Modelling 1D compaction-driven flow in sedimentary basins: a comparison of the Scotian Shelf, North Sea and Gulf Coast

Abstract

Abstract A one-dimensional model of fluid pressure evolution in a compacting sedimentary sequence has been developed and used to investigate some of the physical processes which occur during sediment deposition and burial. It is well known that the permeability assigned to low permeability lithologies, such as shales, has a large effect upon the fluid pressures predicted by basin models. Shales are common in many sedimentary basins, however, the behaviour of their permeability as a function of pressure is poorly constrained. This leads to considerable uncertainty in the predictions of many basin models. Recent measurements of the permeability of overpressured Jurassic shales from the Scotian Basin, off Nova Scotia have yielded values around 10 −21 m 2 (approximately 1 nanodarcy) for a range of effective pressures between 10 and 60 MPa. We have used these results in a number of single phase simulations of one dimensional, compaction-driven, fluid pressure evolution in the Scotian Basin, the North Sea, and the United States Gulf Coast. In all these areas chronostratigraphic data can be used to determine Neogene sedimentation rates, which strongly affect the present-day levels of overpressure. In the Scotian Basin predicted present-day pressures fall below those observed. This is in contrast to the North Sea and Gulf Coast where rapid Neogene sedimentation, together with Cenozoic sediments containing a high percentage of shale, causes predicted levels of compaction-driven overpressuring similar to those observed. The poor agreement between predicted and observed pressures in the Scotian Basin indicates that mechanisms other than compaction disequilibrium, for instance lateral fluid migration, mineral diagenesis, or ice loading, should be considered as causes of overpressuring.