Method of geophysical exploration

Details Method of geophysical exploration Method of geophysical exploration

1999-01-27

2001-01-23

McElheny, Jr., Donald E. (Department: 2862)

Data processing: measuring, calibrating, or testing

Measurement system in a specific environment

Earth science

Reexamination Certificate

active

06178381

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the processing of three dimensional (3D) seismic data. The present invention more particularly relates to a method for processing 3D seismic data using minimal data sets and a method for determining whether seismic data can be decomposed into subsets which approximate minimal data sets.
BACKGROUND OF THE INVENTION
Canning and Gardner contend in a July 1996 article in “The Leading Edge” that a narrow range of azimuths is highly desirable for good prestack imaging. Their argument is based on their observation that migration of wide-azimuth seismic data can generate undesirable artifacts in the migrated output unless very costly survey designs are used. What is desired is a cost-effective method of geophysical exploration which uses a relatively inexpensive seismic survey design to collect wide-azimuth data and which reduces the occurrence of undesirable artifacts when prestack migration is carried out on the wide-azimuth data.
SUMMARY
We have unexpectedly discovered a method of geophysical exploration that provides a cost-effective method of processing wide-azimuth seismic data using prestack migration, without producing the undesirable artifacts which often occur with conventional seismic acquisition and processing techniques.
One aspect of the invention involves the design and/or acquisition of a seismic survey that is constructed from a superposition of minimal data sets.
Another aspect of the invention involves the use of a diagnostic to assess to what extent a real seismic survey design (e.g. one containing gaps and positioning errors) can be approximately decomposed into minimal data sets. In this diagnostic, an ideal minimal data set is one where the trace coordinates lie on a 2-D hyperplane in a 4-D space of acquisition coordinates.
A third aspect of the invention involves seismic processing methods which exploit minimal data set principles to suppress noise in three dimensional (3D) seismic data acquired with land like geometries (i.e. wide azimuth seismic data acquired using conventional land seismic acquisition techniques or other techniques such as ocean bottom cable acquisition techniques which acquire relatively wide azimuth data). The methods include minimal data set slotting of migration input traces (as opposed to conventional common offset slotting) and ordering of traces in minimal data set prestack migrated common output gathers to reveal residual moveout velocity.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention, the embodiments described therein, and the accompanying FIGS.


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patent: 5274603 (1993-12-01), Zibilich, Jr. et al.
T. Padhi and T. K. Holley, “Wide azimuths—why not?”, Feb. 1997,The Leading Edge, pp. 175-177.
“Global spending on 4C data could hit $600 million by 2005”, Aug. 1998,Offshore, p. 51.
Victor Schmidt, “Good bottom couple required for 4D/4C seabed surveys”, Aug. 1998,Offshore, pp. 74, 131.
A. Canning and G. H. F. Gardner, “Another look at the question of azimuth”, Jul. 1996,The Leading Edge, pp. 821-823.

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