Influence of poroelastic behavior on the magnitude of minimum horizontal stress, Sh in overpressured parts of sedimentary basins

Abstract

In many sedimentary basins of the world the minimum hori- zontal stress, S h , is greater in overpressured zones than in normally pressured zones at equivalent depths. A common explanation is that the frictional slip on listric normal faults keeps the difference between vertical stress, S v and S h within certain bounds, and the difference is smaller under lower effective stress (i.e., higher pore pressure, P p ). However, in the overpressured parts of the central North Sea graben, United Kingdom, and the Sable subbasin of the Scotian Shelf, Canada, conventional friction envelopes underestimate the magnitude of S h . These data instead indicate that S h increases at a rate proportional to but less than the rate of increase of P p , a condition consistent with a P p -induced deformation of the rock called poroelastic behavior. This paper argues that, whereas friction may govern S h in normally pressured basins, poroelastic behavior is responsible for the unusually high S h in the overpres- sured parts of these same basins. Data on the P p and S h gradients from these basins suggest that Δ S h /Δ P p ∼ 0.7.