Abstract: Migration velocity analysis is performed using Angle-Domain Common Image Gathers (ACIGs). When the correct velocity model is employed for migration, all ACIG events corresponding to a subsurface location are aligned along a horizontal line. Residual moveout can be performed on each ACIG with a suite of trial residual velocity values, according to an angle-domain residual moveout equation. A best-fit residual velocity value that leads to horizontally-aligned events upon moveout can be selected by generating a distribution of semblance (amplitude summed over a given depth) over residual velocity. Best-fit residual velocity values corresponding to selected subsurface points can be employed to update the initial velocity model using a vertical update, normal ray update, or tomographic update method.

Abstract: A method of migrating seismic event data in the presence of a vertically time-varying velocity field defined by a migration velocity function is provided. The method comprises approximating a migration velocity function by constant stepwise stage velocities. The seismic event data is time stretched and is then successively migrated using residual velocities. After the seismic event data is fully migrated, the effect of time stretching is removed by time unstretching the fully migrated seismic event data by a reverse operation to obtain a finally migrated seismic event data.

Abstract: A method for processing three-dimensional seismic data is provided. The seismic data is at least partially the result of receiving a seismic wave with a seismic receiver. At least a portion of the seismic wave is generated by a seismic source. The source and receiver are both horizontally offset and vertically offset. The method comprises binning at least a portion of the seismic data in common reflection point bins. The method comprises sorting the seismic data within the bin to create common reflection point gathers. The method further comprises analyzing velocity, and applying surface consistent statics corrections to at least a portion of the seismic data within said common reflection point gathers. The method also comprises applying a non-hyperbolic normal moveout equation to at least a portion of said seismic data, and stacking at least a portion of said seismic data within said common reflection point gathers.

Abstract: A new method for refraction tomography is provided that uses differential delay times. Different types of refracted waves including head waves and diving waves are inverted. First, traveltime/offset functions for station in the seismic survey are estimated from first-arrival picks. Next, the traveltime/offset functions are transformed into velocity/depth functions to make up a near-surface model. Then, long-period statics are calculated using the derived near-surface model. Finally, short-period statics are estimated by a surface-consistent decomposition of the traveltime residuals.

Abstract: Methods for determination of pay saturation (SPAY) and water saturation (Sw) from surface seismic data use amplitude changes with angle of incidence in conjunction with rock property relationships to determine pay saturation for a variety of situations. These situations include cases where P-P data is used and anisotropy and absorption are negligible; cases where P-P data is used and anisotropic effects are important; cases where contact events are evident; and cases where P-S data is used and anisotropy and absorption are negligible.

Abstract: A method for processing of seismic data traces utilizes the fact that a series of linear operations applied to vectors can be approximated by application of the linear operations to a set of basis vectors which are then scaled and summed. The method is applied to seismic data traces with a reduction in processing time provided that computation time in creating the basis vectors is small relative to the total computation time in applying the method. Theoretically there is much to be gained in terms of processing speed by implementation of this method on a vector processor that is designed to do multiply and accumulate operations quickly.

Abstract: This invention provides a method for analyzing and compensating for the deleterious effects of irregular illumination of the subsurface due to velocity variations in the subsurface and of irregular spatial sampling of seismic data. For a processing operator, like Kirchoff migration for seismic data, a conventional migration operation is carried out. The output points are analyzed for sampling artifacts caused by irregular surface sampling of the data and those due to ray path distortions. An inverse sampling operator or a filtering operator is determined that is related to dip dependent attributes at the image location. Application of the inverse sampling operator or filtering operator along with the migration or other processing operator to the seismic data compensates for the effects of irregular sampling and of raypath distortion.

Abstract: A seismic processing method to solve an eikonal equation to determine a travel time (t) of a sound wave between a seismic source at a first set of coordinates (x2,y2, z2) and a point underground at a second set of coordinates (x,y,z), comprising determining a distance between the seismic source and the point underground; obtaining a propagation time between the seismic source and the point underground; calculating a velocity variable (v) as a ration of the distance between the seismic source and the underground point divided by the propagation time between the seismic source and the point underground; and extrapolating on the velocity variable to obtain a travel time.

Abstract: The present invention includes a method for overpressure detection and pore pressure change monitoring in subsurface gas, liquid hydrocarbon, or water reservoirs from compressional- and shear-wave measurement data. As part of this method, one or more Poisson's ratios are determined from field-based measurement data and are then compared against known Poisson's ratio values representative of the particular subsurface formation type. By applying a Poisson's ratio—pore pressure criterion that is appropriate for that type of formation, an overpressure in the formation is identified.

Abstract: A seismic velocity analysis method includes tying velocity parameter values such as residual velocity values to geological horizons (reflectors) within a seismic exploration volume. Common image gathers (CIGs) such a common reflection point (CRP) gathers or angle-domain common image gathers (ACIGs) are generated for a set of CIG grid points. Computed best-fit residual velocity values are then snapped to a neighboring horizon or vertically interpolated to the horizon, to generate residual velocity values along the horizon. The residual velocity values for points along the horizon are then selectively employed in updating the velocity model for the volume of interest.

Abstract: A method for determining unknown stress parameters in earth formation measures velocities in four sonic transmissions modes (compression, fast shear, slow shear and Stoneley) at a series of depths. Relationships between measured velocities and other measured values, two independent linear constants, and three nonlinear constants associated with equations of motion for pre-stressed isotropic materials are expressed in a set of four or five velocity difference equations derived from non-linear continuum mechanics. The velocity difference equations are solved using inversion for useful stress parameters, including maximum horizontal stress, minimum horizontal stress, pore pressure, and change in pore pressure over time.

Abstract: A method for correcting seismic amplitudes for geometrical artifacts resulting in non-uniform illumination of reflector surfaces. The illumination is calculated for each offset as a function of spatial position. The amplitudes are scaled by a scale factor which may be the reciprocal of the illumination. Data considered to be poor quality due to low illumination may be discarded, and the amplitudes scaled further to compensate for the discarded data.

Abstract: A subsurface formation may be evaluated through use of data obtained from Stoneley wave propagation in the fluid column within the borehole. Either wave amplitude or phase velocity may be utilized to determine composite lithology parameters. These composite lithology parameters reflect fluid and/or formation characteristics, and functionally relate such characteristics in a manner as to facilitate the determination of formation permeability in a well logging environment.

Abstract: Seismic traveltimes are computed using a conditional high-order method: the traveltime computation operator is second- or higher-order if enough suitable upwind traveltimes are available, and first-order otherwise. Typically, a first-order operator is employed only around singularities, e.g. corners and cusps; a high-order operator is employed for the vast majority of grid points in the target volume. Selectively switching to first-order makes the method relatively simple and computationally efficient, as compared to a pure high-order method. At the same time, most traveltimes are computed to high-order accuracy. In the preferred embodiment, the traveltime front is selectively advanced at its minimum traveltime grid point, using a finite-difference approximation to the eikonal equation. A narrow band propagation zone is used to advance the finite-difference stencil. Tentative traveltimes for the narrow band adjacent to the traveltime front are computed using the eikonal equation and arranged on a heap.

Abstract: A prestack migration method allowing imaging of an underground zone, for a given velocity model of arbitrary complexity. By means of conventional wave propagation and retropropagation modelling tools, the method allows to obtain elementary migrated images associated with the values assumed by a parameter and the sum of the images obtained for the different values of the parameter (post-migration stacking), in the depth domain as well as in the time domain. This migration is obtained at an attractive price (calculation cost) because it is independent of the volume of the results calculated and of the number of seismic traces recorded. Only the volume of the zone in which the waves are propagated, the complexity of the events to be imaged and the desired accuracy have an effect on the calculation cost. Volume images are thus obtained by taking account of all the seismic traces.

Abstract: In one embodiment of the present invention, a method of generating a zero-offset trace, at a zero-offset location on a processing plane, for a time sampled recording is provided. The time sampled recording has a source and receiver, and a source coordinate and a receiver coordinate associated therewith. The time sampled recording also has an amplitude and a sampled time associated therewith. The method comprises reading the source and receiver coordinates and determining an ellipsoid dependant upon the source-receiver offset, the sampled time, and the velocity of the medium. The ellipsoid has the source as one focus and the receiver as the other focus. The method further comprises determining a set of normal points on the ellipsoid and determining the distance between each of the normal points and the zero-offset trace location and dividing twice the distance by the velocity of the medium, wherein the zero-offset travel time for each normal point is determined.

Abstract: The method of the invention is employed for determining the state of saturation in a subterranean formation using only seismic velocity measurements (e.g., shear and compressional wave velocity data). Seismic velocity data collected from a region of the formation of like solid material properties can provide relatively accurate partial saturation data derived from a well-defined triangle plotted in a (&rgr;/&mgr;, &lgr;/&mgr;)-plane. When the seismic velocity data are collected over a large region of a formation having both like and unlike materials, the method first distinguishes the like materials by initially plotting the seismic velocity data in a (&rgr;/&lgr;, &mgr;/&lgr;)-plane to determine regions of the formation having like solid material properties and porosity.

Abstract: A method is described for the measurement of multidirectional far-field source signatures from seismic surveys whereby a vertical cable acquisition technique is provided, vertical cable data are acquired, the proper receivers are specified to measure the signature, data are sorted into common selected receiver gathers CSRG, the direct wave within common receiver gather is properly windowed, the angles of each direct path are computed and the amplitude of the signatures is normalized, so as to obtain the multidirectional far-field signatures of the seismic source array having the same characteristics as those that generated the seismic reflections.

Abstract: A method for calculating seismic velocity for migration purposes as a function of subsurface spatial position that gives the seismic processing analyst direct control of the resulting migration velocity model, and includes a means to ensure that the model is consistent with RMS velocity sweeps computed from available surface seismic or other data. The method involves generating average velocities from the model to compare to the measured RMS velocity data, and comparing the model predictions to actual data on a 3-D interactive visual display allowing quick and easy model adjustment. Other available measured data besides surface seismic data maybe used to develop the model.

Abstract: A method is disclosed for processing three dimensional seismic data, acquired with land-like geometies. The method comprises sorting the seismic data into single fold data sets which approximate minimal data sets and DMOing or migrating the single fold data sets to form minimal data set images. In some aspects the method further comprises sorting the minimal data set images obtained into gathers which are sorted by surface location, and also may be sorted by pseudo offset.

Abstract: A seismic system is provided with a method of reducing distortions caused by motion of a source and receiver in marine seismic measurements. In one embodiment, the seismic system comprises a seismic source, a seismic receiver, a source/receiver interface unit, a processing unit, a data storage unit, a display device, and a user input device. The processing unit is configured to receive seismic measurements from the seismic receiver and to create a seismic velocity model from the received data. The processing unit uses the velocity model to calculate a dilation function that is indicative of distortion caused by motion of the seismic source.

Abstract: The instant invention provides a method for processing converted-wave data into interpretable images using a compact two-parameter model. The method broadly comprises the steps of: collecting both P-wave and converted-wave seismic data; identifying the arrival times of the P-wave and the converted-wave data; computing the vertical velocity ratio from the arrival time data; computing the moveout velocity ratio from the corresponding moveout velocities; computing the effective velocity ratio from the vertical velocity ratio and the moveout velocity ratio; and computing the conversion point from the short-spread P-wave moveout velocity for each reflector, from the effective velocity ratio, the C-wave moveout velocity ratio, and from the arrival time data.

Abstract: A method and device for processing a seismic survey data set including: an actual source location, an actual receiver location, and an actual reflection event location is provided. The actual source location and actual receiver location are over a first layer having a first layer velocity and a first layer ray parameter, and over a second layer having a second layer velocity different from the first layer velocity and a second layer ray parameter different from the first layer ray parameter. The actual reflection event location is located below the first layer. The method comprises: providing the first layer velocity; providing the second layer velocity; providing the first layer ray parameter; providing the second layer ray parameter; determining a correction factor for the position of a ray path end dependant upon the first and second layer velocities and the first and second layer ray parameters; and applying the correction factor to the ray path end, wherein a ray path-corrected ray path end is provided.

Abstract: The method consists in using a first interpreted horizon (H.sub.0) extracted from a seismic block migrated with at least a first value of a velocity (V) known with an uncertainty (.DELTA.V), and is characterized in that it consists in performing the following steps:a) making a second interpreted horizon (H.sub.1) by migration of the first horizon (H.sub.0) using a second value (V+.DELTA.V) of the velocity, equal to the first value (V) plus the uncertainty (.DELTA.V);b) making a third interpreted horizon (H.sub.2) by migration of the first horizon (H.sub.0) using a third value (V-.DELTA.V) of the velocity, equal to the first value (V) less the uncertainty (.DELTA.V);c) selecting a positioning point (X.sub.0) for the well on the said first horizon (H.sub.0) and plotting a vertical (D) which passes through the said point (X.sub.0) and intersects the second and third horizons(H.sub.1 and H.sub.2) at migrated points (X.sub.1, X.sub.2);d) on the said first interpreted horizon (H.sub.

Abstract: It has been found that, rather than merely recording raw data on the seismic vessel for processing on shore, the performance of certain processing on the vessel at a particular time addresses the problems. Specifically, performing pre-stack time migration on raw data as it is being recorded on a seismic ship provides the information needed for quality control of the acquisition process, as well as providing a starting point for velocity analysis in preparation for later depth migration.