Patent Publication Number: US-7708086-B2

Title: Modular drilling apparatus with power and/or data transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application takes priority from U.S. Provisional Application Ser. No. 60/629,374, filed Nov. 19, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to oilfield downhole tools and more particularly to modular drilling assemblies utilized for drilling wellbores in which electrical power and data are transferred between different modules and between rotating and non-rotating sections of the drilling 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 tubing or tubular string, which is usually either a jointed rigid pipe (or “drill pipe”) or a relatively flexible spoolable tubing commonly referred to in the art as “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 wellbore via an annulus between the drill string and the wellbore wall. The mud motor is rotated by the drilling fluid passing through the drilling assembly. A drive shaft connected to the motor and the drill bit rotates the drill bit. 
   A substantial proportion of the current drilling activity involves drilling of deviated and horizontal wellbores to more fully exploit hydrocarbon reservoirs. Such boreholes can have relatively complex well profiles that may include contoured sections. To drill such complex boreholes, drilling assemblies are utilized that include steering assemblies and a suite of tools and devices that require power and signal/data exchange. Conventional power/data transmission systems for such drilling assemblies often restrict placement of certain tools due to difficulties in transferring power or data across individual drilling assembly components such as a drilling motor. 
   The present invention addresses the need for systems, devices and methods for efficiently transferring power and/or data between modules that make up a BHA. 
   SUMMARY OF THE INVENTION 
   In aspects, the present invention relates to devices and methods for conveying power such as electrical power and/or data signal along a wellbore bottomhole assembly (BHA). An exemplary BHA made in accordance with the present invention can be deployed with offshore or land-based drilling facilities via a conveyance device such as a tubular string, which may be jointed drill pipe or coiled tubing, into a wellbore. An exemplary BHA can include equipment and tools that utilize electrical power and can transmit/receive data. A power and/or data transmission line provided in the BHA enables power and/or data transfer among the individual tools or modules making up the BHA. 
   According to one embodiment of the present invention, a drilling motor adapted for use in such a BHA includes a transmission unit that transmits power and/or data between modules or tools positioned uphole and downhole of the motor (hereafter “power/data transmission unit”). An exemplary motor includes a rotor that rotates within a stator. The power/data transmission unit can include power/data carriers that transmit power and/or data across the motor via conductive elements in the rotor and/or the stator. 
   An exemplary power/data transmission unit includes a rotating conductive section in the rotor, a non-rotating conductive section in the stator or adjacent sub, and a power and/or data transfer device. In one embodiment, the rotating conductive section is made up of power and/or data carriers formed by a flexible member, a length compensation device, and a conductive element such as an insulated cable disposed inside the rotor. The non-rotating conductive section includes a non-rotating power/data line made up of a conductive element positioned along a portion of the stator or adjacent sub. The rotating conductive section rotates relative to the non-rotating conductive section. The power/data transfer device is adapted to transfer power and/or data between the rotating conductive section and the non-rotating conductive section. In one embodiment, the power/data transfer device includes a body, conductive elements coupled at one end to an external connector and at the other end to a contact assembly. The contact assembly maintains continuity of power and data transfer between conductive elements and the rotating power/data line. Additionally, the power/data transfer device can include a pressure compensation unit for controlling fluid pressure in the power/data transfer device. The flexible member and the length compensation unit accommodate the changes in radial motion and length of the rotor. 
   In another arrangement, the power/data transmission unit includes conductive elements that transfer power and/or data between the electrical contacts positioned at the ends of the drilling motor. In one embodiment, a threaded connection on a stator housing and a threaded connection on a shaft of the rotor can be provided with electrical contacts. Because the stator housing is stationary relative to the rotor, a power/data transfer device such as a slip ring cartridge or inductive coupling can be used to transfer power and/or data between the conductive elements in the stator and the conductive elements in the rotating shaft. 
   The power/data transmission unit and power/data transfer unit can be employed in multiple configurations, e.g., to transmit or transfer (i) only power, (ii) only data, or (iii) both data and power. Additionally, these units can include two or more carriers, each of which can be formed to carry only power, only data, or both power and data. The nomenclature “power/data” and “unit” are used merely for convenience to refer to all such configurations and not any particular configuration. 
   Exemplary BHA equipment that can also be connected to power and/or data transmission line includes a steering unit, a bidirectional data communication and power (“BCPM”) unit, a sensor sub, a formation evaluation sub, and stabilizers. The BCPM sub provides power to the equipment such as the steering unit and two-way data communication between the BHA and surface devices. The sensor sub measures parameters of interest such as BHA orientation and location, rotary azimuthal gamma ray, pressure, temperature, vibration/dynamics, and resistivity. The formation evaluation sub can includes sensors for determining parameters of interest relating to the formation (e.g., resistivity, dielectric constant, water saturation, porosity, density and permeability), the borehole (e.g., borehole size, and borehole roughness), measuring geophysics (e.g., acoustic velocity and acoustic travel time), borehole fluids (e.g., viscosity, density, clarity, rheology, pH level, and gas, oil and water contents), and boundary conditions. The sensor and FE sub include one or more processors that provide central processor capability and data memory. Additional modules and sensors can be provided depending upon the specific drilling requirements. These sensors can be positioned in the subs and, distributed along the drill pipe, in the drill bit and along the BHA. 
   The equipment described above may be constructed as modules. For example, the BHA can include a BCPM module, a sensor module, a formation evaluation or FE module, a drilling motor module, a stabilizer module, and a steering unit module. Each of these modules can be interchangeable. Each module includes appropriate electrical and data communication connectors at each of their respective ends so that electrical power and data can be transferred between adjacent modules via modular threaded connections. Thus, the transmission line or conductive path formed by one or more conductive elements position in or along the above described modules and subs can be used to provide two-way (bi-directional) data transmission and transfer power along the BHA. 
   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: 
       FIG. 1  illustrates a drilling system made in accordance with one embodiment of the present invention; 
       FIG. 2  illustrates an exemplary bottomhole assembly made in accordance with one embodiment of the present invention; 
       FIG. 3A  illustrates an exemplary power/data transmission unit made in accordance with one embodiment of the present invention for conveying power and/or data through a rotor of a drilling motor; 
       FIG. 3B  illustrates an alternative embodiment to the  FIG. 3A  embodiment wherein an electronics package is positioned in a rotor of a drilling motor; 
       FIG. 3C  illustrates an exemplary power/data transmission unit made in accordance with one embodiment of the present invention for conveying power and/or data through a stator of a drilling motor; 
       FIG. 4  illustrates an exemplary power/data transmission unit made in accordance with one embodiment of the present invention for conveying power and/or data through a rotor of a drilling motor; 
       FIG. 5  illustrates a an exemplary power/data transfer unit made in accordance with one embodiment of the present invention; and 
       FIG. 6  shows a schematic functional block diagram relating to a power and data transfer device for transferring power and data between rotating and non-rotating sections of a bottomhole assembly. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention relates to devices and methods for conveying power such as electrical power and/or data signals. While the present invention will be discussed in the context of a drilling assembly for forming subterranean wellbores, the present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. 
   Referring initially to  FIG. 1 , there is shown an embodiment of a land-based drilling system utilizing a drilling assembly  100  made according to one embodiment of the present invention to drill wellbores. These concepts and the methods are equally applicable to offshore drilling systems or systems utilizing different types of rigs. The system  10  shown in  FIG. 1  has a drilling assembly  100  conveyed in a borehole  12 . The drilling system  10  includes a derrick  14  erected on a floor  16  that supports a rotary table  18  that is rotated by a prime mover such as an electric motor  20  at a desired rotational speed. The drill string  22  includes a jointed tubular string  24 , which may be drill pipe or coiled tubing, extending downward from the rotary table  18  into the borehole  12 . The drill bit  102 , attached to the drill string end, disintegrates the geological formations when it is rotated to drill the borehole  12 . The drill string  22  is coupled to a drawworks  26  via a kelly joint  28 , swivel  30  and line  32  through a pulley (not shown). During the drilling operation the drawworks  26  is operated to control the weight on bit, which is an important parameter that affects the rate of penetration. The operation of the drawworks  26  is well known in the art and is thus not described in detail herein. 
   During drilling operations, a suitable drilling fluid  34  from a mud pit (source)  36  is circulated under pressure through the drill string  22  by a mud pump  38 . The drilling fluid  34  passes from the mud pump  38  into the drill string  22  via a desurger  40 , fluid line  42  and the kelly joint  38 . The drilling fluid  34  is discharged at the borehole bottom  44  through an opening in the drill bit  102 . The drilling fluid  34  circulates uphole through the annular space  46  between the drill string  22  and the borehole  12  and returns carrying drill cuttings to the mud pit  36  via a return line  48 . A sensor S 1  preferably placed in the line  42  provides information about the fluid flow rate. A surface torque sensor S 2  and a sensor S 3  associated with the drill string  22  respectively provide information about the torque and the rotational speed of the drill string. Additionally, a sensor S 4  associated with line  32  is used to provide the hook load of the drill string  22 . 
   In one mode of operation, only the mud motor  104  rotates the drill bit  102 . In another mode of operation, the rotation of the drill pipe  22  is superimposed on the mud motor rotation. Mud motor usually provides greater rpm than the drill pipe rotation. The rate of penetration (ROP) of the drill bit  102  into the borehole  12  for a given formation and a drilling assembly largely depends upon the weight on bit and the drill bit rpm. 
   A surface controller  50  receives signals from the downhole sensors and devices via a sensor  52  placed in the fluid line  42  and signals from sensors S 1 , S 2 , S 3 , hook load sensor S 4  and any other sensors used in the system and processes such signals according to programmed instructions provided to the surface controller  50 . The surface controller  50  displays desired drilling parameters and other information on a display/monitor  54  and is utilized by an operator to control the drilling operations. The surface controller  50  contains a computer, memory for storing data, recorder for recording data and other peripherals. The surface controller  50  processes data according to programmed instructions and responds to user commands entered through a suitable device, such as a keyboard or a touch screen. The controller  50  is preferably adapted to activate alarms  56  when certain unsafe or undesirable operating conditions occur. 
   Referring now to  FIG. 2 , there is shown in greater detail an exemplary bottomhole assembly (BHA)  100  made in accordance with the present invention. The BHA  100  carries a drill bit  102  at its bottom or the downhole end for drilling the wellbore and is attached to a tubular string  24  ( FIG. 1 ) at its uphole or top end. As will be described below, the BHA  100  can include tools that utilize electrical power, measure selected parameters of interest and provide data signals representative of the measurements, and/or operate in response to command signals. 
   In one embodiment, the BHA  100  includes a steering unit  110 , a drilling motor  120 , a sensor sub  130 , a bidirectional communication and power module (BCPM)  140 , stabilizers  190 , and a formation evaluation (FE) sub  160 . To enable power and/or data transfer among the individual tools making up the BHA  100 , the BHA  100  includes a power and/or data transmission line  105 . The power and/or data transmission line  105  can extend along the entire length of the BHA  100  up to and including the drill bit  102 . Thus, for example, the line  105  can transfer electrical power from the BCPM  140  to the steering unit  110  and provide two-way data communication between the surface or BCPM  140  and sensors at the steering unit  110  and/or the drill bit  102 . 
   Referring now to  FIGS. 2 and 3A , there is shown a drilling motor  120  having a power/data transmission unit  150  operably coupled to the data/transmission line  105 . In one embodiment, the drilling motor  120  is a positive displacement motor that includes a rotor  122  disposed in a stator  124  forming progressive cavities  125  there between. Fluid supplied under pressure to the motor  120  passes through the cavities  125  and rotates the rotor  122 . The rotor  122  in turn is connected to the drill bit  102  via a flex shaft  126  connected to a drive shaft  128  having a suitable connection such as a having a threaded pin end. A bearing section  130  supports the drive shaft  128 . At the other end, an upper sub  132  is coupled to the motor  120  and includes a threaded box end  134 . The pin end  128  and box end  134  are merely one type of connection arrangement for connecting the drilling motor  120  to adjacent modules or subs. Other connection device can also be used. Additionally, while the pin end  128  is shown as the termination of the power/data transmission unit  150 , it should be understood that in other embodiments, the termination may be positioned further downhole, e.g., at the steering unit  110  or drill bit  102 . 
   The schematically illustrated exemplary power/data transmission unit includes one or more conductive elements or carriers for transmitting power and/or data across the motor  120  and for enabling two-way or bidirectional data transfer across the motor  120 . In some embodiment, the data and power can be conveyed by conductive elements in the rotor or the stator. In other embodiments, transceivers can be positioned along the motor  120  to transmit the data and/or power. Exemplary arrangements are described below. 
   In embodiments, a power/data transmission unit  150  transfers power and/or data between the ends of the motor housing such as the box end  134  and the pin end  128  of the motor  120 . In an exemplary arrangement, the power/data transmission unit  150  includes an electrical contact  152  at the box end  134  and an electrical contact  160  at the pin end  128 . A non-rotating section is formed by a conductive element  154  that is coupled at one end to the box end contact  152  and coupled at the other end to a power/data transfer unit  156 . A rotating section is formed by a conductive element  158  in the shaft  126  that is coupled at one end to the pin end contact  160  and coupled at the other end to the power/data transfer unit  156 . The power/data transfer unit  156  is adapted to transfer power and/or data from the conductive element  154  in the non-rotating portion of the motor  120  to the conductive element  158  in the rotating flex shaft  126  and drive shaft  128 . A suitable power/data transfer unit can include slip ring cartridges having a non-rotating conductive element that contacts a sliding conductive element (e.g., mating metal rings), inductive couplings, or other transfer devices. Thus, power such as electrical power and data signals are conveyed through the motor  120  via a conductive path formed by the box end electrical contact  152 , the conductive element  154  in the stator  124 , the power/data transfer unit  156 , the conductive element  158  in the shaft  126 , and the pin end electrical contact  160 . 
   Referring now to  FIG. 3B , there is shown another embodiment generally similar to that illustrated in  FIG. 3A . However, in the  FIG. 3B  embodiment, an electronics package  400  is positioned in the rotor  122 . The electronics package  400  is coupled to the conductive element  158 , which runs between an electrical contact  160  at one end  128  of the motor  120  to the power/data transfer unit  156 . The electronics package  400  can include sensors for measuring parameters such as vibration, rotational speed, stresses, a processor for processing or decimating data, digitizers, and PLC&#39;s. The electronics package can also include other known wellbore electronics such as electronics that drive or operate actuators for valves and other devices. 
   Referring now to  FIG. 3C , there is shown another embodiment for transferring power/data across a motor  120 . In the  FIG. 3C  embodiment, a conductive element  154  runs from a contact  152  at one end  134  of the motor  120  to the power/data transfer unit  156 A. More specifically, the conductive element  154  runs through the housing of the sub  132 , the stator  124 , the housing  402  of the flex shaft  126 , and the housing of the bearing section  130 . Thus, the conductive element  154  runs through the non-rotating sections of the motor assembly  120 . In contrast to the  FIG. 3A  embodiment, the power/data transfer unit  156 A is positioned within the bearing section  130  rather than in the sub  132  uphole of the rotor  122 . The conductive element  158 B runs from the power/data transfer unit  156 A to the contact  160 . Optionally, an electronics package  400  can be positioned in the rotor  122  or the stator  124  and connected to the conductive element  158 B and/or the power/data transfer unit  156 A via a suitable conductor  404 . 
   It should be understood that the embodiments illustrated in  FIGS. 3A-3C  are not exhaustive of the variations of the present invention. Rather, these discussed embodiments are intended as examples of how the teachings of the present invention can be applied. 
   In the above-described embodiment, the conductive elements  154  and  158  can be formed of one or more insulated wires or bundles or wires adapted to convey power and/or data. In embodiments, the wires can include metal conductors. In other embodiments, other carriers such as fiber optic cables may be used. The conductive element  154  can be run within a channel or conduit (not shown) in sub  132  and the stator  124 . The conductive element  158  can be run within a bore (not shown) of the flex shaft  126  and drive shaft  128 . 
   Referring now to  FIG. 4 , there is shown an exemplary power/data transmission unit  170  made in accordance with the present invention that transfers power and/or data across the motor  120 . In the  FIG. 4  embodiment, power and/or data signals are transferred across the motor  120  using one or more conductive elements positioned in the rotor  122 . Because of the relative rotational motion between the rotor  122  and the stator  124 , the power/data transmission unit  170  can be considered as having a rotating section or power/signal line in the rotor  122  and a non-rotating section or power/data line in the stator  124  or adjacent sub or module. A power/data transfer unit  174  is used to transfer power and/or data between the rotating and non-rotating sections. Moreover, as is known, the rotor  122  rotates eccentrically in the stator  124  during operation. Thus, the power/data transmission unit  170  compensates for radial and axial movement of the rotor  122  in a manner described below. 
   As shown in  FIG. 4 , the non-rotating section of the power/data transmission unit  170  includes one or more conductive elements  172  positioned along a sub  132  (or stator housing or other adjacent module). The rotating section of the power/data transmission unit  170  is positioned partially inside or on top of the rotor  122  and includes the flexible member  176 , a length compensation device  178 , and a conductive element  180 . Each of these devices include suitable conductors (e.g., metal conductors, fiber optic wires, etc.) to convey power and/or data signals. The power/data transfer unit  174 , which is positioned within the sub  132  with a centralizer  175 , transfer power/data between these rotating and non-rotating sections of the power/data transmission unit  170 . 
   In one embodiment, in the non-rotating section, the conductive element  172  is coupled to the contact  154  at the box end  134  of the sub  132 . The conductive element  172  is run in a channel (not shown) or other suitable conduit formed in the sub  132  and terminates at the power/data transfer unit  174 . The rotating section of the power/data transmission unit  170  is rotatably coupled to the power/data transfer unit  174  by the flexible member  176 . The length compensation unit  178  connects the flexible member  176  to the conductive element  180  to thereby form a conductive path for data/power through the rotor  122 . During operation, the length compensation unit  178  expands and contracts as needed to accommodate the motion of the rotor  122 . The conductive element  180 , which is connected to the length compensation unit  178 , terminates at the pin contact  160  ( FIG. 3 ). The flexible shaft  176  and the length compensation unit  178  absorb or otherwise accommodate the changes in radial motion and length, respectively, of the shaft  122 . The power/data transfer unit  174  transfers power and/or data to and from the rotating flexible shaft  176  in a manner described below. 
   Referring now to  FIG. 5 , there is shown an exemplary power/data transfer unit  174  made in accordance with one embodiment of the present invention. The power/data transfer unit  174  is adapted to transfer power and or data between the non-rotating conductor  174  and the rotating flexible member  176 . In one embodiment, the flexible member  176  includes an outer flexible tubular member  200  and a conductive connector  202 . An isolation sleeve  204  can be used to electrically insulate the conductive connector  202  from the outer tubular member  200 . The conductive connector  202  has at one end a disk-like contact head  206  formed thereon for transferring power and/or data signals to/from the power/data transfer unit  174 . A bearing assembly  208  stabilizes and controls rotation of the flexible member  176  within the power/data transfer unit  174 . The bearing assembly includes a retainer body  210  for retaining bearings  212  and seals  214  for minimizing the entry of unwanted materials into the power/data transfer unit  174 . Additionally, bearings  216  can be used to further stabilize the rotation of the flexible member  176 . 
   Referring now to  FIGS. 4 and 5 , the power/data transfer unit  174  is fixed in the centralizer  175  that is positioned in a bore  133  of the sub  132 . The centralizer  175  includes axial passages (not shown) that allow drilling fluid (not shown) to flow through the bore  133 . The power/data transfer unit  174  includes a body  192  in which are formed channels  194  for receiving conductive elements  196  and an open end  198  adapted to receive the bearing assembly  208  and the flexible member  176 . The conductive elements  196  are coupled at one end to an external connector  209  and at the other end to a contact assembly  218 . The contact assembly  218  maintains continuity of power and data transfer between conductive elements  196  and the rotating conductive connector  202 . An exemplary contact assembly  218  includes a cylinder  220  and a piston  222  biased within the cylinder  220  by a spring  224 . The piston  222  is formed at least partially of a conductive material and is biased into physical engagement with the contact head  206  of the conductive connector  202 . This physical engagement, however, allows the contact head  206  to rotate relative to the piston  222 . Further, axial movement of the flexible member  176  during operation, either toward or from the piston  222 , will not interrupt power/data transfer because the piston  222  can slide forward or backward as necessary to maintain the physical contact with the contact head  206 . 
   Additionally, the power/data transfer unit  174  can include a pressure compensation unit  230  for controlling fluid pressure in the power/data transfer unit  174 . In one embodiment, the interior cavities of the power/data transfer unit  174 , such as the channel  194 , are filled with a hydraulic fluid such as oil. An exemplary pressure compensation unit  230  for controlling the pressure of the fluid in the power/data transfer unit  174  includes a chamber  232  in which a spring  234  biases a piston head  236 . In one arrangement, passages  237  are formed to allow the surrounding pressurized drilling fluid to apply hydrostatic pressure against the piston head  236 . The spring force of the spring  234  is selected to maintain a desired amount of pressure on the hydraulic fluid. Plugs  238  are provided in the body  192  to allow filling and draining of fluid in the power/data transfer unit  174 . Seals are also used as needed to maintain fluid integrity of the power/data transfer unit  174 . 
   It should be appreciated that a drilling motor made in accordance with the present invention enables data and/or power transmission between equipment uphole of the motor and equipment downhole of the motor. For example, power and/or data signals can be transferred from the BCPM  140  to the steering unit  110 . Also, sensors (not shown) in or near the drill bit  102  can transmit data to one or more processors (not shown) uphole of the motor  120 . One exemplary advantage of the present invention is enabling the positioning of electronics and other equipment sensitive to vibration further uphole of the drill bit  102 , which provides some measure of isolation from vibrations caused by the rotating drill bit  102 . Another exemplary advantage is an increase in effectiveness of the drilling motor  120 . That is, because the BCPM  140  can be positioned uphole of the motor  120 , the length between the drill bit  102  and the motor  120  is reduced—which enhances the transmission of rotary power from the motor  120  to the drill bit  102 . 
   Thus, as described above, power and/or data can be transferred between rotating and non-rotating members such as the flexible shaft  176  and power/data transfer unit  174  using a path formed by physical contact by two conductive elements. In other embodiments, an inductive coupling device can be used to transfer electric power and data signals between rotating and non-rotating members as more fully described below. 
   Referring now to  FIG. 6 , there is shown a block functional diagram of a section of the BHA  100  that depicts the method for power and data transfer between the rotating and non-rotating sections of the BHA  100 . In  FIG. 6 , a steering unit  310  is shown disposed on a rotating shaft  328  coupled at one end to the rotor of the drilling motor (e.g., at pin end  128  of  FIG. 3 ) and at the other end to the drill bit  102 . The steering unit  310  includes a non-rotating sleeve or member  360  and receives electrical power generated by the BCPM  140  and/or the surface via methods and devices previously described. 
   In one embodiment, electric power and data are transferred between a rotating drill shaft  328  and the non-rotating sleeve  360  via an inductive coupling. An exemplary inductive power and data transfer device  370  is an inductive transformer, which includes a transmitter section  372  carried by the rotating member  328  and a receiver section  374  placed in the non-rotating sleeve  360  opposite from the transmitter  372 . The transmitter  372  and receiver  374  respectively contain coils  376  and  378 . Power to the coils  376  is supplied by the primary electrical control circuit  380 . The primary electronics  380  conditions the power supplied by the BCPM  140  or other source and supplies it to the coils  376 . These coils  376 , 378  induce current into the receiver section  374 , which delivers AC voltage as the output. The secondary control circuit or the secondary electronics  382  in the non-rotating member  360  converts the AC voltage from the receiver  372  to DC voltage. The DC voltage is then utilized to operate various electronic components in the secondary electronics and any electrically-operated devices. 
   Still referring to  FIG. 6 , a motor  350  operated by the secondary electronics  382  drives a pump  364 , which supplies a working fluid, such as oil, from a source  365  to a piston  366 . The piston  366  moves its associated rib  368  radially outward from the non-rotating member  360  to exert force on the wellbore wall. The pump speed is controlled or modulated to control the force applied by the rib on the wellbore wall. Alternatively, a fluid flow control valve  367  in the hydraulic line  369  to the piston may be utilized to control the supply of fluid to the piston and thereby the force applied by the rib  368 . The secondary electronics  362  controls the operation of the valve  367 . A plurality of spaced apart ribs (usually three) are carried by the non-rotating member  360 , each rib being independently operated by a common or separate secondary electronics. 
   It should be understood that there may be a limited amount of rotation of the non-rotating member  360  relative to the wellbore wall. As noted earlier, in some modes of operation, drill string rotation is superimposed on the rotation of the drilling motor. These types of rotation can cause the surrounding non-rotating member (or sleeve)  360  to slowly rotate. 
   The secondary electronics  382  receives signals from sensors  379  carried by the non-rotating member  360 . At least one of the sensors  379  provides measurements indicative of the force applied by the rib  368 . Each rib has a corresponding sensor. The secondary electronics  382  conditions the sensor signals and may compute values of the corresponding parameters and supplies signals indicative of such parameters to the receiver section  374 , which transfers such signals to the transmitter  372 . A separate transmitter and receiver may be utilized for transferring data between rotating and non-rotating sections. Frequency modulating techniques, known in the art, may be utilized to transfer signals between the transmitter and receiver or vice versa. The signals from the primary electronics may include command signals for controlling the operation of the devices in the non-rotating sleeve. Suitable power transfer devices are discussed in U.S. Pat. No. 6,427,783, which is commonly assigned and which is hereby incorporated by reference for all purposes. Also, drilling systems are discussed in U.S. Pat. No. 6,513,606, which is commonly assigned and which is hereby incorporated by reference for all purposes. 
   It should be appreciated that the above-described arrangements and methods for transferring data and/or power can enhance flexibility in overall design of the BHA  100 . With the benefits of the present invention, the relative positioning of such equipment in the BHA  100  is not necessarily limited by considerations relating to providing electrical and data connections to that equipment. Exemplary BHA equipment that can be connected to power and/or data transmission line  105  are discussed in greater detail below. 
   Referring now to  FIG. 2 , the bidirectional data communication and power module (“BCPM”)  140  uphole of the drilling motor  120  and the steering unit  110  provides power to the steering unit  110  and two-way data communication between the BHA  100  and surface devices. In one embodiment, the BCPM generates power using a mud-driven alternator (not shown) and the data signals are generated by a mud pulser (not shown). The mud-driven power generation units (mud pursers) are known in the art thus not described in greater detail. 
   In one embodiment, the sensor sub  130  can includes sensors for measuring near-bit direction (e.g., BHA azimuth and inclination, BHA coordinates, etc.), dual rotary azimuthal gamma ray, bore and annular pressure (flow-on &amp; flow-off), temperature, vibration/dynamics, multiple propagation resistivity, and sensors and tools for making rotary directional surveys. The sensor sub  130  can include one or more processors  132  that provide central processor capability and data memory. 
   The formation evaluation sub  160  can includes sensors for determining parameters of interest relating to the formation, borehole, geophysical characteristics, borehole fluids and boundary conditions. These sensor include formation evaluation sensors (e.g., resistivity, dielectric constant, water saturation, porosity, density and permeability), sensors for measuring borehole parameters (e.g., borehole size, and borehole roughness), sensors for measuring geophysical parameters (e.g., acoustic velocity and acoustic travel time), sensors for measuring borehole fluid parameters (e.g., viscosity, density, clarity, rheology, pH level, and gas, oil and water contents), and boundary condition sensors, sensors for measuring physical and chemical properties of the borehole fluid. 
   The subs  130  and  160  can include one or memory modules and a battery pack module to store and provide back-up electric power may be placed at any suitable location in the BHA  100 . 
   Additional modules and sensors can be provided depending upon the specific drilling requirements. Such exemplary sensors can include an rpm sensor, a weight on bit sensor, sensors for measuring mud motor parameters (e.g., mud motor stator temperature, differential pressure across a mud motor, and fluid flow rate through a mud motor), and sensors for measuring vibration, whirl, radial displacement, stick-slip, torque, shock, vibration, strain, stress, bending moment, bit bounce, axial thrust, friction and radial thrust. The near bit inclination devices may include three (3) axis accelerometers, gyroscopic devices and signal processing circuitry as generally known in the art. These sensors can be positioned in the subs  130  and  160 , distributed along the drill pipe, in the drill bit and along the BHA  100 . Further, while subs  130  and  160  are described as separate modules, in certain embodiments, the sensors above described can be consolidated into a single sub or separated into three or more subs. 
   Also, the stabilizer  190  has one or more stabilizing elements  192  and is disposed along the BHA  100  to provide lateral stability to the BHA  100 . 
   In some embodiments, the equipment described above is constructed as modules. For example, the BHA  100  can include a BCPM module  140 , a sensor module  130 , a formation evaluation or FE module  160 , a drilling motor module  120 , a stabilizer module  150 , and a steering unit module  110 . Each of these modules can be interchangeable. For example, the BCPM  140  may be connected above the MWD module  130  or above the FE module  160 . Similarly, the FE module  160  may be placed below the sensor module  130 , if desired. Also, one or more of the modules can be omitted in certain configurations. Still further, additional modules not discussed above can be inserted with ease into the BHA  100 . Each module includes appropriate electrical and data communication connectors at each of their respective ends so that electrical power and data can be transferred between adjacent modules via modular threaded connections. Thus, the transmission line or conductive path  105  formed by one or more conductive elements position in or along the above described modules and subs can be used to transfer power and/or data along the BHA. In addition to optimizing equipment safety and operation, modular construction can increase the ease of manufacturing, repairing of the BHA and interchangeability of modules in the field. 
   Referring now to  FIGS. 1-6 , in an exemplary manner of use, the BHA  100  is conveyed into the wellbore  12  from the rig  14 . During drilling of the wellbore  12 , the steering unit  110  can be used to steer the drill bit  102  in a selected direction. The electrical power to operate the motor  350  for the steering unit  110  is generated by the BCPM  140  and conveyed to the motor  350  via the conductive line  105 , including the power/data transmission unit  170 , in the drilling motor  120 . Electrical power, of course, can also be conveyed via the conductive line  105  to the sensors, processors and other electrical devices in the BHA  100 . Additionally, command signals, data signals, sensor measurements can also be transmitted bi-directionally across the conductive path  105 . For example, command signals may be transmitted from the BCPM sent to align or orient the pads of the steering unit to urge the drill bit  102  in a selected direction. 
   The power/data transmission unit and power/data transfer unit can be employed in multiple configurations. For example, the power/data transmission unit and power/data transfer unit can transmit/transfer (i) only power, (ii) only data, or (iii) both data and power. Additionally, the power/data transmission unit and power/data transfer unit can include two or more carriers, each of which can be formed to carry only power, only data, or both power and data. The nomenclature “power/data transmission unit” and “power/data transfer unit” are used merely for convenience to refer to all such configurations and not any particular configuration. 
   Additionally, the terms “rotating” and “non-rotating” in context can either describe rotation relative to an adjacent body or relative to a formation. For example, while parts described as “non-rotating” such as the stator may in certain mode of operation rotate due to rotation of the drill string, the condition being described in the relative non-rotation with respect to the rotor. Moreover, in context, the term “non-rotating” may not necessarily describe an absolute condition. For instance, there may be a relatively small amount of rotation for the part described as non-rotating. 
   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.