The Cook Inlet is a major oil and gas province south-southwest of Anchorage, Alaska. It is located in a forearc basin setting, which developed as a result of plate motion. This plate motion caused the migration and accretion of the Chugach terrain. The overall tectonic regime is compressional with the principal maximum stress orientated northwest to southeast. Thirty thousand feet of Tertiary sediments occupy the basin, and this great thickness is a result of contemporaneous deposition and active tectonics.
The Hemlock formation is nonmarine in origin and comprises sandstone and conglomerates of Eocene and Oligocene age. The rocks include braided stream deposits, alluvial fans shed from the margins, and fluvial deposits that developed in the axis of the basin. The sandstones and conglomerate beds often stack to form large homogenous sedimentary units, which can reach thicknesses greater than 50 ft.
An acoustic imaging tool commonly used in wells drilled with oil-based mud or other highly resistive drilling fluids has been used in the evaluation of this formation. Homogenous rocks have acoustic properties similar to these fluids, resulting in the resolution of very little diagenetic detail. However, dipping surfaces and textural variations were observed on the image and these features contributed to the building of a sedimentological model. Additionally, borehole breakout orientation provided key information regarding borehole stress directions.