Simultaneous sourcing during both seismic acquisition and seismic inversion

Patent metadata

Field	Value
Publication number	US-9772413-B2
Application number	US-201414329431-A
Country	US
Kind code	B2
Filing date	Jul 11, 2014
Priority date	Aug 23, 2013
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

Method for acquiring, at reduced acquisition cost, seismic data using simultaneous, field-encoded sources in the field ( 702 ), and then constructing pseudo source-records ( 703 ) that better meet the requirements for using additional simultaneous computer-encoded sourcing for computer simulations or forward modeling ( 706 ) as part of ( 707 ) iterative FWI (Full Wavefield Inversion) or RTM (Reverse Time Migration), with additional reduction in computational costs. By better meeting the requirements of simultaneous sourcing for FWI or RTM ( 701 ), artifacts and crosstalk are reduced in the output. The method can be used for marine streamer acquisition and other non-fixed spread geometries to acquire both positive and negative offsets and to mitigate the “missing data” problem for simultaneous-source FWI. It can also be used for land data to overcome issues with moving spreads and long continuous records.

First claim

The invention claimed is:

1. method for inferring a subsurface model of velocity or other physical property, comprising:
obtaining seismic data acquired in a survey by advancing a front source and a trailing rear source along a source line with a non-fixed spread of receivers, and activating each source at selected intervals along the source line, wherein every activation location for the rear source falls on a previous activation location for the front source, and wherein a selected field encoding is used for all source shots with the field encoding for the rear source always being the same as was previously applied to the front source at the same activation location, resulting in a series of shot records each simultaneously recording both sources but with each shot recorded by less than a full spread of receivers; and
processing the shot records by steps comprising:
(i) constructing from the shot records a plurality of pseudo super-shot records, constructed such that each has data from a full spread of receivers;
(ii) encoding each pseudo super-shot record and stacking to form a simultaneous-source record of measured data;
(iii) using a computer to simulate the simultaneous-source record of measured data, using the same encoding used in (ii) and also the field encoding, and using an assumed subsurface model of velocity or other physical property;
(iv) comparing the simulated simultaneous-source record with the simultaneous-source record of measured data, determining from that an adjustment to the subsurface model of velocity or other physical property; and making the adjustment to the subsurface model of velocity or other physical property to generate a final model; and
(v) displaying, with a computer, an image generated from the final model that includes subsurface structures.

2. The method of claim 1 , wherein the acquired survey data include at least one additional, simultaneously acquired, parallel source line, wherein each source line has a front source and a trailing rear source with matching source activation locations for all source lines, wherein every activation location for a rear source on any source line falls on a previous activation location for the front source on that source line, and wherein a selected field encoding is used for all source shots with the field encoding for each rear source always being the same as was previously applied to its corresponding front source at the same activation location.

3. The method of claim 1 , wherein the front source and rear source are separated by a fixed distance d that subdivides into an integer number N of shot intervals, such shot intervals being the nominal or average shot interval for the acquisition geometry. The actual shot intervals may randomly vary around this nominal value.

4. The method of claim 3 , wherein N +1 pseudo-shot records are constructed in (i), each of fixed duration and spatial extent, the duration being greater than or equal to a listening time used in the survey and, in addition, is a minimum time for source shot vibrations to be reduced to a predetermined level; and the spatial extent being greater than or equal to a maximum receiver offset distance used in the survey and, in addition, is a minimum distance over which source amplitude is reduced to a predetermined level.

5. The method of claim 4 , wherein (i)-(iii) are repeated a plurality of times using other shot records from other shot locations along the source line, and then (iv) is performed using results from all repetitions of (i)-(iii).

6. The method of claim 5 , wherein all data acquired along the source line are included in at least one pseudo super-shot record.

7. The method of claim 1 , further comprising taking the final model from (iv) and repeating steps (i)-(iv) using different computer encoding in (ii).

8. The method of claim 1 , wherein the field encoding comprises one or more of random time shifts, random source positions, phase rotations, and different sweep functions.

9. The method of claim 1 , wherein the constructing in (i) comprises using one or more of windowing, time shifting, padding time or traces, and appending.

10. The method of claim 1 , wherein the seismic survey comprises:
a marine survey in which a moving vessel tows one or more sources and one or more streamers of receivers; or
a land or ocean bottom survey that involves a rolling spread of receivers as the survey progresses along a survey line.

11. A method of acquiring seismic survey data, comprising: performing the following along a source line, or along each of two or more parallel source lines:
(a) activating a front source with a selected field encoding at a location along the source line with a first partial spread of receivers;
(b) activating a rear source, identical to the front source, duplicating the field encoding in (a), at the same location along the source line with a second partial spread of receivers, wherein the first partial spread and the second partial spread, when combined, make a full spread of receivers for the location along the source line;
(c) repeating (a) and (b) for one or more additional locations along the source line or lines.

12. The method of claim 11 , wherein the field encoding comprises one or more of random time shifts, random source positions, phase rotations, and different sweep functions.

13. The method of claim 11 , wherein the seismic survey comprises:
a marine survey in which a moving vessel tows one or more sources and one or more streamers of receivers; or
a land or ocean bottom survey that involves a rolling spread of receivers as the survey progresses along a survey line.

14. A method for conducting a seismic survey with a plurality of simultaneous sources and a non-fixed spread of receivers, and inferring a subsurface model of velocity or other physical property, comprising:
(a) activating two or more sources with a selected field encoding applied to each source at a location along a source line with a first partial spread of receivers;
(b) activating the two or more sources, or identical sources, duplicating the field encoding in (a), at the same location along the source line with a second partial spread of receivers, wherein the first partial spread and the second partial spread, when combined, make a full spread of receivers for the location along the source line;
(c) repeating (a) and (b) for one or more additional locations along the source line;

then processing records of seismic data recorded by the receivers from the activations in (a)-(c) with steps comprising:
(d) constructing from the shot records a plurality of pseudo super-shot records, constructed to be of the same duration and spatial extent, and such that each has data from a full spread of receiver locations;
(e) computer encoding each pseudo super-shot record and summing to form a single simultaneous-source record of measured data;
(f) using a computer and a subsurface model of velocity or other physical property, simulating with one forward modeling operation a simultaneous-source record of synthetic data to predict the simultaneous source record of measured data;
(g) comparing the simultaneous source record of measured data to the simulated simultaneous source record, determining a misfit, and using the misfit to adjust the subsurface model to generate a final model; and
(v) displaying, with a computer, an image generated from the final model that includes subsurface structures.

15. The method of claim 14 , further comprising taking the final model from (g) and repeating steps (e)-(g) using a different computer encoding in (e).

16.

Assignees

• Krohn Christine E
• Routh Partha S
• Exxonmobil Upstream Res Co

Inventors

• Krohn Christine E
• Routh Partha S

Classifications

• G01V1/3808

  Seismic data acquisition, e.g. survey design · CPC title

• G01V2210/6222

  Velocity; travel time · CPC title

• G01V2210/1423

  Sea · CPC title

• G01V1/303

  for determining velocity profiles or travel times · CPC title

• G01V1/003 Primary

  Seismic data acquisition in general, e.g. survey design (G01V1/3808, G01V1/42 take precedence) · CPC title