Basin Evolution and Petroleum Generation in the National Petroleum Reserve, Alaska

By

D.O. Hayba and E.L. Rowan (U.S. Geological Survey)

Numerical modeling of the National Petroleum Reserve, Alaska (NPRA) provides an integrated analysis of the stratigraphic, thermal and fluid migration history of the region. As part of the U.S.G.S. assessment, we modeled the geologic evolution of 5 regional north-south stratigraphic cross-sections and 2 west-east sections in and adjacent to NPRA. For each section, the stratigraphy is based on recently interpreted reprocessed seismic reflection profiles. Wells located near the sections provide details about the primary lithologies and their matrix characteristics, which have been derived from an analysis of gamma-ray and sonic logs. This approach allowed us to develop internally consistent models with respect to properties such as porosity, permeability, and thermal conductivity. We estimated uplift and denudation from fission track and vitrinite reflectance data, as well as from porosity-depth profiles. We calibrated fluid flow and thermal characteristics of the model against pressure (mud weights), temperature, and vitrinite reflectance data. The resulting model of basin evolution provides a means to estimate the timing of hydrocarbon generation and migration. Our model indicates that source beds in the Late Triassic Shublik Formation and lowermost Kingak Shale (Early Jurassic) reached maturation about 120 +/- 20 Ma in the southern portion of NPRA. The locus of main stage generation then progressed rapidly northward and eastward until about 65 Ma. Thereafter, only minor volumes of oil would have been generated from these source beds in the vicinity of the Barrow Arch. Younger source rocks within the lower Brookian sequence show a similar pattern, with generation commencing about 20–30 m.y.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.