Orthogonal source and receiver encoding

Patent metadata

Field	Value
Publication number	US-10012745-B2
Application number	US-201313748121-A
Country	US
Kind code	B2
Filing date	Jan 23, 2013
Priority date	Mar 8, 2012
Publication date	Jul 3, 2018
Grant date	Jul 3, 2018

Abstract

Method for performing simultaneous encoded-source inversion of geophysical data to estimate parameters of a physical property model ( 41 ), especially adapted for surveys without fixed-receiver acquisition geometry, such as marine seismic surveys with moving source and receivers. The encoding functions ( 32 ) used on the sources to generate one or more simultaneous encoded-source gathers of data ( 35 ), as well as to simulate the same ( 34 ), are orthogonal or pseudo-orthogonal with respect to cross-correlation. In addition, receivers are also encoded, with the receiver encoding being designed to make a given receiver less sensitive to sources to which it was not listening during the survey ( 38 ). The encoding functions may be temporal bandpass filters differing one from another by central frequency, phase, or both. Efficiency of the method may be further improved by grouping several sources into a super-source, grouping the corresponding gathers into a super-gather, and then applying the above encoding strategy.

First claim

The invention claimed is:

1. A computer implemented method for iterative inversion of measured geophysical data to determine a physical properties model for a subsurface region, comprising:
acquiring the measured geophysical data with a source or group of sources and receivers,
using a computer to sum a plurality of encoded gathers of the measured geophysical data, each gather being associated with a single source or group of sources and encoded with a different encoding function selected from a set of encoding functions that are orthogonal or pseudo-orthogonal to each other with respect to cross-correlation, thereby forming a simultaneous encoded gather of measured geophysical data representing a plurality of sources,
then using an assumed physical properties model or an updated physical properties model from a prior iteration to simulate the simultaneous encoded gather of measured geophysical data,
then computing an objective function measuring misfit between the simultaneous encoded gather of measured geophysical data and the simulated simultaneous encoded gather, then optimizing the objective function to determine a model update to the assumed physical properties model and generate the physical properties model of the subsurface region, and
using the physical properties model of the subsurface region in prospecting for hydrocarbons within the subsurface region,
wherein the receivers are encoded to make computation of the objective function less sensitive to one or more of the plurality of sources, relative to at least one other of the plurality of sources, for a given receiver,
wherein the encoding of the receivers is performed using a different encoding function for each receiver, selected to be orthogonal or pseudo-orthogonal with respect to the encoding functions for sources to which the receiver did not listen when the measured geophysical data were measured,
wherein the encoding functions for the receivers and the sources are functions of frequency,
wherein the source or group of sources is encoded with a set of bandpass filters, differing from each other in central frequency, phase, or both, and
wherein the receivers are encoded with a set of notch filters, differing from each other in central frequency, phase, or both, and each of the notch filters is designed to notch out bandpass frequencies of the encoding functions corresponding to the source or group of sources for which that receiver was not active through a combination of corresponding ones of the bandpass filters and the notch filters.

2. The method of claim 1 , wherein the phase differences include polarity switches.

3. The method of claim 1 , wherein the simulated simultaneous encoded gather is simulated in a single simulation operation, wherein source signatures in the simulation are encoded using the same encoding used to encode corresponding gathers of the measured geophysical data.

4. The method of claim 1 , wherein the misfit is measured as a norm of a difference between the simultaneous encoded gather of measured geophysical data and the simulated simultaneous encoded gather or as a cross-correlation between the simultaneous encoded gather of measured geophysical data and the simulated simultaneous encoded gather.

5. The method of claim 1 , wherein the measured geophysical data are full wavefield data from a seismic survey.

6. The method of claim 1 , wherein in some or all of the iterations, different encoding functions are used compared to a preceding iteration.

7. The method of claim 1 , further comprising forming one or more additional simultaneous encoded gathers of measured geophysical data, wherein the model update is determined based on a sum of the objective functions corresponding to each simultaneous encoded gather.

8. The method of claim 1 , wherein computing the objective function comprises computing differences, called residuals, by receiver between the simultaneous encoded gather of measured geophysical data and the simulated simultaneous encoded gather, and applying the receiver encoding to each receiver residual, said receiver encoding being selected to attenuate contributions from sources for which the receiver was inactive, relative to contributions from sources for which the receiver was active, then computing the objective function from the receiver-encoded residuals.

9. A computer-implemented method for inversion of measured geophysical data to determine a physical properties model for a subsurface region, comprising:
(a) acquiring the measured geophysical data with a source or group of sources and receivers;
(b) obtaining a group of two or more gathers of the measured geophysical data,
wherein each gather is associated with a single source or group of sources;
(c) encoding each gather with a different encoding function wherein the encoding is orthogonal or pseudo-orthogonal with respect to cross-correlation;
(d) summing the encoded gathers in the group by summing all data records in each gather that correspond to a single receiver and repeating for each different receiver, resulting in a simultaneous encoded-source gather;
(e) 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;
(f) using the assumed physical properties model, simulating the simultaneous encoded-source gather, encoding source signatures in the simulation using the same encoding functions used to encode corresponding gathers of measured data, wherein an entire simultaneous encoded-source gather is simulated in a single simulation operation;
(g) calculating a difference for each receiver between the simultaneous encoded-source gather made up of measured geophysical data and the simulated simultaneous encoded-source gather, said difference being referred to as the residual for that receiver;
(h) applying different receiver encoding to each residual, said receiver encoding being selected to attenuate contributions from sources for which the receiver was inactive, relative to contributions from sources for which the receiver was active;
(i) computing an objective function from the receiver-encoded residuals, and updating the assumed physical properties model based on the objective function computation;
(j) repeating (c)-(i) at least one more iteration, using the updated physical properties model from the previous iteration as the assumed physical properties model, to produce a further updated physical properties model of the subsurface region; and
(k) downloading the further updated physical properties model or saving it to computer storage and using the further updated physical properties model in prospecting for hydrocarbons within the subsurface region,
wherein, at least one of (b)-(k) are performed using a computer,
wherein the encoding for each gather and the receiver encoding are functions of frequency,
wherein the source or group of sources is encoded with a set of bandpass filters, differing from each other in central frequency, phase, or both, and
wherein the receivers are encoded with a set of notch filters, differing from each other in central frequency, phase, or both, and each of the notch filters is designed to notch out bandpass frequencies of the encoding functions corresponding to the source or group of sources for which that receiver was not active through a combination of corresponding ones of the bandpass filters and the notch filters.

10. The method of claim 9 , wherein each gather in (b) is a multi-shot gather, each multi-shot gather consisting of a plurality of individual-shot gathers having a common set of illuminated receivers.

11. The method of claim 9 , wherein both the enc

Assignees

• Krebs Jerome R
• Cha Young Ho
• Lee Sunwoong
• Dimitrov Pavel
• Mullur Anoop A
• Downey Nathan J
• Routh Partha S
• Exxonmobil Upstream Res Co

Inventors

• Krebs Jerome R
• Cha Young Ho
• Lee Sunwoong
• Dimitrov Pavel
• Mullur Anoop A
• Downey Nathan J
• Routh Partha S

Classifications

• G06F30/20

  Design optimisation, verification or simulation (optimisation, verification or simulation of circuit designs G06F30/30) · CPC title

• G01V2210/66

  Subsurface modeling · CPC title

• G01V1/28

  Processing seismic data, e.g. for interpretation or for event detection (G01V1/48 takes precedence) · CPC title

• G01V1/003 Primary

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

• G01V1/005 Primary

  with exploration systems emitting special signals, e.g. frequency swept signals, pulse sequences or slip sweep arrangements · CPC title