Abstract: The present invention relates to a method to detect areas of acquired seismic data that contain ground roll. The method according to the invention allows the detection of ground roll cone on the basis of an estimate of the local ground roll velocity or even without any knowledge of the ground roll velocity. The method according to the invention is further more very useful for an automatic process of ground roll detection.

Abstract: A method and system of amplitude spectra estimation for seismic data using up-going and down-going wavefields includes gathering up-going and down-going wavefields, separating the up-going and the down-going wavefields from each other and crosscorrelating the up-going wavefields and the down-going wavefields. From the result of the crosscorrelation of the up-going wavefields and the down-going wavefields, an estimate of the amplitude spectra in the frequency domain of the seismic data can be obtained. In this method for amplitude spectra estimation, the gathering may include or may be accomplished by providing pressure and particle velocity detectors to distinguish between the up-going and the down-going wavefields. Also, in this method for amplitude spectra estimation, the gathering may include measuring the down-going waves and the separating may include removing the down-going waves from the seismic data.

Abstract: Lines of existing data are extrapolated to provide additional lines of seismic data by using small inline gates of existing cables. At each frequency slice of a space gate on the existing cables, a 2-D prediction error filter that can predict the data in forward and backward directions is designed. A prediction filter is obtained from the prediction error filter and applied to a cable at an edge of the space gate to predict a first missing cable. By repeating this process using overlapping inline gates, overlapping inline gates of the extrapolated cables may be obtained. By suitable weighting of the inline gates of the extrapolated cables, a complete cable length is extrapolated. The process may be repeated using the first extrapolated cable in the derivation to give additional extrapolated cables. The invention may be used for interpolating cables of dealiased cables between existing cables using a masking and filtering operation in the frequency-wavenumber domain.

Abstract: Method and device intended for synchronized acquisition of seismic signals by one or more acquisition units suited for seismic signal digitizing, allowing to obtain, for each signal, a series y[n] of samples of these signals readjusted from a reference time on, from a first series x[n] of digitized samples of this seismic signal produced from any initial time prior to the reference time. The method essentially comprises detecting a synchronization signal indicative of this reference time (TR), measuring the effective time difference (D) between the reference time and the initial time, determining coefficients of a digital filter (F) suited to compensate for the fractional part (d) of the measured effective time difference, and applying this compensation digital filter to the first series of samples, which allows to obtain a series of digitized samples readjusted from the reference time.

Abstract: Adaptive neural networks can be used to effectively enhance signal detection in the inherently noisy environment of an oil well. The neural network can be either non-recurrent or recurrent in nature. The system is implemented with a computer that accepts input from at least one sensor mounted to the wellhead or near the wellhead. The detected contaminated signal is a combination of the event signal and the noise from the environment. The event signal can be, for example, the detonation of a perforation gun. The noise can be either random or periodic. The use of adaptive filtering allows the noise to be more precisely predicted and then subtracted from the contaminated signal to produce a cleaner representation of the event signal. Once the predicted noise is subtracted, the remaining event signal can be analyzed using voice or sound recognition systems to produce an output describing what event occurred.

Abstract: The methods of the present invention determine the net and gross thickness of reservoir beds, taking into account the internal structure of reservoir beds, using P-P, and/or S-S and/or P-S seismic data acquired in 2-d or 3-d.

Abstract: A method is disclosed for characterizing the subsurface levels of the Earth with a greater degree of accuracy than hitherto. Seismic data samples are migrated and stacked, for example according to known techniques and then spectrum analyzed. The spectrum analysis is applied to a feature of the subsurface and, for example, a particular layer bounded by a pair of horizons would be subject to volume reflection spectral analysis. The analysis is carried out using an orthogonal base by defining the reflection signals in terms of coefficients to a set of orthogonal polynomials. Additional seismic characteristics or attributes may be directly calculated from the polynomial coefficients. These coefficients represent the characteristics of the layer to a high degree of accuracy and may be compared with spectra derived a priori (for example, synthetic spectra or previously characterized spectra) to further assist in analysis of measured seismic data.

Abstract: An apparatus and procedure for passively performing a geophysical survey. The RAP Equipment complex comprises an A/D Conversion Device, an external sensor, an external 12 volt battery, and a Notebook Computer in which resides a Fourier analysis program. The A/D Conversion Device is connected to the serial port of the Notebook Computer. The A/D Conversion Device comprises an Analog/Digital Converter modified to replace its quartz resonator with a Frequency Generator for providing a predetermined sampling rate, and a Signal Amplifier. An external sensor is attached by a cable to the input of the Signal Amplifier. A 12 volt power supply powers the Signal Amplifier, the modified A/D converter, and the Notebook Computer. In use, the external sensor is placed on the ground at the first spot it is desired to take a reading. The ground is then lightly tapped in the near vicinity of the sensor either with one's finger or a hammer.

Abstract: A method for accurately determining travel time separation between dual vertically spaced hydrophones below a water surface to achieve separation of pressure wavefields into an up-going and a down-going wavefield in the frequency domain, and for accurately determining the depth of a vertical mid-point between the dual hydrophones below the water surface.

Abstract: An efficient method for generating residual statics corrections to compensate for surface-consistent static time shifts in stacked seismic traces. The method includes a step of framing the residual static corrections as a global optimization problem in a parameter space. The method also includes decoupling the global optimization problem involving all seismic traces into several one-dimensional problems. The method further utilizes a Stochastic Pijavskij Tunneling search to eliminate regions in the parameter space where a global minimum is unlikely to exist so that the global minimum may be quickly discovered. The method finds the residual statics corrections by maximizing the total stack power. The stack power is a measure of seismic energy transferred from energy sources to receivers.

Abstract: A method and system for processing first and second seismic traces includes rotating the first seismic traces and the second seismic traces to forty-five degrees in the time domain. In one embodiment, the rotated first time domain traces and second time domain traces are transformed to the frequency domain to obtain an amplitude spectrum for each rotated first time domain trace and an amplitude spectrum for each rotated second time domain trace. Each amplitude spectrum is squared to obtain a power spectrum for each transformed and rotated time domain trace. The phase of each transformed rotated time domain trace to zero. The power spectrum for each transformed rotated time domain trace is then averaged. Each transformed rotated time domain trace is divided into time windows. A power spectrum for each window is obtained for the entire of each transformed rotated time domain trace. The power spectra of each window of the transformed rotated time domain trace is summed to obtain a summed first power spectrum.

Abstract: Traveltimes of multiply reflected seismic events in a seismic profile or a model are determined from traveltimes for primary events. The traveltimes for the primary events may be obtained by ray tracing through a velocity model of the subsurface of by picking traveltimes from primary reflection horizons present in an actual seismic data set. The traveltimes for the primary events define a traveltime table for various combinations of source and receiver locations. The traveltime for a multiple corresponding to specified source and receiver positions is then determined by summing the traveltimes for primary events from the source to an interim point and from the interim point to the receiver: the correct location of the interim point corresponding to an actual multiple reflection raypath from the source to the receiver is the one that, according to Fermat's principle, has the minimum value for the sum.

Abstract: A method for improving vibratory source seismic data uses a filter which converts a recorded seismic groundforce signal (including harmonic distortion therein) into a desired short-duration wavelet. A plurality of surveys may be carried out using a plurality of sweeps from plurality of vibrators that have their relative phases encoded, the groundforce signal of each vibrator being measured. The recorded seismic reflection signals are then processed to separate out the signals from each vibrator. In another aspect, harmonics of upto any desired order may be canceled while carrying out multiple surveys with a plurality of vibrators. In a marine environment, the recorded signal from a vibrator towed by a moving vessel is used to derive a Doppler shift correction filter that is applied to reflection seismic data.

Abstract: A system and method is provided for estimating the inverse source wavelet of a seismic shot record for improved accuracy and efficiency in removing high order free surface multiples from the shot record, using a stochastic optimization technique, such as a genetic algorithm procedure, that can more readily accommodate non-linear aspects of this problem. The system and method is applied to a set of measured seismic field data, D.sub.o (x,t), with primary reflections and free surface multiples, where removal of the free surface multiples is determined utilizing an estimate of the inverse of the source wavelet and scale factors made from the seismic data. The system and method automatically optimizes estimates for the inverse of the source wavelet and scale factors.

Abstract: A power spectrum density processor is located near the drill bit while drilling. The power spectral density processor computes the power spectral density of the vibrations generated by the drill bit while drilling. The power spectral density information is telemetered to the surface where it is used to enhance drill bit seismic techniques.

Abstract: In a marine seismic survey, water bottom travel times are obtained by conventional methods. Near offset seismic data are then dereverberated using a suite of possible water bottom reflection coefficients to give a suite of filtered traces. The water bottom reflectivity that gives the minimum value over the suite of processed traces is determined to give a set of selected reflectivities each of the analysis points within a time window. A weight is determined for each analysis time within the time window, the weight being related to the change in the amplitude of the filtered trace at that sample point over the suite of water bottom reflectivities. The selected reflectivities are weighted by the weights and averaged to make a determination of the water bottom reflectivity. This determined water bottom reflectivity is used to process the recorded seismic trace.

Abstract: A method of attenuating multiples in signals recorded during a marine seismic survey is described using a multi-component data set of the survey and summing selected components of the data set after filtering components with a filter that combines recorded data from more that one receiver location and operates indiscriminately on P- and S-wave data.

Abstract: An adaptive system applicable to non-ideal measurement operations wherein the reference signal includes information attempting to be extracted from the primary signal and wherein digital non-linear manipulation is applied to the signal to noise ratio in the reference signal.

Abstract: A method of determining the far-field signature of the seismic wave produced by at least one marine seismic source (20) involving mounting pressure sensing means (2) on the or each seismic source (20) and taking account of both linear and nonlinear components of pressure measurements made by the pressure sensing means (2) to determine the far-field signature of the seismic wave. The invention covers the generation of a seismic wave from a single seismic source and an array of seismic sources and also relates to marine seismic source apparatus.

Abstract: The present invention relates to a control system for a vibrator system capable of generating and applying a reciprocating force to an object, such as the underlying ground or water. The control system is generally provided with a means for outputting a drive signal having a fundamental frequency to the vibrator system to activate the reciprocating of the base plate of the vibrating system and a means for receiving a vibrator output signal indicative of the force applied to the object. The vibrator output signal includes at least one harmonic frequency signal and is delayed with respect to the phase of the initial drive signal. To increase the signal-to-noise ratio of the vibrator system, the control system includes a harmonic distortion reduction means receiving the vibrator output signal for outputting at least one harmonic drive signal to the vibrator system.

Abstract: A method for reconstructing a selected seismic wavefield at a designated common midpoint and offset location from a set of prestack seismic data traces. The method uses actual data traces from other common midpoint and offset locations to reconstruct the selected wavefield at the designated reconstruction location. The method may be used to reconstruct any selected wavefield, including both primary reflection wavefields and secondary wavefields such as water-bottom multiple wavefields, and may be used with both 2-D and 3-D seismic data. If the reconstructed wavefield is a secondary wavefield, it may be subtracted from the prestack seismic data traces to eliminate interference between wavefields. The method may also be used to reconstruct data from missing shots to avoid spatial aliasing problems in other data processing operations.

Abstract: A method for identifying faults and stratigraphic features within seismic data without interpreter bias by processing seismic data to identify the minimum difference between seismic traces. Large values of difference are plotted as display attributes for seismic reflection data interpretation for two-dimensional and three-dimensional seismic data. The large values of difference represent faults and stratigraphic features within the seismic data. Dip azimuth and dip magnitude attributes can be generated and displayed as well.

Abstract: Methods and apparatus are described for reducing the multiple energy in seismic signal acquisitions, in particular for sea bottom acquisition. The method is based on the scattering Born series for free-surface multiples. It is characterized in that only terms of the even sub-series of the scattering Born series are considered for determining the multiple-free data.

Abstract: Three dimensional seismic survey data are acquired and processed using a hexagonal sampling grid. The seismic data are grouped into hexagonal bins defined by the hexagonal grid instead of into rectangular bins defined by a rectangular grid. Method and apparatus which bin the data, although described for square and regular hexagonal grids, are also applicable to rectangles and hexagons of any shape. Because hexagonal binning requires fewer gridpoints than rectangular binning, survey source or receiver interval may be increased, which may help reduce survey cost.

Abstract: A method and computer system for deriving and applying normal moveout phase and time shift corrections to seismic survey traces is disclosed. Normal moveout time-shift corrections are first applied to traces in a common midpoint (CMP) or common depth point (CDP) gather, based upon stacking velocity analysis applied to envelopes of the traces. One offset in the survey, preferably the maximum offset, is selected as the reference point; the NMO time shift at this reference offset is then selected as a reference NMO time-shift. The traces in the gather are each phase-shifted based upon iterated reference phase dispersion values at the reference offset, times the ratio of the normal moveout time-shifts for the trace in the gather to that of the reference offset (raised to a power). Semblance analysis is performed to identify, for each point in normal incidence time and thus for each reflective event, the optimum reference phase dispersion value.

Abstract: Methods and apparatus are described for compressing seismic data. The data compression is achieved by splitting the data into subsets and applying requantization levels to those subsets which depend on a number representing the subset and on time. Further error criteria ensure that the error introduced by the data compression does not affect the data in a time window representing the listening time. The compression ratio can be improved by applying data encoding techniques to the subsets.

Abstract: A method for acquiring and processing seismic survey data from two or more seismic sources activated simultaneously or nearly simultaneously or for a single source moved to and fired at different locations. In one aspect such a method includes acquiring seismic survey trace data generated by the source or sources, attaching source geometry to the traces, soring the traces according to a common feature thereof, (e.g. to CMP order), interpolating data points for discontinuities on the traces, selecting two halves or two portions slightly more than half of the traces, filtering the trace data for each of the two portions to filter out data related to a second one of the two seismic sources, reducing the filtered trace data to two halves of the data and deleting interpolated data, and then merging the two halves to produce refined useful seismic data related to a first one of the seismic sources.

Abstract: An automated quality control system for processing geophysical seismic data and positioning data from a marine navigation system. The invention includes a prospect data logger in communication with system components for accessing the seismic data, for coordinating seismic data processing, and for identifying and storing attribute data relevant to the seismic data and the positioning data. The prospect data logger is capable of storing data in a programmed format, and can be engaged with a display for illustrating data accessible to the prospect data logger. The prospect data logger is capable of automatically performing quality control functions such as checking seismic data and positioning data, of verifying the format of merged seismic and positioning data, of generating a command for indicating an event or for controlling another system component. The prospect data logger can verify storage tape quality immediately after data is inputted, and a record of events can be generated.

Abstract: A method of processing reflection seismic traces based on a D(tau, x2) diagram showing horizontal events (WAH-WDH). For each value of tau the corresponding signal amplitude is analyzed for the various x2 in a time window of less than a predetermined width. The amplitudes are subjected to conventional linear regression minimizing the sum of absolute values of discrepancies from the straight line, or the sum of their squares. Each concentration zone is swept by a straight line pivoting successively about each point with a slope equal to the square of the offset.

Abstract: A computer system for interpreting seismic signals to identify reflective horizons is disclosed. The seismic signals are retrieved and conventional corrections are applied. A seismic survey is displayed, and a human analyst places horizon lines or surfaces above or below suspected reflective events in the survey. The disclosed method then operates on a trace by trace basis to identify the location in time at which the attribute, which may be amplitude, envelope amplitude, phase, frequency and the like, meets a draping criterion. The interpreted horizon is set at the identified depth or time location, and the interpreted horizon points are connected into an interpreted horizon surface (in the case of a 3-D survey). Traces having only weak or no reflections may not have an interpreted surface point, or may have an interpolated point set therefor. An automated and efficient horizon interpretation method and system, even for large surveys of complex geology, is thus provided.

Abstract: A processing system stores a special software known as the Cubemath software. The Cubemath software allows the processing system to process, analyze, and interpret a second set of seismic data relative to a first set of seismic data obtained from either a repeat seismic operation or a single seismic two processing method operation. A first set of 3D seismic data is collected at a particular location on the surface of the earth at time "t1", and a second set of 3D seismic data is collected at that same particular location on the surface of the earth (at a different time "t2" when the repeat seismic operation is being performed).

Abstract: The present invention relates generally to method of seismic data processing which provides a superior method of removing or attenuating some forms of seismic noise and can also be used as a basis for seismic attribute analysis and automatic trace editing. In particular, the present invention is directed toward the application of a Very Short-Time Fourier Transform (VSTFT) to seismic data, coupled with a novel approach to organizing and/or displaying the transformed data, so as to provide highly localized frequency analyses of seismic reflection events. The present invention utilizes a very great number of short overlapping Fourier transform windows, together with a Gaussian weight or taper function, to produce a plurality of near single-frequency "sub-band" traces for each seismic trace so analyzed. Although the present invention can be applied to a single seismic trace, it is preferably applied to a collection of seismic traces that are spatially related.

Abstract: Computer-implemented methods of processing and imaging seismic data by migration and DMO (dip moveout) are subjected to quantitative evaluation. The evaluation is done by a computerized testing procedure. An impulse data set is formed containing a single "live" trace and zero amplitudes for other traces. A selected velocity function is also generated. The impulse data set is then processed by the processing method being evaluated. Estimates of the vertical traveltime, amplitude and phase along each of the impulse-response events are then generated. The estimates so formed are compared against exact values obtained from a model using an integral equation which accurately describes migration or DMO. Users thus are provided with indications of how the processing techniques may be expected to perform on real data.