Timing of Hydrocarbon Generation in the National Petroleum Reserve-Alaska (NPRA) from Burial and Thermal History Modeling

By

W.M. Burns, D.O. Hayba, D.W. Houseknecht, and E.L. Rowan (U.S. Geological Survey)

Burial/thermal history modeling was performed for Ellesmerian, Beaufortian, and Brookian sequences in the National Petroleum Reserve-Alaska (NPRA) to determine the timing of hydrocarbon generation from source rocks within these sequences. One-dimensional and two-dimensional models were calibrated with vitrinite reflectance, compaction, and surface and bottom-hole temperature measurements made at wells. These parameters were interpolated for use at ‘psuedo-wells’ derived from seismic sections, greatly expanding the modeled region. Geochemical data for potential hydrocarbon source rocks were combined with the modeled thermal histories to derive histories of hydrocarbon generation. Source rocks modeled include the Triassic Shublik Formation, shales in the lower portion of the Jurassic Kingak Shale, and the Cretaceous gamma ray zone. Results were compiled in maps of the NPRA for multiple time slices.

Timing of hydrocarbon generation in the NPRA correlates with deposition of the Cretaceous to Tertiary Brookian sequence. Northeastward progradation of the Brookian shelf margin was delineated previously by sequence stratigraphic analysis of the Torok and Nanushuk Formations (Albian to Cenomanian) in seismic reflection data spanning the NPRA. The models indicate that hydrocarbon generation was largely driven by prograding deposition, initiating in the southwest during the Albian and progressing northeastward across most of the NPRA during the Albian and Cenomanian. In the northeastern part of the NPRA, initiation of hydrocarbon generation was delayed until deposition of Turonian to Maastrichtian Brookian strata. Northward thinning of the Brookian sequence onto the Barrow arch limited the degree of thermal maturation and led to incomplete hydrocarbon generation on and adjacent to the arch.

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.