Susitna Basin, Alaska: USGS Oil and Gas Assessment

U.S. Geological Survey. Fact Sheet 2018–3017, version 1.1, May 2018.

Low, forested hills and flats west of Willow, Alaska, looking south: typical of the 4,000-square-mile (10,300 km²) assessment area. The straight line is an old seismic survey cut made by oil explorers. Photo: Richard G. Stanley, USGS, June 21, 2011.

Why look here

The Susitna Basin is a thinly settled region of forested hills and flatlands about 50 miles (80 km) from Anchorage, where natural gas is the main fuel for heat and electricity. With interest in the region's gas supply high, the USGS has finished its first detailed assessment of the basin.

• No commercial production so far; few wells, and most of the basin unexplored.
• But the evidence — field geology, wells, seismic data, gravity and aeromagnetic surveys, reviewed with the Alaska Department of Natural Resources — points to technically recoverable oil and gas in Tertiary rocks (about 66 to 2.6 million years old).

Figure 1: the two assessment units, from Petersville and Talkeetna south to Cook Inlet. White is ice; colors show elevation. USGS.

The petroleum system

The USGS assessed the basin by its source rocks, reservoirs and traps, defining the Susitna Total Petroleum System and two units:

• Susitna Tertiary Sandstone Microbial Gas;
• Beluga Mountain Subthrust Oil.

Source: organic-rich coals and shales. Reservoirs: sandstone and conglomerate. Traps: structural (anticlines, faults) and stratigraphic — for example, ancient river-channel sands sealed by fine floodplain muds.

Figure 3: a 4-meter-thick coal bed west of Willow — coals like this may be the basin's petroleum source. Photo: Richard G. Stanley, USGS, August 3, 2014.

Key inputs

Table 1. Minimum / median / maximum (mean).

Results

Table 2: fully risked. F95 means a 95-percent chance of at least that amount; F5, a 5-percent chance. No natural gas liquids are expected.

• Gas: 0 to 4,672 billion cubic feet, mean 1,679 — about 99.8 percent (1,675) in conventional fields of the microbial gas unit.
• Oil: 0 to 10 million barrels, mean 2 — all in the Beluga Mountain unit.

Sources

Based on Assessment of Undiscovered Oil and Gas Resources of the Susitna Basin, Southern Alaska, 2017, USGS Fact Sheet 2018–3017, by the Susitna Basin USGS Assessment Team (task leader Richard G. Stanley, with Christopher J. Potter, Kristen A. Lewis, Paul G. Lillis, Anjana K. Shah, Peter J. Haeussler, Jeffrey D. Phillips, Zenon C. Valin, Christopher J. Schenk, Timothy R. Klett and others), U.S. Geological Survey; a work of the United States government in the public domain. The map, both photographs and both tables are taken from the fact sheet's PDF, which the import had left out. The text puts the oil unit's share of the gas at "0.02 percent"; 4 of 1,679 billion cubic feet is about 0.2 percent. Methods: USGS Energy Resources Program.