Patent EA-001212-B1 (EA)
Title: Method for time lapse reservoir monitoring
Inventor: ROSS CHRISTOPHER PHILIP
IPC: G01V1/28
Filed: 1997-09-11
Abstract: 1. A method for detecting physical changes in a reservoir, comprising: preparing of at least two seismic survey data sets of the reservoir, a first seismic survey data set is taken at a first time and a second seismic survey data set is taken at a second time; and comparing the results of the first seismic survey data set with the second seismic survey data set, providing: separating the first group of the reflection events (for example, wave impulses) in the first seismic survey data set having a corresponding second reflection event in the second seismic survey data set, wherein: the first reflection event and the second reflection event represent an unchanged portion of geologic structure in or near the reservoir, the first reflection event is represented by a first set of event parameters and the second reflection event is represented by a second set of event parameters; providing an acceptance threshold difference function between the first set of event parameters and the second set of event parameters; determining a crossequalization function to apply to the second set of event parameters, the crossequalization function being characterized in that, upon application of the crossequalization function to the second set of event parameters, whereby a crossequalized set of event parameters is defined, and the difference between the first set of event parameters and the crossequalized set of event parameters is below the threshold difference function; applying the crossequalization function to a third reflection event, the third reflection event being related to the second data set, wherein: a crossequalized third reflection event is defined, the third reflection event has a corresponding fourth reflection event in the first data set, the third and fourth reflection events represent a changing portion of the reservoir; comparing the crossequalized third reflection event to the fourth reflection event by subtracting the crossequalized third reflection event from the fourth reflection event. 2. A method as in claim I wherein said providing said acceptance threshold difference function comprises: iterative selection of event parameter modifications to the second set of event parameters, application of the event parameter modifications to the second set of event parameters, wherein a modified set of event parameters is defined, comparison of the modified set of event parameters to the first set of event parameters, wherein said iterative selection continues until a convergence is reached, and wherein the acceptance threshold difference function comprises the modified set of event parameters at convergence. 3. A method as in claim 2 wherein one of said event parameters comprise amplitude. 4. A method as in claim 2 wherein one of said event parameters comprise phase. 5. A method as in claim 2 wherein one of said event parameters comprise bandwidth. 6. A method as in claim 2 wherein one of said event parameters comprise time. 7. A method as in claim 2 wherein said event parameters comprise amplitude, phase, bandwidth, and time. 8. A method as in claim 1 wherein said determining a crossequalization function comprises: iterative selection of event parameter modifications to the second set of event parameters, application of the event parameter modifications to the second set of event parameters, wherein a rnodified set of event parameters is defined, comparison of the modified set of event parameters to the first set of event parameters, and providing an acceptance threshold difference, wherein said iterative selection continues until a comparison result from said comparison designates a difference between the first set of event parameters and the modified set of event parameters below the acceptance threshold difference. 9. A method as in claim I wherein said providing an acceptance threshold difference function comprises: providing a windowed trace difference between a time window of a first trace from the first seismic survey data set and a time window of a second trace from the second seismic survey data set, wherein the second trace includes reflection events corresponding to reflection events in the first trace and the time window of the second trace is substantially the same as the time window of the first trace, and providing a ratio of the windowed trace difference over the time window of the first trace, choosing the acceptance threshold difference to be less than the ratio. 10. A method as in claim 9 wherein the difference in bandwidth of the time window of the first trace and the time window of the second trace is less than about 25%. 11. A method as in claim 10 wherein the difference in width of the time window of the second trace and the bandwidth of the time window of the first trace is less than about 10%. 12. A method as in claim 1 wherein said providing an acceptance threshold difference function comprises: providing a windowed trace difference between a time window of the square of a first trace from the first seismic survey data set and a time window of the square of a second trace from the second seismic survey data set, wherein the second trace includes reflection events corresponding to reflection events in the first trace and wherein the time window of the second trace is substantially the same as the time window of the first trace, and providing a ratio of the windowed trace difference over the time window of the square of the first trace, choosing the acceptance threshold difference to be less than the ratio. 13. A method as in claim 7 wherein the time window has a length of at least about two reflection events. 14. A method as in claim 13 wherein the time window has a length of at least about five reflection events. 15. A method as in claim 1 wherein said applying the crossequalization function to a third reflection event in the second data set comprises convolution between the crossequalization function and the third reflection event in the second data set. 16. A method as in claim 1 wherein said first data set comprises a trace from a seismic receiver. 17. A method as in claim 1 wherein said first data set and said second data set comprise a summed set of traces from a set of seismic receivers. 18. A method as in claim 1 wherein said first data set and said second data set comprise a summed set of traces from a set of borehole receivers. 19. A method as in claim 1 wherein said first data set and said second data set comprise prestack data. 20. A method as in claim 19 wherein said prestack data comprises CMP data. 21. A method as in claim 19 wherein said prestack data comprises shot data. 22. A method as in claim 19 wherein said prestack data comprises migrated data. 23. A method as in claim 1 wherein said first data set and said second data set are subjected to equivalent prestack processes. 24. A method as in claim 1 wherein the first data set is subjected to the same designature process as the second data set. 25. A method as in claim 1 wherein the first data set is subjected to the same deconvolution process as the second data set. 26. A method as in claim 1 wherein the first data set is subjected to the same noise attenuation processing steps as second data set. 27. A method as in claim 1 wherein the first data set is subjected to the same multiple attenuation processing as the second data set. 28. A method as in claim 1 wherein the same DMO operator is used on first data set as on the second data set. 29. A method as in claim 1 wherein migration on the first data set is conducted with the same velocity field as migration on the second data set. 30. A method as in claim 1 wherein migration on the first data set is conducted with the same migration operator as migration on the second data set. 31. A method as in claim 1 wherein filtering on the first data set is conducted with the same filter as filtering on the second data set. 32. A method of deconvolution of at least two sets of seismic data, the method comprising: preparing at least two sets of seismic data from the same geographic area; and effecting the deconvolution of at least two sets of seismic data, providing designing of a deconvolution operator dependent upon data from at least two of the sets of seismic data, wherein the at least two sets of seismic data were recorded at different times; applying the deconvolution operator in a deconvolution process to both of the at least two sets of data; and conducting further time-lapse processing to form a difference record. 33. A method as in claim 32, wherein the at least two of the sets of data comprises at least three sets of seismic data, wherein each of the at least three sets represents recordings from surveys conducted at different times, and wherein the designing of a deconvolution operator is dependent upon data from each of the sets of surveys. 34. A method as in claim 32, wherein the at least two of the sets of data comprises at least three sets of seismic data, wherein each of the at least three sets represents recordings from surveys conducted at different times, and wherein the designing comprises designing a first deconvolution operator dependent upon data from a first set of data and a second set of data, the first deconvolution operator being applied to the first set of data and the second set of data, and further comprising: designing a second deconvolution operator dependent upon data from the first and a third set of data, the second deconvolution operator being applied to the first set of data and the third set of data. 35. A method as in claim 34, wherein the first set of data represents recordings from a survey taken before a survey represented by the second or third sets of data. 36. A method as in claim 34, wherein the designing of the first deconvolution operator comprises: averaging of a power spectrum for a first ensemble of traces from the first set; inverse transforming the average into a time-domain representation of the average for the power spectrum o