Abstract: A method of performing an electromagnetic measurement of an earth formation includes disposing a downhole tool in a borehole in an earth formation, the downhole tool including an electrically conductive component, at least one electromagnetic transmitter located at a location along the tool, a first receiver located a first distance from the location, and a second receiver located at a second distance from the location. The method also includes applying a single rectangular current pulse having a substantially constant amplitude to the transmitter to generate an electric current in the formation, the current pulse having a specified time duration ?T. The method further includes measuring transient signals during a time period subsequent to the time in response to the generated current, combining the transient signals to generate a combined transient signal, and estimating a resistivity of the formation based on the combined transient signal.

Abstract: A method of performing an electromagnetic measurement of an earth formation includes disposing a downhole tool in a borehole in an earth formation, the downhole tool including an electrically conductive component, at least one electromagnetic transmitter located at a location along the tool, a first receiver located a first distance from the location, and a second receiver located at a second distance from the location. The method also includes applying a single rectangular current pulse having a substantially constant amplitude to the transmitter to generate an electric current in the formation, the current pulse having a specified time duration ?T. The method further includes measuring transient signals during a time period subsequent to the time in response to the generated current, combining the transient signals to generate a combined transient signal, and estimating a resistivity of the formation based on the combined transient signal.

Abstract: A method of processing electromagnetic signal data includes: receiving transient electromagnetic (TEM) signal data from a downhole tool disposed in an earth formation, the downhole tool including at least one conductive component; estimating an initial bucking coefficient based on relative positions of the at least two receivers; combining the TEM signal data using the initial bucking coefficient to estimate an initial formation signal; selecting a plurality of bucking coefficient values based on the initial bucking coefficient and estimating a plurality of formation signals, each formation signal corresponding to one of the plurality of bucking coefficients; and selecting an optimal bucking coefficient from one of the initial bucking coefficient and the plurality of bucking coefficients based on the plurality of formation signals, the optimal bucking coefficient providing suppression of parasitic signals due to the at least one conductive component.

Abstract: A method of processing electromagnetic signal data includes: receiving transient electromagnetic (TEM) signal data from a downhole tool disposed in an earth formation, the downhole tool including at least one conductive component; estimating an initial bucking coefficient based on relative positions of the at least two receivers; combining the TEM signal data using the initial bucking coefficient to estimate an initial formation signal; selecting a plurality of bucking coefficient values based on the initial bucking coefficient and estimating a plurality of formation signals, each formation signal corresponding to one of the plurality of bucking coefficients; and selecting an optimal bucking coefficient from one of the initial bucking coefficient and the plurality of bucking coefficients based on the plurality of formation signals, the optimal bucking coefficient providing suppression of parasitic signals due to the at least one conductive component.

Abstract: A resistivity imaging device injects currents in two orthogonal directions using two pairs of return electrodes and performing impedance measurements of the buttons placed between the returns.

Abstract: A logging tool used in a borehole having non-conductive mud. The tool includes a known inductance in series with an electrode. The quality factor of a circuit that includes the electrode, the inductance and the earth formation is indicative of the resistivity of the formation. The quality factor may be determined using either a plurality of signals or by measuring a transient response.

Abstract: Phase-sensitive measurements are made by a resistivity imaging tool in a borehole having non-conductive mud in a conductive earth formation at a plurality of frequencies. From the phase sensitive measurements, the formation resistivity can be determined with higher sensitivity than is possible with the single frequency measurements. Tool standoff can also be determined from a knowledge of the mud resistivity and/or dielectric constant. Formation resistivity may also be determined when the effect of formation capacitance cannot be ignored.

Abstract: A resistivity imaging tool is used in a borehole having a conductive fluid. Second differences between axially spaced apart electrodes are used in the imaging. A calibration compensates for the effects of borehole rugosity.

Abstract: Impedance measurements made by a galvanic resistivity tool in a borehole in an earth formation are corrected by a factor that depends on the mud conductivity and the mud dielectric constant. Standoff measurements are not necessary.

Abstract: A transverse induction transmitter on an instrument induces currents in an earth formation when it is pulsed. Transient measurements made at transverse and axial receivers are used for determination of a distance to a bed boundary. This may be used to control the drilling direction. Alternatively, a transmitter on an instrument having a conductive body induces currents in the earth formation. Transient signals are measured and the effect of the conductive body is removed by using a reference signal measured in a homogenous space.

Abstract: Measurements made by a resistivity imaging tool in a borehole having non-conductive mud in a conductive earth formation are corrected using the tool standoff. The correction involves removing a calibration signal determined in a medium of high conductivity from the measured impedance. The magnitude and/or the real part of the impedance may be used.

Abstract: A transverse induction transmitter on an instrument induces currents in an earth formation when it is pulsed. Transient measurements made at transverse and axial receivers are used for determination of a distance to a bed boundary. This may be used to control the drilling direction. Alternatively, a transmitter on an instrument having a conductive body induces currents in the earth formation. Transient signals are measured and the effect of the conductive body is removed by using a reference signal measured in a homogenous space.

Abstract: Pulse sequences are applied to a fluid in an earth formation in a static magnetic field having internal gradients. From the received signals, relaxation and diffusion characteristics of the fluid are determined. The determination takes into account the internal field gradients.

Abstract: A method for estimating resistivity of a formation includes exciting an alternating current in the formation through non-conductive mud within a bore hole in the formation using a circuit. The circuit includes a known inductor and the non-conductive mud. A circuit response is measured. The complex impedance of the circuit is computed using the measured response to estimate the resistivity of the formation.

Abstract: A transverse induction transmitter on an instrument induces currents in an earth formation when it is pulsed. Transient measurements made at transverse and axial receivers are used for determination of a distance to a bed boundary. This may be used to control the drilling direction. Alternatively, a transmitter on an instrument having a conductive body induces currents in the earth formation. Transient signals are measured and the effect of the conductive body is removed by using a reference signal measured in a homogenous space.

Abstract: The present invention provides a method and apparatus for performing resistivity measurements for the purpose of geo-steering with 180-degree azimuth resolution. All the measurements represent a complementary set of data acquired in two operational modes. The directional mode providing sensitivity of the received signals to the azimuth characteristics of the formation. The deep mode provides a large depth of investigation for resistivity determination and bed boundary detection. The directional mode can be implemented using one receiving coil placed in between quadruple type transmitter. The deep mode represents either array induction measurements or multiple propagation resisitivity (MPR) measurements that provide high depth of investigation for resistivity determination and bed boundary detection.

Abstract: A transmitter on a bottomhole assembly (BHA) is used for generating a transient electromagnetic signal in an earth formation. A receiver on the BHA receives signals that are indicative of formation resistivity and distances to bed boundaries. The transmitter and receiver may have axes that are parallel to or inclined to the axis of the BHA. The transmitter and the receiver are on a tubular on a damping portion of the BHA that includes cuts for attenuating eddy currents. The damping portion may include non conducting material such as a ferrite on the outer surface.

Abstract: Pulse sequences are applied to a fluid in an earth formation in a static magnetic field having internal gradients. From the received signals, relaxation and diffusion characteristics of the fluid are determined. The determination takes into account the internal field gradients.

Abstract: A transverse induction transmitter on an instrument induces currents in an earth formation when it is pulsed. Transient measurements made at transverse and axial receivers are used for determination of a distance to a bed boundary. This may be used to control the drilling direction. Alternatively, a transmitter on an instrument having a conductive body induces currents in the earth formation. Transient signals are measured and the effect of the conductive body is removed by using a reference signal measured in a homogenous space.

Abstract: The present invention provides a method and apparatus for performing resistivity measurements for the purpose of geo-steering with 180-degree azimuth resolution. All the measurements represent a complementary set of data acquired in two operational modes. The directional mode providing sensitivity of the received signals to the azimuth characteristics of the formation. The deep mode provides a large depth of investigation for resistivity determination and bed boundary detection. The directional mode can be implemented using one receiving coil placed in between quadruple type transmitter. The deep mode represents either array induction measurements or multiple propagation resisitivity (MPR) measurements that provide high depth of investigation for resistivity determination and bed boundary detection.