Analysis of 4-C data for AVO effects at teal south, eugene island 354

摘要

A recent 3-D, 4-C seismic survey at teal South in the Gulf of Mexico poses a number of challenges for AVO analysis, some which are not normally encountered in conventional marine streamer surveys. Among these, some are associated with the use of a sparse grid of ocean-bottom receivers. Before embarking on AVO analysis, thereore, we believe that it is neccessary to demonstrate whether the survey sufficiently samples the AVO rspose of the suburface and also to determine how best to process the survey so as to preserve that response. The former question is related to how evenly the subsurface is illuminated and also to how evenly the upcoming reflected waveflield is smapled at the eafloor. Ideally, both sources and receivers would be finely spaced on regular grids. SInce this is cetainly not the case for our receiver grid, we have less flexibility in dealing with azimuthal variations. That is, the distributiomn of aximuths and offsets in CMP bins will not only be limited, but will exhibit significant cjhanges spatially. Regarding the processing question, tests support applying a conventional AVO-preprocessing sequence. Further, they indicate the AVO analysis of this survey might better be conducted after prestack migration. Using a 3-D PSPI depth migration of common-receiver gathers, we obtained an image volume that compares favorably to that obtained from conventional CMP stack and 3-D poststack time migration. since irregularities in the source grid can affect amplitudes in the output image, we devised a regirdding procedure as an alternative to binning. Our next step is to evaluate whether the proposed processing strategy outperforms conventional processing in conditioning prestack P-P and P-S reflection data for AVO analysis.