Abstract: Recorded seismic traces are gathered into common offset groups. Within each group, the traces are arranged according to shot point number. Mean and standard deviations are determined for each trace. High frequency amplitude variations in the mean and standard deviations caused by variations in source strengths and receiver calibrations are removed to produce traces of low frequency amplitude variations representing subsurface geology or wave propagation effects.

Abstract: A method for detecting errors in estimated seismic velocities used in a normal moveout correction of a gather of traces selected from conventional, common midpoint seismic data. Zero offset reflectivity and amplitude versus offset slope traces are derived from the NMO corrected gather. Analytic traces are calculated for the zero offset reflectivity and amplitude versus offset slope traces. The analytic zero offset reflectivity trace is multiplied by the complex conjugate of the analytic slope trace and the imaginary part of the product indicates estimated velocity errors. The velocity error indicator is used to correct the velocity estimates so that the normal moveout process may be reperformed without the errors caused by incorrect velocity estimates. Alternatively, the velocity error indicator itself is plotted on a seismic section as an indicator of characteristics of subsurface earth formations.

Abstract: A method of geophysical exploration is described for transforming qualitative descriptors of seismic data into a quantifiable decision-making tool to estimate the formation properties as well as economic potential of a selected formation in the earth's subsurface. Qualitative descriptors of the waveform of seismic events contained in a first set of seismic signals are obtained and correlated with formation properties to obtain a series of one or more histograms. Qualitative descriptors of seismic events contained in a second set of seismic data can be obtained and transformed into estimates of formation properties as well as estimates of the economic potential of a selected formation for producing hydrocarbons employing such histograms.

Abstract: The present invention provides novel methods for identifying, characterizing and mapping seismic noise as an aid in evaluating and enhancing seismic data. In particular, an array of seismic receivers can be beam steered to sense seismic energy arriving from a plurality of azimuths. A measure of the strength of the seismic energy for each azimuth can be obtained for a plurality of arrival times, velocities and distances from the array. Displays of the azimuthal distribution of the strength of the seismic energy sensed by the areal array can then be produced for identifying and characterizing seismic noise into seismic data.

Abstract: A space time gate is selected surrounding a coherent noise to be removed from an array of seismic traces. Signal-plus-noise within the selected gate is extracted from the array of seismic traces. Coherent noise within the gated signal-plus-noise is estimated and subtracted from such gated signal-plus-noise to provide a signal estimate. This signal estimate is restored into the array of seismic traces.

Abstract: An improved method of stratigraphic analysis of geophysical data is provided. In one embodiment seismic data are transformed into one or more instantaneous attributes descriptive of the wave-like nature of the seismic signals comprising the seismic data. A stratum in the earth's subsurface, having both lateral and vertical extent, is defined on the seismic data. The instantaneous attributes within the stratum can thereafter be transformed into a descriptor statistically representative of changes in the formation materials comprising the stratum. The descriptor can then be plotted in both cross-sectional and plan view so as to identify and characterize both lateral and vertical variations in the lithology, geology and pore fluid content of the formation materials comprising the stratum.

Abstract: A seismic directional sensor for solid-borne sound has at least one geophone with pronounced directional characteristic. The measuring electrical vibration signals, which are obtained at different circumferential angular positions of the radial longitudinal axis of the geophone and are to be compared with one another, are correlated with the direction of a seismic ray extending at right angles to the longitudinal axis of the geophone, which is ineffective in its neural circumferential angular position.The neutral circumferential angular position is determined by the ratio of the amplitude of the measuring signals which are determined on both sides adjacent to the neutral circumferential angular position in effective circumferential angular positions of the geophone. The vibration pattern of the measuring signals is antiphase in relation to the respective other side.

Abstract: This invention provides a method for compensating for the deleterious effects of irregular spatial sampling of seismic data. The imbalance caused by sparse sampling is corrected by decomposing a processed data gather into its constituent dip and azimuth components, analyzing the movement and scaling of selected attributes of those components and applying an inverse sampling operator to the processed data based upon the analytical results.

Abstract: A method for estimating pore fluid pressure in a subterranean formation is disclosed for use in drilling wells. A pair of velocity-effective stress relations are used to compute pore fluid pressure from velocity data. One relation applies when the current effective stress is the highest ever experienced by the subterranean formation. The second relation accounts for hysteresis effects when the effective stress has been reduced. Pore fluid pressure is found by subtracting the computed effective stress from an estimate of the overburden stress.

Abstract: In a preferred embodiment of the present invention, methods are provided for Kirchhoff-migrating seismic data using a parallel computer. The methods of the present invention preferably use a multiprocessor machine that is interconnected to form a hypercube. The presently preferred method is to build up one or more migrated output traces in each processor (node) designated as a "migration" processor, as input traces are passed from migration node to migration node along a nearest-neighbor chain. When an output trace is completed, it is sent by a migration node to storage via an appropriate I/O processor and the migration node beings building a new output trace. There is essentially no limit to the length of seismic line which can be so migrated. Alternatively, the input traces may be held in the migration nodes and the output traces passed from node to node along a nearest-neighbor chain, or the input and output traces may be passed in opposite directions along the chain.

Abstract: The invention relates to a method for locating correct near vertical boundary or fault positions in a velocity model using common reflection point (CRP) gathers. Conventional migration velocity analysis examines the migrated image for hints to correct the velocity model. Vertical boundaries such as faults or salt flanks must be accurately determined to produce reliable images of deeper reflectors. Previous methods have placed faults by trial and error, since a depth image of a nearly vertical boundary is difficult to produce. The present method examines the sensitivity of CRP gathers to abrupt lateral changes across a nearly vertical fault to determine the location and the dip of a nearly vertical fault from a series of CRP gathers.

Abstract: Balancing of signal amplitudes in recorded seismic data prior to its transformation from its original domain (such as offset-time, or X-T) to a different domain (such as frequency-wave number, or F-K) has been found to cause unwanted repetitive pattern dispersion in the data. This unwanted effect is removed by determining a corrective factor, the ratio of amplitude of the seismic data to its trace envelope, prior to transformation. The data is then transformed into the different domain where meaningful reflection content is enhanced, such as by two-dimensional filtering. The data is then inverse transformed to the original domain. An inverse corrective factor is then applied, restoring the amplitude of the reflection signal component of the data.

Abstract: Disclosed is a seismic surveying and data processing method to filter from seismic data any energy contributions that are not in the seismic line of profile. The surveying method requires a receiver geometry wherein at least one receiver is in and at least one receiver is out of the line of profile, so that in common offset gather or shot record plots, seismic events along the line of profile are aligned in time and out-of-plane energy takes the form of a series of sawtoothed seismic events arriving at different times in the different lines of receivers. Knowing the number of out-of-plane energies and their respective dips allows for the design of a filter, which is applied to the data with a computer, to null and thereby remove the effects of unwanted out-of-plane energy from the seismic survey data.

Abstract: Seismic traces are singularly acquired, digitally converted, normalized according to mean and amplitude, visually displayed for qualitative evaluation, and recorded in conjunction with relevant environmental (acquisition) details. Related pairs of data with differential vertical offsets so recorded are digitally bandpassed according to user specification, limits of dominant waveforms determined with respect to time, crosscorrelated to determine time offset, and average waveform velocity estimated over the depth increment under study, based on the determined time offset and the estimated waveform travel path distance difference.

Abstract: A method of deterministically computer generating a model of a response voltage waveform of a seismic receiver employed in a seismic, particularly marine, data gathering system, the model incorporating factors that have been identified as significant contributions to amplitude, such as directivity, divergence, attenuation, interbed multiples, and transmissivity. The model is generated from the mathematical manipulation of well log data and data gathering system characteristics into a seismic range equation, namely: ##EQU1## where E.sub.r (f)=received energy densityE(f)=radiated energy densityD(.theta..sub.s, .phi..sub.s, f)=source directivity along .theta..sub.s, .phi..sub.s direction at the sourceA.sub.c (.theta..sub.H, .phi..sub.H, f)=Capture area along .theta..sub.H, .phi..sub.H direction at the hydrophone arrayR.sub.T =target reflection coefficientD.sub.

Abstract: The invention relates to a method of structural traveltime tomography which uses mismatched image information observed on common image point gathers to determine the precise location of near vertical boundaries or faults. The method can distinguish an error caused by a misplaced fault from velocity caused errors, then it reduces these errors by correcting the location of the fault. The result is a better depth image from better aligned events, and better correction to the velocities from a follow-up tomography using current velocity tomography.

Abstract: A method for improving the efficiency of pre-stack depth migration includes the steps of deleting a portion of the received data to obtain a representative remaining portion. All the shots are separated into several series, such that within each series the receiver locations are repeating. One or more series of shots is selected for migrating. With each series, receivers are selected from each shot such that their locations are repeating. This allows maximum re-use of the travel time tables and resulting in the best efficiency of the depth migration. The same principal can be applied to three dimensional prestack depth migration to improve its efficiency.

Abstract: A method for predicting the formation pore-pressure ahead of the drill bit while drilling is disclosed. During the drilling process, the drill bit impacting the earth generates a seismic signal. The seismic signal propagate away from the drill bit in a radial fashion with some rays paths propagating directly towards the surface, while others propagating downward are reflected back towards the surface. The direct and reflected seismic signals are received by seismic sensors at one or more locations. The signals produced by the sensors are recorded for later processing. From the recorded signals an interval velocity for each formation behind the drill bit is determined much in the same way a vertical seismic profile is made. From the reflected seismic signals, an acoustic impedance for each formation ahead of the drill bit is determined.

Abstract: Continuity of subsurface formations or beds in the earth between existing wells is investigated. Seismic energy is sent from a seismic source in one of the wells at various selected fixed depths. A number of sensing geophones deployed at selected fixed depths in one or more adjacent wells detect the seismic energy as data. A frequency domain decomposition process is performed on the data in order to determine if any of the formations located between the wells function as waveguides for seismic energy within the frequencies of interest. Those formations exhibiting waveguide properties are indicated as continuous between the wells.

Abstract: A method for attenuating coherent and incoherent noise in seismic signal data is provided. Seismic signal data is transformed from a time-space domain using a Radon-transform domain. In the Radon-transform domain, coherent noise is attenuated by muting and incoherent noise is attenuated by diversity stacking. Data remaining in the Radon-transform domain in transformed back to the time-space domain by an inverse Radon transform.

Abstract: An improved comprehensive system for definition of velocities of acoustic energy of sedimentary rocks is provided. First, geophysical exploration data available in the prior art is collected and organized to be defined as sequences and to define velocity behavior within sequences, and used to obtain consistently reasonable levels of accuracy of velocity distributions known by those skilled in the art. The present invention is particularly attentive to seismic sequence definition and to sequence compaction behavior. Secondly, in accordance with the present invention, means and methods not heretofore known in the art are used to sample well, seismic and other sources of data, on an individual basis, to define to what extent normal compaction behavior and velocities, as previously determined, may have been locally altered by other factors.

Abstract: A method of geophysical exploration is provided for identifying and evaluating stratigraphic prospects associated with step-like changes in elastic impedance from gradational changes in elastic impedance. In particular, the seismic data are bandpass filtered with a plurality of filters each having a different pass band. Measures of the amplitude are obtained for selected reflection events in the seismic data as a function of their associated pass band frequency content. The changes in amplitude as a function of changes in frequency content of the reflection event can thus be employed to identify and evaluate subtle stratigraphic prospects in the seismic data.

Abstract: This is a method for optimizing the coordinates of transducer stations involved in a common mid point gather. Relative reflection-data misalignments between the traces of the gather are attributed to errors in the reported offsets between transducers. Each trace of the gather is iteratively cross-correlated with a pilot trace, using a different offset increment for each iteration. The offset increment that maximizes the correlation coefficient is accepted as the most likely offset residual appropriate to the trace in question. The offset residual is applied to the nominal offset to provide a range measurement vector. The intersection of the range measurement vectors from a plurality of interdependent common mid-point gathers is the best estimate of the transducer location.

Abstract: A method of correcting a seismic signal s(t) provided by a vibration sensor (100) in response to at least one emission signal F(t) produced by a least one seismic vibration generator (200). The real emission signal F(t) differs in phase and amplitude relative to a reference emission signal F(t). The correction method of the invention consists in determining the phase difference .DELTA..phi.(f) and the amplitude ratio A(f) between the real emission signal F(t) and the reference emission signal F(t) as a function of frequency f, and in applying the seismic signal s(t) from the vibration sensor (100) to a filter (304) whose response is defined in phase and amplitude respectively by -.DELTA..phi.(f) and by 1/A(f).

Abstract: A method to adjust a common subsurface feature on seismic traces associated with line misties is provided so that the seismic traces are consistent about the common subsurface feature. The method uses traces which are uniquely located in an x-y coordinate system to reflect the actual location of the traces with respect to an intersection. In this method traces can be associated with a line of seismic data or can be isolated traces such as well-log synthetics or vertical seismic profiles. The traces make up sets of data. An intersection is selected and representative traces from two sets of data are initially selected and form trace pairs. A time gate is determined about a common subsurface features of interest on the representative traces. The time gate isolates a trace gate about the common subsurface feature on each trace leaving only the trace gates in the trace pairs. A time delay is determined for each trace pair.

Abstract: A method of analyzing the structure of a medium particularly useful in seismic prospecting, by generating seismic data represented by recorded traces corresponding to a plurality of source and receivers distributed according to a homeomorphic distribution with respect to predetermined central points in a manner providing predetermined parameters and one-to-one mapping of each element of a target object into an element of its homeomorphic image. A gather of corrected traces is formed and stacked to obtain stacked wavefield characteristics as functions of the time of registration of the data on a predetermined central trace. The stacked wavefield characteristics for a plurality of central traces, and the mentioned predetermined parameters, are then utilized for determining the structure of the medium.

Abstract: Methods of geophysical exploration are provided for estimating the burial conditions of sedimentary material in a selected basin. The burial conditions can include measures of porosity, lithology, pore fluid pressure, effective pressure, and density. In particular, a reference velocity profile is developed for a model of the sedimentary material comprising the basin and is compared to a velocity profile obtained from seismic data to obtain estimates of the burial conditions of the sedimentary material.

Abstract: A seismic ray-tracing model performs economic exploration of subsurface structures, which 1) allows amplitude, frequency, mode, and other "synthetic filtering" of the model's calculations and 2) allows model interpolations, approximations, and other "synthetic sensitivity" terminations of ray-tracing calculations. The model output can be directly matched to the filtration and sensitivity of actual seismic data. The model structure is capable of the extensive calculations similar to current extensive forward models, but ray-tracing calculations are accomplished in discrete pairs (allowing interpolation between divergent ray pairs and partially simulating detector sensitivity) and ray-tracing calculations are terminated if an amplitude under a threshold level signal strength is encountered. The amplitude threshold level can be set to match filtering used on actual seismic data. This sensitivity and filter matching achieves maximum reliability while still avoiding unnecessary calculations, e.g.

Abstract: A method of enhancing geophysical data comprising processing the geophysical data into ordered gathers of seismic signals, transforming the seismic signals of each ordered gather into synthetic traces having reflection event amplitudes of only one polarity, combining the synthetic traces of each ordered gather, and restoring the positive and negative polarities to the reflection events in the combined synthetic traces.

Abstract: A method for calculation of raypaths and wavepaths from traveltime tables for the tomographic estimation of transmission velocities includes picking the earliest traveltime of waves transmitted between different source and receivers locations. A velocity model that describes transmission velocities in a region of interest is obtained. Traveltime from each source position to each point in the region of interest and traveltimes from each receiver loaction to each point in the region of interest are extrapolated. The extrapolated traveltimes from the source and receiver to each point in the region of interest are added together to quantify the path of a wave between one source and one receiver. All points in the region of interest whose total traveltimes are less than half a wavelength greater than the minimum traveltime are found. A representative raypath that passes through the center of the estimated wavepath region for each source and receiver location are saved.

Abstract: Time-coherency traces generated during velocity analysis are displayed in panels where each panel contains traces representing a single selected trial stacking velocity function and a plurality of common midpoint locations along a seismic line of exploration. Points selected from the panels, optimally by comparison with stacked sections, are used to generate a time velocity funtion for stacking, NMO correction, interval velocity determination, or other uses.

Abstract: A method of removing multiple reflection events from seismic records is described. A shallow primary reflection event is used as a model for a deeper primary, and is distorted responsive to the predicted static correction to yield a model for the multiple. The method is applied to common depth point (CDP) records, in which the common-midpoint contribution of the multiple to each CDP record can be assumed to be equal. Preferably, a total least squares correlation step is used to design a convolutional filter applied to the data records to remove the multiples therefrom.

Abstract: A novel method of geophysical exploration is provided whereby shot points and receiver locations are positioned such that seismic data resulting therefrom can advantageously be processed employing 3-D processing techniques to obtain a better image of the earth's subsurface structure. In one embodiment, shot points, or alternatively, receiver locations are arranged along generally sawtooth or zig zag lines so that common midpoint bins of seismic signals include a generally uniform distribution of source-receiver pair azimuths. In another embodiment, both the shot points and receiver locations are arrayed along generally alternating, sawtooth or zig zag lines.

Abstract: A method for processing three-dimensional seismic data to define areal boundaries of hydrocarbon reservoirs. 3-D Seismic data for an area having a producing well is examined to establish an attribute critical parameter that specifically relates to the reservoir structure. Having identified a parameter, the 3-D data can then be examined in a selected time window for presence of the critical parameter and X, Y gridding of its relative value. The relative values are then output to visual plot to provide a plan view of reservoir structure.

Abstract: A method in real time control systems for seismic interference to indicate an acceptable level of interference in relation to the amplitude, angle of incidence, and frequency of a seismic reflection signal, and to remove such interference loaded signals during seismic surveys, comprises steps to determine lower threshold values of coverage, identify interference and amplitude anomaly in the recorded signal of reflection, estimate the expected value of amplitude characteristic of the signal on the basis of recorded amplitude characteristics of recorded signals from one or a plurality of preceding series of survey, mark time windows in which interference and/or amplitude anomaly are identified, generate a table of the number of times a certain time window was marked in the series of recordings of the same point of reflection, assign limits on the number of interference events to various marked time windows, and remove from the recordings those time windows wherein the number of interference events exceeds the l

Abstract: A method of seismic exploration uses recordings from both surface receivers and buried sensors to determine the full elastic effect of the near surface layer on an applied seismic wave. The surface receivers are arranged relative to the seismic source location so that rotational effects may be detected. Buried sensors are located so that vertical effects may be detected. This full elastic effect may be used in subsequent seismic data acquisition to reconcile the effect of the near surface so that the response of the underlying rock formations may be known.

Abstract: A method for producing an inverse vertical seismic profile using a seismic source place down a borehole has been invented. The directly transmitted waves from the seismic source and the secondary reflectances thereof are detected by a sensor(s) on the earth's surface. The method depends only on knowing the relative arrival times at the sensor of the direct waves and the secondary reflectance waves.

Abstract: Regional velocity spectra coherency peaks are associated with peak events on a stacked seismic section of CMP gathers and used for editing siesmic data. In addition, travel time and spatial location along a seismic line data are displayed for stratigraphic and structural interpretation.

Abstract: A method for providing an optimum model having at least two dimensions of a heterogeneous medium, representing the variations of at least one physical parameter, for example the acoustic impedance of underground formations, and satisfying as well as possible the data measured in situ, for example well-logging in wells in studying the sub-soil as well as other data relative to the medium studied, for example geological information and seismic surface recordings. The method includes the construction of a reference model and the definition of covariance operators which model the uncertainties not only in the medium studied but also in the recordings obtained from outside the medium, for example seismic sections. Comparison between the effective recordings and others which are formed on the basis of the constructed model, makes it possible to check the validity thereof.

Abstract: Time-invariant multichannel seismic data filters are applied to seismic data traces for rejecting coherent noise signals within a time-space window. In one embodiment, these filters are applied for rejecting all signals having the same trace-to-trace slopes as the coherent noise signal. Segments of the filtered traces that are within the time-space window are added to corresponding segments of unfiltered traces outside of the time window for producing reconstituted time-variantly filtered traces. In another embodiment, these filters are applied for rejecting the coherent noise signals and passing all other signals within the time-space window and passing all signals outside of the window for producing time-variantly filtered traces.

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

Abstract: A seismic record is enhanced through trace restoration and extrapolation. A set of traces surrounding a missing trace or adjacent an edge of the seismic record are transformed into the frequency domain using a fast Fourier transform. Each frequency of the resultant x-f representation a series of complex numbers, one corresponding to each trace, is selected. Autoregressive model coefficients are estimated for this complex series using a recursive least squares method. A complex number is estimated for trace restoration and extrapolation from the series of complex numbers and autoregressive coefficients. After all frequency components are thus processed restored or extrapolated traces are obtained by an inverse Fourier transform.

Abstract: A method for removing boundary-generated artifacts in synthetic and actual seismic data. After seismic data processing, undesirable boundary-generated artifacts appear in the final seismic section. To remove this unwanted noise from the section, zeros are added to the lower boundary of the seismic section. This essentially pushes the sources of the noise downward in time in the section. After padding with zeros, the seismic data is collapsed to their point sources of origin using the Stolt migration/diffraction algorithm. Once the data are collapsed, the size of the seismic section is reduced to its original size. Following the resizing of the section, the inverse of the earlier applied Stolt algorithm is applied to return the seismic data to its original form, minus the boundary-generated artifacts.

Abstract: A geophone is disclosed which includes at least two transducers having axes which are perpendicular to each other for generating Cartesian coordinate signal components in response to at least vertical and horizontal in-line seismic wave motion of the geophone. The Cartesian coordinate signal components are converted to polar coordinate signal form including vector length, L, and angle, .theta., signal values. Surface wave noise signal components, such as ground roll wave signals, included in the L and .theta. signals are attenuated, or suppressed, to obtain signals L.sub.B and .theta..sub.B proportional to body waves. The L.sub.B and .theta..sub.B signals are converted to Cartesian coordinate signal form for subsequent processing along with outputs from other geophones in a geophone array for locating underground formations, deposits, or the like.

Abstract: A blast recorder and method for monitoring and processing vibrations from blasts, and for displaying the results in a nearly real time basis and in a manner which is easily interpreted by a relatively unskilled field worker and corresponds to a form which closely correspond to the real damage causing aspect of the blast than heretofore.

Abstract: A Monte Carlo statistical method for combining discrete geological measurements of rock properties with continuous measurements of seismic attributes and for converting those combined measurements into a display of the best estimate of subsurface rock classes.

Abstract: A method of processing seismic data involves the input of common depth point data for determination of obliquity of downward propagating energy. Data having known surface offset and travel time is then processed with interval velocities along the depth of survey to solve by matrix inversion for the earth elastic parameters at selected depths.

Abstract: A method for the determination and deconvolution of the signature of an unknown, non-impulsive source signal. The method supposes that that an array of receivers is positioned at the earth's surface to detect and record the seismic signals resulting from the interaction of the source with the earth's subsurface. The traces of data recorded are time-shifted by an amount determined by a coherency analysis of the data. The signal is estimated from the time-shifted data with a weighting factor applied at each trace. A deconvolution filter is determined from the estimate and is weighted at each frequency according to the strength of the source at that frequency. The filter is then applied to the time-shifted data.

Abstract: Methods for interpolation of severely aliased events in which composite wavelets of a section of seismic data traces are separated by wave field decomposition into their component wavelets. The spatially aliased component wavelets are identified to form a first class of wavelets. A second class of wavelets is comprised of non-aliased component wavelets. The wavelets in the second class or non-aliased component wavelets are interpolated in accordance with known techniques, such for example, as sinc interpolation whereas the spatially aliased component wavelets are interpolated in accordance with dip guided interpolation to provide the same number of traces as those comprising the second class of wavelets. The interpolated first and second class of wavelets are summed to provide a section of seismic data substantially free of spatial aliasing.