Induction Resistivity Tool that Generates Directed Induced Fields
In one aspect of the present invention, an induction resistivity tool includes an induction transmitter and an induction receiver located along the length of the tool. The transmitter is located adjacent at least one induction bucking coils of the tool. When activated the bucking coils are configured to direct a field transmitted by the induction transmitter away from the tool at an angle from the central axis of the tool.
Electric resistivity of a downhole formation is often measured from a wireline or drill string component in a well bore to analyze formation parameters. Induction resistivity tools induce a magnetic field into the formation; and thus, are different from electrode resistivity systems, where an electric current is passed through the formation.
U.S. Pat. No. 6,677,756 to Fanini, et al, which is herein incorporated by reference for all that it contains, discloses an induction tool for formation resistivity evaluations. The tool provides electromagnetic transmitters and sensors suitable for transmitting and receiving magnetic fields in radial directions.
U.S. Pat. No. 6,359,438 to Bittar, which is herein incorporated by reference for all that it contains, discloses a resistivity tool for use in an LWD system that includes a transmitter array with multiple transmitters positioned above a pair of receivers. The transmitters are selectively energized, causing current to be induced in the collar of the tool.
U.S. Pat. No. 6,577,129 to Thompson, et al, which is herein incorporated by reference for all that it contains, discloses an electromagnetic wave propagation resistivity borehole logging system comprising multiple groups of electromagnetic transmitter-receiver arrays operating at three frequencies.
U.S. Pat. No. 6,538,447 to Bittar, which is herein incorporated by reference for all that it contains, discloses a multi-mode resistivity tool for use in a logging-while-drilling system that includes an asymmetric transmitter design with multiple transmitters capable of generating electromagnetic signals at multiple depths of investigation.
U.S. Pat. No. 7,141,981 to Folbert, et al, which is herein incorporated by reference for all that it contains, discloses a resistivity logging tool suitable for downhole use that includes a transmitter, and two spaced apart receivers. The measured resistivities at the two receivers are corrected based on measuring the responses of the receivers to a calibration signal.
U.S. Pat. No. 6,218,842 to Bittar, et al, which is herein incorporated by reference for all that it contains, discloses a resistivity tool for use in LWD systems that includes an asymmetric transmitter design with multiple transmitters capable of generating EM signals at multiple frequencies.
U.S. Pat. No. 5,045,795 to Gianzero, et al, which is herein incorporated by reference for all that it contains, discloses a coil array which is installed on a drill collar for use in a resistivity logging system. The drill collar is provided with upper and lower coil support rings. These are toroids which support individual coil segments, and are connected by suitable magnetic shorting bars. The coil segments and shorting bars inscribe a specified solid angle or azimuthal extent.
U.S. Pat. No. 5,606,260 to Giordano, et al, which is herein incorporated by reference for all that it contains, discloses a microdevice which is provided for measuring the electromagnetic characteristics of a medium in a borehole. The microdevice includes at least one emitting or transmitting coil, and at least one receiving coil. The microdevice generates an A.C. voltage at the terminals of the transmitting coil and measures a signal at the terminals of the receiving coil. The microdevice also includes an E-shaped electrically insulating, soft magnetic material circuit serving as a support for each of the coils and which is positioned adjacent to the medium in the borehole.
U.S. Pat. No. 6,100,696 to Sinclair, which is herein incorporated by reference for all that it contains, discloses a directional induction logging tool is provided for measurement while drilling. This tool is preferably placed in a side pocket of a drill collar, and it comprises transmitter and receiver coils and an electromagnetic reflector.
U.S. Pat. No. 6,163,155 to Bittar, et al, which is herein incorporated by reference for all that it contains, discloses a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations.
U.S. Pat. No. 6,476,609 to Bittar, et al, which is herein incorporated by reference for all that it contains, discloses an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled.
BRIEF SUMMARY OF THE INVENTIONIn one aspect of the invention, an induction resistivity tool includes at least one induction transmitter and at least one induction receiver placed along the length of the tool. The transmitter is located between at least one induction bucking coil of the tool, such that when activated the bucking coils are configured to direct the field produced by the induction transmitter at any angle from the central longitudinal axis of the tool.
In some embodiments, the bucking coils on either side of the transmitter may be in electrical communication with separate power sources and at least one of the bucking coils may be in communication with a central processing unit.
The bucking coils may also be disposed at different distances and heights from the transmitter. One bucking coil may have significantly more wire turns then the other. The transmitter or at least one bucking coil may be positioned at an angle with respect to the central longitudinal axis.
In one embodiment, the transmitter may comprise at least one coil wrapped around the circumference of the tool or a plurality of units spaced along the circumference of the tool. These units may be electrically isolated from one another.
Additional bucking coils may be positioned at a distance from the transmitter greater than the distance of the other bucking coils adjacent to the transmitter.
The induction field may approach, overlap, or extend beyond the longitudinal axial position of the bottom of the tool or a drill bit that may be secured to the tool. The tool may also be part of a downhole tool string or a wireline assembly.
In another aspect of the invention, a method for taking an induction resistivity measurement includes the steps of having an induction transmitter and an induction receiver disposed along the length of the resistivity tool and projecting an induction field from the transmitter at an angle less than 90 degrees from the central axis of the tool. The induction field may be projected by activating induction bucking coils on either side of the transmitter. One bucking coil may be energized more than the other or the current through the bucking coil may be individually adjusted. By adjusting the current through the bucking coils, the induction field may sweep over any angle away from the tool.
Another method for taking an induction resistivity measurement includes the steps: having an induction transmitter and an induction receiver disposed along a length of the tool, the transmitter being disposed between the at least one induction bucking coil of the tool, projecting an induction field from the transmitter outward toward the formation, and controlling at least one characteristic of the induction field with at least one of the bucking coils. The characteristics of the induction field include: projected angle, shape, and length. These characteristics may be controlled by changing the current through all of the bucking coils at the same rate, changing the current through at least one bucking coils, changing the current through at least one of the bucking coils inversely, and changing the distance from the transmitter to at least one bucking coil. The projected angle of the induction field may change to such a degree that a portion of the field projects passed the end of the down-hole tool string.
The tool may be part of a down-hole tool string or part of a wireline assembly.
One or more bucking coil may have significantly more wire turns than the other. The bucking coils may be spaced apart from the transmitter along the length of the tool and electrically isolated from one another. The transmitter may comprise a plurality of units spaced along the circumference of the tool that may be individually energized.
The position or angle of at least one of the bucking coils may be changed during an operation.
Each of the transmitter, bucking, and receiver coils may utilize a ferromagnetic material between the coils and the metal tool or between the coils and other coils to direct the field for the purpose of controlling the characteristics of the field and minimizing the effect of the tool.
Referring now to
Referring now to
The transmitter 201 may comprise an array of transmitter units 301 spaced circumferentially around the tool string 100. The transmitter units 301 may be independently excitable. Independently excitable units may focus the induction field in only a portion of the formation adjacent to the excitable units while the remaining portion of the formation is minimally affected or not affected at all. Furthermore it is believed that the ability to concentrate the field in portions of the formation adjacent the well bore will allow for directional measurements of the formation. Data received through directional measurement may verify a current drilling trajectory or it may reveal needed adjustments. Drilling trajectory may be manually adjusted or automatically controlled through the tool.
The transmitter 201 may also comprise one or more bucking coil 302, which may guide the induction field produced by at least one transmitter units 301 by forcing the transmitter's signal deeper or at any angle into the formation. The windings on the transmitter 201 may be in a different direction than the windings in one or more the bucking coil 302. In some embodiments, the bucking coil 302 may generate an augmented induction field or a directed induction field. Examples of transmitter coils that may be used include Halbach arrays and/or electromagnetic coils. Examples of bucking coils that may be used to influence the signal from the transmitter include Halbach arrays, electromagnetic coils. Without the bucking coil 302 the transmitter's signal may travel along the path of least resistance which could be within a shallower region of the formation or even along the surface of or into the tool string component. The bucking coil 302 may generate a directed induction field that will repel the signal away from the tool string component, and thus, deeper into the formation. One or more bucking coil 302 may have a startup or periodic calibration sequence such that when one or more of the transmitter 201 energizes, one or more of the receivers 202 and 203 measures the field strength which allows the tool to adjust the output of the transmitter 201 and one or more bucking coil 302 until the field measured by at least one of the receivers 202 and 203 is at a desired depth or angle. The bucking coils 302 and 303 may also have units that are independently excitable with respect to phase, one or more frequencies, magnitude, and wave shape.
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.
Claims
1. An induction resistivity tool, comprising:
- at least one induction transmitter and at least one induction receiver disposed along a length of the tool;
- the transmitter being disposed adjacent at least one induction bucking coil of the tool;
- wherein when activated the at least one bucking coil is configured to direct a field transmitted by the induction transmitter at an angle less than 90 degrees from a central axis of the tool.
2. The tool of claim 1, wherein at least one bucking coil is in electrical communication with separate power sources.
3. The tool of claim 1, wherein at least one bucking coil is disposed at different heights.
4. The tool of claim 1, wherein at least one bucking coil is disposed at different distances from the transmitter.
5. The tool of claim 1, wherein the transmitter is positioned at an angle with respect to the central axis.
6. (canceled)
7. The tool of claim 1, wherein at least one bucking coil is electrically isolated from another.
8. The tool of claim 1, wherein the transmitter comprises at least one coil wrapped around a circumference of the tool.
9. The tool of claim 1, wherein the transmitter comprises a plurality of units spaced along the circumference of the tool, wherein the units are electrically isolated from one another.
10. The tool of claim 1, wherein at least one of the bucking coils is in communication with a central processing unit.
11. The tool of claim 1, wherein at least one bucking coil is positioned at a distance from the transmitter greater than a distance of another bucking coil from the transmitter.
12. The tool of claim 1, wherein the induction field approaches, overlaps, or extends beyond the axial position of the bottom of the tool or a drill bit secured to the tool.
13. The tool of claim 1, wherein the at least one bucking coil has significantly more wire turns or wire of a different diameter or shape than another bucking coil.
14. The tool of claim 1, wherein the tool is part of a down-hole tool string.
15. The tool of claim 1, wherein the tool is part of a wireline assembly.
16. A method for taking an induction resistivity measurement, comprising the steps of:
- providing at least one induction transmitter and at least one induction receiver disposed along a length of the tool, and
- projecting an induction field from the transmitter at an angle less than 90 degrees from a central axis of the tool,
- processing the measurement based on the tool orientation within the borehole.
17. The method of claim 16, wherein the method comprises activating at least one induction bucking coils in any combination or pattern on either side of the transmitter.
18. The method of claim 16, wherein the method comprises an additional step of energizing one or more of the bucking coils more than one or more other coils.
19. The method of claim 16, wherein the method comprises an additional step of individually adjusting the field strength of the bucking coils.
20. The method of claim 19, wherein the step of adjusting the field strength of the bucking coils cause the angle of the induction field to sweep over a range of angles.
Type: Application
Filed: Mar 19, 2010
Publication Date: Sep 22, 2011
Inventors: David R. Hall (Provo, UT), Harold L. Snyder, JR. (Rockwall, TX), Paula Turner (Pleasant Grove, UT), Clint Cook (Provo, UT)
Application Number: 12/727,896
International Classification: G01V 3/10 (20060101);