Mobil Oil Corporation

Atlantic Richfield Company

Kenneth Paul Allen

John James Sallas

Dennis Corrigan

Maynard S Redeker

A seismic system is provided with a method of reducing distortions caused by motion of a source and receiver in marine seismic measurements. In one embodiment, the seismic system comprises a seismic source, a seismic receiver, a source/receiver interface unit, a processing unit, a data storage unit, a display device, and a user input device. The processing unit is configured to receive seismic measurements from the seismic receiver and to create a seismic velocity model from the received data. The processing unit uses the velocity model to calculate a dilation function that is indicative of distortion caused by motion of the seismic source. Preferably, the processing unit corrects the seismic measurements for this distortion by computing a transform of the seismic measurements, partitioning the transformed measurements into 'dip slices', inverse transforming the individual dip slices, correcting the dip slice measurements according to the dilation function, and adding the corrected dip slice measurements together to obtain the corrected seismic measurements. The disclosed system and method can advantageously provide for more accurate correction for source motion, which in turn yields seismic data having substantially reduced 'smear' when ensemble averaging is performed to reduce seismic noise.

Method and apparatus for doppler smear correction in marine seismology

An apparatus and method for removing the distortion in marine seismic data resulting from the motion of the ship. The ship trails one or more seismic sources and receivers and moves forward at a known velocity. The seismic sources emit seismic waves that travel through the water and reflect off interfaces between rock formations below the ocean floor. The motion of the sources and receivers introduces distortion in the recorded seismic data that can be modeled using Doppler theory. The data preferably is corrected for source motion independently from the correction for receiver motion. The seismic data is first corrected for receiver motion and then for source motion. The technique for correcting for source motion includes correlating the receiver-corrected data with a reference sweep signal, performing an F-K transform, performing an inverse F-K transform on a selected subset of the F-K transformed data, and computing appropriate correction filters for the data resulting from the inverse F-K transform. This process is repeated for all subsets of F-K transformed data and the resulting filtered data are summed together.

Method and apparatus for correcting effects of ship motion in marine

A method for separating and pre-processing vibratory source data includes varying the phase of vibratory sources according to two patterns. A first pattern is used for odd numbered sources while a second pattern is used for even numbered sources. Each pattern begins with a zero phase shift, the zero phase shift occurring at the sweep number corresponding to the position number of the source. The first pattern is one of zero phase shift, ninety degree phase shift, ninety degree phase shift and one hundred eighty degree phase shift. The second pattern is one of zero phase shift, one hundred eighty degree phase shift, ninety degree phase shift and ninety degree phase shift. The patterns are alternated for each source, the beginning of the pattern corresponds to the position of the source in a line. The first source begins with the first pattern. The second source begins with the second pattern, with zero starting at the second sweep. The third source begins with the first pattern, with zero occurring at the third sweep. The fourth source follows the second pattern, with zero being at the fourth sweep.

Method for separation of a plurality of vibratory seismic energy source

A method for recording and pre-processing vertical seismic profile high fidelity vibratory seismic data includes the steps of measuring the motion of the vibrator which is related to the vibrator applied force times a transfer function of minimum phase, causal, linear system relating the actual vibrator output with the measured vibrator motion, separating signals according to the generating source of each, determining a ratio by dividing the vibratory seismic data by the measured motion of the vibrator to remove the unknown applied force leaving the earth reflectivity times a time derivative divided by a minimum phase function, minimum phase band pass filtering the resulting ratio and performing minimum phase deconvolution to remove the time derivative divided by the transfer function of minimum phase.

High fidelity vibratory source seismic method for use in vertical

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. The inverse matrix for the frequency is applied to the recorded geophone vibrations at that frequency, to derive the transfer function, corresponding to the earth response, for each vibrator-geophone path in the survey. A weighting factor may be used to discount the effects of poorly behaved sweeps, and may be based on the ratio of the maximum and minimum eigenvalues for the inverse matrix. Using these derived transfer functions, an earth reflectivity function may be derived for each vibrator-geophone path by applying a minimum phase filter to the separated vibrator-geophone transfer function over frequency; this filter removes the effects of a ##EQU1## term, and yields the earth reflectivity function for the path.

High fidelity vibratory source seismic method with source separation

A method for recording and pre-processing high fidelity vibratory seismic data includes the steps of measuring the motion of the vibrator which is related to the vibrator applied force times a transfer function of minimum phase, causal, linear system relating the actual vibrator output with the measured vibrator motion, separation of signals according to generating source, determining a ratio by dividing the vibratory seismic data by the measured motion of the vibrator to remove the unknown applied force leaving the earth reflectivity times a time derivative divided by a minimum phase function, minimum phase band pass filtering the resulting ratio and performing minimum phase deconvolution to remove the time derivative divided by the transfer function of minimum phase. The method may also include shot ensemble deconvolution, receiver ensemble deconvolution, statics correction, F-K filtering for noise, zero phase spiking deconvolution and model dephasing. A signal directly proportional to the actual signal that the vibrator is sending into the ground is used in pre-processing. The vibrator motion is measured to provide a signal that is used to process the data. The data is divided by the relative of the actual transmitted signal in frequency domain.

High fidelity vibratory source seismic method using a plurality of

A method for generating, recording and pre-processing high fidelity vibratory seismic data in a system that uses a plurality of vibratory sources includes the steps of measuring the motion of each of the vibrators, determining a ratio by dividing the vibratory seismic data by the measured motion of the vibrator to remove the unknown applied force leaving the earth reflectivity times a time derivative divided by a minimum phase function, minimum phase band pass filtering the resulting ratio and performing minimum phase deconvolution to remove the time derivative divided by the transfer function of minimum phase. The method may also include the steps of shot ensemble deconvolution, receiver ensemble deconvolution, statics correction, F-K filtering for noise, zero phase spiking deconvolution and model dephasing. A signal directly proportional to the actual signal that the vibrator is sending into the ground is used in pre-processing. The vibrator motion is measured to provide a signal that is used to process the data. The data is divided by the relative of the actual transmitted signal in frequency domain.

One step inversion/separation scheme using a plurality of vibrator

A method for recording and pre-processing high fidelity vibratory seismic data includes measuring the motion of the vibrator which is related to the vibrator applied force times a transfer function of minimum phase, causal, linear system relating the actual vibrator output with the measured vibrator motion, determining a ratio by dividing the vibratory seismic data by the measured motion of the vibrator to remove the unknown applied force leaving the earth reflectivity times a time derivative divided by a minimum phase function, minimum phase band pass filtering the resulting ratio and performing minimum phase deconvolution to remove the time derivative divided by the transfer function of minimum phase. The method may also include the steps of receiver ensemble deconvolution, statics correction, F-K filtering for noise, zero phase spiking deconvolution and model dephasing. The actual signal that the vibrator is sending into the ground is used in pre-processing. The vibrator motion is measured to provide a signal that is used to process the data. The data is divided by the actual measured motion in the frequency domain.

High fidelity vibratory source seismic method

In marine seismic exploration, measurements of reflectivity and water depth are made from seismograms produced by the firing of a seismic energy source towed by a marine vessel. The measurements are made by generating the auto-correlation coefficients of a window of the seismogram and combining these coefficients for different time lags. The time lag producing the minimum energy in the combined autocorrelation coefficients represents water depth. The reflectivity of the water bottom is obtained by generating an estimate of the reflectivity from the values of the auto-correlation function of the window, and modifying this estimate by a factor which converts the estimate to the reflectivity. The measured water depth and reflectivity are converted into an inverse operator. A linear array of sources is then fired in a sequence such that the acoustic pulses combine to produce a resultant acoustic pressure wave having the inverse time domain operator characteristics.

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Dallas, TX, United States of America

Kenneth Paul Allen