Abstract: The present disclosure relates to a method to produce an image of a subsurface formation using directional measurements. A downhole logging tool having one or more transmitters and one or more receivers, and being capable of making directional measurement, is used to measure the voltage in a particular receiver due to a particular transmitter for one or more transmitter/receiver pairs, at least one of those voltage measurements being a directional measurement. The complex (phasor) voltage recorded on a receiver coil is divided by the complex voltage recorded at another reference receiver coil. Alternatively, we can use the ratio of a receiver voltage at a particular rotation angle of the tool divided by the voltage on the same receiver when the tool has rotated by an angle of 180 degrees. The information in those ratios is combined to produce images of the resistivity of the subsurface formation surrounding the tool.

Abstract: Methods and apparatus for marine geoelectrical exploration use a dipole source, to send electric pulses into the medium. Geometrical probing is performed during current pulses, and probing on transient processes is performed in the intervals. Measurements are taken using measuring apparatus mounted on the seafloor. The apparatus includes, five electrodes: a central electrode with four others around it. During the current flow period and intervals between current pulses, the second electric potential difference between external electrodes and the central electrode, as well as the first electric potential difference between three pairs of external electrodes is measured. Measured values are used to calculate three sets of standard electrical parameters. A model of the medium is produced from the parameters. Techniques disclosed provide for elimination of lateral effect on probing results, and delineation of hydrocarbon accumulation with high contrast.

Abstract: LWD measurements to be used for proactive well placement while drilling a high angle or horizontal wellbore in a reservoir are defined. An initial reservoir model is provided and a section is extracted for a planned wellbore trajectory. A secondary model is generated for the planned trajectory. An area of interest is identified where statistical uncertainty is high. Possible causes of the statistical uncertainty are identified that are not present in the initial reservoir model. A set of parameters are defined based on the possible causes of statistical uncertainty. The area of interest is logged with LWD tool. Sensitivities of the LWD tool response to a subset of parameters are evaluated by performing tertiary model for a range of the subset of parameters. The most sensitive parameters from the subset of parameters and corresponding measurements are identified. LWD measurements are defined based on the most sensitive parameters.

Abstract: The present disclosure relates to a method to produce an image of a subsurface formation using directional measurements. A downhole logging tool having one or more transmitters and one or more receivers, and being capable of making directional measurement, is used to measure the voltage in a particular receiver due to a particular transmitter for one or more transmitter/receiver pairs, at least one of those voltage measurements being a directional measurement. The complex (phasor) voltage recorded on a receiver coil is divided by the complex voltage recorded at another reference receiver coil. Alternatively, we can use the ratio of a receiver voltage at a particular rotation angle of the tool divided by the voltage on the same receiver when the tool has rotated by an angle of 180 degrees. The information in those ratios is combined to produce images of the resistivity of the subsurface formation surrounding the tool.

Abstract: The present disclosure relates to a method to produce an image of a subsurface formation using directional measurements. A downhole logging tool having one or more transmitters and one or more receivers, and being capable of making directional measurements, is used to measure the voltage in a particular receiver due to a particular transmitter for one or more transmitter/receiver pairs, at least one of those voltage measurements being a directional measurement. The complex (phasor) voltage recorded on a receiver coil is divided by the complex voltage recorded at another reference receiver coil. Alternatively, we can use the ratio of a receiver voltage at a particular rotation angle of the tool divided by the voltage on the same receiver when the tool has rotated by an angle of 180 degrees. The information in those ratios is combined to produce images of the resistivity of the subsurface formation surrounding the tool.

Abstract: A method for detecting a subterranean anomaly is provided. The method includes receiving signal data derived from a plurality of transmitters and at least one receiver; calculating a relationship for selected combinations of measurements provided by the signal data; estimating weighting factors for each transmitter, for a condition where there is a substantially equivalent potential across each of the transmitters; applying the weighting factors to the data; and identifying the anomaly in weighted data. Apparatus are also provided.

Abstract: A method for determining electromagnetic induction properties of subsurface rock formations includes determining an eccentering angle of a well logging instrument disposed in a wellbore. The instrument includes at least one triaxial induction transmitter and at least one triaxial induction receiver. The eccentering angle is determined from symmetric cross component measurement differences. The triaxial induction measurements made from the at least one receiver are rotated to an apparent eccentering angle of zero. At least one electromagnetic induction property is determined from the rotated triaxial induction measurements.

Abstract: SUBSTANCE: Invention relates to marine geoelectrical exploration using controlled artificial sources of electromagnetic field. Using a dipole source, an electromagnetic field is generated inside the analysed medium by sending rectangular electric pulses with intervals in between into the medium. Geometrical probing is done along the profile during the current pulse, and probing on transient processes is done during the interval. Measurements are taken using measuring apparatus mounted on the seafloor, consisting of five electrodes: a central electrode with four others around it on corners of a square, two opposite sides of which are parallel to the axis of the profile. During the current flow period and intervals between current pulses, the second electric potential difference between external electrodes and the central electrode, as well as the first electric potential difference between three pairs of external electrodes is measured.

Abstract: Methods for three-dimensionally characterizing a reservoir while drilling a high angle or horizontal wellbore through the reservoir are disclosed. An initial reservoir model for the reservoir is selected and a section is extracted for a planned trajectory of the wellbore. A secondary model is generated by performing secondary modeling for at least part of the planned trajectory. An area of interest is identified within the secondary model where statistical uncertainty is high. Possible causes of the statistical uncertainty are identified for the area of interest within the secondary model that are not present or accounted for in the initial reservoir model. A set of parameters for the area of interest are defined at that are based on the possible causes of statistical uncertainty. The area of interest is logged with at least one logging while drilling LWD tool.

Abstract: The present disclosure relates to a method to produce an image of a subsurface formation using directional measurements. A downhole logging tool having one or more transmitters and one or more receivers, and being capable of making directional measurements, is used to measure the voltage in a particular receiver due to a particular transmitter for one or more transmitter/receiver pairs, at least one of those voltage measurements being a directional measurement. The complex (phasor) voltage recorded on a receiver coil is divided by the complex voltage recorded at another reference receiver coil. Alternatively, we can use the ratio of a receiver voltage at a particular rotation angle of the tool divided by the voltage on the same receiver when the tool has rotated by an angle of 180 degrees. The information in those ratios is combined to produce images of the resistivity of the subsurface formation surrounding the tool.

Abstract: A method for determining electromagnetic induction properties of subsurface rock formations includes determining an eccentering angle of a well logging instrument disposed in a wellbore. The instrument includes at least one triaxial induction transmitter and at least one triaxial induction receiver. The eccentering angle is determined from symmetric cross component measurement differences. The triaxial induction measurements made from the at least one receiver are rotated to an apparent eccentering angle of zero. At least one electromagnetic induction property is determined from the rotated triaxial induction measurements.

Abstract: A method for modeling borehole effects of a transverse array induction tool includes selecting a formation-borehole model having a set of parameters, wherein the set of parameters comprises a direction of tool eccentering; determining initial values for the set of parameters; computing expected responses for a selected set of arrays from the plurality of arrays of the induction tool, wherein the computing is based on the formation-borehole model; comparing the expected responses with actual responses for the selected set of arrays; adjusting values of the set of parameters, if a difference between the expected responses and the actual responses is no less than a predetermined criterion; repeating the computing, the comparing, and the adjusting, until the difference between the expected responses and the actual responses is less than the predetermined criterion; determining the borehole effects from final values of the set of parameters.

Abstract: An induction tool includes a conductive mandrel; at least one array including a transmitter, a bucking coil, and a receiver disposed in an insulating tool body surrounding the conductive mandrel; and an electrode disposed on the insulating tool body at a selected location between the bucking coil and the receiver, wherein the selected location is spaced from the transmitter at a distance corresponding approximately to the harmonic mean of the distance between the transmitter and the bucking coil and the distance between the transmitter and the receiver, and wherein the electrode includes a contact forming a conductive path to the conductive mandrel. Additional electrodes may be disposed above and below each transmitter and receiver coil to reduce sensitivity to eccentricity of the tool in the borehole.

Abstract: A composite shell adapted to cover a source or sensor, particularly for subsurface applications. The shell provides transparency to the passage of signals to or from the source or sensor. The shell is adapted with a uniform semi-conductive surface providing a path for electric currents flowing within a subsurface borehole to short near the source or sensor.

Abstract: A method for modeling borehole effects of a transverse array induction tool includes selecting a formation-borehole model having a set of parameters, wherein the set of parameters comprises a direction of tool eccentering; determining initial values for the set of parameters; computing expected responses for a selected set of arrays from the plurality of arrays of the induction tool, wherein the computing is based on the formation-borehole model; comparing the expected responses with actual responses for the selected set of arrays; adjusting values of the set of parameters, if a difference between the expected responses and the actual responses is no less than a predetermined criterion; repeating the computing, the comparing, and the adjusting, until the difference between the expected responses and the actual responses is less than the predetermined criterion; determining the borehole effects from final values of the set of parameters.

Abstract: A composite shell adapted to cover a source or sensor, particularly for subsurface applications. The shell provides transparency to the passage of signals to or from the source or sensor. The shell is adapted with a uniform semi-conductive surface providing a path for electric currents flowing within a subsurface borehole to short near the source or sensor.

Abstract: An induction tool includes a conductive mandrel; at least one array including a transmitter, a bucking coil, and a receiver disposed in an insulating tool body surrounding the conductive mandrel; and an electrode disposed on the insulating tool body at a selected location between the bucking coil and the receiver, wherein the selected location is spaced from the transmitter at a distance corresponding approximately to the harmonic mean of the distance between the transmitter and the bucking coil and the distance between the transmitter and the receiver, and wherein the electrode includes a contact forming a conductive path to the conductive mandrel. Additional electrodes may be disposed above and below each transmitter and receiver coil to reduce sensitivity to eccentricity of the tool in the borehole.