Abstract: One embodiment relates to a method of wavefield regularization for geophysical data acquisition of seismic geophysical data. Measured traces, are obtained from an array of sensors. For each grid point on a processing grid, best-fitting traces of the measured traces are found. Using the best-fitting traces, spectral amplitudes of down-going and up-going wavefields are computed. The down-going and up-going wavefields are subsequently transformed to an output grid in a space-time domain. Another embodiment relates to an apparatus for wavefield regularization of geophysical data acquisition. Other embodiments, aspects and features are also disclosed.

Abstract: A circuit for obscuring gate switching noise includes a synchronous clock source; an asynchronous clock source; at least one current source; and a random number generating circuit for receiving clock inputs from the synchronous clock source and the asynchronous clock source, the random number generating circuit generating randomly changing asynchronous digital control signals for controlling the current source.

Abstract: A method for interpolating irregularly sampled seismic data, including receiving seismic data acquired at irregularly spaced seismic sensors in a survey area, defining a plurality of regularly spaced locations in the survey area, forming an annular ring around one of the plurality of regularly spaced locations, and interpolating the seismic data inside the annular ring to estimate seismic data that would have been acquired at the one of the plurality of regularly spaced locations.

Abstract: Multiple twisted or rotated arrays are provided. For example, a memory alloy may allow manufacture of multiple rows of elements on a flat substrate. The memory of the alloy is activated to twist different rows in different ways, such as two adjacent substantially parallel but oppositely rotated arrays. By selecting different apertures along a given twist, different planes are scanned due to the difference in direction of the elements of the aperture. By selecting different apertures on differently rotated arrays, a larger volume may be scanned.

Abstract: To process seismic data, a combined four-dimensional (4D) binning and regularization procedure is performed on the seismic data, where the combined 4D binning and regularization procedure includes computing measures associated with regularization of the seismic data, computing measures associated with 4D binning, and processing the seismic data according to the regularization measures and 4D binning measures.

Abstract: Method intended for absolute preserved amplitude processing of data obtained by seismic prospecting known as VSP.

Abstract: An apparatus and method for removing the distortion in marine seismic data resulting from the motion of the ship. The ship trails one or more seismic sources and receivers and moves forward at a known velocity. The seismic sources emit seismic waves that travel through the water and reflect off interfaces between rock formations below the ocean floor. The motion of the sources and receivers introduces distortion in the recorded seismic data that can be modeled using Doppler theory. The data preferably is corrected for source motion independently from the correction for receiver motion. The seismic data is first corrected for receiver motion and then for source motion. The technique for correcting for source motion includes correlating the receiver-corrected data with a reference sweep signal, performing an F-K transform, performing an inverse F-K transform on a selected subset of the F-K transformed data, and computing appropriate correction filters for the data resulting from the inverse F-K transform.

Abstract: A method for performing a seismic survey with even fold. An inline direction and a crossline direction are selected. Seismic signals are generated at a plurality of source locations positioned along one or more source lines. The source locations are substantially equally spaced, and the source lines are substantially parallel to each other. Seismic signals are detected at a plurality of receiver locations positioned along a plurality of receiver paths having longitudinal axes parallel to the inline direction, and substantially equally spaced in each receiver path. Each receiver path is positioned along its axis, and extends in a regular pattern on both sides of the axis. The axes are substantially parallel to each other. A desired fold, F.sub.i, is determined in the inline direction, and a desired fold, F.sub.x, is determined in the crossline direction. A number of receiver channels, NC.sub.i, per receiver path in the inline direction, a spacing, RI.sub.

Abstract: A method for attenuating water column reverberations in a dual sensor seismic signal, whereby a pressure signal and a velocity signal are transformed from the time domain to the frequency domain, generating a transformed pressure signal and a transformed velocity signal, respectively. Values for weighting factors K.sub.p and K.sub.v are selected and multiplied times the transformed pressure signal and the transformed velocity signal, respectively, generating a weighted pressure signal and a weighted velocity signal, respectively. The weighted pressure signal and the weighted velocity signal are summed, generating a summed signal. Values for ocean bottom reflectivity R and Z, the frequency domain delay operator for two-way travel time in the water layer, are determined. A weighted inverse Backus filter is calculated and multiplied times the summed signal, generating a filtered signal. The filtered signal is transformed from the frequency domain to the time domain.

Abstract: A method and apparatus for the exploration of hydrocarbons comprising the steps of: obtaining a set of seismic signal traces distributed over a predetermined three-dimensional volume of the earth; dividing the three-dimensional volume into a plurality of analysis cells having portions of at least two seismic traces located therein; computing outer products of the seismic traces within each cell; forming the covariance matrix for each cell from these outer products; computing the dominant eigenvalue and the sum of the eigenvalues of the covariance matrix of each cell and computing a seismic attribute from the ratio of the dominant eigenvalue to the sum of the eigenvalues of the covariance matrix of each cell; and forming map of the seismic attributes of selected groups of cells.

Abstract: A method for generating a thinned array having an optimal directional response wherein an initial population of possible element occupancy patterns is generated and a relative fitness value for each of the element occupancy patterns in the initial population is determined. Successive populations are generated by manipulating the element occupancy patterns using reproduction, crossover, mutation, elitism, and equality operators. The array response of each occupancy pattern in the successive population is evaluated to determine a fitness value for each. The process of generating and evaluating successive populations is repeated for a specified number of generations, until the maximum population fitness does not significantly increase between generations, or until the population diversity decreases.

Abstract: A method of geophysical exploration for acquiring and processing multicomponent seismic data obtained with seismic sources generating shear waves having time-varying polarizations and seismic receivers recording at least two modes of propagation of the imparted shear waves is provided. More particularly, a method is described for acquiring multicomponent seismic data with torsional seismic sources and multicomponent seismic receivers, as well as a method for processing such multicomponent seismic data so as to ameliorate the effects of shear wave splitting in displayed seismic data. Additionally, principal time-series signals can be obtained which are representative of formation properties along principal axes of an anisotropic formation essentially free of the effects of shear wave splitting.

Abstract: The present invention provides a novel method for obtaining quality indices for objectively characterizing seismic velocity estimates in geophysical data bases.

Abstract: A method for seismic trace interpolation by dip range analysis is disclosed. In the preferred embodiment, a series of dip ranges are defined by a plurality of dips. A trace estimate for each of the dip ranges is generated by filtering with a mathematically integrated time shift in each frequency component of each seismic trace appearing in the dip range. These filtered frequency components are then passed through a low pass filter. The sum of the filtered frequency components is the trace estimate. The seismic traces are then demodulated to obtain the trace envelopes whose values along the above mentioned dips are examined for continuity. A continuity factor is developed for each dip and then each of the continuity factors is summed and the sum divided by the number of continuity factors to obtain a weighting function. The weighting functions are multiplied with the trace estimates, and the results summed to obtain the interpolated trace.

Abstract: Coherent noise on seismic records is suppressed by reformatting the common shot gathers to common receiver gathers. Pairs of seismic traces from a common receiver gather are corrected for differential normal moveout, weighted in inverse relation to the RMS signal power, and combined to generate compressed common receiver gathers. The compressed common receiver gathers may be reformatted as common midpoint gathers for further processing.

Abstract: A method is disclosed for developing a weight function for a trace stack from the weight functions derived from the respective weight functions of an ensemble of individual separate input traces. Also disclosed is the method of developing the resulting weighted trace stack. Finally, disclosed also is a method of noise suppression utilizing weight function manipulation from a plurality of related seismic traces.

Abstract: A method is disclosed to provide optimal or near-optimal vertical stacking of seismic records within the constraints imposed by real time data acquisition procedures. This method is characterized by forming output seismic traces which are a sum of prorated input traces, such proration being performed by application of smoothly varying weight functions derived from estimated signal and noise power levels within each input trace. Each weight function is computed using frequency domain filtering techniques to obtain a well behaved bandlimited time series for each function. The method also includes a procedure for clipping grossly large noise spikes in the input traces before the stacking procedure is performed, thereby guarding the weight calculation procedure against aliasing effects induced by such spikes.

Abstract: Method and apparatus for digitally deriving arrays from seismic data. Indentical parallel processing elements connected between common input/output buses are each preselected to derive different pluralities of arrays. Array specifications defining the arrays are downloaded into the processing elements. A scan sample set of spatially distributed seismic receivers is periodically generated and placed on the input bus. Each processing element, in response to array specifications, captures and stores all receiver output signals in the scan required to derive its respective arrays, derives its assigned arrays, and delivers resultant array samples to the output bus. Double input and output buffering in the processing elements is provided whereby receiver capture, array derivation, and outputing processes occur simultaneously in each processing element.

Abstract: The present invention is a multiline beamformer for use in a medical ultrasound scanner using a phased array transducer. Lines of ultrasound energy are generated having a pressure at the array aperture corresponding to sin (.pi.x)/.pi.x, where x is the normalized distance of the array element measured from the center of the array. This transmitted energy creates a flat field in space which can then be received in multiple receive lines, using bundled, parallel time delays.

Abstract: In accordance with the present invention, progressive changes in amplitude as a function of offset of common gathers can be more easily identified by emphasizing the degree of amplitude variation between traces of each gather along a seismic line, and after generating semblance coefficients, displaying the resulting "weighted" offset traces or representations of such traces as function of either horizontal offset or centerpoint values. A significant --and progressive --change in P-wave reflection coefficient as a function of the angle of incidence (within sections) indicates valuable characteristics, say the fluid hydrocarbon-bearing potential and/or lithology of the reflecting horizon.

Abstract: A method and apparatus are disclosed for signal-to-noise optimization of seismic-trace signals during seismic prospecting utilizing plural initiations of a low energy surface seismic source. The method and apparatus optimize signal-to-noise ratio by vertically stacking, that is, summing, inverse power weighted seismic-trace signals from each of the plural initiations wherein the exponent used for weighting is selectable for optimizing the signal-to-noise ratio of the composite seismic-trace signal. The range of exponents provided is correlated to the range of ambient noise, including nonstationary noise, commonly encountered during seismic prospecting, especially vibroseis seismic prospecting, for the purpose of optimizing the quality of seismic-trace data.

Abstract: This disclosure relates to improved methods and apparatus for vertically stacking seismic-trace data collected by a digital field recorder during seismic prospecting utilizing plural initiations of a low energy surface seismic source. Seismic-trace data generated by consecutive seismic source initiations and acquired at a common detector location is weighted and summed together, and the sum is normalized prior to being recorded. Accordingly, the signal-to-noise ratio of the seismic-trace data is improved. The methods and apparatus by which the weighting values are calculated and applied provides computational simplifications which reduce the program storage requirements and increase the computation speed of the microcomputer circuit preferably used to perform the calculations and leads to savings in hardware power, size, and complexity.

Abstract: A method is provided for obtaining wide band seismograms made from a plurality of narrow band seismic surveys using vibrator type sources. Several different narrow frequency band seismograms are obtained using vibrator type signal sources. The narrow band seismogram having different frequency band responses are stacked, or added together, to provide a single wide band seismogram having improved signal to noise characteristics.

Abstract: A multi-channeled digital seismic field stacking system is disclosed for obtaining the composite response to a variable source array. A variable source array is synthesized by applying preselected weighting coefficients to the seismic signals produced in response to a selected number of surface energy impulses. The seismic signals produced by these impulses are amplified, multiplexed and digitized to obtain digital samples to which are applied the weighting coefficients. A digital multiplier is used to multiply each digital sample by a weighting coefficient to obtain a weighted digital sample. Each digital sample is multiplied by two weighting coefficients, a partial and a final. The partial weighted samples from each of the impulses are summed together to form a partial stack, while the final weighted samples are summed together to form a final stack. The variable source array which is synthesized covers two station intervals.

Abstract: Seismic traces synthesizing the response of subsurface formations to a cylindrical or plane wave are obtained for a succession of shotpoint locations along a seismic line of profile. The traces obtained are then wavefront steered and the steered traces and original trace for each shotpoint are summed. Groups of these traces for a line of profile are assembled to form a steered section. A number of these sections are then individually imaged or migrated, and the migrated sections are summed to form a migrated two-dimensional stack of data from cylindrical or plane wave exploration. Reflectors may then be located by finding common tangents.The traces for those shotpoints of the several lines which lie in planes perpendicular to the lines are then assembled and processed in the foregoing manner to obtain three dimension migrated seismic data.

Abstract: A novel array of vertically and horizontally spaced hydrophones is shown which is capable of high ratio of desired signal to noise because of good directional sensitivity when used with any seismic source. Alternatively, a novel directionally sensitive array of vertically and horizontally spaced seismic sources is disclosed for use in seismic surveying with any spread of hydrophones or geophones, again attaining a high ratio of desired signal to noise. A reception pattern (in the first case) and a radiation pattern (in the second place) is produced which essentially eliminates reception or radiation at all frequencies except for waves within a predetermined angle with respect to the array. The sensitivity is essentially constant within such angle for all frequencies and essentially zero outside it.