Abstract: A computer-implemented method and system of correcting seismic survey data for the effects of NMO stretch is disclosed. The method operates upon a CDP gather of seismic survey data after normal move-out correction (NMO) has been applied. A semblance analysis is used to derive a stretch coefficient .kappa. profile over the gather, as a function of time and offset. The values of the stretch coefficient profile .kappa. are used in producing a time-varying filter that is applied, preferably by way of a time-domain multiplication, to incremental windows in time for each trace, with the products added to one another to generate a corrected trace. After all of the traces in the gather are corrected, an event-weighted filter is applied to the traces by way of a correlation operation, to remove high-frequency artifacts in the corrected traces. The corrected and filtered traces are then ready for stacking and conventional processing.

Abstract: Methods for processing sonic logging data obtained by a sonic imaging tool or an MWD tool are provided. The sonic logging data are bandpass filtered and sampled according to techniques such as integer band decimation, quadrature modulation, and single side band modulation to provide compressed signals which can be reconstructed if desired. The compressed signals are alternatively stored for downloading and further processing, sent uphole for processing, or processed downhole. The processing preferably involves processing the analytic portion of the compressed signals according to an improved semblance processing technique where the semblance function is calculated over a time window utilizing coarse slowness and time sampling steps. The slowness and time sampling steps are dictated by the parameters of the bandpass filter and the inter-receiver spacing of the tool. The waveform for each receiver is preferably interpolated based on the time step size to provide those data points necessary for stacking.

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 for improving the signal to noise ratio from a pair of detectors such as geophones which each detect a noisy signal comprising a signal of interest (S) and a noise signal (N), wherein the signal of interest (S) has a different moveout across the pair of detectors from that of the noise signal (N), and the noise signal (N) from a given source is detected at the first detector at a time .DELTA.t before the corresponding noise signal is detected at the second detector, the method comprising delaying the noisy signal (S+N) detected at the first detector by an amount .tau. being greater than the moveout of the signal of interest but not more than .DELTA.t and subtracting the delayed signal from that detected at the second detector by means of an adaptive filter so as to minimize the power in the resultant signal. The signal detected at the first detection and optionally the resultant signal can also be delayed by an amount .tau..sub.

Abstract: A system for compensating for noise induced in a sensor data stream from a sensor array towed by a towing device includes a towing device motion data input receives a towed motion data stream representative of towing motion of the towing device. A sensor array input for receiving the sensor data stream. An adaptive filter connected to the towing device motion data input and the sensor array input for receiving the towed motion data stream from the towing device motion data input and the sensor data stream from the sensor array input and for generating a corrected sensor data stream representing sensor array data with ship motion noise attenuated therefrom.

Abstract: A method for adaptively creating a filter for removing coherent environmental noise from a multitrace digitized seismic recording requires the presence, on the recording, of a limited sample of pure noise that is uncontaminated by desired signal. The pure noise sample is used to discover the location of the noise source and from that discovery, to extrapolate and reconstruct the characteristics of the noise envelope as it would appear on the seismic recording. The reconstructed noise envelope is used as a noise reference for input to a conventional iterative adaptive noise cancellation filter loop. For stability, the loop gain is minimized by temporally and spatially averaging the filter coefficients for each sample interval.

Abstract: A method for 3 dimensional, one pass migration of post stack seismic data is implemented on a massively parallel computer. The quality of the migration and speed of execution makes possible iterative 3D post stack depth migrations. The depth migration method computes in the frequency domain and downward continues one or more frequency planes through all depth levels of interest. For a single frequency, at each depth level, the method extrapolates a shifted position for each x,y position by applying a filter for 2D convolution. A processing component is assigned to each subgrid of x,y spatial positions and the processing components operate concurrently in parallel to determine filter coefficients independently for each x,y spatial position and to extrapolate the x,y shifted positions. The filter coefficients are derived independently at each x,y position by storing a limited table of filter coefficients in local memory of each processing component.

Abstract: A method and apparatus for attenuating bulge wave noise from data recorded by seismic streamers is provided. The apparatus includes a marine seismic streamer having a seismic detector and an accelerometer. The accelerometer is secured between the lead-in section and the seismic detector. Intra-shot and inter-shot accelerometer and seismic detector signals are recorded. The method utilizes inter-shot and an intra-shot adaptive processing loops. The inter-shot adaptive processing loop derives inter-shot complex weights from inter-shot accelerometer signals and inter-shot seismic detector signals. The intra-shot adaptive processing loop models bulge wave noise in the intra-shot seismic detector signals by combining the inter-shot complex weights with intra-shot accelerometer signals. Bulge wave noise attenuation is achieved by subtracting the intra-shot bulge wave noise model from the intra-shot seismic detector signals.

Abstract: An adaptive transversal filter is incorporated with an SP conductor extending through a logging cable to the surface from an SP electrode supported on a sonde. This logging cable is operated in a noisy environment and there is the risk of noise on the logging cable obscuring the SP signal. The SP signal is obtained at the surface and is passed through a filter system. One input to the filter system utilizes an AC ammeter connected to the AC power source for the logging cable and that signal is input to a multi-stage adaptive transversal filter. The filter output is a recreation of the noise imposed on the SP conductor and when summed with the SP output signal, provides a signal which is substantially noise free.

Abstract: To provide an accurate reproduction of a signal detected in a noisy environment, a primary signal sensor and a plurality of "signal-free" reference sensors are used. Information collected from the primary sensor and the reference sensors is compared to derive correlation data. A matrix, representing correlation data in the time domain or cross-spectral density information in the frequency domain, is constructed based on the computed correlation data. The matrix is transformed to a diagonal matrix using a singular value decomposition algorithm and a threshold value is selected with reference to one of the larger eigenvalues of the diagonalized matrix. Components of the diagonalized matrix are compared to the threshold and values greater than the threshold are used together with primary sensor correlation data to compute Wiener filter constants. The reference sensor outputs are modified by the filter constants and modified sensor outputs are subtracted from the primary sensor output.

Abstract: Method for removing coherent noise from a series of seismic traces. Each seismic trace included in the series is Fast Fourier Transformed into the frequency domain. For each frequency of the resultant f-x representation, a series of N complex numbers, one corresponding to each trace, is selected. The selected series of complex numbers corresponding to each frequency are processed to produce autoregressive model coefficients from which a polynomial rooting provides complex roots related to wavenumbers and decay constants. Amplitudes and phases for complex non-stationary spatial sinusoids associated with the estimated wavenumbers are then determined. For all frequencies f, the collection of determined wavenumbers, decay constants, amplitudes and phases constitute an f-k representation of the seismic traces.

Abstract: In seismic exploration, seismic reflection from subsurface formations are recorded in the form of a time-distance of seismic traces. This array is transformed into a time-wavenumber domain. Wavenumbers at which coherent noise resides within the time-wavenumber domain are determined. Frequencies corresponding to such wavenumbers are removed by filtering. The frequency-filtered, time-wavenumber domain of seismic traces are then transformed back into a time-distance array of seismic traces.

Abstract: An apparatus (10) for providing while drilling information on a subterranean geologic formation (28) includes a drilling rig (12) and a rotary drill bit (18) attached to the drilling rig (12) for providing seismic waves as it drills in the earth (16). Geophones (20) are spaced from the rotary drill bit (18) in the earth (16) and receive indirect seismic wave paths (26) and seismic wave paths (30) reflected from the subterranean geologic formation (28) the seismic waves provided by the drill bit (18). A reference sensor (24) is located on the drilling rig (12). The seismic signals sensed by the reference sensor (24) and by the geophones (20) are cross-correlated to separate the drill bit generated signals from interference signals by combining the reference signals and the signals received by the geophones (20).

Abstract: An ultrasonic echographic imaging device for two dimensions (x, y), includes an adaptive filter for reducing the interference noise in the images obtained. A first circuit differentiates the signal (E(x, y)) applied to the adaptive filter and a second circuit forms the weighted sum of the signal (S(x, y)) leaving the adaptive filter (200) and the signal (dE(x, y)/dy) output of the differentiating circuit.

Abstract: A method for locating hydrocarbon reservoirs or other geological anomalies by determining lithological parameters including Poisson's ratio, density and seismic wave velocity. Such parameters are determined by quantitatively relating reflection wave amplitude to corrected source-detector offset data.

Abstract: An apparatus (10) for determining while drilling in the earth with a drill bit (12) the positions of seismic wave reflecting geologic formations (15, 17) has seismic wave sensors (A, B) positioned in the earth near its surface (42). The sensors (A, B) are disposed at known positions with respect to the borehole. The drill bit (12) generates the seismic waves. The sensors (A, B) receive the seismic waves both directly and by reflection from the geologic formations (15, 17). Adaptive filters (20, 26) are connected to each of the sensors (A, B). A summing circuit (34) receives outputs from the adaptive filters (20, 26). The converged impulse responses of the adaptive filters provide information about the amplitude of the reflected waves and their arrival times at the surface, thus allowing detection of the reflecting horizons and their location and physical characteristics.

Abstract: An apparatus (10) for providing while drilling information on a subterranean geologic formation (28) includes a drilling rig (12) and a rotary drill bit (18) attached to the drilling rig (12) for providing seismic waves as it drills in the earth (16). Geophones (20) are spaced from the rotary drill bit (18) in the earth (16) and receive in direct seismic wave paths (26) and seismic wave paths (30) reflected from the subterranean geologic formation (28) the seismic waves provided by the drill bit (18). A reference sensor (24) is located on the drilling rig (12). The seismic signals sensed by the reference sensor (24) and by the geophones (20) are cross-correlated to separate the drill bit generated signals from interference signals by combining the reference signals and the signals received by the geophones (20).

Abstract: A seismic exploration method and apparatus in which non-uniformly distributed noise signals generated by wind, machinery, or surface wave propagation and received by the sensing geophones are cancelled by the utilization of adaptive filter processing. A number of horizontally sensitive geophones are disposed along the surface of the earth to detect surface waves induced in the surface of the earth at a plurality of spaced locations throughout an entire area of investigation. Similarly, a number of wind noise and mechanical noise detectors are utilized to detect airwave and noise signals at a plurality of locations throughout the area of investigation.

Abstract: Method and apparatus for cancelling nonstationary sinusoidal noise from seismic data. An estimate of the sinusoidal noise component is applied to a contaminated signal containing both a sinusoidal noise component and a non-sinusoidal data component to cancel the sinusoidal noise component of the signal. The estimate of the sinusoidal noise component is determined using continuous adjustments of the phase, frequency and amplitudes of the quadrature outputs of a local signal. The estimate of the sinusoidal noise component is subtracted from the contaminated signal and the resultant signal, which is an estimate of the data component of the contaminated signal, is utilized in adjusting the phase, frequency and amplitudes of the local reference sine-cosine signal.

Abstract: The output of a local oscillator is applied to an external signal to produce a feedback error signal. The feedback error signal is utilized in adjusting the phase, frequency and amplitudes parameters of the local reference sine-cosine quadrature components which comprise the output of the local oscillator signal. Adjusting the parameters modifies the output of the local oscillator. The modified output of the local oscillator is applied to the external signal to continuously modify the feedback error signal, which in turn, continuously modifies the output of the local oscillator until the frequency and phase of the local oscillator signal is locked to that of the external signal.

Abstract: A method for restoring to filtered seismic data at least some of the ramdom background noise associated with the data in its form prior to filtering. The method includes the steps of filtering seismic data in a two-dimensional filter; generating a noise signal representing the random background noise associated with the data; filtering the noise signal in an inverse filter corresponding to the two-dimensional filter; and adding the inverse-filtered first signal to the filtered seismic data. In one embodiment, the noise signal is generated by filtering a copy of the data in a least-mean-squares adaptive filter to remove substantially all coherent energy therefrom. In another embodiment, the noise signal is an independently generated white noise signal having beginning and end times matching those of the seismic data. This white noise signal is the bandpass filtered to cause its frequency content to match that of the seismic data.

Abstract: In an acoustic well logging system having an acoustic transmitter in a sonde and spaced acoustic receivers, an acoustic transmitter control circuit enabling transmission of high frequency pulses, acoustic receivers therefor, received signal frequency filter selector means and a digital signal processing system assist in data processing. The received signal is passed through high and low frequency filters, the filters being selectively switched, the signals are converted to digital form and then available for further processing.

Abstract: A signal processing system in a transmitter/receiver system for reducing undesired amplitude, frequency and/or phase distortions arising due to variations from transmitter pulse to transmitter pulse. A plurality of sequential samples of transmitted pulses are averaged and a plurality of filter coefficients are determined therefrom. The coefficients are used in a plurality of filters which respond to a plurality of sequential samples of received pulses, the filters providing output signals in which such distortions are reduced.

Abstract: An equalizer is provided with a branching device for branching a digitally modulated signal into two outputs. A series of weighting devices weights one of the outputs of the branching means, and a series of second weighting devices equal to or fewer in number than the first weighting devices weights the remaining output of the branching means. Combining elements equal in number to the first weighting devices combine two or three inputs, and delaying means fewer in number than the combining elements are interconnected with the combining elements in a sequential, alternating manner. The outputs of the first weighting devices are respectively applied to the combining elements while those of the second weighting devices are respectively applied to selected ones of the combining elements. The invention provides a construction where the number of taps of the equalizer may be easily increased without creating the necessity of combining circuits having an increased number of inputs.

Abstract: The system for suppressing an ambient noise signal which comtaminates a desired signal includes a noise pickup detector for detecting the ambient noise signal. A noise discriminator processes the detected noise signal into noise data. A reference noise generator converts the noise data into a reference noise signal. The noise generator automatically adjusts the reference noise signal to correspond with changes in the noise signal as it is being detected. A filter filters the reference noise signal into an error signal which is adapted to remove the noise signal from the contaminated signal. A cross-correlator cross-correlates the contaminated signal with the reference noise signal and adjusts the filter to produce the required error signal.

Abstract: An earth impedance determination and compensation system for use with a seismic vibrator utilizes output signals from accelerometers on the baseplate and reaction mass portions of the vibrator to create a signal indicative of the near-surface weathered earth layer impedance below the baseplate. The impedance signal is utilized to generate parameter signals which are indicative of the compressional and shear wave patterns generated by the baseplate and may be used to more rapidly and accurately design seismic source arrays to optimize the wave pattern emanating therefrom. One of the parameter signals is directly indicative of the travel time thickness of the weathered surface layer and may be used to accurately determine the static correction factor attributable solely to weathered layer topography.

Abstract: A method for recursively, continuously estimating the noise and signal components of a seismic trace. More particularly, a method for suppressing the noise component in seismic data so as to enhance the resolution of seismic events contained therein. The signal component of each seismic trace is determined recursively from the preceding estimate of the signal component in each preceding seismic trace.

Abstract: A method and apparatus are disclosed for acoustically investigating a borehole casing cement bond. A sonde is provided which is adapted to be lowered into a borehole and which includes a plurality of acoustic transducers arranged in a helical array around the sonde. A short duration acoustic pulse is directed at the borehole casing from each transducer and the reflection signal generated thereby is coupled to an autoregressive adaptive filter which automatically adjusts its filter coefficients to achieve a desired output signal. The adjusted filter coefficients are then utilized to determine the frequency and decay rate of the reflection signal and the frequency and decay rate of the reflection signal may be utilized to determine selected characteristics of the casing and the cement bond. In a preferred embodiment of the present invention, an additional transducer is mounted a selected distance from a fixed reflector to obtain standard transmission characteristics.

Abstract: Statistical variations in simultaneous shallow and deep investigation nuclear borehole logs are reduced using digital moving average data processing while maintaining responsiveness to formation changes, by transitioning through a combination of long and short filtered data as a function of the statistical variation of the deep log data differences of the long and short derived averages. Borehole rugosity is also indicated as a function of the difference between the shallow and the deep log indexes of the differences between their respective narrow and wide derived averages.

Abstract: In portable seismic data acquisition units, an adaptive seismic signal processor and method for resampling and bandpassing selected frequencies of an input digital signal. The adaptive seismic signal processor and method provide an output digital signal having a frequency domain and resampling rate which can be selected from one of a plurality of predetermined frequency domains and sampling rates during the course of acquisition of the input digital signal without substantial loss or deterioration thereof.

Abstract: A method of seismic exploration of the subsurface of the earth. Seismic reflection data are gathered in a selected area. The seismic data are combined with available non-seismic data to define an initial two-dimensional lithologic model. Based upon the initial model, a set of synthetic seismic data is generated. The degree of correspondence between the set of synthetic reflection data and the gathered seismic data is determined. The initial model-parameters are systematically perturbed during a series of iterations until a desired degree of correspondence has been achieved, resulting in a final lithologic model.

Abstract: A method is disclosed for estimating the impulse response of the earth from Vibroseis data. Based on a time domain system identification approach, the earth's impulse response is estimated by operating on the seismic trace data and the vibrator pilot. Two implementations are discussed. The first is an adaptive method using a sliding data window and the uncorrelated trace data. Preferably, the process used to control the adaptation is the fast Kalman estimation (FKE) technique. This technique, based on recursive least squares, has a fast convergence rate and desirable computational requirements. The second implementation is non-adaptive. It uses the Levinson recursion technique to compute the Wiener filter solution based on the pilot autocorrelation function and the correlated trace data. Simulations demonstrate the capability of the system identification model to resolve reflection events.

Abstract: The detection of low-flying aircraft is accomplished using both a microphone and geophone as sensors and a signal processing system for measuring the correlation between the seismic and acoustic signals. The signal processing system contains two amplification and band-limiting circuits, a delay circuit, an adaptive noise cancelling circuit, two signal smoothing circuits and a comparison circuit. The two amplification and bandlimiting circuits enhance a selected portion of the seismic and acoustic signals received by the sensors. The optional delay circuit is applied to the input acoustic signal, allowing the user the option of sensing or rejecting the detection of jet aircraft. The adaptive noise cancelling circuit generates an error signal by subtracting the signal components which are correlated between the seismic and acoustic signals from the input seismic signal. The first signal smoothing circuit improves the quality of the input seismic signal for comparison.

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: 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: A time variant filter system is employed for removing spurious noise content from a received seismic data signal. The filter passband tracks delayed versions of the pilot signal of a vibrator seismic source. The resulting recorded portion of the received seismic signal is thus restricted to a desired time-frequency band (which is expected to contain the significant mapping information) prior to being recorded. The band is made adjustable in order to allow for optimization with respect to the particular geologic region being prospected.

Abstract: Seismic exploration method and apparatus in which interference signals received by the sensing geophones from the seismic vibration source are cancelled by employing a signal representative of the seismic vibration source and combining it with the output from the sensing geophones.

Abstract: A method and apparatus for digital time-variant filtering are disclosed. The digital time-variant filters are implemented using the Hilbert transform and a time-varying instantaneous frequency control function for controlling the cutoff frequency. The digital time-variant filters are adaptable to various filtering processes, that is, as either a high-cut, low-cut, band-pass, or reject filter. The various digital time-variant filters are stable in that no unusual transients occur in the output signal; are flexible in that the cutoff frequency is controlled by a selectable time-varying control function signal; and are efficient in that computational requirements are only twice to 16 times that of known digital time-invariant filters.

Abstract: In magnetotelluric exploration, channels of measurements of the earth's electric and magnetic field are digitized. Blocks of digital samples are transformed into frequency domain representations of the power spectra, including amplitude and phase, at selected harmonics. The coherence between the power spectra from different channels is determined and compared to a threshold. The power spectra which have a coherence exceeding the threshold are stacked and recorded on magnetic tape.

Abstract: This specification discloses an automatic computer-implemented technique for filtering a two-dimensional array of data in the frequency domain. The program converts the array of numbers by Fourier transformation into the real and imaginary part of the frequency domain. In this domain, undesired waves present in the original array can be completely removed by the elimination from the frequency domain of the components of the Fourier-transformed array which fall within (or, if desired, outside of) a convex polygon of arbitrary shape. The system then re-transforms the remaining data back to the time domain, but the undesired components have been filtered. The program can cause the computer to produce a visual reproduction of the filtered array, or it may simply re-format the data of this array on a tape for further computer processing. Accordingly, this invention permits precision spatial filtering of undesired components from the original array.