Estimation of pressure-saturation changes for unconsolidated reservoir rocks with high VP/VS ratio

ABSTRACTWe find that conventional time-lapse seismic pressure-saturation discrimination methods become unstable for high VP/VS ratios. Using first-order approximations in the amplitude variation with offset (AVO) gradient and intercept changes and in the rock-physics models increase the inaccuracy in pressure-saturation changes estimates. We propose a new method, based on a stepwise linear approximation to the intercept and gradient reflectivity changes, to estimate pressure and saturation changes. The applicability of the new method is tested on synthetic data over a range of 0%–50% gas saturation and 0–3.5 MPa pore-pressure changes. The new method is more consistent and provides better estimates compared with conventional methods. In the presence of random noise (up to 15%), the estimates are reasonably better for the new method. We use this new method to investigate the feasibility of pressure-saturation discrimination for a shallow unconsolidated sand reservoir in which an underground blowout occurred...

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