Abstract: Seismic measurements are taken during drilling operations by an array of seismometers placed on the earth's surface about the axis of a drillstring connected to a conventional drillbit and wherein the drillstring has an arrangement of strain gages and accelerometers mounted thereon in such a way as to measure axial and torsional vibrations of the drillstring. Signals indicating vibrations induced by the drillbit or another source and transmitted through the drillstring are compared with signals received by the seismometer array to determine the characteristics of the formation based on measurement of acoustic velocity from direct and reflected transmission of acoustic vibrations through the formation.

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: The invention is a method for improving quality of seismic data generatd with a source positioned substantially at the lower end of a drill string within a wellbore. A pilot signal is detected at the upper end of the drill string for cross-correlation with signals detected by field sensors positioned at the earth's surface displaced from the wellbore. Noise is reduced in the pilot signal by detecting the noise wih a sensor positioned to be sensitive to the noise but substantially insensitive to the acoustic signal transmitted up the drill string from the source. The frequency band within which there is high coherence between the energy in the noise signal and the pilot signal is determined. The noise signal is then amplified by a factor equal to the average ratio of the energy amplitude of the pilot signal to the noise signal within this frequency band, and this weighted noise signal is substracted from the pilot signal to reduce the noise in the pilot signal.

Abstract: Method of interpolating additional seismic traces between existing seismic traces obtained during the exploration of a subsurface formation. Seismic traces are recorded upon a datum surface in accordance with standard seismic data acquistion methods. Forward and backward wave equation datuming of the data set at the same velocity estimates new measurements for originally acquired data deemed unsatisfactory by propagating measured seismic traces to a fictitious datum plane using wave theory to create a second set of seismic traces and datuming the second set of seismic traces, again using wave theory, back to the original datum plane to create a third set of seismic traces. The third set of seismic traces will include new seismic traces to be used in place of the originally acquired unsatisfactory data.

Abstract: The invention comprises a method of geophysical exploration wherein a signal is generated at the lower end of a drill string and propagates into the earth and up said drill string. The signal is detected at the top of said drill string and at other locations substantially at the earth's surface. The signal detected at the top of the drill string is utilized to develop an operator to reduce the magnitude of drill string multiples in the signal detected by the field sensors.

Abstract: The invention relates to a method and apparatus for processing data from a seismic survey.In accordance with the invention, the data is regrouped to form a plurality of seismic images (A1, A2, A3, B1, B2, B3, C1, C2, C3). These images being defined by image elements defined in spatial position with respect to an operation direction (D) and having a grey level of predetermined amplitude, the method consisting for each pair of images (Ai,Bj) of carrying out processing by correlation of the amplitude of the grey levels, in order to establish an intercorrelation coefficient and to compensate the localization errors in the position of the images.Application to mono-, bi- or tri-dimensional marine geophysical prospecting.

Abstract: Method of restoring null traces in seismic records. A trace for which restoration of the data is desired, as well as adjoining traces on each side of the null trace are selected. A series of cross-correlations are determined for all points on the selected trace. Restoration of the data points is conducted by transforming the series of points of the adjacent traces corresponding to the maximum cross-correlation for the point into a Fourier representation, zero-padding the Fourier representation and producing a restored data point from the zero-padded data representation. The procedure is repeated for each point along the trace being restored. This procedure interpolates a trace between two original traces without altering the original data.

Abstract: A sonic well logging system and apparatus for determination of seismic wave velocities from a seismic wave propagating in a subterranean formation about a wellbore. The system includes the process of imparting a seismic wave into the subterranean formation about the wellbore, and receiving the seismic wave after it has interacted with the subterranean formation at a plurality of semismic receivers positioned in the wellbore. The seismic waves are transformed at each of the seismic receivers into a seismic signal and these signals nonlinearly staked for a selected position in the wellbore to generate a velocity spectrum of seismic wave velocities. Coherency peaks are then selected from the velocity spectrum with each coherency peak having associated therewith a unique seismic wave velocity, such as P-wave, S-wave, tube wave and the like.

Abstract: A method of three-component seismology wherein seismic energy induced vertical, radial and transverse particle movement is detected at plural spaced positions along a survey line to produce orthogonal data signals, and the different orthogonal data signals are variously processed both separately and interactively to develope novel signal relationships which improve indication and identification of steeply dipping reflections, out-of-plane reflections, and the like.

Abstract: A process for non-linear matching of time analog signals, particularly seismic signals, that have generally similar response characteristics but different time bases is disclosed. The process models the signals to be matched as a stretched version of each signal with additive noise, and a match curve is estimated adhering to a global criterion of maximization of the likelihood function. The global criterion is further optimized in accordance with the principle of path optimality and other a priori information may also be considered. The match curve may then be used to identify such as correlated signal events, conparison of signal sections, and numerous seismic data processing functions using multidata or multisensor time analog data input.

Abstract: Method of instantaneous acoustic logging within a wellbore.The method is characterized in that it consists of locating on drill-pipe and ground recordings elementary recordings corresponding to one and the same depth level of the drilling tool, in grouping these elementary recordings in pairs, then in intercorrelating said recordings of the pairs so as to produce in respect of each pair a correlated signal which is representative of the acoustic energy produced and of the difference in travel times of the waves received on sensors from which the pair of recordings has been obtained.A particular application is for the determination of a seismic wellbore profile.

Abstract: The invention is a method of performing a plurality of vibratory seismic surveys simultaneously. A plurality of vibratory sources transmit signals into the earth. Each vibratory source successively transmits the same signal, except that an offset phase of the signal is selectively shifted for successive transmissions. The offset phase of the signal transmitted by each vibratory source is selected to enable the signal from each of the vibratory sources to be recovered by data processing.

Abstract: Method for the processing of recordings of signals resulting from a seismic exploration of a medium.It consists, after grouping recordings in pairs and crosscorrelation of the recordings of each pair, in grouping the elementary crosscorrelation functions thus obtained in at least one family in which the measuring spaces are included in a same predetermined reference space, in transforming the time variables of the said functions in order to bring the measuring space dimension to that of the reference, then in adding the transformed functions.Application in particular to acoustic logging seismic reflection or refraction.

Abstract: In seismic exploration, the ratio of the velocities of compressional and shear wave data is automatically determined by cross-correlating a compressional wave trace against a window of the shear wave trace to produce a set of correlation coefficients as a function of P wave time. The shear wave window is shifted by an increment of time. The steps of cross-correlating and shifting the window are repeated to form a grid of correlation coefficients. Points on the grid represent the correlation coefficients between a point on one trace and a point on the other trace. The path of maximum correlation coefficients, or maximum likelihood functions, through the grid identifies the V.sub.p /V.sub.s profile. This path is selected by a process which includes selecting the best path between two points and then increasing the number of points in the sequence until the best path through the grid is determined.

Abstract: A well logging tool employing at least one transmitter and at least one receiver is incrementally advanced through a borehole. A plurality of recorded well log traces from successive ones of the incremental depth points for a single transmitter-receiver pair are correlated to identify a moveout trend for the recorded waveforms about the measured arrival time of the waveform on the center trace of such plurality of traces. A second correlation of the center trace of the plurality of traces with the next successive depth trace is carried out in accordance with the identified moveout trend to determine the arrival time of the acoustic waveform on such next successive depth trace with respect to the measured arrival time of the center trace.

Abstract: A method of processing seismic data enables correlation of P and S-wave seismic traces. First, P and S-waves are transmitted into the subsurface. The two-way vertical travel times are then measured for each wave to different depths so as to yield two sets of time-depths pairs. Mathematical functions relating two-way vertical travel time, T.sub.s or T.sub.p, and depth are fitted to each set of time-depth pairs. These functions are combined to yield an expression relating T.sub.s and T.sub.p. This expression may be utilized to rescale one of the traces to yield correlated P and S-wave traces.

Abstract: Disclosed is a method for constructing an optimal pilot trace from a gather of seismic traces, which pilot trace can be used to obtain statics estimates for time correction of the gathered traces prior to common depth point stacking. During construction of the optimal pilot trace, the statics estimates are inherently obtained.

Abstract: A method of enhancing the signal to noise ratio of seismic data includes the steps of repeatedly obtaining, from at least one array of seismic detectors, analog signals representative of sensed vibrations or pressure waves. Each analog signal is converted to discrete digital values on a time correlation basis until a predetermined quantity of analog signals have been converted. In each time correlation, the two most positive digital values and the two most negative digital values are removed. The remaining values for each time correlation are averaged so as to provide a digital representation of the analog signals.

Abstract: To utilize indirect-path signals in a receiver for fixed and mobile transmitter-receiver stations of a TDMA spread-spectrum digital radio system, coherent detection is employed. At the same time, the signal imaging the multipath profile is continuously regenerated by a regeneration circuit. The regeneration circuit provides a phase-coherent signal employed for demodulating the received signal.

Abstract: Seismic pulse waveforms are generated for travel through subsurface formations. Both normally-reflected and obliquely-reflected waveforms from subsurface interfaces are recorded. The differential phase change between the normally-reflected and obliquely-reflected waveforms are determined for each interface. The fluid characteristics of the porous subsurface layers are identified as gas-saturated or water-saturated in response to the relative amounts of phase change, a gas-saturated layer providing a larger phase change than a water-saturated phase change.

Abstract: A chirp transform correlator having asynchronous operation is made possible by the use of a pair of paralleled signal processing channels to which the unknown signal to be correlated is applied. The two channels include sweeping local oscillators which are interlaced in timing so that any arbitrarily timed unknown input signal will be fully transformed by one or the other of the channels.

Abstract: An automated seismic processing system and method are disclosed, including an array of CMOS microprocessors for unattended battery-powered processing of a multi-station network. According to a characterizing feature of the invention, each channel of the network is independently operable to automatically detect, measure times and amplitudes, and compute and fit Fast Fourier transforms (FFT's) for both P- and S- waves on analog seismic data after it has been sampled at a given rate. The measured parameter data from each channel are then reviewed for event validity by a central controlling microprocessor and if determined by preset criteria to constitute a valid event, the parameter data are passed to an analysis computer for calculation of hypocenter location, running b-values, source parameters, event count, P- wave polarities, moment-tensor inversion, and Vp/Vs ratios.

Abstract: A seismic wave generator and method of using it, which comprises a vertical array of sources at known spacings, for detonation in a seismic wave propagating medium of known seismic velocity; means to initiate the sources in time sequence in a selected series of known different time intervals and recording the seismic waves at a distant location to provide a first electrical signal; and correlating the first electrical signal with a second electrical signal derived from the pattern of initiation, as modified by the travel times of the waves between the several separate charges.

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: 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 of seismic exploration using acoustic logging comprises transmitting and receiving sound waves, recording all of the signals received by the receivers, the respective positions of the emitter-receiver pair which give rise to each recording, grouping the recordings in pairs so that each recording of a given pair of sound paths have a common path segment and a part which is not common to both which is located facing the geological stratum of interest and the difference in time of arrival for at least one type of wave is measured for each pair.

Abstract: Maximum likelihood estimation theory is applied to the determination of the ratio of P-wave velocity to S-wave velocity (V.sub.p /V.sub.s) from P-wave and S-wave seismic sections obtained along the same line of exploration. For a certain statistical model, the optimal estimator for V.sub.p /V.sub.s is determined, and shown to be equivalent to maximizing the simple mathematical correlation between P-wave and stretched S-wave seismogram segments. The maximum likelihood method provides a data-dependent formula for the mean square error associated with the V.sub.p /V.sub.s estimate. Alternatively, the latter formula provides a measure of the V.sub.p /V.sub.s information contained in the data. The information measure also provides optimal weighting for computing multitrace V.sub.p /V.sub.s averages, and provides for the determination of the statistical error in such averages.

Abstract: The invention relates to seismic prospecting of the sub-surface.At least two adjacent focuses F and F', at least one reflecting interface H and directions such as (D.sub.1) and (D.sub.2) are selected in the sub-surface. A seismic trace, from which a portion containing the effect due to the reflecting interval is extracted, is made to correspond to each direction and to each focus. The correlation function between the two trace portions relative to two adjacent focuses and the same direction is then determined. The correlation functions obtained are finally summed for the different directions.Application to high resolution seismic prospecting.

Abstract: An improved method for three-dimensional seismic exploration of the subterranean structure of the earth is disclosed wherein arrays of sources of acoustic energy and of detectors of reflected energy are used. The configurations of both arrays are conjointly experimented with to improve the signal-to-noise ratio of the resultant data; the signals output by the detectors are summed, and are correlated with those output with respect to all acoustic energy emitted within a given array of sources.

Abstract: In seismic exploration windows from a pair of contiguous traces are used in a process which determines the coherent noise on a basis trace and removes this coherent noise from a prediction trace. The operator of a digital filter is determined by autocorrelating the basis trace, cross-correlating the window of the basis trace, with the window of the prediction trace, and selecting the filter operator which produces the least error between the cross-correlation function and the product of the autocorrelation function and the operator.

Abstract: A method determines the extent of subsurface reactions in which random acoustic signals are radiated from a whole area covered by the reaction or from a boundary region, hereafter termed reaction front, between largely undisturbed rocks and those already covered by the reaction. The signals are recorded by at least two receivers positioned at different locations outside the reaction area. The recorded signals are cross-correlated as a function of a time shift between the recorded signals so that at least one surface confining the reaction area is determined from the cross-correlation.

Abstract: A method of seismic exploration by which substantially plane or substantially cylindrical seismic energy waves are simulated by combining reflectional signal traces of conventional spherical seismic waves. Seismic sources and receivers are established in sets at positions such that at least one of the sets includes a plurality of positions spaced over an extent of the area being explored having either one or two dimensions which are large relative to a seismic energy wavelength. Seismic energy is imparted into the earth from the sources and signals are generated in response to seismic energy received at the receivers. The generated signals are then combined into a form simulating the reflection response of the earth to seismic energy having a substantially continuous wavefront in either one dimension, simulating a cylindrical seismic energy wave, or two dimensions, simulating a plane seismic wave.

Abstract: A well-logging method and apparatus in which a fast real time portion of a logging signal is sequentially sampled at discrete times. These sampled segments are stored and then are clocked out of storage over an expanded time period.The rms amplitude portion of the logging signal occurring prior to the compression wave part of the logging signal (the nominal noise level) may be used for AGC regulation of an amplifier which amplifies the time-expanded output.A similar development of an rms value can be used for establishing a threshold level for a peak detector, which level is set slightly higher than such rms value. The first three successive samples greater than the threshold level detected by the detector are presumed to be the first three samples of the compression wave. This presumed compression wave is recorded and convolved against the expanded-time digital form of the logging signal to locate the compression wave in a second received signal and, later, the similarly appearing "shear" wave.

Abstract: A search is made down each trace of a seismic record at the approximate period of the multiple events to find a trace segment which most resembles a selected later segment of the same trace. An autocorrelation procedure is initially employed to determine the approximate period of the multiples and a crosscorrelation procedure is then employed to determine the time alignment of the two segments which produces maximum correspondence between the two segments. The degree of correspondence is determined by a "least-squares-fit" procedure. A portion of the earlier segment is subtracted from the later segment. The amount of the earlier segment to be subtracted is determined by the degree of correspondence. The procedure is incremented along the trace until the entire trace has been processed. Each trace is handled in the described manner until the entire record has been processed.

Abstract: In depth correlation of logs according to the subject invention, the starting data is an array of correlograms on a depth v. shift coordinate system. Unreliable correlation coefficients are eliminated to leave only valid ones, then valid clusters of correlation coefficients are examined to find reliable indications of trends in shift and in changes in shift. These indications are used to compute the shift and the corresponding depth which would result in a corrected correlation between the two logs from which the correlograms are derived.

Abstract: A method of and apparatus for determining the precise position of the drill bit on the bottom of a long drill string in a deep borehole in the earth, during a drilling operation. The method comprises placing a plurality of geophones in a three-dimensional array near the surface of the earth, above the expected position of the drill bit in the earth, causing at least a low energy seismic source to be initiated near the drill bit in the earth, repeating the source a number of times, and determining at the surface of the earth the times of initiation of each of the seismic waves. Responsive to the known times of initiation, stacking each of the repeated geophone signals from each of the geophones, for each of the repetitions of the source, whereby each of the stacked signals will be in-phase with those that resulted from earlier and later repetitions of the source. Several embodiments of an improved downhole seismic source are described, and an improved type of three-dimensional array.

Abstract: The accuracy of well logging data transmitted from a downhole location to the surface of the earth is verified by generating the data at the downhole location, storing the data in a subsurface assembly in the well, transmitting signals corresponding to the data to the surface through a first transmission system while keeping the data stored in the subsurface assembly, and recording the signals transmitted to the surface through the first transmission system. Thereafter, the subsurface assembly is transferred to the surface, and signals corresponding to the stored data are transmitted through a second transmission system from the assembly to an electronic processing system. The signals transmitted through the second transmission system are then compared with the signals transmitted through the first system.

Abstract: An illustrative embodiment of the present invention includes methods for Seismic Data Processing which may be used to enhance the signal/noise ratio of seismic signals taken by use of the Common Depth Point or Hundred Percent Coverage survey techniques. The methods preserve time alignment and amplitude of the signals while effectively removing the noise therefrom. Small portions of the record centered at a selected time on a selected trace are processed to extract the coherent signal component from the reference trace as determined by comparison with other spacewise adjacent traces. Output records comprising the enhanced signal data and the noise data are produced.

Abstract: A method of enhancing a "gather" formed of a plurality of unmoved out common depth point (CDP) data traces. The gather is formed of a plurality of seismic traces arranged in a display in which time varies along the horizontal axis and distance between source and detector (range) varies along the vertical axis. The gather is incrementally processed by cross correlating trace segments within a defined area or search window. To this end, the center trace within the window is selected as a reference trace which is multiplied by a taper function and cross correlated with the other traces in the window to provide a coherent trace and a separate noise trace, both of which are produced in the output. The window is shifted on the gather and the procedure is repeated until every trace has been processed. In the cross correlation technique, the trace segments in the window are examined along a derived hyperbolic curve.

Abstract: This invention relates to an improved system for employing seismic techniques for surveying the subsurface structures of the earth. The invention relates particularly to an improved system for generating, collecting and processing the data during the course of exploration with a group of trucks that travel over the surface of the earth and intermittently stop to perform the required operations. The processing aids in the performance of the generating and collecting step and in the further processing of the collected data. And the data resulting from processing in this invention are transferred to a computer center for further processing. In this system, use is made of two programmable computers to facilitate concurrent processing of seismic waves received in successive setups in different ways.

Abstract: This invention relates to an improved system for employing seismic techniques for surveying the subsurface structures of the earth. The invention relates particularly to an improved system for generating, collecting and processing the data during the course of exploration with a group of trucks that travel over the surface of the earth and intermittently stop to perform the required operations. The processing aids in the performance of the generating and collecting step and in the further processing of the collected data. And the data resulting from processing in this invention are transferred to a computer center for further processing. In this system, use is made of two programmable computers to facilitate concurrent processing of seismic waves received in successive setups in different ways.

Abstract: A system and method for carrying out seismic operations with low energy sources, which involves operating the source at spaced points along a seismic spread, the source points are spaced far enough apart so that their seismic waves originate at different points and travel by different paths to the geophones. The geophone outputs cannot be time stacked. The geophone signals are amplified at constant gain and digitized to 1 bit. If the low energy source is a vibratory source, the 1 bit signals are correlated with a 1 bit version of the sweep signal. The resulting correlograms are digitized to 1 bit and C.D.P. stacked and displayed. If the low energy source is impulsive, the 1 bit amplified signals are C.D.P. stacked and displayed. In C.D.P. stacking, the determination of optimum velocity can be carried out by 1 bit processing.