Abstract: A method is disclosed for determining interval anisotropic parameters. The method includes determining normal moveout (NMO) velocities and effective anelliptical parameters from seismic data traces. The NMO velocities are processed to obtain interval NMO velocities. The NMO velocities, effective anelliptical parameters and interval NMO velocities are inverted to obtain the interval anisotropic parameters. In one embodiment, the inversion includes damped least squares. In one embodiment, the inversion is preconditioned.

Abstract: P-wave velocity in a near-surface region of a land area is estimated from a combination of seismic data based upon waves in the near-surface region generated in response to a shock in each of a plurality of upholes drilled in the land area and vibrator dynamic data generated in the near-surface region in response to vibrator action on the land area.

Abstract: A method of processing sonic wireline or logging while drilling data acquired in a borehole that includes filtering the sonic data to attenuate tool-borne and borehole-borne arrivals; migrating the filtered sonic data; and beamforming the filtered and migrated sonic data to determine a position of a reflector with respect to the borehole. The sonic data may be processed down-hole, transmitted to the surface, and used for geosteering purposes while drilling. The filter may comprise an adaptive noise-attenuating filter capable of attenuating noise arising from different borehole modes from desired signal and allowing for changes in the source signature.

Abstract: The invention comprises a system for processing seismic data to estimate time shift resulting from velocity anisotropy in the earth's subsurface. A gather of seismic data traces is formed and selected seismic data traces included in said gather within selected time windows are cross-correlated to estimate the time shift in the seismic data traces included in said gather resulting from velocity anisotropy in the earth's subsurface.

Abstract: The present invention provides methods to be used in seismic data processing to address problems encountered during data acquisition. The present invention provides a multi-step process to reduce aliasing of seismic data along time slices.

Abstract: The present invention provides a method for reducing water bottom reflection time differences. The method includes selecting a plurality of trace groups, each trace having an offset from a midpoint and a water bottom reflection time. The method also includes determining a rate of change of the water bottom reflection time of each trace and generating a model water velocity and a model water bottom reflection time for each trace midpoint using a preselected function of the water bottom reflection times and the rates of change. Furthermore, the method includes generating a plurality of water bottom reflection time corrections for the traces in each trace group using a pre-selected function of the water bottom reflection times, the model water bottom reflection times, the model water velocities, and the trace offsets.

Abstract: The present invention provides methods to be used in seismic data processing to address problems encountered during data acquisition. The present invention provides a multi-step process to reduce aliasing of seismic data along time slices.

Abstract: Near-offset and far-offset seismic data volumes are time-aligned by first selecting a plurality of time shifts. The near-offset and far-offset seismic data volumes are cross-correlated at the plurality of time shifts. An initial time-shift volume and a maximum correlation volume are created from the maximal cross-correlations at the plurality of time shifts. Areas of high time shift from the initial time-shift volume and areas of low cross-correlation from the maximum correlation volume are determined. The determined areas of high time shift and low cross-correlation are filtered from the initial time-shift volume, generating a filtered time-shift volume. The filtered time-shift volume is applied to the far-offset seismic volume to generate a time-aligned far-offset volume.

Abstract: A method of seismic imaging a subsurface formation using an array of seismic sources and an array of seismic receivers located subsurface, wherein there is a complex transmission medium between the two sets by creating a virtual source at a selected receiver within the array, time-reversing a portion of the signal related to the selected source and receiver and convolving the time-reversed portion of the signal with the signal at adjoining receivers within the array and repeating the process for signals attributable to various surface sources to create a seismic image of a target formation.

Abstract: Temporal and/or spatial frequencies of spatially and digitally sampled 2-D or 3-D seismic data above the Nyquist frequency are preserved in full time migration of partial time migration (DMO) of 2-D and 3-D are preserved. Use is made of the fact that migration operators applied to input seismic data produce an output that need not correspond to prespecified temporal or spatial sampling values, and for sufficiently long migration operators, gives substantially uniform sampling at higher rates than the spatial and temporal Nyquist frequencies. Exact values of the partial migrated outputs are accumulated in an output buffer prior to combining them to give a migrated output with high temporal and/or spatial frequencies preserved.

Abstract: Methods are provided for automatic detection of linear seismic events and the detected events are used in correction of statics and geometry error.

Abstract: A method for using S-waves recorded at sea floor to determine anellipticity relating to at least one rock substrate is provided. In particular the method comprises identifying an S-wave event in recorded pre-stack seismic data and then determining at least one anisotropy parameter by adjusting moveout of a corresponding modeled S-wave event to agree with moveout of the identified S-wave event. The method is particularly applicable to mode converted S-waves in seismic signals.

Abstract: The present invention provides a method of migrating seismic records that retains the information in the seismic records and allows migration with significant reductions in computing cost. The present invention comprises phase encoding seismic records and combining the encoded seismic records before migration. Phase encoding can minimize the effect of unwanted cross terms while still allowing significant reductions in the cost to migrate a number of seismic records.

Abstract: A method of migrating seismic data using offset checkshot survey measurements. The offset checkshot survey measurements involve raypaths similar to the migration raypaths for the seismic data, and are used to determine direct arrival traveltimes to receivers in a borehole. Embodiments of the invention provide for direct use of the traveltimes in migration, or indirect use of the traveltimes in migration via construction of a migration velocity model. The velocity model embodiments further provide for either traveltime error correction via use of interpolated error functions or construction of migration error tables. The invention can be employed for time, depth or Kirchhoff migration, in either two or three dimension, and in either prestack or poststack applications. The invention may be used to migrate any type of seismic data, including compressional-wave, shear-wave, and converted-wave seismic data.

Abstract: A seismic reflection data acquisition and processing method and device for prospecting in tectonically complex environments are disclosed. In particular, the seismic reflection data acquisition and processing method is useful for providing a summation rate tensor field and a 3D image unit, e.g. in 3D earth seismics or complex tectonics.

Abstract: A method for producing high vertical resolution seismic images from crosswell data is disclosed. In accordance with one aspect of the disclosure, a set of vertically spaced, generally horizontally extending continuous layers and associated nodes are defined within a region between two boreholes. The specific number of nodes is selected such that the value of a particular characteristic of the subterranean region at each of the nodes is one which can be determined from the seismic data. Once values are established at the nodes, values of the particular characteristic are assigned to positions between the node points of each layer based on the values at node within that layer and without regard to the values at node points within any other layer. A seismic map is produced using the node values and the assigned values therebetween. In accordance with another aspect of the disclosure, an approximate model of the region is established using direct arrival traveltime data.

Abstract: An improved method for eliminating reflections from artificial model boundaries encountered in finite-difference acoustic wave propagation computations is based on applying two different boundary conditions at the artificial boundary. In this method one boundary condition generates reflections having the same polarity as the incident acoustic wave, and the other boundary condition generates reflections with opposite polarity. To apply the improved method simply compute both boundary conditions on a small narrow region adjacent the artificial boundary on a separate set of grids and average the two solutions.

Abstract: A method for the determination of migration velocities in seismic processing in which a blasting point S is associated with receivers (R.sub.1 to R.sub.n) which are separated by offsets such that in a given speed range, a first set of traces derived from the blasting point and registered on the receivers, and a second set of traces in constant and colinear offset to the first set are migrated. Two migrated images of the part of the site corresponding to the two sets of traces are obtained. The two images are correlated by means of a spatial two-dimensional correlation, the result thereof determining the deviation between the migration used and the investigated velocity. The result is particularly useful in the seismic prospection of a site.

Abstract: A novel fault framework method and apparatus automatically computes the relationships between intersecting fault surfaces. When faults are loaded into the novel fault framework apparatus, all intersecting fault pairs are determined and the fault fault intersection lines are computed and stored. The intersecting fault pairs are presented and available for automatic calculation of the major/minor and above/below fault pair relationships. The geometry of both intersecting fault surfaces are examined on either side of the fault fault intersection line. This, in combination with the relative size of the faults, is analyzed to compute the major/minor and above/below relationships based on geologic assumptions and knowledge of the origin of the fault surface data. When the relationships between intersecting faults is defined, the minor fault is appropriately truncated.

Abstract: A method for determining a substantially optimal NMO velocity function for use in stacking a CMP gather of seismic data traces. The method begins with an initial estimate of the NMO velocity function for the CMP gather. This initial estimate is typically determined through conventional seismic velocity analysis. The method then picks a first velocity-traveltime pair falling on the initial estimate of the NMO velocity function and conducts a two-dimensional interpolative search of trial velocity-traveltime pairs in the neighborhood of the pick to find a substantially optimal velocity-traveltime pair. This substantially optimal velocity-traveltime pair is the trial velocity-traveltime pair having the highest stack response and is substituted for the pick in the NMO velocity function. The method then proceeds to find substantially optimal velocity-traveltime pairs to replace each of the other picks on the initial estimate of the NMO velocity function.

Abstract: A system and method for synchronizing collection of seismic data used for seismic surveys. In one embodiment, positioning signals received from a positioning system, such as the Global Positioning System, are used to acquire a highly accurate time value. Data collection is then initiated at a prespecified time using the time determined from the positioning signal.

Abstract: A method for acquisition of seismic data from an area surveyed using a group of seismic energy sources and a group of seismic streamer cables, particularly a marine area, includes forming a first group A from at least two elements of either seismic energy sources S or seismic streamer cables C having a spacing X between said elements, forming a second group B from at least two of the other elements of sources S or cables C than that forming group (A), spacing the elements in group B a distance equal to X multiplied by the number of elements in group A, forming a group C from at least two subgroups each consisting of a group A, spacing said subgroups in group C in distance equal to the distance between two elements in group B multiplied by the number of elements in group B, the spacing between two adjacent subgroups being equal to the lateral distance between midpoints between the subgroups, and forming further groups as desired D, E, F etc.

Abstract: A method for producing seismic images from seismic data obtained from two different datums. Traveltimes between the two datums are determined from either measurements or an assumed velocity field. An extrapolation of the data to simulated source and receiver locations is carried out using any form of the wave equation which does not require velocity field information. After extrapolation, the data at the simulated source and receiver locations is processed using standard seismic imaging techniques. The method can be applied to simulate borehole, crosshole, or multi-borehole seismic data.

Abstract: A standoff compensation system is disclosed for use in an acoustic LWD system. An acoustic transducer is provided to measure the standoff distance between the logging tool and the borehole wall. The present invention includes a downhole processor for determining an index value which is used to align received acoustic formation signal measurements based upon the measured standoff distance. The index value can either be calculated by the downhole processor or can be retrieved from a pre-calculated look-up table in ROM. The processor then shifts the received acoustic formation signals based upon the index value assigned to each formation signal. The aligned acoustic formation signals are stacked, so that a single acoustic formation signal can be obtained for each firing period and either stored in downhole memory, used immediately, or transmitted by telemetry to the surface. The firing of the acoustic formation transmitters occurs in a rapid firing mode, followed by a relatively long idle.

Abstract: A method of migrating seismic data using offset checkshot survey measurements. The offset checkshot survey measurements involve raypaths similar to the migration raypaths for the seismic data, and are used to determine direct arrival traveltimes to receivers in a borehole. Embodiments of the invention provide for direct use of the traveltimes in migration, or indirect use of the traveltimes in migration via construction of a migration velocity model. The velocity model embodiments further provide for either traveltime error correction via use of interpolated error functions or construction of migration error tables. The invention can be employed for time, depth or Kirchhoff migration, in either two or three dimension, and in either prestack or poststack applications.

Abstract: A method is provided for processing seismic data samples obtained from seismic signals propagating in an anisotropic medium. The data samples are associated with scattering angles and azimuth at each migration dip at each image point of the medium. An inverse operator is then applied to the samples so as to provide intermediate anisotropic elastic parameter combinations for each migration dip at each point of the medium. The inverse operator comprises an inverse of a scattering function for variations in elastic parameters from a reference medium against scattering angle and migration dip. The intermediate anisotropic elastic parameter combinations are then migrated to their proper locations.

Abstract: A method of prestack time migration based on the principles of prestack Kirchhoff time migration that can be applied to both 2-D and 3-D data. Common scatter point (CSP) gathers are created as an intermediate step for each output migrated trace. Normal moveout (NMO) and stacking of CSP gathers is performed to complete the prestack migration process. The method of the present invention allows the CSP gathers to be formed at any arbitrary location for velocity analysis, or to prestack migrate a 2-D line from a 3-D volume. The CSP gather is similar to a CMP gather as both contain offset traces, and both represent a vertical array of scatter points or reflectors. The CSP gather is formed from all the input traces within the migration aperture. Samples in the input traces are assigned an equivalent offset for each CSP location, then copied into the appropriate offset bin of the CSP gather in an efficient manner. The input time samples remains at the same time when copied to the CSP gather.

Abstract: A method for three dimensional migration of a two dimensional grid of seismic data. The method involves computation of three dimensional time-dip functions at the intersections of lines in the grid. Inverse raytracing is used to correctly position the reflection events in the three dimensional volume encompassed by the grid. Migration of the seismic data is performed onto image surfaces defined from the correctly positioned reflection events.

Abstract: The invention relates to a method of processing seismic data in which a volume of raw focusing data is constituted by downwards extrapolation of seismic data obtained by means of at least one seismic source and of sensors disposed at the surface at regular abscissas along a prospecting section. For a subset of said volume corresponding to a given extrapolation depth and for a contiguous set of abscissas along the prospecting section, zero offset downwards migration is performed to a first set of depths greater than said extrapolation depth in order to constitute a first block of focusing analysis migrated data, and similarly inverse zero offset migration is performed upwards to a second set of depths less than said extrapolation depth in order to constitute a second block of focusing analysis migrated data.

Abstract: A method of determining a reference seismic velocity model that includes lateral and vertical variations in a stratified subterranean medium is disclosed. The invention recognizes that each unknown prestack traveltime curve may be expressed as the sum of a best fit hyperbola and a non-hyperbolic perturbation term. After the best fit hyperbola has been determined and used to correct the traces for normal moveout (NMO), the non-hyperbolic perturbation term is solved for using a simulated annealing technique. In addition, the problem of topologically representing a subsurface having complicated horizon geometries is bypassed by assuming a smooth and continuous, rather than a layered and discontinuous, velocity model. This assumption facilitates raytracing and in most cases, results in a model that more accurately represents the velocity function. Error minimization during model updates is achieved by solving a linear system of equations subject to a set of constraint equations.

Abstract: A method for the synchronization of systems for seismic surveys, wherein the systems are composed of subsystems and may be land-based or marine, consists in the survey system being supplied with an absolute time standard and in a time code based on the absolute time standard being generated in the survey system. There is further provided at least one programmable event generator in the survey system and this is synchronized with the absolute time standard. The time for a specific event is predetermined on the basis of given parameters and supplied with the time code which corresponds to this time. The time for a determined event is then supplied to the subsystems which are also provided with the absolute time standard. The event can thereby be executed in one or more of the subsystems on the basis of the supplied absolute time standard and a synchronization is obtained with the desired accuracy.

Abstract: Disclosed is a technique for processing seismic data to enable the data to be migrated without stacking. Seismic data provided in common midpoint gathers are converted to a domain defined in terms of the travel time and the first power of velocity of reflected waves, and migration is performed in this domain. The migrated seismic data is converted back to the offset domain, wherein velocity analyses may be performed prior to stacking of the data.

Abstract: Excellent likeness of impulse response function r.sub.o (t) of a given linear space is obtained by exciting the space through a transmitting transducer with a compressible probing signal x(t) which is a string of lowpass narrow p(t)-wavelets polarity-controlled by a single cycle of an m-sequence and processing received raw-data by cross-correlating it with a special reference s(t) which is cyclical repetition of the same m-sequence. Cross-correlating x(t) directly with s(t) yields compressed version of x(t) (denoted e(t)) which is p(t) multiplied by length of the m-sequence. e(t) equivalently excites the space to give processed output which is the likeness of r.sub.o (t). e(t) is free from side-lobes and readily made arbitrarily slim by choosing p(t) slim; keeping duration and energy of x(t) fixed, e(t) characterizes an area invariant of the slimness of e(t) or p(t).

Abstract: A depth migration method for seismic data involves a depth migration in the omega-x domain with an added transform in the wavelet domain. The input to the migration is one spike at a given time and x position (or Common Depth Point). This is as if instead of using a collection of seismic traces as input to the processing sequence, traces are used which would be all null except one which contains a spike. The processing sequence involved for seismic traces is the same as the one involved for the spike (or impulse). The only difference is the input itself being the seismic trace rather than the impulse spike.

Abstract: A set of raw common shot gathers are resorted as common receiver gathers. The wavefield envelopes from the common receiver gathers are migrated using one half the near-surface velocity to provide migrated data sets. The migrated data sets are resorted back into common shot gathers and subtracted from the original raw common shot gathers to provide coherent-noise-reduced data sets.

Abstract: A process for depth migration of seismic wave information that has been derived from geological media that causes rapid lateral velocity variations in seismic waves. The process includes the step of decomposing wavefields recorded at the earth's surface using Gaussian beams as basic functions. Then, according to the process, the set of Gaussian beams is extrapolated downward into the earth to obtain the subsurface wavefield. Finally, the wavefield is processed to provide depth-migrated images of subsurface reflectors.

Abstract: The mispositioning of reflectors in a velocity analysis enhanced common-offset time migrated image is corrected by carrying out inverse migration on the time image, followed by zero-offset depth migration.

Abstract: In areas where the velocity gradient is strong or exhibits a significant positive curvature, the usual phase shift f-k migration methods cannot properly image overtuned dips due to diving waves. In this disclosure, an Airy operator is substituted for the classical phase shift operator.

Abstract: A method is disclosed for a two-step residual migration of dipping seismic events. A first migration pass is done using a fully-vertically-variable but laterally-invariable migration velocity that is selected from a first-stage mmigration velocity function. The first-stage velocity function approaches, but is less than, the velocity minima as determined by scanning the true velocity field in an area of interest. The second migration pass is performed with the aid of a dip-dependent residual migration velocity. The residual migration velocity is defined as the square root of the difference between the true migration velocity and a second migration velocity appropriate to the migrated time following the first migration pass.

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 static correction includes a three step process which eliminates the problems of assuming hyperbolic moveout curves and forming base traces from common midpoint gathers while addressing long spatial wavelength variations. First, after calculating and applying an approximate high-frequency static correction to the individual shot and receivers (using traditional automatic methods), depth migration iterations are employed to coarsely tune the near-surface velocity layer. Second, after applying this correction, the remaining statics are incorporated into the model by tomography, which accounts for the velocity and thickness of the weathering layer and buried anomalies. Third, any residual misalignments are addressed using a multi-windowed statics adjustment within the common image point (CIP) gathers.

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 enhancing seismic data is described for attenuating undesired coherent noise in both stacked seismic signals as well as in unstacked ordered gathers of seismic signals. In particular, coherent noise, as represented by reflection events, is identified to be attenuated, and a datum line is constructed in the seismic data. Each seismic signal can then be nonhyperbolically time-shifted so as to align the identified reflection event with the datum line. The seismic data can then be filtered with a dip filter having a dip angle corresponding to that of the datum line to attenuate the aligned reflection event.

Abstract: A method for migrating seismic data for formations that are located in geological media that cause seismic waves to be refracted so substantially that the waves turn upward. The method includes the steps of tabulating a first phase shift function as a function of the wave vector and the angular frequency of seismic waves in the geological media, tabulating a second phase shift function, storing the tabulated values of the first and second phase shift functions, calculating a third phase shift function based upon the first and second phase shift functions; and migrating recorded seismic data using the first, second and third phase shift functions.

Abstract: A method for removing residual moveout includes sorting the results of common offset depth migration into common image point gathers. A subset of image point gathers are selected for analysis. Each common image point gather is separated vertically into windows, each of which centers on a strong event. For each window, all the offset traces are summed to produce a brute stack trace to be used as an anchor. All offsets are cross-correlated to the anchor to determine how much each trace window should be shifted to sum most constructively with the anchor. A set of dynamic shifts is produced, which when applied, will remove the residual moveouts and produce a truly flat image for stacking. These shifts vary with depth and offset and can be interpolated between the selected image point gathers.

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: Velocity spectra are computed from unmigrated CMP gathers after correction for dip moveout. The velocity spectra are then migrated to their true spatial position. The migrated velocity spectra are then used to calculate a migrated dip section.

Abstract: A method for improving velocity models so that constant-offset migrations estimate consistent positions for reflectors includes tomographic estimation of seismic transmission velocities from constant-offset depth migrations. A method of converting inconsistencies in reflector positioning from constant-offset migrations into equivalent errors in modeled travel times is introduced, so that conventional methods of traveltime tomography can improve the velocity model. An improved velocity model allows a more accurate migrated image of the subsurface. The estimated velocity model can also detect anomalous regions of geologic significance, such as low velocity gas accumulations and irregular near surface weathering. In an alternate embodiment the procedure can be iterative and allow alternating improvements in the positions of reflectors and in the velocity model.

Abstract: A method for rapidly and efficiently generating traveltime tables for application in depth migration initially includes receiving a velocity model which may include a plurality of velocities in multiple layers between various subsurface reflectors. The model is plotted on a two dimensional grid with the subsurface reflectors identified. A traveltime to the first reflector is determined. Traveltimes from the sources on each layer boundary to all grid points above the next reflector are determined. For the initial iteration, the layer boundary is the surface and the source is the actual source used in shooting the line. For layers below the surface there will be more than one source or secondary source. The actual determination of traveltimes for these lower layers may be done by comparing the traveltimes to all points on the first reflector. The minimum traveltime is selected as the true traveltime to the first reflector. Next, all points where the reflector intersects the grid are found.

Abstract: The present invention provides improved methods for processing seismic data which include the effects of offset dependence of reflection amplitudes. The methods of the present invention provide a way to estimate and remove the effect of stretch and small moveout velocity errors on the measurement of offset dependence for the case of small offsets (less than about 30 degrees angle of reflection). Further, the methods of the present invention provide an improved estimate of the correct movement velocity.