Simultaneous Source Inversion for Marine Streamer Data With Cross-Correlation Objective Function

• US 20120143506A1
• Filed: 09/01/2011
• Published: 06/07/2012
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: Anatoly Baumstein, Jerome R. Krebs, Partha S. Routh, Spyridon Lazaratos
• Original Assignee: Anatoly Baumstein, Jerome R. Krebs, Partha S. Routh, Spyridon Lazaratos
• Inventors: Routh, Partha S., Krebs, Jerome R., Lazaratos, Spyridon, Baumstein, Anatoly
• Granted Patent: US 8,688,381 B2
• Time in Patent Office: Days
• US Class Current: 702/2
• CPC Class Codes: G01V 1/005 with exploration systems emitting special signals, e.g. frequency swept signals, pulse sequences or slip sweep arrangements
• CPC Class Codes: G01V 1/282 Application of seismic models, synthetic seismograms
• CPC Class Codes: G01V 1/303 for determining velocity profiles or travel times
• CPC Class Codes: G01V 1/38 specially adapted for water-covered areas G01V1/28 takes precedence
• CPC Class Codes: G01V 2210/614 Synthetically generated data
• CPC Class Codes: G16Z 99/00 Subject matter not provided for in other main groups of this subclass

Abstract

Method for simultaneous full-wavefield inversion of gathers of source (or receiver) encoded (30) geophysical data (80) to determine a physical properties model (20) for a subsurface region, especially suitable for surveys where fixed-receiver geometry conditions were not satisfied in the data acquisition (40). The inversion involves optimization of a cross-correlation objective function (100).

Claims

1. A computer-implemented method for simultaneous encoded-source inversion of measured geophysical data, acquired under conditions where the fixed-receiver assumption of simultaneous encoded-source inversion is not valid, to determine a physical properties model for a subsurface region, comprising the following steps wherein all summing, simulating, computing, and updating are performed on a computer that is programmed to perform them:

(a) obtaining a group of two or more encoded gathers of the measured geophysical data acquired under conditions where the fixed-receiver assumption is not valid, wherein each gather is associated with a single generalized source, or alternatively with a single receiver, and wherein each gather is encoded with a different encoding function selected from a set of non-equivalent encoding functions;

(b) summing the encoded gathers in the group by summing all, or selected, data records in each gather that correspond to a single receiver or alternatively to a single source, and repeating for each different receiver or alternatively for each different source, resulting in a simultaneous encoded gather;

(c) assuming a physical properties model of the subsurface region, said model providing values of at least one physical property at locations throughout the subsurface region;

(d) simulating a synthetic simultaneous encoded gather of data, using the assumed physical properties model, wherein the simulation uses encoded source signatures, and wherein an entire simultaneous encoded gather is simulated in a single simulation operation;

(e) computing an objective function measuring cross-correlation between the simultaneous encoded gather of measured data and the simulated simultaneous encoded gather;

(f) updating the physical properties model by optimizing the objective function;

(g) iterating steps (a)-(f) at least one more time using the updated physical properties model from the previous iteration as the assumed physical properties model in step (c), resulting in a further updated physical properties model; and

(h) downloading, displaying, or saving the further updated physical properties model to computer storage.

2. The method of claim 1, wherein the objective function is given by or is mathematically equivalent to:

3. The method of claim 2, further comprising approximating the objective function by:

4. The method of claim 1, wherein the encoding function used on a gather in step (a) is changed in at least one of the iterations.

5. The method of claim 4, wherein two or more sets of encoding functions are used at each iteration and are designed to obtain an average gradient of the objective function.

6. The method of claim 1, wherein all encoding functions are changed in every iteration.

7. The method of claim 1, further comprising obtaining at least one additional group of two or more encoded gathers of the measured geophysical data as in step (a), and performing step (b) for each additional group, then accumulating the corresponding computed objective functions from step (e), wherein the updating of the physical properties model in step (f) is determined by maximizing the accumulated computed objective functions.

8. The method of claim 1, wherein said encoded gathers of measured data are encoded by temporally convolving all traces from the gather with the encoding function selected for the gather.

9. The method of claim 1, wherein the two or more encoded gathers of measured data are obtained by obtaining gathers of data from a geophysical survey in which data are acquired from a plurality of simultaneously operating, uniquely encoded source devices.

10. The method of claim 1, wherein the measured geophysical data are from a seismic survey of the subsurface region.

11. The method of claim 10, wherein the generalized seismic sources are either all point sources or all plane-wave sources.

12. The method of claim 1, wherein the encoded source signatures used in the synthetic simultaneous encoded gather simulation either use the same encoding functions used to encode the simultaneous encoded gather of measured data or are functions made by temporally convolving measured or estimated source signatures with the same encoding functions used to encode the corresponding measured gather in step (a), wherein the measured geophysical data include measured or estimated source signatures of each source activation.

13. The method of claim 8, wherein the encoding functions are of a type selected from a group consisting of linear, random phase, chirp, modified chirp, random time shift, and frequency independent phase encoding.

14. The method of claim 8, wherein the encoding functions are of one type for some sources and of another type for other sources.

15. The method of claim 1, wherein the encoding functions are optimized to improve quality of the objective function.

16. The method of claim 1, wherein the simulating in step (d) is performed with a finite difference, finite element or finite volume simulation code.

17. The method of claim 10, wherein the physical property model is a model of seismic wave velocity, seismic elastic parameters, seismic anisotropy parameters or seismic anelasticity parameters.

18. The method of claim 1, wherein a global objective function optimization method selected from a group consisting of Monte Carlo, simulated annealing, genetic or evolution algorithm is used to update the model.

19. The method of claim 1, wherein a local objective function optimization method selected from a group consisting of gradient line search, conjugate gradients or Newton'"'"'s method is used to update the model.

20. The method of claim 1, wherein maximizing the objective function comprises computing a gradient of the objective function with respect to parameters of the physical properties model.

25. The method of claim 1, wherein the encoding is performed by multiplying each gather and each source signature by a selected encoding function, and wherein in each iteration of step (g) one or more encoding functions are set equal to zero such that the data records not zeroed correspond to source activation locations that are more separated, on average, than in the measured geophysical data before encoding, with all data records being used, i.e. not being zeroed, as the iterations progress.

26. The method of claim 25, wherein the encoding functions are used to randomly choose the shots in each iteration that will result in increased shot spacing.

27. The method of claim 1, wherein the measured geophysical data being inverted are full-wavefield seismic data.

21. A computer-implemented method for simultaneous encoded-source inversion of measured geophysical data, acquired under conditions where the fixed-receiver assumption of simultaneous encoded-source inversion is not valid, to determine a physical properties model for a subsurface region, comprising:

(a) obtaining measured geophysical data from a geophysical survey of the subsurface region in which the fixed-receiver assumption was not valid;

(b) using a programmed computer to invert the measured data by iterative inversion comprising using an assumed or updated physical properties model to simultaneously simulate survey data representing a plurality of survey sources, or alternatively a plurality of receivers, wherein source or receiver signatures in the simulation are encoded, resulting in a simulated simultaneous encoded gather of geophysical data, the inversion further comprising determining a model update for a next iteration by optimizing an objective function measuring cross-correlation between the simulated simultaneous encoded gather and a corresponding simultaneously encoded gather of the measured geophysical data; and

(c) downloading or displaying an updated physical properties model or saving it to computer memory or data storage.

22. The method of claim 21, wherein some or all of the geophysical data are partitioned into a plurality of data groups in a way that increases separation between source activation locations for within each data group as compared to the some or all of the geophysical data before partitioning, and the simulated simultaneous encoded gather for each iteration corresponds to a different data group with all groups being used in the course of the iterations.

23. A computer program product, comprising a non-transitory computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement a method for simultaneous encoded-source inversion of measured geophysical data, acquired under conditions where the fixed-receiver assumption of simultaneous encoded-source inversion is not valid, to determine a physical properties model for a subsurface region, said method comprising:

(a) inputting a group of two or more encoded gathers of the measured geophysical data, wherein each gather is associated with a single generalized source, or alternatively with a single receiver, and wherein each gather is encoded with a different encoding function selected from a set of non-equivalent encoding functions;

(b) summing the encoded gathers in the group by summing all data records in each gather that correspond to a single receiver or alternatively to a single source, and repeating for each different receiver or alternatively for each different source, resulting in a simultaneous encoded gather;

(c) inputting a physical properties model of the subsurface region, said model providing values of at least one physical property at locations throughout the subsurface region;

(d) simulating a synthetic simultaneous encoded gather of data, using the assumed physical properties model, wherein the simulation uses encoded source signatures, and wherein an entire simultaneous encoded gather is simulated in a single simulation operation;

(e) computing an objective function measuring cross-correlation between between the simultaneous encoded gather of measured data and the simulated simultaneous encoded gather;

(f) updating the physical properties model by optimizing the objective function; and

(g) iterating steps (a)-(f) at least one more time using the updated physical properties model from the previous iteration as the assumed physical properties model in step (c), resulting in a further updated physical properties model.

24. A method for producing hydrocarbons from a subsurface region, comprising:

(a) performing a seismic survey of the subsurface region, wherein the fixed-receiver assumption of simultaneous encoded-source inversion is not satisfied;

(b) obtaining a velocity model of the subsurface region determined by a method comprising;

inverting the survey'"'"'s measured data by iterative inversion comprising using an assumed or updated velocity model to simultaneously simulate survey data representing a plurality of survey sources, or alternatively a plurality of receivers, wherein source or receiver signatures in the simulation are encoded, resulting in a simulated simultaneous encoded gather of geophysical data, the inversion further comprising determining a velocity model update for a next iteration by optimizing an objective function measuring cross-correlation between the simulated simultaneous encoded gather and a corresponding simultaneously encoded gather of the measured data;

(c) drilling a well into a layer in the subsurface region identified at least partly from an interpretation of structure in the subsurface region made using an updated velocity model from (b); and

(d) producing hydrocarbons from the well.