BRISTOL BAY BASIN, ALASKA PENINSULA, FRONTIER HYDROCARBON BASIN: NEW INSIGHTS
REIFENSTUHL, Rocky, Alaska Division of Geological
& Geophysical Surveys,
3354 College Road, Fairbanks, AK 99709, [email protected]
Regional hydrocarbon-focused fieldwork
and analyses by the Alaska Division of
Geological
and Geophysical Surveys and the Division of Oil and Gas, along with a
consortium of consulting geologists provides abundant new baseline exploration
data. New field data codifies the fundamental reservoir characteristics of
potential basin targets, places the reservoir data in a stratigraphic and
sequence stratigraphic framework, and summarizes the structure, organic
geochemistry, and hydrocarbon potential of this frontier basin (see
wwwdggs.dnr.state.ak.us). Project data catalyzed interest in the October 2005
area wide lease sale ($1.3 million; 37 tracts) near Port Moller town site and
Herendeen Bay. The area hosts a prolific seep of dry natural gas which, based on
carbon and deuterium isotopes, suggest thermally mature Mesozoic strata lie at
depth. Petroleum system plays in the Herendeen Bay region are within both the
Mesozoic and Tertiary sections. Oil seeps (~1/2 barrel/day) from the Jurassic
age Shelikof Formation south of Puale Bay. The Kamishak Formation, a Triassic
age shallow-water limestone yields total organic carbon (TOC) to 2.4%, hydrogen
index (HI) of 598 and oxygen index (OI) of 22. Middle Jurassic age Kialagvik
clastic marine rocks yield up to 3.5% TOC, up to 680 HI, and average 22 OI. Such
values are encouraging for potential hydrocarbon sources. The Miocene age Bear
Lake Formation, an important reservoir in play models, is at least 3,700 feet
(~1,200 meters) thick, and comprises a deepening-upward succession. Porosity and
permeability values range from 1 to 35 percent and 0.001 to 1,000 millidarcies.
The sand/organic siltstone ratio is estimated at 80/1. Siliceous coal and
carbonaceous siltstone occur throughout the formation. Thin, siliceous coal
deposits also occur in the underlying Upper Cretaceous rocks. These thin, but
common, coal deposits create the possibility for biogenic methane production.
The Oligocene age Stepovak Formation and the Eocene and Paleocene age Tolstoi
Formation include organic-rich marine strata. Tolstoi Formation rocks yield TOC
to 8.9%, and 253 HI and 8 OI. Publicly-available seismic and field data suggest
structural traps and unconformities, particularly at the base of the Pliocene
Milky River Formation. Seals are presumed to be thin and intraformational.