Coding seismic sources
AssigneeTexaco Inc.
InventorWilliam S. Currie
Life of this patent
Estimating the term…
Abstract
One or more seismic sources impart seismic pulses into the earth in a coded sequence. The coded sequence is composed of a minimum of three cycles of a Galois sequence of order N, where N is a positive integer. The response of subsurface formations to the coded sequence is obtained and correlated with one cycle or the outgoing Galois sequence of the same order. Correlation properties of the Galois sequences provide a way to sum a large number of seismograms that are superimposed in time, improving the signal to noise ratio while keeping the field time in which the seismograms are obtained to a minimum. Using this encoding technique, responses of subsurface formations to concurrent activation of each of several sources can be obtained and separated from each other.
Claims32
A method of seismic exploration with a coded sequence of impulses of finite time duration for correlation with a deconvolution operator to form a reflection wavelet which avoids end effects resulting from correlation, comprising the steps of:
- (a) activating a seismic source to emit impulses of at least three cycles of a Galois sequence of finite time duration and of order N,N being a positive integer greater than one;
- (b) sensing the response of subsurface formations to the emitted cycles of impulses at a seismic detector;
- (c) correlating the sensed response of the subsurface formations with a cycle of the Galois sequence to form at least three cycles of a correlation product, the first and last cycles containing end effects due to the finite time duration of the coded sequence of impulses;
- (d) discarding the first and last cycles of the correlation product containing the end effects;
- and
- (e) forming a record of the result of said steps of correlating and discarding.
A method of seismic exploration with a coded sequence of impulses of finite time duration for correlation with a deconvolution operator to form a reflection wavelet which avoids end effects resulting from correlation, comprising the steps of:
- (a) activating a seismic source to emit impulses of a cycle of finite time duration and of a Galois sequence of order N,N being a positive integer greater than one;
- (b) sensing the response of subsurface formations to the emitted cycle of impulses at a seismic detector;
- (c) correlating the sensed response of the subsurface formations with a cycle of the Galois sequence to form at least three cycles of a correlation product, the first and last cycles containing end effects due to the finite time duration of the coded sequence of impulses;
- (d) discarding the first and last cycles of the correlation product containing the end effect;
- and
- (e) forming a record of the result of said steps of correlating and discarding.
Dependencies are inferred from the claim text.