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.