Abstract

Mud weight and pore pressure (drill stem test, repeat formation tester) data from 250 exploration wells were used to investigate the fluid pressure regime of the Beaufort-Mackenzie Basin. Four patterns of pore pressure variation with depth are recognized, each of which is associated with a specific tectono-stratigraphic domain and reflects the interplay between compaction and tectonics, or other geological factors causing or redistributing the overpressure. Overpressure in the southwest Beaufort Sea is likely to be a result of a combination of compaction and northeast-southwest contractional tectonics. In the north, shale diapirism may create fracture systems on top of anticlines, causing migration of overpressured fluid to a shallower depth. In the center of the Mackenzie Delta, where listric faulting prevails, compaction is the major controlling factor and the depth of overpressure depends on lithology and rate of deposition. Overpressure is mainly confined to Tertiary sedimentary successions but it may exist in pre-Tertiary strata (as inferred from mud weight data in a few wells) along the southeast basin margin, possibly in association with gas generating source rocks of Cretaceous age. The spatial variations of pore pressure at given depths, as well as along specific stratigraphic sequences, indicate that basin-scale flow is primarily driven by the upward expulsion of overpressured fluids. Analysis of pore pressure patterns suggests that regional fault zones can be both a barrier and a preferred flow path network to deep fluid fluxes. In general, fault zones are more likely to be regional barriers to lateral flow in an aquifer, but are the preferred flow networks for vertical fluid migration.