Method of seismic surveying

• US 7,050,356 B2
• Filed: 03/31/2003
• Issued: 05/23/2006
• Est. Priority Date: 04/06/2002
• Status: Expired due to Fees

• Current Assignee: WesternGeco LLC
• Original Assignee: WesternGeco LLC
• Inventors: Jeffryes, Benjamin Peter
• Primary Examiner(s): Keith, Jack
• Assistant Examiner(s): Hughes, Scott A.
• Application Number:
  US10/403,135
• Publication Number:
  US 20030210609A1
• Time in Patent Office: 1,149 Days
• Field of Search: 367/14, 367/23, 367 39- 41
• US Class Current: 367/41
• CPC Class Codes: G01V 1/005 with exploration systems emitting special signals, e.g. frequency swept signals, pulse sequences or slip sweep arrangements

Abstract

A method of seismic surveying comprising the steps of actuating the or each vibrator in a first vibrator group at time T0, and subsequently actuating the or each vibrator in a second vibrator group at time T1 that satisfies T0<T1<T0+S1+L where S1 is the sweep time of the first vibrator group and L is the listening time. At least one of the first vibrator group and the second vibrator group comprises at least two vibrators. The first group and the second group of vibrators may be the same group, or they may be different groups. This method enables the time required to complete a seismic survey to be reduced compared to the prior art “simultaneous shooting” and “slip-sweep shooting” techniques.

In a case where the first group and the second group of vibrators are different, the method may further comprise actuating the or each vibrator in the first vibrator group at time T2, where T1<T2<T1+S2+L and S2 is the sweep time of the first vibrator group, and then actuating the or each vibrator in the second vibrator group at time T3 where T2<T3<T2+S1+L and where T3−T2≠T1−T0. The varying time delay between a shot of the first vibrator group and the corresponding shot of the second vibrator group means that harmonic noise will occur at different times in the shot records so that the noise may be eliminated by appropriately combining the shot records.

Claims

1. A method of seismic surveying comprising the steps of:

actuating the or each vibrator in a first vibrator group at time T0; and

actuating the or each vibrator in a second vibrator group at time T1, where T0<

T1<

T0+S1+L where S1 is the sweep time of the first vibrator group and L is the listening time and wherein T1−

T0<

(n−

1) S1 f₀/n(f₁−

f₀), where n is a natural number, f₀ is the lower frequency limit of the vibrator sweep and f₁ is the upper frequency limit of the vibrator sweep;

wherein at least one of the first vibrator group and the second vibrator group comprises at least two vibrators.

2. A method as claimed in claim 1 wherein the second vibrator group is the first vibrator group.

3. A method of seismic surveying as claimed in claim 1, further comprising the step of actuating the or each vibrator group at least as many times as there are vibrators in the respective group and such that the contribution from each vibrator in a group may be determined by algebraic operation on receiver records of sweeps made by the respective group.

4. A method as claimed in claim 1, comprising the further step of actuating the or each vibrator in a third vibrator group at time T2, where T1<

T2<

T1+S2+L where S2 is the sweep time of the second vibrator group.

5. A method as claimed in claim 1, further comprising estimating from the acquired data the noise in the acquired data owing to the m^th harmonic, where m≦

n.

6. A method as claimed in claim 1, further comprising the steps of

actuating the or each vibrator in the first vibrator group at time T2, where T1<

T2<

T1+S2+L where S2 is the sweep time of the second vibrator group; and

actuating the or each vibrator in the second vibrator group at time T3 where T2<

T3<

T2+S1+L;

wherein the first vibrator group is different from the second vibrator group; and

wherein T3−

T2≠

T1−

T0.

7. A method as claimed in claim 6 wherein the j^th vibrator group contains N_j vibrators and is actuated N_j+1 times.

8. A method of seismic surveying comprising the steps of:

actuating a first vibrator at time T0;

actuating a second vibrator different from the first vibrator at time T1, where T0<

T1<

T0+S1+L where S1 is the sweep time of the first vibrator and L is the listening time;

actuating the first vibrator at time T2, where T1<

T2<

T1+S2+L where S2 is the sweep time of the second vibrator; and

actuating the second vibrator at time T3 where T2<

T3<

T2+S1+L and where T3−

T2≠

T1−

T0.

9. A method as claimed in claim 8 wherein T3−

T2>

T1−

T0.

10. A seismic surveying arrangement comprising:

a plurality of vibrators; and

a control means adapted to actuate the or each vibrator in a first vibrator group at time T0 and to actuate the or each vibrator in a second vibrator group at time T1, where T0<

T1<

T0+Si+L where S1 is the sweep time of the first vibrator group and L is the listening time and adapted to actuate the first and second groups of vibrators such that T1−

T0>

(n−

1) S1 f₀/n (f₁−

f₀), where n is a natural number, f₀ is the lower frequency limit of the vibrator sweep and f₁ is the upper frequency limit of the vibrator sweep.

11. A seismic surveying arrangement as claimed in claim 10 wherein the control means is adapted to actuate the or each vibrator group at least as many times as there are vibrators in the respective group and such that the contribution from each vibrator in a group may be determined by algebraic operation on receiver records of sweeps made by the respective group.

12. A seismic surveying arrangement as claimed in claim 10 or 11 wherein the first vibrator group is different from the second vibrator group;

and wherein the control means is further adapted to actuate the or each vibrator in the first vibrator group at time T2, where T1<

T2<

T1+S2+L where S2 is the sweep time of the second vibrator group and to actuate the or each vibrator in the second vibrator group at time T3 where T2<

T3<

T2+S1+L and where T3−

T2≠

T1−

T0.

13. A seismic surveying arrangement as claimed in claim 10, further comprising a processor for estimating from acquired data noise in the acquired data owing to the m^th harmonic, where m≦

n.

14. A seismic surveying arrangement comprising:

a plurality of vibrators; and

a control means adapted to;

a) actuate a first vibrator at time T0;

b) actuate a second vibrator different from the first vibrator at time T1, where T0<

T1<

T0+S1+L where S1 is the sweep time of the first vibrator and L is the listening time;

c) actuate the first vibrator at time T2, where T1<

T2<

T1+S2+L where S2 is the sweep time of the second vibrator; and

d) actuate the second vibrator at time T3 where T2<

T3<

T2+S1+L and where T3−

T2≠

T1−

T0.

15. A seismic surveying arrangement as claimed in claim 14 and adapted to actuate the second vibrator group at time T3 where T3−

T2>

T1−

T0.

16. A seismic surveying arrangement as claimed in claim 14 wherein the control means comprises a programmable data processor.

17. A storage medium containing a program for the data processor of a seismic surveying arrangement as defined in claim 16.