Assessment of undiscovered gas resources in Upper Devonian to Lower Cretaceous strata of the western North Slope, Alaska, 2021

The U.S. Geological Survey (USGS) assessed the potential for undiscovered, technically recoverable gas resources in conventional accumulations in Upper Devonian to Lower Cretaceous strata of the western North Slope of Alaska, including adjacent State waters (fig. 1). The western North Slope lies north of the Brooks Range, west of the National Petroleum Reserve−Alaska (NPR−A), and east of the Chukchi Sea. The western North Slope was included in previous assessments of (1) conventional resources of the Cretaceous Nanushuk and Torok Formations in the NPR−A and adjacent areas (Houseknecht and others, 2017) and (2) continuous resources of the entire North Slope (Houseknecht and others, 2012). Thus, rocks considered in this assessment are limited to strata older than the Torok Formation and younger than the acoustic basement (fig. 2). The assessment area contains sparse subsurface data, including three exploration wells (fig. 1) drilled between 1978 and 1982 and about 500 miles (800 kilometers) of vintage (1970−1971) two-dimensional (2D) seismic data. These were supplemented by geologic maps of the western North Slope and adjacent areas (for example, Mull and others, 2000). Additional well and 2D seismic data from the NPR−A and Chukchi Sea were used to construct a more robust geologic framework for the assessment. Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 1,407 billion (1.4 trillion) cubic feet of gas in conventional accumulations in Upper Devonian to Lower Cretaceous strata of the western North Slope, Alaska.