4-D MODELING OF THE SHUBLIK-IVISHAK(!) PETROLEUM SYSTEM, NORTH SLOPE, ALASKA

The Triassic Shublik Formation is the major petroleum source rock unit on the North Slope of Alaska. A calibrated numerical model depicts the three-dimensional evolution of petroleum system elements through time (4-D) in a 620 x 250 km area covering most of the North Slope. The model predicts the timing of generation and migration of petroleum from the Shublik Formation and its accumulation in Triassic Ivishak Sandstone and other reservoirs. Model input included structure and stratigraphy for key horizons, maps of unit thickness, lithology, paleobathymetry, heat flow, original total organic carbon, and Rock-Eval pyrolysis hydrogen index. The Shublik source rock was modeled using oil-prone Type IIS kerogen kinetics. Satisfactory model runs, including risk analyses, required about 24 hours of computation time using parallel processing on a Linux-based Beowulf cluster.

The model shows that progradation of the Cretaceous-Tertiary Brookian foreland basin sequence from west (120 Ma) to east (33 Ma) resulted in thermal maturation of rock sequences in western and eastern depocenters south of the regional basement high, the Barrow arch. Petroleum generation from the Shublik Formation began during the Early Cretaceous in the western depocenter. Deposition of the Albian-Cenomanian Torok and Nanushuk formations induced subsidence that drove petroleum to the north toward the Barrow arch. Subsidence in the eastern depocenter was slower and drove petroleum northward toward Prudhoe Bay beginning about 40 Ma. Proportionally more oil and gas originated from the eastern than the western depocenter based on the original distribution of organic richness within the Shublik Formation prior to thermal maturation. Liquid petroleum accumulations in the Barrow area degassed to form free gas phases due to uplift and pressure release. Oil and gas accumulations remain on highs in the Prudhoe Bay and Simpson Peninsula areas.