Seismic monitoring of pressure depletion evaluated using azimuthal AVO data?

Azimuthal AVO is investigated as a possible tool for time-lapse monitoring of pressure depletion in reservoirs for which fluid replacement or the signature due to fluid movement is negligible. A feasibility study is carried out for both onshore and offshore acquisitions, which have non-repeatable geometries between the baseline and monitor surveys. Modeling, followed by anisotropy estimation reveals that lack of repeatability between the different survey vintages as a significant challenge, particularly in the presence of background noise. The condition of a repeatable geometry is more critical than for the P-P stacked response. For the geometry data used in this study, anisotropy estimates rapidly become unstable when pre-stack noise levels exceed 3 to 5 percent. Pressure drops in the reservoir must exceed 15 MPa in maximum fold areas for the OBC survey, and 7 MPa onshore, to permit detection of the corresponding anisotropy changes. The study suggests constraint using production data is necessary for more accurate resolution of pressure changes.