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Wave-equation migration of common-receiver gathers for AVO analysis

ChevronTexaco, Houston, Texas, U.S.

Corresponding author: guypurnell@chevrontexaco.com

The first 20% of the full text of this article appears below.

During the 1980s and 1990s, we developed a number of recursive wave-equation algorithms for prestack depth migration in the shot domain. Much of that work was driven by development of the vertical-cable recording technique. However, we applied the algorithms to image a variety of 2D and 3D land and marine surveys. Virtually all of those projects were oriented toward obtaining better structural images and without concern for preserving relative amplitude information.

Increasing interest in prestack amplitude analysis of migrated data led us to revisit that decision and to evaluate the possibility of analyzing AVO (or AVA) within image gathers. Developers of other wave-equation-based algorithms have presented similar evaluations and have achieved useful results. However, our production algorithms are sufficiently different that the applicability of their results to our project work is not clear. Consequently, we decided to conduct our own study, starting with a modeling-based approach—rather than a theoretical one—to analyze application of one of our 3D shot-record depth migration algorithms to synthetic and real data. The immediate value of this would be as a measure of the "amplitude-friendliness" of an existing production algorithm under specific conditions. Beyond that, it would help us gauge the potential value of allocating additional theoretical and/or development work to enhance its usefulness as a tool for amplitude studies in projects involving wave-equation shot-record migration.

The real data set we selected for testing is an OBC survey recorded by Texaco in 1997 at Teal South Field (Eugene Island Block 354) in the Gulf of Mexico. This survey was used 24 4C receiver groups fixed in a sparse pattern on the seafloor, about 82 m deep (Figure 1). The source was a small air-gun array towed at a depth of 3 m and was deployed at locations on a finer (nominally 25 x 25 . . . [Full Text of this Article]