Reservoir Potential of Late Triassic Kamishak Formation: Puale Bay, Alaska Peninsula

Sralla, Bryan¹, Robert B. Blodgett² (1) Hewitt Mineral Corporation, Ardmore, OK (2) United States Geological Survey (contractor), Anchorage, AK

Despite numerous oil and gas seeps and organic-rich source rocks, many workers have discounted the hydrocarbon potential of the Alaska Peninsula province based on a perception that the Jurassic age lithic sands and silts are poor reservoirs, owing to secondary zeolite cementation.  Emerging evidence suggests that the search for reservoir rock should be refocused on the Upper Triassic (Norian) Kamishak Formation carbonate.  The Kamishak was deposited near the equator along an emergent arc complex, contemporaneous with the organic-rich Shublik Formation of the Alaska North Slope and Tethyan carbonates elsewhere. Deposition began in a shallow-water, tropical environment. The lower part of the Kamishak is typified by biostromal limestone with abundant colonial scleractinian corals, brachiopods, bivalves, and gastropods.  These outcrops are partially dolomitized, bioclastic wackestone and packstone, fractured, with possible localized solution-collapse breccia.  Intercrystalline porosity associated with sucrosic-textured dolomitic limestone, and scattered grain-moldic porosity is also observed.  The remainder of the Kamishak documents a transgressive sequence, grading from shallow-water bioclastic carbonates upward into organic-rich, argillaceous, medium-bedded limestone with abundant Monotis (Pacimonotis) subcircularis.  The Bear Creek #1 well, completed in 1959, encountered the Kamishak from a depth of 5,000 (1524 m) to 6,600 feet (2012 m). The microlog indicated mudcake and permeability from a depth of 6080 (1853 m) to 6590 feet (2009 m).  Gas flowed to the surface along with the recovery of a large volume of saltwater during a drill-stem test from 6080 (1853 m) to 6200 feet (1890 m). Average effective permeability of at least 15.5 md was calculated using the Darcy Flow Equation.  The new hypothesis suggests that Kamishak carbonates may represent a previously unrecognized high-quality drilling target beneath several of the large anticlines located along the Alaska Peninsula.