Method of three dimensional seismic prospecting

• US 4,159,463 A
• Filed: 10/21/1977
• Issued: 06/26/1979
• Est. Priority Date: 10/18/1973
• Status: Expired due to Term

• Current Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Original Assignee: Daniel Silverman
• Inventors: Silverman, Daniel
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US05/844,355
• Time in Patent Office: 613 Days
• Field of Search: 340/15.5 CC, 340/15.5 CP
• US Class Current: 367/59
• CPC Class Codes: G01V 1/04 Details
• CPC Class Codes: G01V 1/375 Correlating received seismic signals with the emitted source signal
• CPC Class Codes: G01V 2210/127 Cooperating multiple sources

Abstract

A method of seismic prospecting involving at least a first and second spaced apart vibratory sources, cotemporaneously vibrating with the same or different reference signals, and recording into a common geophone at a point distant from both sources. The method involves recording at least two records, one record includes the first vibrator V1 responsive to a first reference signal R1 and the second vibrator V2 responsive to a second reference signal R2. In the second record the second vibrator repeats the reference signal R2, while the first vibrator is responsive to the first reference signal R1, but in opposite phase, -R1. When the two received records are added, the components due to the first vibrator are in opposite phase or polarity, and cancel, leaving only the part due to the second vibrator. When the two records are subtracted, the part due to the second vibrator cancels, and all that remains is the part due to the first vibrator.

Claims

1. A method of seismic prospecting in which a plurality of seismic vibratory sources, at a plurality of spaced source points, cotemporaneously radiate seismic signals into the earth, each source responsive to an individual reference signal;

the seismic signals which travel by different paths and are received at a receiver and form a single composite received signal, comprising the steps of;

(a) repeating said radiations from said spaced sources a plurality of times, each source using its same reference signal on each repetition and forming a plurality of composite received signals;

each composite received signal including a component from each of said sources;

(b) on each repetition of said sources coding the transmission from none, or some, but not all of said sources, in a selected first manner;

(c) making at least one selected stack of said plurality of composite received signals, with none, or some, but not all of the individual composite received signals in said at least one stack being coded in a second manner, related to said first manner;

whereby the result of said at least one stack is the summation of the repeated transmission components from a selected one of said plurality of spaced sources.

2. The method as in claim 1 in which said coding in said first manner involves inverting the polarity of at least one of said individual reference signals on a selected basis;

and said coding in a second manner involves inverting the polarity of at least one selected composite received signal in said stack, in a selected manner.

3. The method as in claim 1 including the step of making as many selected stacks with corresponding selected coding, as there are spaced sources and source points;

whereby the contribution received signal from each source point to said composite signal can be determined.

20. The method as in claim 1;

and wherein

(d) there are two spaced apart source points P1, P2;

(e) there are two cotemporaneous reference signals R1, R2;

(f) there are two vibratory sources V1, V2;

(g) there are at least a first and a second raidation from both sources, which provide a first and a second composite received signal;

(h) on the first radiation coding only first source V1 by reversing the polarity of reference signal R1;

(i) On the second radiation coding neither of the sources.

21. The method as in claim 1;

and wherein

(d) there are three source spaced points P1, P2, P3;

(e) there are three cotemporaneous reference signals R1, R2, R3;

(f) there are three vibratory sources V1, V2, V3;

(g) there are at least four successive radiations;

space="preserve" listing-type="tabular">______________________________________ (h) ______________________________________ on the first V1(Direct) V2(Direct) V3(Direct) radiation on the second V1(Direct) -V2(Inverted) V3(Direct) radiation on the third V1(Direct) V2(Direct) -V3(Inverted) radiation on the fourth V1(Direct) -V2(Inverted) -V3(Inverted) radiation (i) ______________________________________ the first stack is;

S1 + S2 + S3 + S4;

the second stack is;

S1 - S2 + S3 - S4;

the third stack is;

S1 + S2 - S3 - S4. ______________________________________

22. The method as in claim 1;

and wherein

(d) there are four spaced apart source points P1, P2, P3, P4;

(e) there are four cotemporaneous reference signals R1, R2, R3, R4;

(f) there are four vibratory sources V1, V2, V3, V4;

(g) there are at least eight successive radiations;

space="preserve" listing-type="tabular">______________________________________ (h) ______________________________________ on the first radiation +V1 +V2 +V3 +V4 ;

on the second radiation +V1 -V2 +V3 +V4 ;

on the third radiation +V1 +V2 -V3 +V4 ;

on the fourth radiation +V1 -V2 -V3 +V4 ;

on the fifth radiation +V1 +V2 +V3 -V4 ;

on the sixth radiation +V1 -V2 +V3 -V4 ;

on the seventh radiation +V1 +V2 -V3 -V4 ;

on the eighth radiation +V1 -V2 -V3 -V4 ;

______________________________________ (i) ______________________________________ the first stack is;

S1 + S2 + S3 + S4 + S5 + S6 + S7 + S8 ;

the second stack is;

S1 - S2 + S3 - S4 + S5 - S6 + S7 - S8 ;

the third stack is;

S1 + S2 - S3 - S4 + S5 + S6 - S7 - S8 ;

the fourth stack is;

S1 + S2 + S3 + S4 - S5 - S6 - S7 - S8 ______________________________________ .

4. The method of seismic prospecting comprising;

(a) providing a first selected reference signal R1(t) fora vibratory source, of selected time duration D1;

(b) inverting the polarity of said reference signal during a selected portion of said duration D1 to form a first modified reference signal R1(t);

(c) radiating a first seismic signal into the earth responsive to said first modified reference signal, R1(t) at a first point on the earth;

(d) receiving the seismic signal radiated at said first point, at a second point distant from said first point, to provide a first received signal; and

(e) correlating said first received signal with said modified first reference signal R1(t).

5. The method as in claim 4 in which said selected portion of said duration D1 is D1/2.

6. The method as in claim 5 in which said selected portion of said duration D1 comprises a plurality of spaced time segments;

whereby the sum of the plurality of spaced time segments when said reference signal is inverted equals the sum of the time segments when said reference signal is not inverted.

10. The method as in claim 4 in which said modification comprises 4 equal time segments, with alternate segments of direct and inverted polarity.

11. The method as in claim 4 in which said modification comprises 2 equal segments, one of said segments direct, and the other of inverted polarity.

7. The method of seismic prospecting comprising;

(a) providing a first selected reference signal R1(t) for a vibratory seismic source, of selected time duration D1;

(b) inverting the polarity of said reference signal during a selected portion of said duration D1 to form a first modified reference signal R1(t);

(c) radiating a first seismic signal into the earth responsive to said first modified reference signal, R1(t) at a first point on the earth;

(d) radiating a second seismic signal of time duration D2 into the earth responsive to a second reference signal R2(t) co-temporaneously with said first seismic signal, at a second point on the earth spaced from said first point;

(e) receiving the seismic signals radiated at said first and second points, at a third point distant from said first and second points, to provide a first composite received signal, which includes components of both said first and second seismic signals; and

(f) correlating said first composite received signal separately both with said modified first reference signal R1(t), and

with said second reference signal, R2(t).

8. The method as in claim 7 in which said first and second reference signals are the same.

9. The method as in claim 7 in which said first and second reference signals are different.

12. In the method of seismic prospecting in which at least a first and a second seismic source cotemporaneously radiate into the earth, first and second vibratory seismic signals responsive respectively to a first and to a second reference signal, at first and second spaced-apart points, respectively, which seismic signals are received at a third point spaced from said first and second points, to form a composite received signal, the method of separating from said composite received signal one of said first and second seismic signals comprising;

(a) coding in a first selected manner said first reference signal prior to said radiation;

(b) coding said composite received signal in a second selected manner related to said first selected manner, to provide a first coded composite received signal;

(c) repeating the transmissions from said first and second sources, without coding either of said sources; and

(d) producing a second uncoded composite received signal.

14. The method as in claim 12 in which said selected stack comprises;

adding said coded first composite received signal, and said uncoded second composite signal;

whereby the sum will be a function substantially of the seismic signal from said first source.

15. The method as in claim 12 in which said selected stack comprises;

subtracting from said uncoded second composite signal, said first coded composite signal;

whereby the remainder will be a function substantially of the seismic signal from said second source.

16. The method as in claim 12 in which said two sources have the same starting time and same time duration.

17. The method as in claim 12 in which said two sources have different starting times but overlap in time duration.

18. The method as in claim 12 in which said first and second reference signals are the same.

19. The method as in claim 12 in which said first and second reference signals are different.

13. The method of seismic prospecting comprising

(a) generating a first train of time-spaced unidirectional electrical pulses of continually changing time interval between adjacent pulses;

(b) inverting alternate pulses of said train to provide a second train of alternately reversing electrical pulses;

(c) responsive to said second train, applying to the earth a corresponding train of alternately reversing forces at a first point on the earth; and

(d) detecting the seismic waves generated by said train of alternately reversing forces after passing through the earth, at a second point distant from said first point.