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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to drilling oil wells. More specifically, the invention relates to directional drilling and the use of downhole steering. Even more specifically, the invention relates to an apparatus for transferring power between a rotating member and a non-rotating member of a bottom hole assembly. 
     2. Description of the Related Art 
     To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a drilling assembly (also referred to herein as a “Bottom Hole Assembly” or “BHA”). The drilling assembly is attached to the bottom of a drill tube, which is usually either a jointed rigid pipe (commonly referred to as the drill pipe) or a relatively flexible spoolable tubing (commonly referred to in the art as the “coiled tubing”). The string comprising the tubing and the drilling assembly is usually referred to as the “drill string.” When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the surface and/or by a mud motor contained in the drilling assembly. In the case of a coiled tubing, the drill bit is rotated by the mud motor. During drilling, a drilling fluid (also referred to as the “mud”)is supplied under pressure into the tubing. The drilling fluid passes through the drilling assembly and then discharges at the drill bit bottom. The drilling fluid provides lubrication to the drill bit and carries to the surface rock pieces disintegrated by the drill bit in drilling the borehole. The drilling fluid passing through the drilling assembly rotates the mud motor. A drive shaft connected to the motor and the drill bit rotates the drill bit. 
     It is well known that formations capable of producing significant amounts of oil and gas (hydrocarbons) are increasingly difficult to find. In addition, economic, political and environmental concerns can make it impossible to place a drilling system directly over a promising formation. As a result, a substantial proportion of the current drilling activity involves drilling of deviated and horizontal borehholes to more fully exploit the hydrocarbon reservoirs. In deviated and horizontal drilling, the wellbore is intentionally drilled at an angle from vertical by special downhole drilling tools to guide the drill assembly in the desired direction. These wellbores are drilled to reach a part of a formation or reservoir, which cannot be drilled by a straight or vertical hole because of the environmental, political, or economic reasons mentioned. Such boreholes can have relatively complex well profiles. To drill such complex boreholes, steerable drilling assemblies are sometimes utilized. A particular drilling assembly includes a plurality of independently operable force application members to apply force on the wellbore wall during drilling of the wellbore to maintain the drill bit along a prescribed path and to alter the drilling direction. Such force application members may be disposed on the outer periphery of the drilling assembly body or on a non-rotating sleeve disposed around a rotating drive shaft. These force application members are moved radially outward from the drilling assembly by electrical devices or electro-hydraulic devices to apply force on the wellbore in order to guide the drill bit and/or to change the drilling direction outward. In such drilling assemblies, there exists a gap between the rotating and the non-rotating sections. To reduce the overall size of the drilling assembly and to provide more power to the ribs, it is desirable to locate the devices (such as motor and pump) required to operate the force application members in the non-rotating section. It is also desirable to locate electronic circuits and certain sensors in the non-rotating section. Thus, power must be transferred between the rotating section and the non-rotating section to operate mechanical devices and the sensors in the non-rotating section. 
     In drilling assemblies which do not include a non-rotating sleeve as described above, it is desirable to transfer electrical and mechanical power between the rotating drill shaft and the stationary housing surrounding the drill shaft. The power transferred to the rotating shaft may be utilized to operate sensors or mechanical devices in the rotating shaft and/or drill bit. Power transfer between rotating and non-rotating sections having a gap therebetween can also be useful in other downhole tool configurations. 
     The present invention, which is especially desirable in a space-restrictive application such as the drilling of very small deviated boreholes, provides contactless inductive coupling to convert electrical power in one section to mechanical power in another section where the sections are rotating and non-rotating sections of downhole oilfield tools, including the drilling assemblies containing rotating and non-rotating members. This direct transfer and conversion has the desirable characteristic of requiring fewer components than other tools that transfer electrical power to operate electrically controlled devices to perform mechanical functions such as operating pumps. Direct conversion means fewer parts, thus leading to more economical, reliable and compact tool designs. 
     SUMMARY OF THE INVENTION 
     In general, the present invention provides apparatus for power transfer over a nonconductive gap between rotating and non-rotating members of downhole oilfield tools. The gap may contain a non-conductive fluid, such as drilling fluid or oil for operating hydraulic devices in the downhole tool. The downhole tool, in one embodiment, is a drilling assembly wherein a drive shaft is rotated by a downhole motor to rotate the drill bit attached to the bottom end of the drive shaft. A substantially non-rotating sleeve around the drive shaft includes a plurality of independently operated force application members, wherein each such member is adapted to be moved radially between a retracted position and an extended position. The force application members are operated to exert the force required to maintain and/or alter the drilling direction. In the preferred system, one or more mechanically operated devices such as hydraulic units provide energy (power) to the force application members. A transfer device transfers electrical power between the rotating and non-rotating members, and the electric power is converted directly to mechanical power. An electronic control circuit or unit associated with the rotating member controls the transfer of power between the rotating member and the non-rotating member. 
     In a preferred embodiment, the present invention is particularly suited for a Rotary Closed-Loop System (RCLS) type tool for drilling deviated boreholes with very small hole sizes. A RCLS system is an automated directional drilling system that contains its own programmed controller and steering sub, and drills continuously in the rotary mode. A non-rotating, orienting sleeve controls steering expanding force application members. Precisely controlled force on the force application members produces resultant force vectors that maintain inclination alignment and direction within the program well path. Course corrections are made continuously while drilling, with no trips required for tool adjustments. Real-time surface monitoring permits changes to the wellpath program if desired. This technology increases the rate-of-penetration, improves hole quality, and enables greater extended reach capability. The embodiment may also comprise measurement while drilling (MWD), geosteering and automated rotary drilling capability. 
     In general, one or more steering ribs are controlled by hydraulic pressure. A motor located on the rotating shaft of a bottom hole assembly driving an axial piston pump in the non-rotating sleeve manages the generation of hydraulic pressure. The motor windings are positioned on the rotating shaft and a magnetically polarized rotor is located on the non-rotating sleeve. There would be one motor for controlling a hydraulic pump for each steering rib. Rotation control of the motor controls the variable piston pressure, and no electrical transmission to the sleeve is required to control the ribs. In the preferred embodiment, the motor will run in drilling mud. Feedback regarding the position of the non-rotating sleeve will be measured by sensors in the non-rotating sleeve or by markers. These methods of feedback and the sensors required are well known in the art. An added benefit of this arrangement is that no hydraulic pressure has to be transmitted from the rotating shaft to the sleeve. 
     In an alternative embodiment of the invention, a power transfer device transfers power from the non-rotating housing to the rotating drill shaft. The power transferred to the rotating drill shaft is directly converted to electrical power to operate one or more sensors or electrically operated devices in the drill bit and/or the bearing assembly. 
     The power transfer device may also be provided in a separate module above the mud motor to transfer power from a non-rotating section to the rotating member of the mud motor and the drill bit. The power transferred may be utilized to operate devices and sensors in the rotating sections of the drilling assembly, such as the drill shaft and the drill bit. 
     Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
     FIGS. 1A-1B show a cross-sectional view of a portion of the drilling assembly with the steering device and the control device disposed in the bearing assembly of the drilling assembly. 
     FIG. 1C shows a rib of the steering device of FIG. 1A in the retracted and extended positions. 
     FIG. 2 is a detailed cutaway schematic view of an embodiment of the present invention wherein the stator is disposed on a rotating shaft and the rotor is disposed on the non-rotating sleeve in a bottom hole assembly including one steering member. 
     FIG. 3 is a schematic view of an embodiment of the drilling assembly according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1A-1B show a schematic diagram of a steering device  30  integrated into a bearing assembly  20  of a drilling motor  10 . The drilling motor  10  forms a part of the drilling assembly  100  (FIG.  3 ). The drilling motor  10  contains a power section  12  and the bearing assembly  20 . The power section  12  includes a rotor  14  that rotates in a stator  16  when a fluid  52  under pressure passes through a series of openings  17  between the rotor  14  and the stator  16 . The fluid  52  may be a drilling fluid or “mud” commonly used for drilling wellbores or it may be a gas or liquid and gas mixture. The rotor  14  is coupled to a rotatable shaft  18  for transferring rotary power generated by the drilling motor  10  to the drill bit  50 . 
     The bearing assembly  20  has an outer housing  22  and a through passage  24 . A drive shaft  28  disposed in the housing  22  is coupled to the rotor  14  via the rotatable shaft  18 . The drive shaft  28  is connected to the drill bit  50  at its lower or downhole end. During drilling of the wellbores, drilling fluid  52  causes the rotor  14  to rotate, which rotates the shaft  18 , which in turn rotates the drive shaft  28  and hence the drill bit  50 . It is important not to confuse the terminology associated with the drill motor  10  and the electromagnetic motor  510  (FIG.  2 ). The terms rotor and stator are used in reference to each motor, and those skilled in the art are aware of the physical and operational differences between the two motors. 
     Continuing with FIGS. 1A-1B, the bearing assembly  20  contains within its housing  22  suitable radial bearings  56   a  that provide lateral or radial support to the drive shaft  28  and the drill bit  50 , and suitable thrust bearings  56   b  to provide axial (longitudinal or along the wellbore) support to the drill bit  50 . The drive shaft  28  is coupled to the shaft  18  by a suitable coupling  44 . The shaft  18  is a flexible shaft to account for the eccentric rotation of the rotor. Any suitable coupling arrangement may be utilized to transfer rotational power from the rotor  14  to the drive shaft. During the drilling of the wellbores, the drilling fluid  52  leaving the power section  12  enters the through passage  24  of the drive shaft  28  at ports or openings and discharges at the drill bit bottom  53 . Various types of bearing assemblies are known in the art and are thus not described in greater detail here. 
     In the preferred embodiment of FIGS. 1A-1B, a steering device, generally represented by numeral  30  is integrated into the housing  22  of the bearing assembly  20 . The steering device  30  includes a number of force application members  32 . Each force application member is preferably placed in a reduced diameter section  34  of the bearing assembly housing  22 . The force application members may be ribs or pads. For the purpose of this invention, the force application members are generally referred herein as the ribs. Three ribs  32  equally spaced in or around the outer surface of the housing  22 , have been found to be adequate for properly steering the drill bit  50  during drilling operations. Each rib  32  is adapted to be extended radially outward from the housing  22 . FIG. 1C shows a rib  32  in its normal position  32   a,  also referred to as the retracted or collapsed position, and in a fully extended position  32   b  relative to the borehole inner wall  38 . A separate piston pump  40  independently controls the operation of each steering rib  32 . For short radius drilling assemblies, each such pump  40  is preferably an axial piston pump  40  disposed in the bearing assembly housing  22 . 
     Still referring to FIGS. 1A-1B, it is known that the drilling direction can be controlled by applying a force on the drill bit  50  that deviates from the axis of the borehole tangent line. This can be explained by use of a force parallelogram depicted in FIG.  1 A. The borehole tangent line is the direction in which the normal force or pressure is applied on the drill bit  50  due to the weight on bit, as shown by the arrow WOB  57 . A side force applied to the drill bit  50  by the steering device  30  creates a force vector that deviates from the borehole tangent line. If a side force or rib force such as that shown by arrow  59  is applied to the drilling assembly  100 , it creates a force  54  known as bit force on the drill bit  50 . The resulting force vector  55  then lies between the weight-on bit and bit force lines depending upon the amount of applied rib force. 
     The present invention is particularly suited for so-called closed-loop drilling systems for drilling small diameter deviated boreholes. The closed-loop drilling systems usually are automated directional drilling systems that contain their own programmed controller and steering mechanisms which can effect continuously controlled drilling of deviated holes. In one type of drilling assembly used in closed-loop drilling systems, a precisely controlled force on the expanding pads (or ribs) produces resultant force vectors that maintain inclination alignment and direction within the programmed well path. Course corrections are-made either periodically or continuously while drilling, with no trips required for tool adjustments. Real-time surface monitoring permits changes to the wellpath program if desired. This technology increases the rate-of-penetration, improves hole quality, and enables greater extended reach capability. This embodiment will be explained in detail later with reference to FIG.  2 . In general, one or more, and preferably three, steering ribs are controlled by hydraulic pressure. A motor located on the rotating shaft of a bottom hole assembly driving an axial piston pump in the non-rotating sleeve manages the generation of hydraulic pressure. The motor windings are positioned on the rotating shaft and a magnetically polarized rotor is located on the non-rotating sleeve. Preferably, there would be one motor for controlling a hydraulic pump for each steering rib. However, one motor could also control multiple pumps and one pump could control multiple steering ribs. Rotation control of the motor controls the variable piston pressure, and no electrical transmission to the sleeve is required to control the ribs. In the preferred embodiment, the motor will run in drilling mud. Feedback regarding the position of the non-rotating sleeve will be measured by sensors in the non-rotating sleeve or by markers. These methods of feedback and the sensors required are well known in the art. An added benefit of this arrangement is that no hydraulic pressure has to be transmitted from the rotating shaft to the sleeve. 
     Referring now to FIG. 2 for a more detailed description of the preferred embodiment, a schematic of a portion of the BHA  500  is shown which comprises a rotating member or shaft  502  and a non-rotating sleeve  504 . The non-rotating sleeve  504  and rotating shaft  502  are coupled via bearings  514 , which may be mud-lubricated. The BHA  500  includes a plurality of electric motors  510 . In this embodiment the motors  510  are used to control the deployment and retraction of a plurality of steering ribs  532 , one of which is shown in the figure. Each motor  510  comprises a stator  508  and a magnetically polarized rotor  516 . Each rotor  516  is rotatably disposed in or on the non-rotating sleeve  504  such that the rotor  516  can provide rotational movement relative to forces generated by the reaction between the rotor magnetic field and electric current in windings of the stator  508 . The stator  508  and rotor  516  are separated by an electrically nonconductive gap  538 , which can be filled with non-conductive drilling mud or oil. To protect the stator  508  a shield  534  is placed between the stator  508  and gap  538 . In the figure, a rotating shaft  502  rotating about the centerline  506  of the BHA assembly  500  has a plurality of stators  508  disposed thereon. The stators  508  may be any suitable conductive winding material. Electric sinusoidal power  512  is supplied to each stator  508  by a controller (not shown). The controller is capable of varying the magnitude of current supplied to each stator  508 , and each stator current is independently controlled with respect to the current supplied to other stators. A processor (not shown) may be integrated into the controller or located at a suitable location on the string down hole or even on the surface. The processor would include the drilling profile. One or more sensors mounted on the BHA  500  would send data relating the orientation of the BHA and the direction of drilling to the processor. The processor would, in turn, adjust the controller current based on the feedback from the sensors. The controller adjustments would result in the modification of current levels being sent to stators  508 . The actual operational and component descriptions of the motors are not sufficiently different, so the description herein is limited to the description of one motor. 
     When an alternating sinusoidal current, generally referred as ac current or simply current, energizes stator  508 , the current flows through the windings of the stator. The magnetic field of the rotor  516  propagates across the gap  538  and encompasses the stator  508 . Forces imparted on the charged particles (current) in the stator loops are met with equal forces in the opposite direction from the charged particles. Since the rotor is rotatably mounted and the stator is not, the magnetically polarized rotor  516  then is forced into movement. The forces of this action are proportional to the amount of current supplied to the stator  508  as well as the rotational speed of the rotating shaft  502  and the intensity of the magnetic field of the rotor. Thus, controlling the current supplied to the stator  508  or the rotational speed of the shaft  502  controls the force (or mechanical power) of the rotor  516 . Since the rotational speed of the shaft is typically dictated by parameters such as desired rate of penetration (ROP), formation material, type of drill bit used etc, varying the controller output current is used to maintain a desired power output of the motor. To do this, feedback sensors detecting the rotational speed of the shaft  502  would be required to send the data to the processor. The processor would process the shaft data along with other data to vary the controller current accordingly. As the current supplied by the controller to the stator  508  changes polarity, the forces between the rotor and charged particles within the stator windings reverse direction thereby forcing the rotor  516  to realign again. The continuous reversal of polarity of current in the windings of the stator  508  forcing the rotor to continuously realign creates rotational mechanical power in the rotor  516 . This mechanical power may be utilized in any desired application requiring mechanical power. In this embodiment, the mechanical rotor power is used to drive a pump  524 . The pump  524  is preferably an axial piston pump, and it is used to hydraulically control the deployment of a steering rib  532 . When supplying deployment force to rib  532 , the pump supplies hydraulic fluid  520  by drawing the fluid  520  from a sealed fluid reservoir  518 . The pump  524  is connected to fluid line  526 , and the fluid line  526  is connected to an extensible member (piston) fluid chamber  528 . A piston  530  movably connected to the piston fluid chamber  528  either extends or retracts relative to the pressure supplied by the fluid  520  entering or exiting the piston fluid chamber  528 . The rib  532 , disposed in recessed section  540  is positioned between the borehole wall  542  and the piston  530 . The extension or retraction of the piston  530  controls the radial movement of the rib  532 . 
     As the rotor  516  begins to rotate due to the presence of the alternating stator current, the pump  524  connected to the rotor  516  begins to operate. The pump operation pressurizes the fluid line  526  with the hydraulic fluid  520 . When the pump  524  pressurizes the fluid line  526 , fluid  520  passes from the reservoir  518  via the fluid line  526  and on to the piston fluid chamber  528 . The piston fluid chamber  528  fills with fluid  520  and pressurizes relative to the power supplied by the rotor  516 . When the pressure rises, the piston  530  extends thereby extending the rib  532 . The extended rib  532  thus supplies a force to the borehole wall  542 . This exerted force tends to direct the BHA  500  in a direction opposite from the direction of the force being supplied against the borehole wall  542 . The rotating drill bit (not shown in this figure) then begins to deviate from the vertical thereby drilling along a path controlled by the rib steering mechanism of the present invention. As stated above, three ribs independently controlled and equally spaced on or about the BHA  500  in this manner would be sufficient to adequately control the drilling path for deviated boreholes. This is accomplished by independently controlling the force applied to the borehole wall  542  in a combination of three directions and varying magnitudes as described above with respect to the parallelogram in FIG.  1 B. 
     When retraction of a steering rib is desired, the current being supplied is reduced or terminated by the processor and controller to deactivate the pump  524 . With the pump  524  deactivated, the fluid  520  in the piston fluid chamber  528  returns to the sealed reservoir  518 . There are multiple hydraulic methods well known in the art for accomplishing the depressurization of hydraulic systems, and any suitable arrangement may be utilized. One such arrangement has the fluid returning to the reservoir via a separate fluid return line  544  through a bleed valve  546 . Axial piston pumps may also have a bleed valve (not shown) to relieve the pressure from the fluid line. 
     FIG. 3 shows a configuration of a drilling assembly  100  utilizing the steering device  30  (see FIGS. 1A-1B and  2 ) of the present invention in the bearing assembly  20  coupled to a coiled tubing  202 . The drilling assembly  100  has the drill bit  50  at the lower end. As described earlier, the bearing assembly  20  above the drill bit  50  carries the steering device  30  having a number of ribs that are independently controlled to exert desired force on the drill bit  50  during borehole drilling. An inclinometer (z-axis)  234  is preferably placed near the drill bit  50  to determine the inclination of the drilling assembly. The mud motor  10  provides the required rotary force to the drill bit  50  as described earlier with reference to FIGS. 1A-1B. A knuckle joint  60  may be provided between the bearing assembly  20  and the mud motor  10 . Depending on the drilling requirements, the knuckle joint  60  may be omitted or placed at another suitable location in the drilling assembly  100 . A number of desired sensors, generally denoted by numerals  232   a-   232   n  may be disposed in a motor assembly housing  15  or at any other suitable place in the assembly  100 . The sensors  232   a-   232   n  may include a resistivity sensor, a gamma ray detector, and sensors for determining borehole parameters such as the fluid flow rate through the drilling motor  10 , pressure drop across the drilling motor  10 , torque on the drilling motor  10 , and speed of the motor  10 . 
     The control circuit  80  may be placed above the power section  12  to control the operation of the steering device  30 . A slip ring transducer  221  may also be placed in the section  220 . The control circuits in the section  220  may be placed in a rotating chamber, which rotates with the motor  10 . The drilling assembly  100  may include any number of other devices. It may include navigation devices  222  to provide information about parameters that may be utilized downhole or at the surface to control the drilling operations and/or the azimuth. Flexible subs, release tools with cable bypass, generally denoted herein by numeral  224 , may also be included in the drilling assembly  100 . The drilling assembly  100  may also include any number of additional devices known as measurement-while-drilling devices or logging-while-drilling devices for determining various borehole and formation parameters, such as the porosity of the formation, density of the formation, and bed boundary information. The electronic circuitry that includes microprocessors, memory devices and other required circuits is preferably placed in the section  230  or in an adjacent section (not shown). A two-way telemetry  240  provides two-way communication of data between the drilling assembly  100  and the surface equipment. Conductors  65  placed along the length of the coiled tubing may be utilized to provide power to the downhole devices and the two-way data transmission. 
     The downhole electronics in the section  220  and/or  230  may be provided with various models and programmed instructions for controlling certain functions of the drilling assembly  100  downhole. A desired drilling profile may be stored in the drilling assembly  100 . During drilling, data/signals from the inclinometer  234  and other sensors in the sections  220  and  230  are processed to determine the drilling direction relative to the desired direction. The control device, in response to such information, adjusts the force on force application members  32  to cause the drill bit  50  to drill the borehole along the desired path. Thus, the drilling assembly  100  of the present invention can be utilized to drill short-radius and medium radius boreholes relatively accurately and, if desired, automatically. 
     An alternative embodiment may have the motor components located on the BHA, such that electrical power is generated in the non-rotating sleeve by the use of mechanical power in the rotating portion of the BHA. In this configuration electric motor stators are disposed on or about the non-rotating sleeve. A plurality of rotors is disposed about the rotating shaft. The constantly rotating magnetic field of the rotors creates an electrical current in the stator windings. This electric power can be conditioned and controlled to operate electrical devices in the non-rotating sleeve. 
     The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.

Summary:
The present invention provides apparatus for power transfer over a nonconductive gap between rotating and non-rotating members of downhole oilfield tools. The gap may contain a non-conductive fluid, such as drilling fluid or oil for operating hydraulic devices in the downhole tool. The downhole tool, in one embodiment, is a drilling assembly wherein a drive shaft is rotated by a downhole motor to rotate the drill bit attached to the bottom end of the drive shaft. A substantially non-rotating sleeve around the drive shaft includes a plurality of independently operated force application members used to exert the force required to maintain and/or alter the drilling direction. In the preferred system, one or more mechanically operated devices such as hydraulic units control the force application members. A transfer device transfers electrical power between the rotating and non-rotating members, and the electric power is converted directly to mechanical power. An electronic control circuit or unit associated with the rotating member controls the transfer of power between the rotating member and the non-rotating member.