Abstract

The Almond Formation in the Greater Green River Basin is a prolific producer of oil and gas (100,000,000 BO and 0.8 TCFG as of 1986; Wyoming Oil and Gas Conservation Commission, 1987). This paper reports on a regional study of the organic richness and thermal maturity of shales and coals in the Almond Formation, and on a series of hydrous pyrolysis experiments. Analyses of total organic carbon and vitrinite reflectance, and "Rock-Eval"-type analyses for Tmax, production index, hydrogen index, and genetic potential were conducted. The shales are moderate to rich petroleum source rocks, and are in the liquid oil window throughout the depth range sampled (~4,500 - 14,500 feet). Hydrous pyrolysis experiments on samples of Almond Formation coals indicate that they may be a source of liquid hydrocarbon, up to 27 mg oil / g coal. Additionally, the coals are prolific producers of gas, up to 7.5 x 10^-6 mole natural gas / g coal in the experiments. Maturation trends in the hydrous pyrolysis experiments were very similar to those seen in the core samples, indicating that hydrous pyrolysis is a viable tool for studying the maturation of these coals. About 20% of Almond Formation production is from "tight" gas sands that are overpressured and produce little or no water, conditions indicating that the Almond may contain abnormally pressured compartments. Analysis of maturity-depth trends within the Almond also suggests that this may be the case.