Abstract: A method for displaying seismic data to provide direct indications of the presence of hydrocarbons. Seismic data is processed using conventional amplitude versus offset techniques to obtain zero offset reflectivity, or A, traces and the amplitude versus offset slope, or B, traces. AB cross plots of each trace are then generated. Each sample point on the cross plot is then assigned a value corresponding to its deviation from the regression line of the cross plotted AB points. The assigned values are then plotted in their corresponding time sample positions to generate a trace or display providing a direct indication of hydrocarbons.

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 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 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: Method for determining at least one characteristic of a casing cemented in a borehole, such as cement bond and casing thickness, from a reflected acoustic signal S(t) obtained by directing an acoustic pulse at a substantially normal incidence towards a radial sector of the wall of the casing, the pulse stimulating thickness resonance within the walls of the casing. The method according to the invention comprises the steps of: determining a first time window corresponding to a first portion of signal S(t) including the initial reflection from the casing and subsequent acoustic returns due to resonance, determining a second time window corresponding to a second portion of signal S(t) mainly including the initial reflection from the casing, and determining the casing characteristic from information related to resonance contained in the first time window while normalizing the information by information contained within the second time window.

Abstract: The present invention provides methods for processing seismic data which include performing normal moveout velocity analysis in such a manner as to include the effects of the offset dependence of reflection amplitude and simultaneously determining from the seismic data the moveout velocity and the variation of reflection amplitude with offset.

Abstract: A method of geophysical exploration is provided for identifying and evaluating stratigraphic prospects associated with step-like changes in elastic impedance from gradational changes in elastic impedance. In particular, the seismic data are bandpass filtered with a plurality of filters each having a different pass band. Measures of the amplitude are obtained for selected reflection events in the seismic data as a function of their associated pass band frequency content. The changes in amplitude as a function of changes in frequency content of the reflection event can thus be employed to identify and evaluate subtle stratigraphic prospects in the seismic data.

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.

Abstract: A method is provided for enhancing processing and evaluating seismic data. More particularly, a novel method is described for enhancing and evaluating common depth point seismic data. Common depth point (CDP) gathers of seismic signals are processed to suppress random noise and coherent noise and to enhance primary reflection events while preserving geologically-induced amplitude variations as a function of range for the primary reflection events. The processed CDP gathers of seismic signals can then be processed to obtain attributes descriptive of amplitude variations as a function of range for the selected primary reflection event whereby formation lithology and fluid content can be evaluated.

Abstract: Seismic reflection events are enhanced by separating the events from seismic data, increasing the amplitude of the events, and adding the events back into the seismic data.

Abstract: A blast recorder and method for monitoring and processing vibrations from blasts, and for displaying the results in a nearly real time basis and in a manner which is easily interpreted by a relatively unskilled field worker and corresponds to a form which closely correspond to the real damage causing aspect of the blast than heretofore.

Abstract: Method to process seismic data to yield useful information regarding the subsurface area explored. Generated seismic energy travels into a subsurface formation where it is distorted and attenuated. The distorted and attenuated seismic pulse is detected by a geophone or other seismic receiver and recorded. The received seismic traces are first compensated for the attenuation effects of the earth filter and the compensated seismic traces are then used to produce a close approximation of a zero-phase, band-limited output wavelet of the reflectivity of the geophysical formation under exploration.

Abstract: A method is disclosed to provide optimal or near-optimal vertical stacking of seismic records within the constraints imposed by real time data acquisition procedures. This method is characterized by forming output seismic traces which are a sum of prorated input traces, such proration being performed by application of smoothly varying weight functions derived from estimated signal and noise power levels within each input trace. Each weight function is computed using frequency domain filtering techniques to obtain a well behaved bandlimited time series for each function. The method also includes a procedure for clipping grossly large noise spikes in the input traces before the stacking procedure is performed, thereby guarding the weight calculation procedure against aliasing effects induced by such spikes.

Abstract: Disclosed is separation of the compressional and shear components of the wavefield measured in 3-component vertical seismic profiling. The separation involves working in the zx plane defined by the borehole axis (z) and the surface seismic source space therefrom along the x-axis, and in successive and overlapping windows each defined by (i) a depth interval centered at the depth level currently being processed and including several depth levels above and below and (ii) a time interval sufficiently long to allow the relevant seismic wavefield to be measured by the geophones. The total wavefield measurements in a window are rotated to give the wavefield along the borehole axis (z) and that perpendicular to it in the zx plane of interest.

Abstract: A method for identifying anomalous noise amplitudes in seismic records by deriving a measured amplitude factor over predetermined periods of time or time windows for a predetermined number of traces comprising the records is disclosed. A noise-free amplitude factor for the same periods of time and number of traces is also computed using a Gauss-Siedel method of matrix inversion. A ratio of the measured and noise-free amplitude factors is made to determine a correction factor which is compared to a user defined threshold value for determining a presence of anomalous noise amplitudes in the seismic records. Based on the comparison of the correction factor to the threshold value, the user determines whether to suppress or correct traces experiencing the anomalous noise amplitudes.

Abstract: Process for the detection of heterogeneities of a medium. It is defined in that logs of the attenuation of the shear waves and STONELEY waves are produced, the variations of each attenuation log in relation to a mean value are determined, and then the variations are compared with one another in such a manner as to determine the nature of the heterogeneity or of the petrophysical characteristic which has produced these variations. Application in particular in the area of oil and more particularly in the exploration of a medium. FIG. 9.

Abstract: Method for determining the presence of hydrocarbons in subsurface geological formations by comparative assessment of compressional wave reflection information and shear wave reflection information estimated from acquired compressional wave information from common depth point gathered compressional wave traces using variations in the amplitude of the gathered compressional waves with source-receiver offset.

Abstract: An improved method is disclosed for obtaining shear wave data from common depth point gathered compressional wave traces using variations in the amplitude of the gathered compressional waves with source receiver offset. The gathered compressional waves are corrected for normal moveout and the normal moveout corrected waves are further corrected for residual normal moveout by correcting stacking velocities of the normal moveout corrected traces.

Abstract: An improved method is disclosed for obtaining shear wave data from common depth point gathered compressional wave traces using variations in the amplitude of the gathered compressional waves with source receiver offset. The shear wave data is determined from measured compressional amplitude offset values and incident angles of shear wave data. The incident angles are determined from the offsets and smoothed interval velocity functions.

Abstract: A seismic marine survey is carried out by traversing a line of exploration with an acoustic energy source, an array of spaced-apart receivers, and a recording system. Seismic reflection signals recorded by the receivers are digitized to provide a plurality of digital data samples. A logarithmic value is determined for each digital data sample. These logarithmic values are plotted to provide a seismogram with the seismic reflection signals being recorded in side-by-side trace relationship.

Abstract: A seismic marine survey is carried out by traversing a line of exploration with an acoustic energy source, an array of spaced-apart receivers, and a recording system. A plurality of receivers along the receiver array are selected and the maximum amplitude wavelets of the seismic reflection signals recorded from such receivers are compared to identify any trend in a select seismic survey parameter.

Abstract: Method to process seismic data to yield useful information regarding the subsurface area explored. Seismic data which is acquired from the seismic exploration is autocorrelated and the amplitude spectrums estimated, stacked and averaged to reduce the effects of nonwhite reflectivity upon the data. The amplitude spectrum is cepstral windowed a first time to reduce the effects of reflectivity leakage on the amplitude spectrum, amortized at both low and high frequencies so that the amplitude spectrum will approximate the analog wavelet and cepstral windowed a second time to eliminate any remaining rapidly varying components of the amplitude spectrum. The resultant amplitude spectrum is then used to estimate the phase spectrum for the wavelet and a two-sided least squares filter is then designed to shape the estimated seismic wavelet into a zero-phase, low sidelobe output wavelet.

Abstract: The present invention provides a method of seismic exploration for obtaining a measure of the subterranean formation rock properties. Incident angle ordered gathers of seismic signal are processed to obtain a measure of the reflection coefficient as well as attributes descriptive of variations in amplitude of the seismic signal as a function of incident angle. Such attributes, when plotted on an angle dependent amplitude diagram, are transformed into a most probable estimate of the subterranean formation rock properties as well as a diagnostic of relative lithology and pore fluid contrast.

Abstract: A method and apparatus for filtering seismic data are provided. More particularly, the method and apparatus of the present invention attenuate surface wave generated noise in seismic-trace signals. Seismic data comprising multicomponent seismic-trace signals acquired with single station, multicomponent geophone arrays are comb filtered to produce a plurality of comb filtered signals for each component of the multicomponent seismic-trace signal. The comb filtered signals are sorted into orthogonal sets and a measure of rectilinearity for each orthogonal set is obtained. Surface wave generated noise can then be attenuated in each orthogonal set with its respective measure of rectilinearity.

Abstract: A method is disclosed for obtaining shear wave data from common depth point gathered compressional wave traces using variations in the amplitude of the gathered compressional waves with source-receiver offset. The shear wave data can be used to generate pseudo-shear wave seismic sections.

Abstract: A method of discriminating between linear and nonlinear regions of measured data is based upon two hypotheses, one of which is a hypothesis that a response is merely a result of inherent randomness and the other of which is a hypothesis that the response is a result of a true nonlinear change greater than a value M. It is also based upon a relative cost between accepting the latter hypothesis when the former is true versus accepting the former hypothesis when the latter is true. A resulting probabilistic criterion (M/2)+(.sigma..sup.2 /M) [1n(P.sub.H0 /P.sub.H1)C] is graphically implemented for deriving offset values which can be used in a specific embodiment to construct tabular values defining linear/nonlinear regions from a presumed hypothetical straight line response.

Abstract: A method for processing and displaying seismic data. More particularly, a novel method for enhancing the display of common depth point seismic data. Common Depth point gathers of seismic data are processed to enhance the signal-to-noise ratio by reducing the averaging effects of lateral variations in the subterranean formation on the seismic data as well as reducing the averaging of range dependent amplitude variations in the seismic data.

Abstract: A variable amplitude/phase color seismic display is provided which increases the ease with which interpreters can locate peaks, troughs and other information of interest.

Abstract: Disclosed is separation of the compressional and shear components of the wavefield measured in 3-component vertical seismic profiling. The separation involves working in the zx plane defined by the borehole axis (z) and the surface seismic source, and in successive and overlapping windows each defined by (i) a depth interval centered at the depth level currently being processed and including several depth levels above and below and (ii) a time interval sufficiently long to include the receipt of the relevant seismic energy by the geophones.

Abstract: A method for quantitatively distinguishing seismic events on a seismic record for inferring changes in the geological character of the subterranean formations. Reflection coefficients are obtained for such seismic events and a first set of attributes indicative of amplitude variations in the offset seismic signals corresponding to the seismic event as a function of incident angle are obtained therefrom. The first set of attributes provide a seismologist with a diagnostic tool for quantitatively evaluating subtle changes in the seismic event. A second set of attributes which are functions of the first set of attributes provide the seismologist with additional diagnostic tools for evaluating subtle changes in the seismic events.

Abstract: An improved apparatus and method for calculating automatic gain correction to be applied to seismic samples is disclosed which features apparatus and method for calculation of the average absolute value of a window of samples in the vicinity of the sample being processed, the calculation being performed a first time with the window shifted toward a first side of the sample and a second time with the window shifted toward a second side of the sample, and selecting for use in gain correction the minimum of the two calculated average absolute values, such that high amplitude samples in the vicinity of relatively low amplitude events is precluded from causing unrealistic shadowing around such events.

Abstract: Data points for a sinusoidal waveform are assigned 2 bit values which indicate the state of the amplitude (positive or negative) and the slope of the sinusoidal signal at the particular data point (positive or negative). The 2 bit values for a plurality of sinusoidal waveforms are compared to determine the phase misalignment between the plurality of sinusoidal waveforms.

Abstract: A method of processing geophysical seismic data so as to enhance its evaluation and interpretation. A plurality of response waveform characteristics are developed from a seismic signal. The response waveform characteristics can provide empirical basis for correlating a seismic signal fo formation geology and lithology. In accordance with the present invention, the response waveform characteristics are chromatically quantified and the intensity of which can be modulated so as to enhance the signal-to-noise ratio of the displayed response waveform characteristics.

Abstract: A method and apparatus for enhancing the resolution of true variations of a seismic signal amplitude as a function of range. A time-variant bandpass filter is impressed upon the seismic data having a bandpass frequency dependent upon the range between the seismic sources and the seismic receivers of a common depth point array of seismic sources and seismic receivers. A maximum bandpass frequency is derived from the maximum range between the seismic sources and the seismic receivers of a common depth point array of seismic sources and seismic receivers. The maximum bandpass frequency is adapted to accommodate time varying ranges as well as time varying stacking velocities so as to produce a seismic signal having enhanced resolution of amplitude variations of the seismic signal.

Abstract: A method for applying automatic gain control to seismic signals is disclosed which features least means squares fitting the average absolute value of the data in windows of a seismic trace to an exponential function, wherein values for the parameters defining the function are derived and applying a gain function using these parameters to the data.

Abstract: In seismic exploration, aliasing caused by coarse sampling along a line of exploration is corrected by trace interpolation. The interpolated traces are obtained by inserting zero amplitude traces between seismic traces. Transformation into the f-k domain and filtering of the aliased regions in the f-k domain produces properly interpolated traces when transformed to the x-t domain.

Abstract: In accordance with the present invention, progressive changes in amplitude as a function of offset of common gathers can be more easily identified by displaying difference envelopes of "near" and "far" amplitude vs. time traces of each gather, as a function of common groups of centerpoints. A significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence (within sections) indicates valuable characteristics, such as hydrocarbon-bearing potential and/or lithology of the reflecting horizon.

Abstract: A method of seismic exploration, wherein one or more vibratory sources are employed to generate an input signal whose frequency varies as a function of time and wherein the signal is reflected and refracted to detector stations from subsurface beds, in which the sources are tested for signal accuracy with respect to a reference. The method includes generating at a first location a system reference signal having a pattern of predetermined phase and frequency characteristics and generating at a first source a vibrator control signal or a motion detector signal. The vibrator control signal or the motion detector signal is converted to constant amplitude so that the signal pattern is represented principally by phase and frequency. The system reference signal is correlated with the vibrator control signal or the motion detector signal to generate a cross-correlation function.

Abstract: In accordance with the present invention, progressive changes in amplitude as a function of offset of common gathers can be more easily identified by emphasizing the degree of amplitude variation between "near" and "far" amplitude vs. time traces of each gather along a seismic line, and displaying the resulting near and far offset sections side-by-side. A significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence (within sections) indicates valuable characteristics, say the fluid hydrocarbon-bearing potential and/or the lithology of the reflecting horizon.

Abstract: Acoustic signals are transmitted in a direction substantially perpendicular to the borehole axis, from different levels of at least three determined generatrices of the borehole wall. Reflected acoustic signals are received from the same direction at different levels of these generatrices. A train of signals is derived from each reflected acoustic signal and at least a group of significant elements of this signal train is selected. The groups of significant elements of the signals obtained for the different generatrices are correlated. The interval between signal trains corresponding to the maximum correlation corresponds to one and the same geological formation and is representative of the dip angle of this formation.

Abstract: In the injection of fluids into subsurface geological formations, such as for the purpose of recovering a mineral in that formation, it is important that the flow progress of that fluid is known at all points in the subsurface. This information is provided by injecting a selected fluid into the formation. This fluid may be a gas, or a liquid, or a mixture of gas and liquid. When this fluid is in the subsurface formation there will be a mixture of gas and liquid in selected proportion in the formation. This mixture in a geologic formation overlain by a shale, for example, will have a much higher reflection coefficient. A source of seismic waves is operated at the surface, and the received reflections are compared between spaced positions on the surface.

Abstract: A method, when practiced, enhances seismic data so as to suppress noise in the seismic data. The seismic data was generated in a conventional manner by at least one receiver apparatus whose position does not substantially change. The method includes combining at least two elementary seismograms to form noise seismograms containing little or none of the desired signal. The number of different noise seismograms so derived is at least equal to the number of elementary seismograms to be combined to form a final seismogram. The probability distribution of noise is determined for each trace of the noise seismograms from the probability distributions of noise in the traces of the noise seismograms. The most probable form of the desired signals is derived from the probability distribution of noise in the traces of the elementary seismograms to provide the enhanced seismic data.

Abstract: A method for determining the lithology of subterranean structures based on attenuation of wave energy is disclosed which features a wave model based on a two-way solution to the wave equation rather than one-way solutions previously proposed. Rather than measuring amplitude of the wave as a function of its attenuation, energy flux density is measured which provides a two-way wave solution. In a preferred embodiment, pressure gradient measuring transducers are used to measure the energy flux density.

Abstract: Apparatus for determining the position of a gas-saturated porous rock in the vicinity of a deep borehole in the earth, drilled to a selected depth below the expected position of the porous rock. The apparatus includes a source of seismic waves of selected characteristic, positioned at a selected point in the borehole, with an array of geophones positioned on the earth in known positions around the borehole. These geophones are adapted to receive the seismic waves generated by the source in the borehole, after traveling upwardly through the earth, and to produce corresponding facsimile electrical signals. If the seismic waves from the source, in their upward movement to the surface, pass through a gas-saturated porous rock they will be attenuated, and therefore the signals from the geophones which are in the shadow of this gas-saturated rock will show a change of character and/or an attenuation.

Abstract: A method for deriving seismic information of more generalized nature over a relatively large and previously unexplored expanse of land to determine relevant strike, dip, velocity and related information. The method consists of the placing of a plurality of seismic sources and receivers in respective lines arranged in a cross pattern, each line being generally at right angles each to the other, and thereafter exciting the sources and recording the received energy for further processing to derive the strike, dip and velocity information for selected strata by using travel times of signal return.

Abstract: A method is disclosed for improving the signal-to-noise ratio of low level seismic signals resulting from weak acoustic sources. The method has application to the summation of signals from swept-frequency sources. A reference model of the level of a valid seismic signal is built for each of a number of time windows during a seismic-data recording cycle. The model is selected by obtaining the average of the absolute magnitudes for each time window from a number of sweeps to form a set of averages. The median of each set is selected and is padded by a suitable coefficient to provide the reference model for each time window. Subsequently, a normal recording is made. Each data sample amplitude of the recording is compared with the reference model corresponding to the time window that includes the data sample. If the amplitude level of the data sample exceeds the reference model level, that sample is suppressed prior to summing.

Abstract: In one exemplar embodiment, an improved method is provided for compensating received propagated seismic signals for the absorption by the earth of all frequencies of a vibrator source signal. The received seismic data is crosscorrelated with the original source signal and a Fourier amplitude spectral analysis obtained. Then an attenuation function is determined by the attenuation exhibited by the spectrum. The quantified attenuation function is then applied as a compensation function to the original source signal to obtain a "weighted" vibrator sweep signal that is then used in crosscorrelating with the received seismic data to compensate for the frequency dependent attenuation in the earth of received propagated seismic data.

Abstract: A machine and method processing seismic survey signals to reduce the effect of noise bursts by determining the power level of the signals recorded during a seismic survey and removing those portions of the signal which deviate from the remainder of the signals by unacceptable amounts.

Abstract: An apparatus and method for improving seismic resolution involving the application of scaling factors to seismic data which compensate for amplitude decay as a function of time, frequency and source-to-receiver distance (position). Each seismic trace associated with a common source-to-receiver distance is first separated into a plurality of frequency band-limited component traces. A time-variant amplitude scale factor (or its equivalent) is generated for each component trace. These scale factors are then applied to the component trace thus compensating for amplitude decay of the component trace. Upon recombination of the component traces a multidimensional amplitude scaled (MIDAS) seismic trace is recovered. The apparatus and method are particularly useful in creating a high-frequency extension of the frequency bandwidth resulting in improved resolution upon further processing or display. The method can be implemented as part of the field procedure or during subsequent computer processing.

Abstract: A new and improved method of forming a color graphic display from seismographic input data is disclosed. The input data sequence is processed to obtain the absolute value of each amplitude value and to select the maximum amplitude value of each oscillation of the waveform. A predetermined number of the largest selected values are classified into a first range of values, the remaining values are scaled according to magnitude into a preset number of ranges and an assignment table is formed with each range being represented by a primary or secondary color. Data corresponding to a first group of ranges of input data is processed to form a representation for a particular color. Similarly, the remaining data groups, corresponding to the remaining ranges, are processed to form a representation of the remaining colors. The image of each representation is sequentially transferred to a sheet and the images are colored with their respective colors, thus producing a color display of the seismic data.