Abstract: A method for performing velocity analysis while eliminating the effects on weak signals caused by strong signals includes migrating each event of the pre-stack trace to a single location instead of all possible locations. This correct location is determined by ray-tracing through a velocity model. The input trace is divided into many windows, and each window is migrated to a place determined by ray-tracing the center of the window through the model. If the velocity model is accurate, each event will be migrated to the proper location yielding an accurate depth section with no migration artifacts. As a by-product, if the model is not accurate, the post-migrated parts (PMP's) provide a clean velocity analysis.

Abstract: In applying residual movement correction to common offset depth migrated data, common offset depth migration is applied using the best available velocity/depth model. Post migrated parts, which are depth migrated common midpoint gathers, are saved. The post migrated parts are treated as if they were in time not depth. Normal movement based on a constant velocity is removed. Velocity functions time-velocity pairs, are derived for the post migrated parts with normal movement removed using a standard velocity analysis program. Normal moveout based on these velocity functions is applied. The events on the post migrated parts ae not imaged to the same depth. The corrected post migrated parts are then stacked and displayed.

Abstract: A method for derivation of interval velocities from post-migration parts first includes the step of determining the apparent depth and slope of an event. The apparatus depth of an event is measured. The travel time of the recorded reflection for a particular offset is determined by ray-tracing through the old model and recorded. A trial velocity is assigned to the layer between events in the new model. The depth of the reflector is varied up or down until the computed travel time agrees with the measured travel time, keeping the source/receiver separation constant. A new velocity for the layer between reflectors is selected for which the depths at each offset are the same.

Abstract: The present invention provides a three dimensional before stack depth migration of two dimensional or three dimensional seismic data. Ray tracing is used to move before stack trace segments to their approximate three dimensional position. The trace segments are scaled to depth, binned, stacked and compared to the model. The model can then be changed to match the depth trace segments which will be stacked better, moved closer to their correct three dimensional position and will compare better to the model.

Abstract: In seismic exploration, a survey may be conducted using multiple seismic energy sources activated substantially simultaneously. A series of shots is made at each shot point, with a determinable time delay between the activation of each source for each shot. There must be at least two different determinable time delays in each series of shots. The seismic signals are recorded. A method of processing the signals to separate signals from each source is provided. For each signal receiver, the amplitudes of the signals from each shot in the series is summed. The signals are then time shifted, so that the signals from the second source to be activated are received at the same time, and the amplitudes for the series are summed. This step is repeated for each subsequently activated source. Time domain operators are derived, the operators and the summations Fourier transformed to the frequency domain, in which the signals received from each source are readily calculated.

Abstract: A method for properly migrating seismic data which has been elevation-static corrected. The method is comprised of assigning a zero (or very small) migration velocity for data located below a datum, yet above the original recording surface elevation. A best estimated earth velocity is input into the migration algorithm to represent the earth below the original recording surface. For seismic data collected in water-covered environments where the water bottom is irregular, the method contemplates that the data lying above the water bottom are migrated using the migration velocity of water. The data lying at or below the water bottom are migrated with a migration velocity of zero. In a second step, are elevation-static corrected and migration is performed where the velocity is zero between the datum and the original surface. Data below the surface is migrated using the estimated earth velocity.

Abstract: A method for migrating seismic data in the frequency-wave number domain is provided for migrating the seismic data having large vertical and lateral velocity variations in a fast, efficient and accurate manner. A root-mean-square (RMS) velocity function is derived from a set of seismic data samples comprising a body of seismic data. A best fit migration velocity is determined from the seismic data so as to provide a best migration. The seismic data may then be partitioned into a series of discreet frames and stretched according to a predetermined algorithm. Each partition is migrated in series by a portion of the RMS Velocity function until the data are fully migrated. After migration, the migrated seismic data are inversely stretched vertically followed by an inverse lateral stretch to remove any distortion instilled in the data by the initial data stretching.

Abstract: A computationally-economical method for converting a set of aerially-distributed seismic traces into a new, clearly-resolved, three-dimensional display of a volume of the earth without use of dip-dependent or azimuth-dependent migration velocities.

Abstract: The present invention relates generally to a method of geophysical exploration and more particularly to a novel method for imaging multicomponent seismic data to obtain better depth images of the earth's subsurface geological structure as well as better estimates of compressional and shear wave interval velocities. In particular, measures are obtained of imparted seismic wavefields incident on reflecting interfaces in the earth's subsurface and of resulting seismic wavefields scattered therefrom. The incident and scattered seismic wavefields are employed to produce time-dependent reflectivity functions representative of the reflecting interfaces. By migrating the time-dependent reflectivity functions, better depth images of the reflecting interfaces can be obtained. For a dyadic set of multicomponent seismic data, the dyadic set of multicomponent seismic data are partitioned so as to separate the variously coupled incident and reflected wavefields in the recorded multicomponent seismic data.

Abstract: Seismic data are passed through a preselected number of migration stages. During each stage, data are migrated a plurality of times, where the migration-velocity function is a minor fraction of the velocity required to fully migrate the data in a single stage. The cascaded migration migrates data having steeply-dipping events with greater accuracy and with less noise or artifacts than does a single-stage migration.

Abstract: A computationally-economical method for converting a set of areally-distributed seismic traces into a new, clearly-resolved, three-dimensional display of a volume of the earth without use of dip-dependent or azimuth-dependent migration velocities.

Abstract: A well logging tool employing at least one transmitter and at least one receiver is incrementally advanced through a borehole. A plurality of recorded well log traces from successive ones of the incremental depth points for a single transmitter-receiver pair are correlated to identify a moveout trend for the recorded waveforms about the measured arrival time of the waveform on the center trace of such plurality of traces. A second correlation of the center trace of the plurality of traces with the next successive depth trace is carried out in accordance with the identified moveout trend to determine the arrival time of the acoustic waveform on such next successive depth trace with respect to the measured arrival time of the center trace.

Abstract: Three-dimensional seismic prospecting is conducted using a less than complete multifold array of seismic sources and receivers which are positioned so that the resulting system of linear static connection equations according to common depth point are continuously coupled.

Abstract: Disclosed is a method for constructing an optimal pilot trace from a gather of seismic traces, which pilot trace can be used to obtain statics estimates for time correction of the gathered traces prior to common depth point stacking. During construction of the optimal pilot trace, the statics estimates are inherently obtained.

Abstract: By using wave tracking rather than a downward continuation concept, two sets of elastic wave fields (one generated by a seismic source, the other recorded by multicomponent geophones) are migrated separately and are then imaged. The process is repeated for common shot gathers, and then the images (associated with each common midpoint gather), are stacked.As a consequence of wave tracking, migration operations are preferably performed in the time domain using finite difference discretization equations involving vector properties of the fields but without having to reduce the latter to one-way wave equations.

Abstract: This invention relates to a method of increasing resolution of high-intensity amplitude events in seismic records provided by common midpoint collection methods (CMP) wherein nonsymmetrical travel paths of incident and reflected rays of the generated conventional waves are taken into account prior to trace stacking irrespective of dip or depth of the target reflector. In accordance with the invention, the converted phases of the conventional seismic wave, are processed as to define a series of common reflection point (CRP) coordinates each associated with a gather of converted traces as if a source associated with a given corrected trace was placed at each CRP and activated followed immediately by the relocation of a detector at the CRP and the reception of converted phases of the generated wave comprising the trace.

Abstract: This invention relates to a method of increasing resolution of high-intensity amplitude events in seismic records provided by common midpoint collection methods (CMP) wherein nonsymmetrical travel paths of incident and reflected rays of the generated conventional waves are taken into account prior to trace stacking due to the dip and depth of the target reflector.

Abstract: Disclosed is a method for estimating and correcting source and receiver statics contained in recorded and gathered seismic traces. Measurements based on the time of arrival of reflection and refraction signal components in the recorded and gathered traces are used to produce source-receiver statics estimates, which are in turn used to correctly time shift the individual traces of the gather for subsequent common depth point (CDP) gathering and stacking.

Abstract: The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast (with the overburden rock) has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence (within a gather of data) indicates the lithology of the reflecting horizon and the capping strata.

Abstract: In a seismic recording and processing system in which a line of sources and a separate line of receivers are provided and each of the source operations from each of the source points is recorded on all receiver points. A method is described for determining the differential static correction between each adjacent pair of source points in terms of the differences in travel times from each pair of source points, to all pairs of receiver points. This is provided even though the lines of source points and receiver points may be parallel to or at angles to each other, and the spacings of source points and receiver points in their separate lines may be the same or different.

Abstract: The field locations of seismic shot points are chosen to produce partial multifold data, the static correction equations of which are at least partially coupled. The seismic cross sections resulting therefrom are substantially improved.

Abstract: The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast with the overburden rock has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence occurs. Thus, differentiating between high-intensity amplitude anomalies of nongas- and gas-containing media is simplified: progressive change in amplitude intensity of resulting traces generated by the field array as a function of offset between each source-detector pair, is associated with the last-mentioned medium only.

Abstract: In marine seismic exploration, the distortion introduced by an anomalous surface layer is removed from seismograms. The surface layer travel time, obtained for example from fathometer readings, is converted to a model depth section of the anomalous surface layer. Another model depth section includes an assigned control layer without the anomaly. From these two depth sections, time corrections are obtained. These time corrections are applied to the seismograms at the time of reflection from each of the subsurface interfaces.

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: Multiplexed seismic data representing a plurality of seismic channels intensity modulates each sweep of the electron beam of a cathode-ray tube. Each successive sweep of the electron beam is photographically reproduced on a rotating drum plotter to provide a seismic record section. The modulation of the cathode-ray tube is further controlled to provide for various seismic trace presentations on the record section, including wiggle traces, variable area traces, wiggle-variable area traces, and symmetrical-variable area traces.

Abstract: Common depth point seismic signals from a plurality of seismic receivers are recorded on a field recorder. A first time shifter corrects the seismic signals for multiple normal moveout. A linear dip filter rejects unwanted multiple reflection signals. A second time shifter reverses the multiple normal moveout correction of the first time shifter. A third time shifter corrects the primary reflection signals for normal moveout. The primary reflection signal are then stacked and recorded as a composite common depth point seismic signal.

Abstract: In common depth point (CDP) seismic exploration, a pilot trace is produced from the stacked trace for each CDP set of traces. The pilot trace is crosscorrelated with each trace of the CDP set during selected time windows. The crosscorrelation time shifts are applied to each trace of the CDP set. The time shifted traces of each CDP set are stacked to form a static corrected seismic record section.

Abstract: A seismic data processing method in which seismic traces (each trace containing a signal resulting from reflection of a seismic signal at a location within the earth, and each trace being associated with at least one point in a two-dimensional spatial grid (x,y)) are subjected to Fourier transformations, the coefficients of the Fourier-Transformed traces are subjected to a recursive KF migration operation, and the migrated traces are thereafter inverse-Fourier-transformed. When displayed, the processed seismic data accurately represents the position within the earth of whatever caused the reflection. The method may be employed to process stacked seismic traces, each associated with a single point (x,y) in the grid, or may be employed to process unstacked seismic traces, each associated with both a seismic source location (x.sub.s,y.sub.5) and a different seismic receiver location (x.sub.r,y.sub.r) in the grid.