Patent Application
20100224356
None.
The present invention relates generally to downhole tools having rotating components, for example, including directional drilling tools such as a steering tool or a mud motor. More particularly, embodiments of this invention relate to a downhole assembly including a non-contact apparatus for transmitting electrical power and/or data between first and second members of the assembly that are disposed to rotate with respect to one another (such as a shaft rotating in a housing).
As is well-known in the industry, hydrocarbons are recovered from subterranean reservoirs by drilling a borehole (wellbore) into the reservoir. Such boreholes are commonly drilled using a rotating drill bit attached to the bottom of a drilling assembly (which is commonly referred to in the art as a bottom hole assembly or a BHA). The drilling assembly is commonly connected to the lower end of a drill string including a long string of sections (joints) of drill pipe that are connected end-to-end via threaded pipe connections. The drill bit, deployed at the lower end of the BHA, is commonly rotated by rotating the drill string from the surface and/or by a mud motor deployed in the BHA. Mud motors are also commonly utilized with flexible, spoolable tubing referred to in the art as coiled tubing. During drilling a drilling fluid (referred to in the art as mud) is pumped downward through the drill string (or coiled tubing) to provide lubrication and cooling of the drill bit. The drilling fluid exits the drilling assembly through ports located in the drill bit and travels upward, carrying debris and cuttings, through the annular region between the drilling assembly and borehole wall.
In recent years, directional control of the borehole has become increasingly important in the drilling of subterranean oil and gas wells, with a significant proportion of current drilling activity involving the drilling of deviated boreholes. Such deviated boreholes often have complex profiles, including multiple doglegs and a horizontal section that may be guided through thin, fault bearing strata, and are typically utilized to more fully exploit hydrocarbon reservoirs. Deviated boreholes are often drilled using downhole steering tools, such as two-dimensional and three-dimensional rotary steerable tools. Certain rotary steerable tools include a plurality of independently operable blades (or force application members) that are disposed to extend radially outward from a tool housing into contact with the borehole wall. The direction of drilling may be controlled, for example, by controlling the magnitude and direction of the force or the magnitude and direction of the displacement applied to the borehole wall. In such rotary steerable tools, the blade housing is typically deployed about a rotatable shaft, which is coupled to the drill string and disposed to transfer weight and torque from the surface (or from a mud motor) through the steering tool to the drill bit assembly. Other rotary steerable tools are known that utilize an internal steering mechanism and therefore don't require blades (e.g., the Schlumberger PowerDrive rotary steerable tools).
Directional wells are also commonly drilled by causing a mud motor power section to rotate the drill bit through a displaced axis while the drill string remains stationary (non-rotating). The displaced axis may be achieved, for example, via a bent sub deployed above the mud motor or alternatively via a mud motor having a bent outer housing. The bent sub or bent motor housing cause the direction of drilling to deviate (turn), resulting in a well section having a predetermined curvature (dogleg severity) in the direction of the bend. A drive shaft assembly deployed below the power section transmits downward force and power (rotary torque) from the drill string and power section through a bearing assembly to the drill bit. Common drive shaft assemblies include a coaxial shaft (mandrel) deployed to rotate in a housing.
The non-rotating sections (e.g., the above described housings) commonly include MWD and/or LWD sensors, electronic components and controllers, and electrical actuators (e.g., solenoid actuated valves and switches used to control steering blades). In the above described drilling assemblies a gap typically exists between the rotating and non-rotating sections (e.g., between the shaft and housing). Thus electrical power must be stored and/or generated in the non-rotating section or transferred across the gap from the rotating section to the non-rotating section. Moreover, in order to provide electronic communication between the rotating and non-rotating sections, data must also be transferred back and forth across the gap.
Techniques for transmitting electrical power and electronic data across the gap between rotating and non-rotating tool sections are known in the art. For example, sealed slip rings are sometimes utilized. While slip rings have been used commercially, failure of certain slip ring components is a known cause of downhole tool failure. For example, slip ring seals have been known to fail, which can result in a loss of communication with the tool and the need to trip out of the borehole. Loss of electrical contact between the slip ring contact members (e.g., due to wear) is also a known cause of tool failure. The electrical performance of slip rings is also susceptible to both long term and short term degradation when exposed to oil. Furthermore, when used with heavier grade lubricating oils, liftoff of the contacts may occur. Interruption of the electrical current can then cause burning of the oil and contamination to the contacts. Slip ring assemblies can also be difficult to assemble between a shaft and sleeve.
Inductive coupling devices are also known for transferring power and/or data between rotating and non rotating tool sections. For example, U.S. Pat. No. 6,540,032 to Krueger discloses an inductive coupling for transferring power and data between rotating and non-rotating sections of a downhole drilling assembly. While inductive coupling devices are known in commercial oilfield applications, there remains a need for improved devices for non-contact transmission of data and electrical power between tool sections. For example, inductive couplings are known to be highly sensitive to the spacing between the transmitter and receiver (i.e., the clearance between the shaft and sleeve). In rotary steerable deployments, inductive couplings tend to exhibit low transmission efficiencies owing to the relatively large gap between the shaft and the blade housing. Owing to the demand for smaller diameter and less expensive rotary steerable tools (and downhole tools in general) and to the increased demand for electrical power in such tools, there is a need for improved non-contact power and data transmission devices.
The present invention addresses the need for improved non-contact power and data transmission devices in downhole tools including downhole drilling assemblies. Aspects of this invention include a non-contact electrical coupling device suitable for transmitting electrical power and/or data across a gap between rotating components in a downhole tool. Exemplary embodiments of the invention include at least first and second wound toroidal cores deployed about a shaft. At least one of the wound toroidal cores is rotationally fixed to the shaft, while at least another is rotationally fixed to a housing deployed about the shaft. The shaft forms a portion of a conductive loop that extends through the toroids. The invention may be thought of as including first and second transformers that share a single turn winding (the conductive loop). The first wound toroidal core forms the primary of the first transformer. The conductive loop forms a single-turn secondary of the first transformer and a single-turn primary of the second transformer. The second wound toroidal core forms the secondary of the second transformer. Aspects of the invention typically further include electronic control circuitry for transmitting and receiving the electrical power and/or data.
Exemplary embodiments of the present invention may advantageously provide several technical advantages. For example, exemplary embodiments of this invention provide a non-contact, high-power electrical transmission path and a high-speed data communication channel across a gap between first and second rotating members of a downhole assembly. Moreover, exemplary embodiments of the invention also provide for simultaneous non-contact transmission of electrical power between the first and second tool members.
Exemplary embodiments of the invention may be advantageously configured for high-power and high-efficiency electrical transmission (especially as compared with conventional inductive coupling devices). Moreover, the invention does not utilize a magnetic field to transmit electrical energy across an air gap (as with prior art inductive couplings). Those of ordinary skill in the art will appreciate that the presence of the air gap in an inductive coupling reduces the effective magnetic permeability of the magnetic path, which can significantly reduce the overall efficiency of the coupling. The invention utilizes the afore-mentioned low impedance conductive loop to transmit electrical energy between the rotating components and is therefore advantageously unaffected by the clearance (the size of the gap) between the rotating components (e.g., between the shaft and housing on a rotary steerable tool) or between similar parts of a rotary transformer.
In one aspect the present invention includes a downhole tool. The downhole tool includes a shaft deployed in a housing and configured to rotate with respect to the housing. The downhole tool further includes a non-contact electrical coupling device configured to transmit an electrical signal between the shaft and the housing. The electrical coupling device includes at least first and second axially spaced wound toroidal cores deployed about the shaft. The first wound toroidal core is rotationally coupled with the shaft and the second wound toroidal core is rotationally coupled with the housing.
In another aspect the invention includes a downhole tool. The tool includes a shaft deployed in a housing, the shaft disposed to rotate with respect to the housing. The tool further includes first and second transformers sharing a single-turn conductive loop. At least a first wound toroidal core forms a primary of the first transformer, the first wound toroidal core being deployed about the shaft and rotationally coupled with the shaft. At least a second wound toroidal core forms a secondary of the second transformer, the second wound toroidal core being deployed about the shaft and rotationally coupled with the housing. The second wound toroidal core is axially spaced from the first wound toroidal core. The conductive loop forms both a single-turn secondary of the first transformer and a single-turn primary of the second transformer. The conductive loop includes a portion of the shaft that extends through central windows of the first and second wound toroidal cores.
In still another aspect the present invention includes a downhole tool having a shaft deployed in a housing and configured to rotate with respect to the housing. The shaft is supported in the housing by at least first and second longitudinally spaced bearings. A non-contact electrical coupling device is configured to transmit an electrical signal between the shaft and the housing. The electrical coupling device includes first and second longitudinally spaced sets of wound toroidal cores deployed about the shaft and between the first and second bearings. Each of the sets includes a plurality of longitudinally spaced wound toroidal cores, the first set of wound toroidal cores being rotationally coupled with the shaft and the second set of wound toroidal cores being rotationally coupled with the housing. The shaft, the first bearing, the housing, and the second bearing, in combination, form a conductive loop that passes through a central window of each of the wound toroidal cores.
In yet another aspect the present invention includes a rotary steerable tool having a shaft deployed in a steering tool housing and configured to rotate with respect to the housing. The shaft is supported in the housing by at least first and second longitudinally spaced bearings. A plurality of blades are deployed on the housing and disposed to extend radially outward from the housing and engage a wall of a borehole. Engagement of the blades with the borehole wall is operative to eccenter the housing in the borehole. A non-contact electrical coupling device is configured to transmit electrical power from the shaft to the housing. The electrical coupling device includes first and second longitudinally spaced sets of wound toroidal cores deployed about the shaft and between the first and second bearings. Each of the sets includes a plurality of longitudinally spaced wound toroidal cores, the first set of wound toroidal cores being rotationally coupled with the shaft and the second set of wound toroidal cores being rotationally coupled with the housing. The shaft, the first and second bearings, and the housing in combination forming a conductive loop that passes through a central window of each of the wound toroidal cores.
The foregoing has outlined rather broadly the features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other methods, structures, and encoding schemes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Referring first to
It will be understood by those of ordinary skill in the art that methods and apparatuses in accordance with this invention are not limited to use with a semisubmersible platform 12 as illustrated in
Turning now to
To steer (i.e., change the direction of drilling), one or more of blades 150 are extended into contact with the borehole wall. The steering tool 100 is moved away from the center of the borehole by this operation, thereby altering the drilling path. It will be appreciated that the tool 100 may also be moved back towards the borehole axis if it is already eccentered. To facilitate controlled steering, the rotation rate of the housing is desirably less than 0.1 rpm during drilling, although the invention is not limited in this regard. By keeping the blades 150 in a substantially fixed position with respect to the circumference of the borehole (i.e., by preventing rotation of the housing 110), it is possible to steer the tool without constantly extending and retracting the blades 150. Non-rotary steerable embodiments are thus typically only utilized in sliding mode (although they may be rotated when steering is not desired). In rotary steerable embodiments, the tool 100 is constructed so that the housing 110, which houses the blades 150, remains stationary, or substantially stationary, with respect to the borehole during directional drilling operations. The housing 110 is therefore constructed in a rotationally non-fixed (or floating) fashion with respect to a shaft 115 (
The above-described control and manipulation of the blades 150 is known to consume electrical power. For example, in one commercially serviceable embodiment, the blades 150 are extended via hydraulic actuation with solenoid-actuated controllable valves being utilized to increase or decrease hydraulic fluid pressure at the individual blades. Electrically-powered hydraulic pumps have also been disclosed for controlling blade actuation (U.S. Pat. No. 6,609,579). The steering tool housing 110 typically further includes electronic components for sensing and controlling the position of each of the blades. Steering tool embodiments typically further include one or more microcontrollers, electronic memory, and like. Such electronics typically consume relatively little electrical power as compared to the solenoids and/or electrical pumps described above, although the invention is not limited in regard to electric power consuming components deployed in the tool housing 110.
It will be appreciated that steering tool functionality is advantageously enhanced by providing improved data transmission between housing 110 and rotating shaft 115. For example, closed-loop steering techniques, such as geo-steering techniques, commonly require communication with LWD sensors deployed elsewhere in the drill string. Typical geo-steering applications make use of directional formation evaluation measurements (azimuthally sensitive LWD measurements) made very low in the BHA, for example, in a rotating stabilizer located just above the drill bit and/or even in the drill bit. To enable true closed-loop control, such directional formation evaluation measurements are advantageously transmitted in substantially real time to electronic module 140. Electronic module 140 is also advantageously disposed in electronic communication with a downhole telemetry system (e.g., a mud pulse telemetry system) for transmitting various steering tool data up-hole. Such telemetry systems are typically deployed at the upper end of the BHA.
Turning now to
In the exemplary embodiment shown, coupling device 300 includes at least first and second substantially coaxial, axially offset wound toroidal cores 330 and 340 deployed about the shaft 205. The first wound toroidal core 330 is rotationally fixed to the shaft 205 (i.e., is disposed to rotate with the shaft). The second wound toroidal core 340 is rotationally fixed to the housing 210 (i.e., is disposed to rotate with the housing). It will therefore be appreciated that the first and second wound toroidal cores are disposed to rotate relative to one another about the longitudinal axis of the shaft 205. Each of the wound toroidal cores 330 and 340 further includes a magnetically permeable toroidal core having multiple windings of insulated wire wrapped thereabout. The insulated wires wound about the first toroidal core are electrically connected (as depicted at 352) to an AC power source 350 (e.g., a downhole turbine or an inverter that is further coupled to a battery pack). The insulated wires wound about the second toroidal core are electrically connected (as depicted at 362) to electrical load 360.
In the exemplary embodiment depicted on
With continued reference to
With continued reference to
It will be appreciated that wound toroidal cores 330 and 340 may be wound with the insulated wire to include substantially any number of turns. As depicted on
As described above, exemplary embodiments of electrical coupling device 300 may be configured for transmitting electrical power and data in either direction across gap 215 (from the shaft 205 to the housing 210 or from housing 210 to the shaft 205). It will be appreciated that data transmission requires the transmission of significantly less electrical energy (typically many orders of magnitude less energy) than that of power transmission. For example, data transmission often only requires an electrical current on the order of a few microamps or less. Useful power transmission, on the other hand, typically involves transferring at least a milliamp of electrical current and often involves the transmission of multiple amps of electrical current. Thus it will be appreciated that exemplary embodiments of the invention intended for data transmission only may be configured differently than embodiments that are intended for electrical power transmission (or both electrical power and data transmission).
Exemplary embodiments of the invention may be advantageously configured for high power electrical transmission (e.g., up to about 200 Watts). One difficulty in achieving high power transmission is that the electrical current in the primary of the transmitting transformer 270 is stepped up by a factor of N in the single-turn secondary (the conductive loop 390 including the shaft 205, radial bearings 315 and 317, and the housing 210). In other words, in an exemplary embodiment in which N=100, a primary current of 5 amps in the primary of the transmitting transformer 370 is stepped up to about 500 amps in the single-turn secondary. Such large electrical currents in the single-turn secondary (conductive loop 390) can result in significant IR losses even when the resistance of the shaft, bearings, and housing are extremely low (which they typically are owing to the large cross sectional area of those components). Those of skill in the art will readily recognize that such power losses are proportional to the square of the electrical current (Ploss=I2·R).
Therefore, in certain embodiments it may be advantageous to configure the electrical coupling device so as to reduce the electrical current induced in the single-turn secondary (the shaft, bearings, and housing). This may be accomplished, for example, by reducing the number of turns N in the primary of the transmitting transformer 380. However, when it is desirable to step down the voltage from the power supply to the electrical load (e.g., when a high voltage turbine is utilized as the power supply), there is a limit as to how far N can be reduced and still achieve the desired ratio of N to M.
With reference now to
While the exemplary embodiment depicted on
It will further be appreciated by those of skill in the art that the wound toroidal cores 330 and 340 advantageously utilize a highly magnetically permeable core so as to reduce transformer losses (the use of a highly permeable core ensures that substantially all of the magnetic flux produced by the electrical current in the winding remains in the core). While toroidal cores having substantially any suitable magnetic permeability may be utilized, those having a relative magnetic permeability of greater than about 10,000 are preferred. Preferred core materials also advantageously have a high Curie temperature (e.g., greater than about 150 degrees C. or greater than about 200 degrees C.) and a high magnetic field saturation so as to reduce losses at the particular frequencies utilized. Preferred embodiments of the invention may include toroidal cores fabricated from, for example, Supermalloy, Amorphous Alloy E, Permalloy 80, and Magnesil (available from Magnetics, Inc., Pittsburg, Pa.) and Metglas® 2714A and Metglas® 2605 (available from Allied-Signal), although the invention is not limited in this regard. Preferred toroidal core embodiments may also include tape wound cores, e.g., as available from Magnetics (which is a division of Spang & Co., Pittsburg, Pa.). Such tape wound cores may be advantageously deployed in a metallic or non-metallic casing so as to prevent mechanical damage to the core during downhole deployment. Encased and/or encapsulated tape wound cores are also available from Magnetics.
With reference now to
Turning now to
With continued reference to
When transmitting data, a data signal is received at the serial communication driver 420 from bus 430. The digital control circuit 418 converts the digital signal to an analog signal which is used to modulate a carrier frequency at the antenna driver 416. It will be understood that substantially any known modulation techniques may be utilized, for example, including amplitude, frequency, and phase modulation. Conventional digital modulation schemes, for example, including QAM, DSL, ADSL, TDMA, FDMA, and the like, may also be utilized. In one advantageous embodiment, a carrier frequency in the range from about 10 to about 100 kHz is utilized, although the invention is not limited in this regard. Antenna driver 416 transmits the On-Off Keying modulated data signal through the tuning circuit 412 to the corresponding wound toroidal core 330, 340 (
As stated above, the exemplary embodiment shown is also configured to transmit electrical power from the rotating shaft 205 to the tool housing 210, i.e., from wound toroidal core 330 to wound toroidal core 340 (or analogously from transformer 370 to transformer 380) (
With continued reference to
Referring now to
As stated above, the invention is not limited to rotary steerable or even steering tool embodiments. Exemplary embodiments in accordance with the invention may also be utilized, for example, in downhole motors (mud motors). Conventional mud motors typically include a bearing housing deployed below the power section, the bearing housing typically including a mandrel deployed to rotate in an outer housing. In one exemplary embodiment of the invention, a first wound toroidal core 330 may be deployed on the outer surface of the mandrel and a second wound toroidal core 340 may be deployed on an inner surface of the housing (similar to the embodiment depicted on
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
