Prestack Waveform Inversion

Full waveform prestack inversion based on a genetic algorithm to transform seismic information to elastic earth parameters.

Prestack waveform inversion (PSWI) is a nonlinear inversion process that estimates elastic model attributes (compressional velocity, shear velocity, and density) from prestack seismic data using a genetic algorithm. The inversion utilizes wave equation–based forward modeling that can be run in both the angle or tau-p domains. Wave equation modeling is more accurate than convolutional modeling, thus enabling more accurate prediction of reservoir properties.

Within the inversion workflows, PSWI has several applications:

• In areas where well data is absent, it is used to synthesize 1D well response by modeling compressional velocity, shear velocity, and density. Several common depth point (CDP) locations are selected and subsequently interpolated as part of the background model building.

• In areas of sparse well distribution, PSWI is used to supplement the derived background, providing model inputs in areas where the well data cannot adequately or reliably describe the acoustic information.

• In small, selected areas, PSWI is run on multiple gathers to address reservoir-specific issues that cannot be solved by more conventional AVO-type inversion routines. Because PSWI is a compute-intensive process, these reservoir-focused areas are initially targeted by AVO inversion before running the full waveform inversion on specific gathers.

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