ABSTRACT:

We study the effects of a highly permeable sand layer on pore pressure and stresses near a salt diapir by using a forward hydro-mechanical finite-element model. We compare a salt basin entirely composed of mudrocks to the same basin but with a highly permeable sand layer across its bottom. We show that the sand layer causes a significant increase in pore pressure near the diapir by transmitting overpressure from deep sediments far from the diapir. This pressure increase makes it difficult to safely drill wellbores near the diapir. We examine the stress history of mudrocks at the crest of the sand layer and show that the pore pressure increase near diapir causes unloading of sediments, which is a crucial finding for seismic prediction of pore pressure in these sediments. Overall, our results offer an insight into the effects of basin sand layers on pore pressure distribution, seismic pore pressure prediction, and wellbore design near salt diapirs.

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