Method and apparatus for directional measurement of subsurface electrical properties
First Claim
1. A directional instrument for measuring while drilling electrical properties of rock formations adjacent to a borehole, comprising:
- a) a transmitter coil coupled to a signal generator for providing to the transmitter coil an oscillating voltage at a frequency of between 1 KHz and 200 KHz;
b) at least one receiver coil disposed coaxially to the transmitter coil, the axis of the coils defining the axis of the instrument, the at least one receiver coil being coupled to a signal processing circuit for determining an electrical property of the rock formation from signals received; and
c) a conductive reflector spaced from the transmitter coil, the reflector being generally parallel to the axis of the instrument, the transmitter coil, the at least one receiver coil, and the conductive reflector included in a side pocket of a conductive collar in a drill string including a drill bit so the directional measuring instrument can perform measurement while drilling.
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Accused Products
Abstract
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. The reflector, which may be a layer of highly conductive material placed between the coils and the body of the drill collar, serves to focus the electromagnetic fields generated and sensed by the tool in the direction away from the reflector, thus providing a directional response to formation conductivity with a relatively high depth of investigation. In preferred embodiments of the invention, magnetically permeable cores are placed within the coils to concentrate the magnetic fields that pass through them. Circuitry is described for balancing the mutual inductive coupling of the coils by injecting a direct current signal through one or more of the coils, which alters the magnetic permeability of the core material. The magnitude of the direct current required to achieve a balanced condition may be derived from the quadrature phase component of the return signal. Circuitry is also provided for generating a transmitted signal and for processing the return signals, including digital-to-analog conversion circuitry for providing digital data for transmission to the surface. This tool may be employed to provide real-time directional conductivity information that may be used to detect and follow bed boundaries in geosteering operations.
193 Citations
37 Claims
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1. A directional instrument for measuring while drilling electrical properties of rock formations adjacent to a borehole, comprising:
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a) a transmitter coil coupled to a signal generator for providing to the transmitter coil an oscillating voltage at a frequency of between 1 KHz and 200 KHz; b) at least one receiver coil disposed coaxially to the transmitter coil, the axis of the coils defining the axis of the instrument, the at least one receiver coil being coupled to a signal processing circuit for determining an electrical property of the rock formation from signals received; and c) a conductive reflector spaced from the transmitter coil, the reflector being generally parallel to the axis of the instrument, the transmitter coil, the at least one receiver coil, and the conductive reflector included in a side pocket of a conductive collar in a drill string including a drill bit so the directional measuring instrument can perform measurement while drilling. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A directional resistivity tool for measurement while drilling adapted to provide a measurement of formation resistivity on a selected side of a borehole, comprising:
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a) a conductive drill collar having formed therein a side pocket and a flow channel; b) an electromagnetic reflector formed in the side pocket; c) a transmitter coil disposed within the side pocket and operably coupled to a signal generator providing an oscillating voltage at a frequency of between 1 KHz and 200 KHz., the transmitter coil positioned with respect to the electromagnetic reflector such that a portion of the output of the transmitter is redirected by the electromagnetic reflector toward the formation and away from the conductive drill collar; and d) at least one receiver coil disposed within the side pocket and spaced from the transmitter coil, the receiver coil being coupled to a signal processing circuit. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26)
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27. A method of measuring while drilling electrical properties of subsurface formations adjacent a borehole in a selected azimuthal direction from the borehole while the borehole is being drilled with a bit, comprising:
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a) providing a directional electrical property measuring tool disposed in a side pocket of a conductive drill collar near the bit, the directional electrical property measuring tool including a transmitter coil, one or more receiver coils, and a conductive reflector; b) energizing the transmitter coil with a selected periodic signal having a frequency of between 1 KHz and 200 KHz; c) reflecting a portion of the output of the transmitter coil toward the subsurface formation; d) detecting return signals using the one or more receiver coils; and e) processing the return signals to determine an electrical property of the subsurface formation. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
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Specification