Abstract: A method for suppressing measurement system signature, or artifacts, that arise when controlled source electromagnetic survey data are inverted to obtain a resistivity image of a subsurface region. The method involves identifying regions (47) where the image has low or rapidly varying sensitivity to data acquired by a given receiver, typically regions close to and under the given receiver. Then, in the iterative inversion process where a resistivity model is updated to minimize an objective function, the model update is modified (48) to reduce the impact of such low sensitivity regions on the update.

Abstract: Method for reducing the time needed to perform geophysical inversion by using simultaneous encoded sources in the simulation steps of the inversion process. The geophysical survey data are prepared by encoding (3) a group of source gathers (1), using for each gather a different encoding signature selected from a set (2) of non-equivalent encoding signatures. Then, the encoded gathers are summed (4) by summing all traces corresponding to the same receiver from each gather, resulting in a simultaneous encoded gather. (Alternatively, the geophysical data are acquired from simultaneously encoded sources.) The simulation steps needed for inversion are then calculated using a particular assumed velocity (or other physical property) model (5) and simultaneously activated encoded sources using the same encoding scheme used on the measured data. The result is an updated physical properties model (6) that may be further updated (7) by additional iterations.

Abstract: Method for reducing the time needed to perform geophysical inversion by using simultaneous encoded sources in the simulation steps of the inversion process. The geophysical survey data are prepared by encoding (3) a group of source gathers (1), using for each gather a different encoding signature selected from a set (2) of non-equivalent encoding signatures. Then, the encoded gathers are summed (4) by summing all traces corresponding to the same receiver from each gather, resulting in a simultaneous encoded gather. (Alternatively, the geophysical data are acquired from simultaneously encoded sources.) The simulation steps needed for inversion are then calculated using a particular assumed velocity (or other physical property) model (5) and simultaneously activated encoded sources using the same encoding scheme used on the measured data. The result is an updated physical properties model (6) that may be further updated (7) by additional iterations.

Abstract: Method for identifying, determining and correcting source-related phase errors in data from a controlled source electromagnetic survey by using data from ordinary survey receivers, i.e. without benefit of source monitoring data. Abrupt anomalies indicating source malfunctions are identified (71) in the time domain by plotting time intervals between neighboring zero crossings or by zero-lag cross correlation between consecutive bins of receiver data, and the amount of the time error (73) can be determined by performing cross correlation between two bins on either side of an anomaly. In the frequency domain, transmitter anomalies can be identified by looking for discontinuities in plots of phase vs. offset, and the corrective phase shift can be determined by matching the phase on one side of the anomaly to that on the other side. A global time/phase shift (76) can be determined by using phase frequency-scaling behavior at near offsets.

Abstract: Method for transforming electromagnetic survey data acquired from a subsurface region to a subsurface resistivity model indicative of hydrocarbon accumulations or lack thereof. In one embodiment, data are selected for two or more non-zero frequencies (100), and a structural model of the region is developed based on available geological or geophysical information. An initial resistivity model of the region is developed based on the structural model (101), and the selected data are inverted to update the resistivity model (106) by iterative forward modeling (103) and minimizing an objective function (105) including a term measuring mismatch between model synthesized data and measured survey data, and another term being a diffusive regularization term that smoothes the resistivity model (104). The regularization term can involve a structure or geology constraint, such as an anisotropic resistivity symmetry axis or a structure axis, determined from the a priori information (102).

Abstract: Method for using seismic data from earthquakes to address the low frequency lacuna problem in traditional hydrocarbon exploration methods. Seismometers with frequency response Select Receivers of Desired Frequency Ranges and Design Survey Seismometer Configuration down to about 1 Hz are placed over a target subsurface region in an array with spacing suitable for hydrocarbon exploration (21). Data are collected over a long (weeks or months) time period (22). Segments of the data (44) are identified with known events from earthquake catalogs (43). Those data segments are analyzed using techniques such as trayeltime delay measurements (307) or receiver function calculations (46) and then are combined with one or more other types of geophysical data acquired from the target region, using joint inversion (308-310) in some embodiments of the method, to infer physical features of the subsurface indicative of hydrocarbon potential or lack thereof (26).

Abstract: Method for determining receiver orientation angles in a controlled source electromagnetic survey, by analyzing the survey data. For a given survey receiver, two data subsets are selected. (43, 44). The two subsets may be from two offset ranges that are geometrically symmetrical relative to the receiver location. Alternatively, the second subset may be a computer simulation of actual survey data. In either instance, an orientation is assumed for the receiver (45), and that orientation is used to compare component data from the two subsets that can be expected to match if the assumed orientation angle(s) is (are) correct (46). The mismatch is ascertained, and the assumed orientation is adjusted (45) and the process is repeated.

Abstract: There is provided a system and method for creating a physical property model representative of a physical property of a region. An exemplary method comprises transforming information from a model domain that represents the physical property model into simulated data in a data domain, the data domain comprising simulated data and measured data representative of a plurality of observations of the region. The exemplary method also comprises determining an areal misfit between the simulated data and the measured data representative of the plurality of observations of the region. The exemplary method additionally comprises performing an evaluation of the areal misfit based on known criteria. The exemplary method comprises adjusting data in the data domain or information in the model domain corresponding to a region in the model domain based on the evaluation of the areal misfit.

Abstract: Method for identifying, determining and correcting source-related phase errors in data from a controlled source electromagnetic survey by using data from ordinary survey receivers, i.e. without benefit of source monitoring data. Abrupt anomalies indicating source malfunctions are identified (71) in the time domain by plotting time intervals between neighboring zero crossings or by zero-lag cross correlation between consecutive bins of receiver data, and the amount of the time error (73) can be determined by performing cross correlation between two bins on either side of an anomaly. In the frequency domain, transmitter anomalies can be identified by looking for discontinuities in plots of phase vs. offset, and the corrective phase shift can be determined by matching the phase on one side of the anomaly to that on the other side. A global time/phase shift (76) can be determined by using phase frequency-scaling behavior at near offsets.

Abstract: A method for suppressing measurement system signature, or artifacts, that arise when controlled source electromagnetic survey data are inverted to obtain a resistivity image of a subsurface region. The method involves identifying regions (47) where the image has low or rapidly varying sensitivity to data acquired by a given receiver, typically regions close to and under the given receiver. Then, in the iterative inversion process where a resistivity model is updated to minimize an objective function, the model update is modified (48) to reduce the impact of such low sensitivity regions on the update.

Abstract: Method for reducing the time needed to perform geophysical inversion by using simultaneous encoded sources in the simulation steps of the inversion process. The geophysical survey data are prepared by encoding (3) a group of source gathers (1), using for each gather a different encoding signature selected from a set (2) of non-equivalent encoding signatures. Then, the encoded gathers are summed (4) by summing all traces corresponding to the same receiver from each gather, resulting in a simultaneous encoded gather (Alternatively, the geophysical data are acquired from simultaneously encoded sources.) The simulation steps needed for inversion are then calculated using a particular assumed velocity (or other physical property) model (5) and simultaneously activated encoded sources using the same encoding scheme used on the measured data. The result is an updated physical properties model (6) that may be further updated (7) by additional iterations.

Abstract: Method for rapid inversion of data from a controlled-source electromagnetic survey of a subterranean region. Selected (51) common-receiver or common-source gathers of the data are reformed into composite gathers (52) by summing their data. Each composite gather is forward modeled (in the inversion process) with multiple active source locations (53). Computer time is reduced in proportion to the ratio of the total number of composite gathers to the total number of original common-receiver or common-source gathers. The data may be phase encoded to prevent data cancellation. Methods for mitigating loss of far offset information by data overlap in the summing process are disclosed.

Abstract: A method for performing pre-stack time migration of seismic data in a region where the subsurface seismic wave propagation velocity varies in both the vertical direction and a horizontal direction. The migration is performed in the wave number—frequency domain and involves using travel time maps to find a linear fitting of the migration phase shift for a given ray parameter and at a given vertical depth versus horizontal position. The slope and intercept parameters from the linear fit are used to adjust a known pre-stack time migration equation, with the accuracy of the linear approximation requiring mild horizontal velocity variation.

Abstract: A method for performing pre-stack time migration of seismic data in a region where the subsurface seismic wave propagation velocity varies in both the vertical direction and a horizontal direction. The migration is performed in the wave number—frequency domain and involves using travel time maps to find a linear fitting of the migration phase shift for a given ray parameter and at a given vertical depth versus horizontal position. The slope and intercept parameters from the linear fit are used to adjust a known pre-stack time migration equation, with the accuracy of the linear approximation requiring mild horizontal velocity variation.