Several conventional logging while drilling (“LWD”) calipers for determining the borehole diameter currently exist. However, current LWD calipers are limited in various ways. Some of the caliper measurements are secondary, in that they involve small changes in other quantities that are the primary property being measured. For example, a common type of LWD tool measures rock formation resistivity using 2 MHz electromagnetic waves. The resistivity caliper is based on small changes in the phases and amplitudes of the electromagnetic waves, and it does not work in oil based mud, and it only provides an average diameter. The LWD tool that measures rock formation density uses gamma-rays, which pass through the drilling fluid (or “mud”). As the mud has a different density than the rock formation, subtle differences in the count-rates at two detectors depend on the gap between the density sensors and the borehole wall. The density caliper can only be acquired while drilling, and is limited to measuring relatively small washouts, e.g., less than 1 inch. The ultrasonic caliper sends pulses toward the borehole wall and records the round-trip travel time. However, it has a relatively limited range in relatively heavy muds and cannot be obtained on the trip out. In wireline, mechanical calipers are used where one or more arms are deployed when logging out of the borehole. The mechanical wireline calipers make direct and accurate measurements of the borehole diameter, and can even measure non-circular boreholes.
A logging while drilling (LWD) caliper includes a drill collar, at least one movable pad, a hinge coupler, a power transmitter and a power receiver. The hinge coupler couples the movable pad to the drill collar in such a way that the movable pad can move between an open position and a closed position. The power transmitter is coupled to the drill collar in such a way that the power transmitter receives power from the drill collar. The power receiver is coupled to the movable pad in such a way that the power receiver provides power to the movable pad. Also, the power transmitter is coupled to the drill collar and the power receiver is coupled to the movable pad in such a way that power is transmitted from the power transmitter to the power receiver whereby the movable pad moves between the open position and the closed position.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
In the Figures, like reference numerals refer to like parts throughout the various views unless otherwise indicated. For reference numerals with letter character designations such as “102A” or “102B”, the letter character designations may differentiate two like parts or elements present in the same figure. Letter character designations for reference numerals may be omitted when it is intended that a reference numeral to encompass all parts having the same reference numeral in all figures.
Referring initially to
The controller 106 and the drilling system 104 may be coupled to the communications network 142 via communication links 103. Many of the system elements illustrated in
The links 103 illustrated in
The drilling system 104 and controller 106 of the system 102 may have RF antennas so that each element may establish wireless communication links 103 with the communications network 142 via RF transceiver towers (not illustrated). Alternatively, the controller 106 and drilling system 104 of the system 102 may be directly coupled to the communications network 142 with a wired connection. The controller 106 in some instances may communicate directly with the drilling system 104 as indicated by dashed line 99 or the controller 106 may communicate indirectly with the drilling system 104 using the communications network 142.
The controller module 101 may include software or hardware (or both). The controller module 101 may generate the alerts 110A that may be rendered on the display 147. The alerts 110A may be visual in nature but they may also include audible alerts as understood by one of ordinary skill in the art.
The display 147 may include a computer screen or other visual device. The display 147 may be part of a separate stand-alone portable computing device that is coupled to the logging and control module 95 of the drilling system 104. The logging and control module 95 may include hardware or software (or both) for direct control of a bottom hole assembly 100 as understood by one of ordinary skill in the art.
A drill string 12 is suspended within the borehole 11 and has a bottom hole assembly (“BHA”) 100, which includes a drill bit 105 at its lower end. The surface system includes platform and derrick assembly 10 positioned over the borehole 11, the assembly 10 including a rotary table 16, kelly 17, hook 18 and rotary swivel 19. The drill string 12 is rotated by the rotary table 16, energized by means not shown, which engages the kelly 17 at the upper end of the drill string. The drill string 12 is suspended from a hook 18, attached to a traveling block (also not shown), through the kelly 17 and the rotary swivel 19, which permits rotation of the drill string 12 relative to the hook 18. As is known to one of ordinary skill in the art, a top drive system could alternatively be used instead of the kelly 17 and rotary table 16 to rotate the drill string 12 from the surface. The drill string 12 may be assembled from a plurality of segments 125 of pipe and/or collars threadedly joined end to end.
In the embodiment of
The bottom hole assembly 100 of the illustrated embodiment may include a logging-while-drilling (LWD) module 120, a measuring-while-drilling (MWD) module 130, a roto-steerable system and motor 150, and the drill bit 105.
The LWD module 120 is housed in a special type of drill collar, as is known to one of ordinary skill in the art, and can contain one or a plurality of known types of logging tools. Also, it will be understood that more than one LWD 120 and/or MWD module 130 can be employed, e.g., as represented at 120A. (References, throughout, to a module at the position of 120A can alternatively mean a module at the position of 120B as well.) The LWD module 120 includes capabilities for measuring, processing, and storing information, as well as for communicating with the surface equipment. In the present embodiment, the LWD module 120 includes a directional resistivity measuring device.
The MWD module 130 is also housed in a special type of drill collar, as is known to one of ordinary skill in the art, and can contain one or more devices for measuring characteristics of the drill string 12 and the drill bit 105. The MWD module 130 may further include an apparatus (not shown) for generating electrical power to the downhole system 100.
This apparatus typically may include a mud turbine generator powered by the flow of the drilling fluid 26, although it should be understood by one of ordinary skill in the art that other power and/or battery systems may be employed. In the embodiment, the MWD module 130 includes one or more of the following types of measuring devices: a weight-on-bit measuring device, a torque measuring device, a vibration measuring device, a shock measuring device, a stick slip measuring device, a direction measuring device, and an inclination measuring device.
The foregoing examples of wireline and drill string conveyance of a well logging instrument are not to be construed as a limitation on the types of conveyance that may be used for the well logging instrument. Any other conveyance known to one of ordinary skill in the art may be used, including without limitation, slickline (solid wire cable), coiled tubing, well tractor and production tubing.
The drilling system can include a rotary steerable system having an LWD tool or caliper that uses one or more moveable pads to push the drill bit in a particular direction. These moveable pads typically are hinged on one side and are activated by hydraulic pistons or other suitable means to create side forces. A similar mechanical construction can be used for the moveable arm that measures the borehole size.
The movable pad contains electronics that receive power from the drill collar, but without using wires between the pad and the drill collar. Instead, power can be provided by an alternating magnetic field that has a transmitting coil in the drill collar and a receiving coil in the movable pad. The distance between the moveable pad and the drill collar is monitored by measuring the coupling between the transmitting and receiving coils. Alternatively, the movable pad contains a second coil that transmits an alternating magnetic field that is measured by a sensor in the drill collar.
The degree of pad opening corresponds to the borehole diameter and borehole shape in case the borehole is not circular. If the LWD tool rotates, then the pad opening can be measured versus the tool face angle, thus providing a 360 degree caliper. There are various means for forcing the movable pad 202 against the borehole wall 204, such as a spring or hydraulic piston or other suitable means.
Because the movable pad 202 continually moves in and out with changing borehole diameters or as the drill collar 206 rotates, connecting the pad to the drill collar 206 with wires is impractical and would result in low reliability. Consider a typical situation where the drill collar 206 rotates at 180 rotations per minute (RPM) and the movable pad 202 flexes each revolution. In a 100 hour bit run, the movable pad 202 moves 100 hr·3600 S/hr·3 RPS=1,080,000 times. This may lead to wire fatigue. Such wires might also be pinched by the pad closing with cuttings present. The movable pad 202 can be powered instead without the use of wires by installing a power transmitter 208 on the drill collar 206 and a power receiver 212 on the movable pad 202.
The power transmitter 208 may include a multi-turn coil, e.g., wrapped on a ferrite core. The power receiver 212 can be a coil mounted in the movable pad 202 and also with a ferrite core to enhance the coupling between the power transmitter 208 and the power receiver 212. Possible positions of the power transmitter 208 and the power receiver 212 are indicated in
A typical frequency might be in the 50 kHz to 300 kHz range. On the moveable pad 202, the power receiver 212 has self inductance LR and resistance RR. A series tuning capacitor CR is chosen such that it cancels the receiver coil inductance at the operating frequency
As is well known, the coils may also be placed in resonance by capacitors placed in parallel with the coils. In either series or parallel tuning, the above equations for the resonant frequency apply. In addition, both coils may be associated with high quality factors, defined as:
The quality factors, Q, may be greater than or equal to about 10 and in some embodiments greater than or equal to about 100. As is understood by one of ordinary skill in the art, the quality factor of a coil is a dimensionless parameter that characterizes the coil's bandwidth relative to its center frequency and, as such, a higher Q value may thus indicate a lower rate of energy loss as compared to coils with lower Q values.
The mutual inductance between the two coils is M, and the coupling coefficient k is defined as:
While a conventional inductive coupler has k≈1, weakly coupled coils may have a value for k less than 1 such as, for example, less than or equal to about 0.9. If the coils are loosely coupled such that k<1, then efficient power transfer may be achieved provided the figure of merit, U, is larger than 1 such as, for example, greater than or equal to about 3: U=k√{square root over (QTQR)}≧3.
The remainder of the electronics and electrical components in the pad are represented by the load impedance ZL. The optimum power transfer occurs when the impedances are chosen such that RS=RT√{square root over (1+k2QTQR)} and ZL=RR√{square root over (1+k2QTQR)}. These impedances may be accomplished by choice of component values or by the use of matching circuits, as is well known.
The power transmitter 208 produces an alternating magnetic field whose flux generates a voltage in the power receiver 212. This induced voltage drives a current in the receiver circuitry that provides power to the load. Other circuit elements, not shown, may be used to improve the efficiency of the power transfer to the movable pad 202 or to store power, such as rechargeable batteries.
An example showing one possible arrangement of the power transmitter 208 and the power receiver 212 is shown in
A set of coils 222 wrapped around a ferrite core 224 are oriented such that the magnetic poles are aligned with the axis of the hinge 207 (not shown). The ferrite cores 224 may be rectangular in shape and wrapped with multiple turns of wire.
There are other possible arrangements of the power transmitter 208 and the power receiver 212. For example, the magnetic poles could be perpendicular to the hinge axis, rather than parallel. The ferrites could be rods, rather than rectangular solids. Other power transmitter and receiver arrangements are described hereinbelow.
The position of the movable pad 202 relative to the drill collar 206 can be obtained in different ways. One way is to monitor the voltage in the power receiver 212 if the voltage decreases as the movable pad 202 is progressively opened. Such would be the case for the arrangement shown in
An alternative approach to measuring the pad position is illustrated in
The solenoid 232 generates a second magnetic field at a different frequency than that of the power transmitter 208. The magnetometer 234 has a bandpass filter that passes the signal from the solenoid 232, but blocks the signal from the power transmitter 208. The magnetometer signal thus depends on the separation between the moveable pad 202 and the drill collar 206. For example, suppose that the length of the solenoid 232 is 2D=50 mm, and has its axis parallel to the hinge axis. The magnetometer 234 in the drill collar 206 is centered on the solenoid 232 when the movable pad 202 is closed. The magnetic signal B of the magnetometer 234 approximately varies with the distance d between the solenoid 232 and the magnetometer 234 according to the equation:
An alternative to using this equation is to measure the magnetometer signal versus the moveable pad position, and to form a look-up table of pas position versus the magnetometer signal. The magnetic field is plotted versus distance d in
The output of the magnetometer 234 is bandpass filtered to reject the power transmitter frequency f and the Earth's magnetic field. If the drill collar 206 is rotating, the Earth's magnetic field produces an alternating magnetic signal with a frequency of a few Hertz, e.g., 3 Hz, at 120 RPM. The power transmitter 208 might operate at 100 kHz, and the solenoid 232 might operate at 50 kHz. The bandpass filter can be centered at 50 kHz. The output from the bandpass filter can be converted to a digital value and stored in memory and/or transmitted to the surface. This eliminates the need to transmit data from the movable pad 202 back to the drill collar 206.
There are other possible circuits to perform the frequency down conversion. For example, the input frequency can be converted to a square wave and down converted to f/N using flip-flops. Lower frequencies than f/2 also are possible.
Consider the drill string rotating at 3 Hz, and suppose that the position of the movable pad 202 is recorded every 10 degrees, then there are 36 samples per 0.33 seconds or 108 samples per second. This is easily within the sampling ability of the magnetometer 234.
There are other possible arrangements for the power transmitter 208 and the power receiver 212. For example,
A solid metal tube would attenuate the magnetic field alternating at the frequency f. The power transmitter 208 is mounted in the drill collar 206 opposite the power receiver 212. In this mounting configuration, the magnetic coupling is not a function of the position of the movable pad 202, and relatively strong coupling is possible. Because the voltage induced in the power receiver 212 is not a function of the position of the movable pad 202, the separate solenoid 232 and magnetometer 234 are used to monitor the position of the movable pad 202.
Another configuration of the power transmitter 208 and the power receiver 212 is shown in
Another caliper configuration is shown in
Another application is shown in
The power transmission and pad position configurations described herein can apply to measurements other than a caliper. For example, the moveable pad can contain electromagnetic, nuclear, or acoustic sensors. These configurations can be used for formation evaluation or for borehole imaging. In either case, knowing the pad position improves the quality of the formation evaluation or borehole imaging measurements.
Although only a few embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.
In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, sixth paragraph for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.
This application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 61/704,610, entitled “Mechanical Caliper System For A Logging While Drilling Borehole Caliper,” and filed on Sep. 24, 2012, U.S. Provisional Patent Application Ser. No. 61/704,805, entitled “System And Method for Wireless Power And Data Transmission In A Mud Motor,” and filed on Sep. 24, 2012, and U.S. Provisional Patent Application Ser. No. 61/704,758, entitled “Positive Displacement Motor Rotary Steerable System And Apparatus,” and filed on Sep. 24, 2012, the disclosures of which are hereby incorporated by reference in their entireties.
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