown in  FIG. 2  is comprised of a stator  30  and a rotor  32  positioned in a housing  33 , housing  33  having a threaded pin end  35  and a threaded box end  50 . Unlike prior art mud motors, rotor  32  has an axially extending passageway  34  which terminates on its upper end in a valve seat  36 . Valve assembly  12  comprises a housing  38  defining a bore  40  in which is slidably mounted a valve carrier  42  which carries on its lower end a valve element  44 . Operation of valve carrier  42  vis-à-vis reciprocal movement of valve element  44  in bore  40  is via electrical and/or hydraulic power through connection  46 , e.g., a wireline, extending to the surface. Valve assembly  12  includes a threaded pin connection  48  which is complimentary to a threaded box  50  in motor  14 . It can thus be seen that when valve assembly  12  is connected to motor  16 , threaded pin  48  will connect and seal in the threaded box connection  50 . Thus, valve element  44  can be selectively engaged and disengaged from valve seat  36  by reciprocating valve carrier  42  in bore  40 . 
         [0015]    As noted above, the assembly of the present invention uses a novel arrangement of a bypass valve and two, axially spaced motors, an upper motor  14  located proximal the top of the assembly  10  that is used to induce rotation or stop rotation of that portion of the assembly  10  below the motor  14 , and a bottom motor  20  which is used to rotate the drill bit  28 . 
         [0016]    In operation and with bypass valve  12  in the closed position such that valve element  44  is seated in valve seat  36 , flow of drilling fluid through passageway  34  is prevented. Accordingly, drilling fluid flowing downwardly through valve assembly  12  into motor  16  will, in the conventional manner, cause rotor  32  to rotate inside stator  30  effecting rotation of the portion of the assembly  10  below motor  14 . It will be understood that rotor  32 , when the valve assembly  12  is closed, will rotate at a higher speed and hence a lower torque than required to rotate the portion of the assembly  10  below motor  14 . Accordingly, to reduce speed and increase torque, gear reduction assembly  16  is employed and has a gearing system designed to provide the desired rotational speed to the portion of the assembly  10  below motor  14 . By way of example only, if rotor  32  is operating at 150 rpms, gear reduction assembly  16  may reduce the rotational output of lower motor  16  to 10 rpms or less as desired. It will be understood that when the valve assembly  12  is closed and the remainder of the assembly below motor  14  is rotating, assembly  10  will drill in a straight direction and will continue drilling in a straight direction as long as valve assembly  12  remains closed. In this regard, the portion of the assembly  10  below motor  14  will rotate around an axis generally coincident with the axis of motor  14  meaning that motor  26  and drill bit  28  will be precessing around such axis. 
         [0017]    To orient assembly  10  and drill in a desired curved, direction, valve  12  would be opened allowing drilling fluid to pass through passageway  34  effectively bypassing the lobed cavities between rotor  32  and stator  30 . Further, closing of bypass valve  12  will cause the rotary brake and/or the anti-torque unit to be engaged. Accordingly, rotor  32  will not rotate and the portion of the assembly  10  below motor  14  will not rotate in any direction. Thus, that portion of assembly  10  can be clocked to a desired, fixed tool face. It will be understood that intermittent opening and closing of valve  12  can be used to orient the assembly  10  to the desired tool face. Once a desired orientation has been achieved and with valve assembly  12  still closed, drilling mud passing through lower motor  26  will cause drill bit  28  to rotate and drill in the direction of the fixed tool face. At this stage, only drill bit  28  will be rotating, the remainder of the orienter assembly  10  will be stationary vis-à-vis rotational movement 
         [0018]    It can be seen that the assembly  10  of the present invention, as is conventional, contains a rotating mandrel or tool joint  18  to conventionally connect the desired number of collars, magnetic or non-magnetic, as desired. Additionally, the assembly  10  can contain an MWD tool  22  of the logging tool and an orientation/float sub  24  as required, all of which are conventional and well known to those skilled in the art. 
         [0019]    As noted above, at the lower motor  26  of assembly  10  has a bent housing which is connected to the drill bit  28 . It is to be understood that upper motor  14  is used to induce or stop rotation of that portion of the assembly  10  below motor  14  as necessary and provides the ability, in combination with the valve assembly  12 , to determine the desired orientation. Bottom motor  26 , on the other hand, is only used to rotate the drill bit  28 . 
         [0020]    It will be appreciated by those skilled in the art, that when the orienter assembly  10  is connected to coiled tubing, at no time will bypass valve assembly  12  and motor  14  rotate. It will further be understood that when a straight borehole is being drilled, the entire portion of the assembly below motor  14  will be rotating, as noted above, the bent portion of motor  26  and bit  28  precessing around an axis coincident with an axis passing through motor  14 . It will further be understood, that when it is desired to drill a curved borehole, and once the assembly has been clocked to the proper orientation, only drill bit  28  will be rotating, drill bit  28  following the desired tool face direction. 
         [0021]    In cases where the assembly  10  is connected to jointed pipe, the description above with respect to the assembly  10  being connected to coiled tubing applies with the exception, that since a jointed pipe string, unlike coiled tubing, can and normally is rotated, motor  14  and bypass valve  12  would be rotating in the borehole since they are fixedly connected to the jointed pipe string. 
         [0022]    The anti-torque unit or rotary brake unit has been shown as being incorporated in the gear reduction assembly  16  and below upper mud motor  14 , it will be understood that the anti-torque/rotary brake could be above mud motor  14  and more particularly be a part of the bypass valve assembly  12 .