A 4-D Petroleum System Model for the North Slope, Alaska

Kenneth E. Peters¹, Carolyn Lampe², Kenneth J. Bird¹, and Leslie B. Magoon^1
1 U.S. Geological Survey, Menlo Park, CA
² Integrated Exploration Systems, 52072 Aachen, Germany

A calibrated numerical model depicts the geometry and three-dimensional evolution of petroleum systems through time (4-D) in a 620 x 250 km area covering most of the North Slope. 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. Modeling of four source rocks improves understanding of the origin and distribution of petroleum: Hue Shale-gamma ray zone (Hue-GRZ), pebble shale unit, Kingak Shale, and Shublik Formation. The amount of oil-prone organic matter in Triassic Shublik source rock generally exceeded that of the other units prior to thermal maturation, although all generated some petroleum. The Shublik source rock was modeled using Type IIS kerogen kinetics, while Type II was used for the other source rocks.

Progradation of the Cretaceous-Tertiary Brookian sequence from west (120 Ma) to east (33 Ma) resulted in western and eastern depocenters south of the Barrow arch. Petroleum generation began during the Early Cretaceous in the southwest. Deposition of the Torok Formation and Nanushuk Group induced subsidence that drove petroleum to the north. Oil and gas accumulations remain on highs in the Prudhoe Bay and Simpson Peninsula areas. Beginning about 40 Ma, subsidence in the eastern depocenter drove petroleum northward toward Prudhoe Bay. Liquid accumulations in the Barrow area degassed to form free gas phases due to uplift and pressure release. Satisfactory model runs, including risk analyses, required about 24 hours of computation time using parallel processing on a Linux-based Beowulf cluster.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005