Abstract: A discrete, minimally-equipped standard seismic calibration system is permanently installed over a subsurface reservoir structure that contains fluids of economic interest. Changes in the fluid content as a function of long-term time lapse may introduce changes in the acoustical characteristics of the reservoir rock layers, producing a corresponding change in the seismic signature recorded by the calibration system. The difference between two signatures over a selected time epoch defines a time-lapse calibration signature. The time lapse calibration signature can be applied to reduce the results of different conventional seismic data-acquisition systems of different vintages and technologies to a common standard.

Abstract: An apparatus and method are disclosed for eliminating a noise signal from at least one source during an acoustic measurement of a subsurface geological formation or borehole. The apparatus includes a longitudinal body for positioning in the borehole and a transmitter supported by the body for transmitting acoustic signals into the formation and borehole. A sensor, substantially isolated within the body, is used to detect one or more noise signals and a receiver is carried by the body for receiving acoustic signals traversing the formation and borehole, and for receiving one or more noise signals. A processor is connected to the sensor and receiver for processing the acoustic signals and noise signals coupled from the receiver and the noise signal coupled from the sensor into a preferred formation or borehole signal by determining the noise signal received at the receiver using the noise signal received in the sensor and a propagation factor for the noise signal between the sensor and receiver.

Abstract: A method and system for producing an indicator for amplitude-versus-offset (AVO) analysis of seismic survey data is disclosed. According to the disclosed method and system, a raw AVO indicator is generated for each of multiple depth points, from the AVO intercept and gradient coefficient values. The indicator is generally a positive amplitude number for those locations having petrophysical importance, while the background neighboring points will have a zero or negative value for the raw indicator. Statistics are derived for a group of depth points that surround the depth point under analysis, in time and in space, from which a probability function may be evaluated, assuming a distribution of values in the background trend of AVO intercept and gradient values, and based upon which the raw AVO indicator will be modified. In one embodiment, the probability function is evaluated to determine the loci of points that are within the background to a certain statistical confidence.

Abstract: A method of analyzing a spatial series of waveforms, each waveform of which contains components arising from at least two substantially uncorrelated features, includes the steps of sorting the waveforms into groups or bins according to values of one or more of the features, determining a mean waveform for each group or bin, subtracting the mean waveform from each waveform in the group or bin, returning the waveforms to the original order of the series and determining a remaining feature. Binning, the process of sorting waveforms into groups based on values of features, can be performed for one feature determined from the waveform or for several features. All that is required is that the binning criteria are substantially uncorrelated with the feature of interest. An example of a binning criterion can be frequency or period of a component of the waveform. Also a value of a physical parameter calculated from the waveform can be used as a binning criterion.

Abstract: A method for determining the anisotropic properties of an unknown earth formation by means of seismic exploration includes generating seismic signals for propagation through the unknown formation. A range of seismic data samples generated by the propagation of the signals through the unknown formation is detected, and the detected samples are affected by the anisotropic properties of the unknown formation. A group of postulated anisotropic properties which would cause known perturbations in seismic signals are selected for the unknown formation. The detected range of seismic data samples from the unknown earth formation is compared with estimated ranges that could have been produced by seismic signals propagating through earth formations made up with differing weighting of components of the postulated anisotropic properties.

Abstract: An unconstrained transformation filter operator that is efficient in terms of computer resources and that improves circularly symmetric migrated impulse response for steep dips. The filter operator combines selected desirable attributes of the more efficient McClellan transformation filter with selected desirable attributes of the more accurate Laplacian transformation filter. The novel filter operator is not constrained along the k.sub.x and k.sub.y spatial axes by the requirement that it equal cos (k). The transformation filter is averaged over all azimuths to improve its accuracy of response.

Abstract: A method of suppression of burst coherent noise in seismic data is provided comprising (a) comparing a threshold amplitude characteristic acceptance value for a time window of a reference trace to an amplitude characteristic of a test trace of a set of traces within the window and; (b) applying a non-zero scalar to the test trace in the time window if an amplitude of the test trace within the time window is not within the threshold amplitude characteristic acceptance value.

Abstract: A method for seismic data interpretation for the purposes of identification of oil, gas and water accumulation locations and delineation of their contours uses a model of discrete media with inhomogeneous stresses. For a selected reflection horizon, the relative value of overall pressure gradient is calculated on the basis of instantaneous amplitudes and frequencies of seismic signals using a derived relationship between the reflection coefficients of elastic waves and the stress condition parameter. The calculation technique uses estimates of instantaneous amplitudes and frequencies smoothed over the entire seismic horizon or its fragment. A generalized model of normal (lithostatic) pressure is excluded, and the final interpreted parameters have the sense of relative estimates of anomalous pressure caused by basin dynamics.

Abstract: A computer-operated method for analyzing seismic data to discern the presence of hydrocarbon-bearing formations is disclosed. According to the disclosed method and system, amplitude-versus-offset (AVO) analysis is performed to assign, for each depth point in a survey region, an AVO intercept value and an AVO gradient value; the AVO intercept value corresponds to the zero-offset response for acoustic reflections from the depth point, while the AVO gradient value corresponds to the rate of change of the amplitude as a function of the angle of incidence of the acoustic energy (typically, with the square of the sine of the angle).

Abstract: A high speed microseismic event detector constructed in accordance with the present invention uses a point derivative comb to quickly and accurately detect microseismic events. Compressional and shear waves impinging upon microseismic receiver stations disposed to collect waves are converted into digital data and analyzed using a point derivative comb including assurance of quiet periods prior to declaration of microseismic events. If a sufficient number of quiet periods have passed, the square of a two point derivative of the incoming digital signal is compared to a trip level threshold exceeding the determined noise level to declare a valid trial event. The squaring of the derivative emphasizes the differences between noise and signal, and the valid event is preferably declared when the trip threshold has been exceeded over a temporal comb width to realize a comb over a given time period.

Abstract: A method of modelling at least travel time and apparent dip from seismic data that has been processed by at least one migration operator comprising the steps of taking the mid-point (N.sub.1) of a source (S)/receiver (R) system, applying ray tracing to the system relative to a given reflector, processing the parameters of the ray using a migration operator to obtain a first point of arrival (N'.sub.1) marked on the model, determining the offset (.DELTA.e1), and proceeding iteratively at each new point of arrival (N'.sub.i) until the offset (.DELTA.E) is less than or equal to the predetermined offset (.DELTA.e).

Abstract: A method is provided for processing data representing energy passing through a medium and subjected to multiple internal reflections. The method may be applied to reflection data, in which case multiple internal reflections have an odd number of reflections, or to transmission data, in which case multiple internal reflections have an even number of reflections. An inverse scattering series is constructed and represents physical properties of the region. The series is a power series having odd and even terms. Portions of the odd data (for reflection data) or even terms (for transmission data) are selected and linearly combined with the data so as to attenuate the multiple internal reflections.

Abstract: The invention is concerned with the analysis of velocity data such as sonic data obtained from wells. The invention includes analyzing time versus depth data and generating velocity versus depth data and generating velocity versus depth function. A significant feature is the recognition that translating the observed time versus depth data along the time axis in time-depth domain can be used to obtain a match with a time versus depth curve corresponding a velocity versus depth function. The invention also makes use of visual displays which show degree-of-fit data in parameter spaces. These displays represent an important means for generating velocity versus depth functions.

Abstract: A method of monitoring short-term and long-term deformation changes in a geological space and predicting geodynamic events in a region, such as earthquakes, landslides, dilatations and subsidence events, which includes the steps of performing measurements of one or more hydrosphere parameters using a network of observation wells covering the region, calculating various mathematical parameters and preparing various diagrams, and using the diagrams prepared as a basis for detecting and predicting the time of a possible future geodynamic event.

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 separating the effects of the earth response on vibratory energy from individual ones of multiple vibrators to geophones, in generating a seismic survey, is disclosed. According to the disclosed method, measurements of the actual vibrations generated at the source are made, in addition to the geophone measurements of the refracted and reflected vibrations, both over a number of frequency sweeps. The source and geophone vibrations are first transformed into frequency domain representations, by way of Discrete Fourier Transforms. An inverse matrix of the recorded frequency-domain source vibrations is then generated for each frequency. When the number of sweeps equals the number of vibrators, the inverse matrix is merely the multiplicative inverse of the source measurements; if the number of sweeps exceeds the number of vibrators, the inverse matrix is the generalized inverse of the original matrix.

Abstract: An apparatus for correcting for nonlinearities in modulation systems includes a transmitter (24, 28, 48, 50, 52) for transmitting a time varying modulated radar signal (56). A receiver (58, 62) receives an echo signal (60) resulting from reflection of the transmitted modulated signal (56). A mixer (48) compares the transmitted signal against the echo signal and providing a comparison signal indicative of the comparison. The comparison signal is sampled by an A/D converter (74). The A/D convertor (74) provides a sampled comparison signal to a controller/DSP (22). Controller/DSP (22) resamples the sampled comparison signal at selected resample times and effectively varies the selected resample times to correct for nonlinearities in the comparison signal resulting from nonlinearities of the transmitted time varying modulated signal.

Abstract: A method of separating the effects of the earth response on vibratory energy from individual ones of multiple vibrators to geophones, in generating a seismic survey, is disclosed. According to the disclosed method, measurements of the actual vibrations generated at the source are made, in addition to the geophone measurements of the refracted and reflected vibrations, both over a number of frequency sweeps. The source and geophone vibrations are first transformed into frequency domain representations, by way of Discrete Fourier Transforms. An inverse matrix of the recorded frequency-domain source vibrations is then generated for each frequency. When the number of sweeps equals the number of vibrators, the inverse matrix is merely the multiplicative inverse of the source measurements; if the number of sweeps exceeds the number of vibrators, the inverse matrix is the generalized inverse of the original matrix.

Abstract: A computer-aided method for providing a de-aliased output data set d.sub.L (t,x.sub.L,y.sub.L) from a spatially aliased, three-dimensional, input data set of known seismic signals, a(t,x,y), where L is an interpolator. The known data set is zero-padded by L. The zero-padded data set is zero-masked. The zero-padded data set is divided by a zero-padded, zero-masked data set to provide an interpolation operator H.sub.L. L-1 zero traces are interleaved between the known traces of data set a(t,x,y) to provide a zero-inserted data set c.sub.L ((t,x.sub.L,y.sub.L) whose transform is C.sub.L (m,k.sub.xL,k.sub.yL). The product of (H.sub.L) with (C.sub.L) is (D.sub.L) which is inverse-transformed to provide the desired de-aliased data set d.sub.L (t,x.sub.L,y.sub.L).

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: Apparatus and method are disclosed for use with a horizon picking method for 3D seismic data. Variables such as picking method, whether simple or iterative, score required of an iterative method and .DELTA.T between target wavelets and seed wavelet are input into the computer. During the picking process, parameters as to the number of successful picks and the number of failed picks because of the method of picking and because of failed picks due to the score not being achieved in the iterative method and because of failed picks due to the difference in time between the target wavelet and the seed wavelet being greater than the .DELTA.T variable are recorded. The number of score failures to pick a target wavelet from a seed wavelet is recorded where the score achieved is less than the input score. A characteristic of such number of score failures, such as the percentage of score failures to the total number of picking tries, is displayed on a CRT screen.

Abstract: A method of analyzing geological survey data of the potential field measurement type is disclosed. According to the disclosed method, discrete measurement values of the potential field, either the gravitational or magnetic field, are retrieved from memory, corresponding to either a one-dimensional or two-dimensional survey region of the earth. The discrete values are first preconditioned by the application of a noise-reduction digital filter, preferably of the Weiner type. The disclosed method then performs decomposition of the filtered discrete values using the Daubechies scale function and wavelet function of length 2. According to the preferred method, the second level low-frequency component of the first level high-frequency component is generated, and expanded by a factor of four to correspond to the range of the input discrete values. Interpolation is performed to fill in values between adjacent coefficients of this component.

Abstract: A method for processing multi-source multi-component shear wave seismic data. The method comprises the steps of: acquiring four component shear wave seismic data; converting the data into a matrix that is a function of an angles of rotation relative to a reference axis; computing a time independent norm of the elements of the matrix; and finding the angles of rotation where the difference between the sum of the norms of the in-line elements and the sum of the norms of the cross-line elements is maximized.

Abstract: A method and apparatus for adjusting the results of a seismic survey according to well log data obtained from wells within the survey region is disclosed. The disclosed method operates on one seismic horizon at a time, and first applies well log data, arranged by location of the wells in the survey region, to the seismic survey. Deviation values are calculated for each well location, as a signed difference between the actual depth data for the geological interface and a deduced horizon depth from the seismic survey. A difference function is evaluated for each survey point to be adjusted in the survey region (ranging from a single point to all survey points), preferably as a weighted average of the deviations at the wells, where the weighting is inversely related to the distance of the well from the survey point under adjustment.

Abstract: A method for determining the reliability of time processed seismic reflection data near a significant velocity differential overhang includes displaying the seismic reflection data as a seismic section showing impedance differential interfaces. The position of an edge of the velocity differential overhang is located and acoustic velocity values are interpreted. A set of curves representing boundaries of reliability for predetermined dip values is determined. The set of curves representing boundaries of reliability may be displayed. The display of the set of curves representing boundaries of reliability may be overlaid on the seismic section representing the seismic reflection data. The dip angle for an interface of interest is approximated. The interface of interest is compared with the curve representing boundaries of reliability for the dip angle for the interface of interest to determine the extent of reliability of the data used to map the end of the interface under the overhang.

Abstract: Disclosed is a method for creating a gain function for seismic data and to processing methods for utilizing such a gain function. The method of creating the gain function generally includes representing the seismic data as a plot of the logarithm of amplitude versus time. Various order polynomial functions are subsequently fitted to the plotted seismic data. The best fitting polynomial is then selected from these various order polynomials, the inverse of which is the gain function. This gain function can be utilized in a seismic processing method.

Abstract: Disclosed is a sonic well tool for performing acoustic investigations of subsurface geological formations penetrated by a borehole, and a method of logging formation data. The well tool generally includes a longitudinally extending body for positioning in said borehole. The tool also includes a transmitter supported by the body for transmitting acoustic energy, and at least two receivers. One of the receivers is positioned on the interior of the sonic tool to receive the acoustic signals that traverse the sonic well tool. The second receiver is positioned on the exterior of the sonic tool and receive sonic signals that traverse the sonic tool and those that traverse the formation. The apparatus further includes a processor for subtracting the well tool signal of the first receiver from the combined well tool and formation signal of the second receiver.

Abstract: Sparsely spatially-sampled seismic time-scale trace gathers may be aliased for certain spatial and temporal frequencies. Aliasing may be avoided by application of a spatial interpolation scheme that uses the phase difference between the f-k phase spectra of the odd and the even traces to generate an interpolation operator in the f-k domain. The operator is multiplied point-by-point with the f-k transform of the original recorded trace gather. The resulting complex product is inverse transformed to the t-x domain whereupon the interpolated traces are interleaved between the original recorded traces to unwrap the aliased events.

Abstract: The invention utilizes 3-D and 4-D seismic surveys as a means of deriving information useful in petroleum exploration and reservoir management. The methods use both single seismic surveys (3-D) and multiple seismic surveys separated in time (4-D) of a region of interest to determine large scale migration pathways within sedimentary basins, and fine scale drainage structure and oil-water-gas regions within individual petroleum producing reservoirs. Such structure is identified using pattern recognition tools which define the regions of interest. The 4-D seismic data sets may be used for data completion for large scale structure where time intervals between surveys do not allow for dynamic evolution. The 4-D seismic data sets also may be used to find variations over time of small scale structure within individual reservoirs which may be used to identify petroleum drainage pathways, oil-water-gas regions and, hence, attractive drilling targets.

Abstract: A method for eliminating sinusoidal noise without affecting the response of the formation means that the actual formation responses of the logging tools are recovered, and the logs can be used quantitatively. Removal of sinusoidal noise from a log is accomplished in three steps. First, the log is reduced to a zero-mean, stationary series. Second, the wavenumber of the sinusoidal noise is identified by its peak in the Fourier amplitude spectrum. And third, the noise is removed by applying a zero-phase notch filter. In order to preserve the quantitative data integrity, the low wavenumber trend is kept. Preserving the quantitative data integrity is accomplished by approximating the log with a least-squares cubic spline which retains the overall log character, ignoring the sinusoidal noise. A zero mean stationary series is formed by subtracting the least-squares cubic spline from the data. The remaining steps, Fourier analysis and filtering are performed on the difference series.

Abstract: A method of reducing effects of noise in seismic signals generated by a plurality of seismic sensors at spaced apart locations from a seismic source is disclosed. Each of the signals is represented by a signal trace in a record section. The method includes the steps of isolating noise in the signal traces, time aligning corresponding portions of the noise in the traces thereby generating time-aligned noise traces, stacking the time-aligned noise trace to generate a stacked noise trace, replicating the stacked noise trace at each corresponding trace position in the record section, restoring the replicated traces to the original trace time positions by reversing the step of time-aligning to generate noise signature traces, comparing the noise signature traces to corresponding signal traces to generate filters which substantially minimize a measure of the difference between the noise signature traces and the signal traces.

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: Apparatus and method are disclosed for use with a horizon picking method for 3D seismic data. Variables such as picking method, whether simple or iterative, score required of an iterative method and .DELTA.T between target wavelets and seed wavelet are input into the computer. During the picking process, parameters as to the number of successful picks and the number of failed picks because of the method of picking and because of failed picks due to the score not being achieved in the iterative method and because of failed picks due to the difference in time between the target wavelet and the seed wavelet being greater than the .DELTA.T variable are recorded. Parameters as to successful picking percentage of all target traces attempted to be picked and failure percentages are displayed simultaneously with the picked horizon and the input picking parameters.

Abstract: A method of geophysical prospecting wherein nonhyperbolic distortion is reduced from marine seismic data, or land seismic data over a low seismic velocity layer, is disclosed. The method comprises replacing the seismic velocity of the water or low seismic velocity layer with sediment seismic velocity and using analytic ray tracing to determine a mapping function to correct recorded seismic data for removal of the distortion, which occurs because of the high seismic velocity contrast at the water or low seismic velocity layer.

Abstract: A method for generating improved displays of seismic data by processing seismic amplitude versus offset data to correct for overburden effects. Analytic traces are calculated for the zero offset reflectivity, A, trace and the amplitude versus offset slope, B, trace of the AVO data. Statistics for the A and B traces within a selected window in time and common depth point space about a selected sample point are calculated. The statistics include root mean square amplitudes of the A and B traces and the correlation coefficient. Desired statistics are selected and used with the measured statistics to correct the A and B traces.

Abstract: A method for measuring the principal axis of fracture-induced formation anisotropy. Amplitude vectors are measured from CMP gathers oriented along in-line and cross-line wavefield trajectories. The amplitude vectors are resolved with the known orientations of the seismic lines of survey to estimate the azimuth of the anisotropic axis.

Abstract: A method for translating seismic time data via seismic depth data to seismic depth/lithology data, enabling reduced-risk location of hydrocarbons. Reducing dry hole risk is accomplished by introducing a new work domain which provides a several-fold increase in parameters per data point corresponding to geophysical space and associated with seismic sequence data. This work domain provides improved separation and definition and quality control of a panoply of relevant geofactors which in turn provide enhanced material information about a plurality of sedimentary rock properties. The enhanced material information is quality-controlled to be geologically possible, then further quality-controlled to be consistent with probability via quantification of burial history, depositional facies distribution and data resolution.

Abstract: Methods for generating seismic data and creating a seismic section are disclosed in which the difference in offsets between stacked traces is limited.

Abstract: The invention is a method and apparatus for measuring the quality of acoustic coupling between a wellbore wall and a borehole seismic sensor system. The system includes the steps of positioning the system at a desired depth in the wellbore and activating a locking mechanism powered by a DC motor. The motor then has broadband AC applied to it to cause vibration of the system. The output of at least one seismic sensor in the system is processed in a spectrum analyzer, and the result is checked for the presence or absence of natural resonance of the system. In a particular embodiment, the system response to the broadband AC is used to generate an inverse filter operator to compensate the system response to a geophysical survey for partial acoustic coupling.

Abstract: A method for cascading or linking seismic vibrator sweeps to form a cascaded sweep sequence. According to the method, a first cascaded sweep sequence is generated containing N sweep segments linked end-to-end. The N sweep segments are substantially identical, except that the initial phase angle of each sweep segment within the sweep sequence is progressively rotated by a constant phase increment of about 360/N degrees. A second cascaded sweep sequence is generated consisting of (i) N consecutive sweep segments linked end-to-end which correspond to said first cascaded sweep sequence and (ii) an additional sweep segment linked to the N consecutive sweep segments which is positioned and phased so as to substantially suppress harmonic ghosts during correlation. One of these cascaded sweep sequences is used for the vibrator sweep sequence and the other is used for the correlation reference sequence.

Abstract: A method for obtaining seismic data in frigid regions without interference from flexural ice waves. In an exemplary embodiment, seismic data is produced by using an energy source to generate a seismic wave in a floating ice sheet. Seismic disturbances caused by the energy source are detected by one or more hydrophones and geophones, which produce hydrophone and geophone response signals, respectively. In a first embodiment, the hydrophone response signal is integrated. The integrated signal and/or the geophone response signal are scaled, and the two signals are then added. Alternatively, instead of integrating the hydrophone response signal, the geophone response signal may be differentiated prior to scaling and summing. A method is also disclosed for overcoming phase errors that might be introduced, for example, by the use of a transformer-coupled hydrophone.

Abstract: A method for processing seismic vibrator data. The method utilizes a deterministic signature deconvolution of the vibrator data to compress the impulse response of the data resulting in sharper, clearer seismic images than are possible using cross-correlation techniques. The method may be used in place of or in addition to cross-correlation. Further, the method may be implemented in either the time domain or the frequency domain.

Abstract: A method of correcting a seismic pulse waveform for use in deconvolution of reflected pulse data. The source pulse waveform is measured by a hydrophone positioned vertically beneath the acoustic source. The phase error is calculated based on the depth of the source and the depth of the measuring hydrophone. The calculated error is subtracted from the phase spectrum of the measured waveform. The resulting waveform provides an accurate representation of the true far field waveform, leading to an improved expression of the waveform actually incident upon the marine floor.

Abstract: A method for displaying seismic attributes in an open three-dimensional format is provided. The conventional two-dimensional variable-amplitude traces that represent the magnitude of a selected seismic attribute as a function of time are converted to three-dimensional format. The three-dimensional converted traces are hung beneath a model of their corresponding data-gathering stations to provide a forest of seismic traces in a wire-frame environment. The open configuration of the seismic traces permits the interpreter to see a perspective view of the structure of the subsurface of the earth from any desired viewing angle.

Abstract: A multivibrator waveform monitoring system uses a plurality of seismic energy sources for giving vibrations to strata and a prospector, connected to a geophone, for measuring reflected vibrations. Each of the plurality of seismic energy sources includes a vibrator, a communication unit and a control unit for controlling the starting of the vibrator based on phase difference cancellation information and an operation starting instruction from the prospector. The prospector includes a communication unit and a synchronization control unit for controlling the synchronization of each of the seismic energy sources.

Abstract: The method sequentially determines dips and corresponding estimated dip components of traces in a panel of data. The method can be applied to any data which can be represented as a function of two coordinates. In particular, the method can be applied to seismic data traces. The method in one embodiment sums data on traces along a preselected range of trial dips on a panel of data. The energy of the summed data with their corresponding trial dip are then displayed. The dip which has the peak of maximum energy on the display is then selected as a valid dip. An estimated dip component of the selected dip is then determined and subtracted from the traces along the selected dip. The process is then repeated, sequentially, determining a dip and an estimated dip component from the panel of data until the desired number of dips and estimated dip components are determined or the residual energy of the remaining data on the traces are below a preselected value.

Abstract: In the exploration for petroleum or natural gas, drilling targets are identified by locating local maxima of horizontal gradient in the top-of-geopressure surface of a region of exploration. The probability of finding hydrocarbon deposits is significantly improved where the drilling targets are local maxima of the horizontal gradient in the top-of-geopressure surface which coincide with local maxima of subsurface heat flow in the region of exploration, particularly where the local maxima in the horizontal gradient of the top-of-geopressured surface is concentrated across major fault offsets and are parallel to the predominant strike directions of the faults. The top-of-geopressure surface may be remotely sensed by performing complex trace analysis on reflection seismic traces gathered for the region of exploration to derive corresponding reflection strength attribute traces.

Abstract: A method of processing seismic data wherein seismic data signals having a first part which shows a slow variation in offset and a second part which shows a slow variation in midpoint, is modelled using a model which allows the two parts to be separated. The individual parts may be reconstructed from the model. One of the parts corresponds to offset dependent noise and can be effectively removed from the seismic data.

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

Abstract: A 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.