HR: 14:40h
AN: NG33B-04 INVITED     [Abstracts]
TI: Amplitude-variation-with-offset and nonlinear prestack waveform inversion
AU: * Mallick, S
EM: SMallick@houston.westerngeco.slb.com
AF: WesternGeco, 10,001 Richmond Avenue, Houston, TX 77042 United States
AB: Use of prestack data for quantitative analysis of hydrocarbon reservoirs has gained popularity over the past decades. Most of these quantitative studies rely on the seismic reflection amplitude variation with offset or AVO analysis. AVO makes a simple assumption that every reflection event on the prestack seismic data is a primary P-wave reflection, and there is no contamination of these reflections from other wave modes. Using synthetic data for a finely layered elastic model, we demonstrate that such a simple assumption is incorrect, and there is a lot of interference of P-wave reflection amplitudes with other wave modes, especially at high offsets/angles. To properly model such interference, it is necessary to use prestack waveform inversion (PSWI), where these effects are correctly accounted for. Over the recent years, PSWI has been successfully used not only in a variety of reservoir applications but also in geo-hazard analyses such as pre-drill pore-pressure prediction and shallow water flow analysis. The problem of PSWI is nonlinear in nature. In this paper, we use a nonlinear optimization methodology, based on genetic algorithm (GA) for inversion. Such an inversion is computer intensive, since it must compute many forward synthetic models to obtain an estimate of the optimum earth model at a given common midpoint (CMP) location. To effectively apply inversion over large areas, we therefore combine PSWI with poststack inversion methodologies in a hybrid inversion scheme. Using a variety of synthetic and real data examples, application of PSWI and hybrid inversion methodologies will be discussed during the presentation.
DE: 7260 Theory and modeling
DE: 3260 Inverse theory
SC: Nonlinear Geophysics [NG]
MN: 2004 AGU Fall Meeting