Natural gas reserves in conventional traps are well known in Alaska, but methane reserves in coal beds associated with these gas fields remain undetermined. Due to declining conventional gas reserves in the Cook Inlet basin, the State of Alaska and the USGS are interested in promoting studies of environmentally favorable alternate energy sources. Methane stored in coal beds can be modeled if the burial history, rank of the coals (i.e., gas generated), shallow structure (gas traps), and depth to the coals (pressure acting to hold gas in) are known. Changes in burial depth, erosion rates, and geothermal gradient affect the distribution of vitrinite reflectance (Ro) values, methane formation, and potential storage in coal beds. Therefore, a complete understanding of the stratigraphic relations is necessary to adequately assess methane production. These factors make the Cook Inlet Basin an ideal setting to document and test a high-resolution, thermal maturation model for coal bed methane resource potential.

We propose the construction of a model for assessing the coal bed methane potential of the Kenai Group in Cook Inlet Basin. Ash bed partings in coal beds and Ro samples from coal beds and coaly fossils will be collected from core and outcrop. ⁴⁰Ar/³⁹Ar dating and Ro measurements will be completed on these samples. Published data, including well logs, regional tectonic studies, coal-quality, and seismic data, will be used to supplement this information.

The data produced by the methods above will be used to formulate a chronostratigraphic and thermal framework of the basin. Multiple ⁴⁰Ar/³⁹Ar dates will allow for complete correlation and delineation of stratigraphic relations between wells and outcrops across the basin. Ro measurements will determine the thermal histories at these locations. Basin-mod software will be used to determine the burial history of the basin. Using this data, a model will be constructed to produce basin-wide, maturity isopach maps showing areas of potential coalbed methane generation and storage. These isopach maps will be used to assess coal bed methane reserves and may be used for future resource production planning.