RESERVOIR CHARACTERIZATION OF THE BEAR LAKE AND MILKY RIVER FORMATIONS, BRISTOL BAY BASIN, ALASKA PENINSULA

The Miocene Bear Lake and Pliocene Milky River Formations are exposed along the coast near Port Moller on the Alaska Peninsula, and in the mountains to the northeast. The Bear Lake Formation may be as thick as 1,000 m in outcrop, and is 2,368 m thick in the Gulf Sandy River Federal No. 1 well. The Milky River Formation is 465 m thick at its type locality onshore, and 1,012 m thick in the Sandy River No. 1 borehole. We measured sections and sampled for palynology, organic geochemistry, and porosity and permeability to determine the reservoir potential of each formation. New measurements from sandstones have yielded porosity values as high as 16.9 percent in the Bear Lake Formation, and 42.0 percent in the Milky River Formation. Palynology was used to determine the relative stratigraphic positions between measured sections. An angular unconformity defines the contact between the steeply dipping and locally tightly folded Bear Lake Formation and the gently dipping Milky River Formation. Publicly available seismic data suggests that this unconformity may be a regional feature, but that its characteristics change offshore, particularly in the North Aleutian Shelf COST No. 1 well area. There, it appears to be both an unconformity and a downlap surface, with clinoforms of the Milky River Formation prograding northward over the Bear Lake Formation. Ongoing surface stratigraphic and subsurface studies will help to evaluate the lateral extent of this apparently regionally significant unconformity.