Method and apparatus for determination of optimum velocity in processing seismic signals from low energy sources

Claim 2

In a seismic prospecting system for generating seismic waves in the earth, having: a low energy seismic source; a plurality of geophones at spaced positionsdistant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising: (a) operating said source in CDP format, whereby each source operation is at a different spaced-apart independent position, (b) amplifying and digitizing to one bit a plurality of geophone signals which comprise a plurality of traces, in each of a plurality of records from a plurality of source points; (c) CDP stacking said 1 bit digitized signals; and wherein (d) the CDP fold is at least 40; and wherein the process of determining the optimum velocity for said CDP stack includes the steps of: (e) making a first CDP gather of a plurality of traces, centered about a first CDP point; (f) selecting at least a first seismic velocity as a function of depth; (g) applying normal movement, using a first selected velocity function, to said traces in said first gather; (h) stacking said NMO corrected traces and digitizing to 1 bit to form a first 1 bit stacked first CDP trace; (i) repeating steps (c) to (f) at at least one pair of spaced CD points to obtain at least one pair of first 1 bit stacked CDP traces, corresponding to said first velocity; and (j) determining the coherence between said at least one pair of first 1 bit stacked CDP traces corresponding to said first velocity.

Claim 3

The method as in claim 1 including the additional step of: (k) repeating steps (f) to (j) to obtain at least one pair of spaced CD Points, the coherence between at least one pair of second 1 bit stacked CDP traces corresponding to a second velocity, which is different in a first selected way from said first velocity.

Claim 4

The method as in claim 2 including the additional step of: (i) comparing the coherence values obtained for said pair of first 1 bit stacked CDP traces and said pair of second 1 bit stacked CDP traces for said first and said second velocities.

Claim 5

The method as in claim 2 including the additional steps of: (m) obtaining the coherence values between a plurality of pairs of adjacent traces of a first 1bit stacked plurality of CDP traces; (h) obtaining the coherence values between a plurality of pairs of adjacent traces of a second 1 bit stacked plurality of CDP traces; and (o) comparing the coherence values between a plurality of selected pairs of CDP traces in said first stack with the same plurality of selected pairs in said second stack.

Claim 6

The method as in claim 1 in which said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises, correlating one of said pairs of traces with the other of said pair of traces.

Claim 7

The method as in claim 1 in which said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises; (a) determining the value of the sum of the two traces of said pair of traces, on the basis that, at each comparison point; ______________________________________ FIRST TRACE SECOND TRACE SUM ______________________________________ positive positive 1 positive negative 1 negative positive 1 negative negative 0; and ______________________________________ (b) determining the ratio of the total number of 1's to the total number of 0's.

Claim 8

The method as in claim 1 in which said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises; (a) setting a value of (+1) to each digitized 1 bit and a value of (-1) to each digitized 0 bit; and (b) algebraically adding the (+1) and (-1) values to all the digitized values, and dividing that number by the total number of (+1) and (-1) values.

Claim 9

The method as in claim 1 in which said seismic source is a vibratory source, driven by a variable frequency sweep signal, and in which said step (b) includes the substeps of; (b1) amplifying said geophone signals (b2) correlating said amplified geophone signals with said sweep signal to obtain correlated geophone signals; and (b3) digitizing to 1 bit said correlated geophone signals, to form a plurality of traces.

Claim 10

In a seismic prospecting system having; a vibratory source driven by a reference sweep signal, a plurality of geophones at spaced positions distant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising the steps of; (a) operating said source in CDP format, whereby each source operation is at a different spaced-apart independent position and operating said source at a number of spaced positions; (b) amplifying and digitizing said received signal to form 1 bit received signals; (c) digitizing said reference sweep signal; (d) correlating each digitized received signal with said digitized reference sweep signal to form multi-bit correlograms; (e) digitizing said correlograms to 1 bit; (f) CDP stacking said 1 bit digitized correlograms; and wherein (g) the CDP fold is at least 40 ; and wherein the process of determining the optimum velocity for said CDP stack includes the steps of; (h) making a first CDP gather at a first CD Point of said 1 bit digitized correlograms; (i) choosing a first seismic velocity, and applying normal moveout corrections to the traces of said first CDP gather, and stacking said NMO corrected traces and digitizing to 1 bit to provide a first 1 bit stacked first CDP trace; (j) repeating steps (h) and (i) with a second selected CD Point and said first velocity, and producing a first 1 bit stacked second CDP trace; and (k) determining the first coherence between said first and second CDP traces.

Claim 11

In a seismic prospecting system having; a vibratory source driven by a reference sweep signal, a plurality of geophones at spaced positions distant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising the steps of; (a) operating said source in CDP format, whereby each source operation is at a different spaced-apart independent position and operating said source at a number of spaced positions; (b) amplifying and digitizing said received signal to form 1 bit received signals; (c) digitizing said reference sweep signal; (d) correlating each digitized received signal with said digitized reference sweep signal to form multi-bit correlograms; (e) digitizing said correlograms to 1 bit; (f) CDP stacking said 1 bit digitized correlograms; and wherein (g) the CDP fold is at least 40 ; and wherein the process of determining the optimum velocity for said CDP stack includes the steps of; (h) making a first CDP gather at a first CD Point of said 1 bit digitized correlograms; (i) choosing a first seismic velocity, and applying normal moveout corrections to the traces of said first CDP gather, and stacking said NMO corrected traces and digitizing to 1 bit to provide a first 1 bit stacked first CDP trace; (j) repeating steps (h) and (i) with a second selected CD Point and said first velocity, and producing a first 1 bit stacked second CDP trace; and (k) determining the first coherence between said first and second CDP traces.

Claim 12

The method as in claim 9 including the additional steps of (i) repeating steps (h) and (j) for a second value of velocity applied to said first and second CDP traces, to obtain second 1 bit stacked first and second CDP traces, and determining the second coherence of these second CDP traces; and (m) comparing said first and second coherences.

Claim 13

In a seismic prospecting system for generating seismic waves in the earth, having: a seismic source a plurality of geophones at spaced positions distant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising: (a) operating said source in CDP format, by moving said source sequentially to spaced-apart independent positions, (b) amplifying and digitizing to one bit a plurality of geophone signals which comprise a plurality of traces, in each of a plurality of records from a plurality of source points; (c) making a first CDP gather of a pluralty of traces, centered about a first CDP point; (d) selecting at least a first seismic velocity as a function of depth; (e) applying normal moveout, using a first selected velocity function, to said traces in said first gather; (f) stacking said NMO corrected traces and digitizing to 1 bit to form a first 1 bit stacked first CDP trace; (g) repeating steps (c) to (f) at at least one pair of spaced CD Points to obtain at least one pair of first 1 bit stacked CDP traces, corresponding to said first velocity; and (h) determining the coherence between said at least one pair of first 1 bit stacked CDP traces corresponding to said first velocity; and wherein said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises; (i) determining the value of the sum of the two traces of said pair of traces, on the basis that, at each comparison point; ______________________________________ FIRST TRACE SECOND TRACE SUM ______________________________________ positive positive 1 positive negative 1 negative positive 1 negative negative 0; and ______________________________________ (j) determining the ratio of the total amount of 1's to the total number of 0's.

Claim 14

In a seismic prospecting system for generating seismic waves in the earth, having: a seismic source a plurality of geophones at spaced positions distant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising: (a) operating said source in CDP format, by moving said source sequentially to spaced-apart independent positions, (b) amplifying and digitizing to one bit a plurality of geophone signals which comprise a plurality of traces, in each of a plurality of records from a plurality of source points; (c) making a first CDP gather of a pluralty of traces, centered about a first CDP point; (d) selecting at least a first seismic velocity as a function of depth; (e) applying normal moveout, using a first selected velocity function, to said traces in said first gather; (f) stacking said NMO corrected traces and digitizing to 1 bit to form a first 1 bit stacked first CDP trace; (g) repeating steps (c) to (f) at at least one pair of spaced CD Points to obtain at least one pair of first 1 bit stacked CDP traces, corresponding to said first velocity; and (h) determining the coherence between said at least one pair of first 1 bit stacked CDP traces corresponding to said first velocity; and wherein said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises; (i) determining the value of the sum of the two traces of said pair of traces, on the basis that, at each comparison point; ______________________________________ FIRST TRACE SECOND TRACE SUM ______________________________________ positive positive 1 positive negative 1 negative positive 1 negative negative 0; and ______________________________________ (j) determining the ratio of the total amount of 1's to the total number of 0's.

Claim 15

In a seismic prospecting system for generating seismic waves in the earth, having: a seismic source a plurality of geophones at spaced positions distant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising: (a) operating said source in CDP format, by moving said source sequentially to spaced-apart independent positions, (b) amplifying and digitizing to one bit a plurality of geophone signals which comprise a plurality of traces, in each of a plurality of records from a plurality of source points; (c) making a first CDP gather of a plurality of traces, centered about a first CDP point; (d) selecting at least a first seismic velocity as a functiion of depth; (e) applying normal moveout, using a first selected velocity function, to said traces in said first gather; (f) stacking said NMO corrected traces and digitizing to 1 bit to form a first 1 bit stacked first CDP trace; (g) repeating steps (c) to (f) at at least one pair of spaced CD Points to obtain at least one pair of first 1 bit stacked CDP traces, corresponding to said first velocity; and (h) determining the coherence between said at least one pair of first 1 bit stacked CDP traces corresponding to said first velocity; and wherein said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises; (i) setting a value of (+1) to each digitized 1 bit and a value of (-1) to each digitized 0 bit; and (j) algebraically adding the (+1) and (-1) values to all the digitized values, and dividing that number by the total number of (+1) and (-1) values.

Claim 16

In a seismic prospecting system for generating seismic waves in the earth, having: a seismic source a plurality of geophones at spaced positions distant from said source; means to amplify and digitize the geophone signals; the method of operation and processing the seismic data comprising: (a) operating said source in CDP format, by moving said source sequentially to spaced-apart independent positions, (b) amplifying and digitizing to one bit a plurality of geophone signals which comprise a plurality of traces, in each of a plurality of records from a plurality of source points; (c) making a first CDP gather of a plurality of traces, centered about a first CDP point; (d) selecting at least a first seismic velocity as a functiion of depth; (e) applying normal moveout, using a first selected velocity function, to said traces in said first gather; (f) stacking said NMO corrected traces and digitizing to 1 bit to form a first 1 bit stacked first CDP trace; (g) repeating steps (c) to (f) at at least one pair of spaced CD Points to obtain at least one pair of first 1 bit stacked CDP traces, corresponding to said first velocity; and (h) determining the coherence between said at least one pair of first 1 bit stacked CDP traces corresponding to said first velocity; and wherein said step of determining the coherence between a selected pair of adjacent 1 bit stacked CDP traces comprises; (i) setting a value of (+1) to each digitized 1 bit and a value of (-1) to each digitized 0 bit; and (j) algebraically adding the (+1) and (-1) values to all the digitized values, and dividing that number by the total number of (+1) and (-1) values.