Print this pageJennie L. Ridgley1, S.M. Condon2, T.C. Hester2, L.O. Anna2, T. Cook2, N.S. Fishman2, E.L. Rowan3, P.G. Lillis2
(1) U.S.Geological Survey, Denver, CO
(2) U.S.Geological Survey, Lakewood, CO
(3) U.S.Geological Survey, Menlo Park, CA
ABSTRACT: Shallow Biogenic Gas Resources of Montana- A Reassessment
In 1995, the U.S. Geological Survey estimated that 40 tcf of undiscovered, continuous (unconventional) gas existed in Cretaceous shallow biogenic gas plays of Montana. Much of this resource was in hypothetical plays and was based on analogy to similar gas plays in the greater southeast Alberta gas field in Alberta and Saskatchewan, Canada. As a follow-on to the 1995 USGS assessment, multidisciplinary studies were implemented to evaluate controls on this type of gas accumulation in Montana, to better define the play boundaries, and to reassess the undiscovered resource. These studies have resulted in a revised depositional model for the Milk River Formation and Eagle Sandstone and recognition of structural control on the distribution of potential reservoirs in the Greenhorn and Belle Fourche Formations. Integration of geology and hydrology with gas and water geochemistry has led to reinterpretation of the timing/origin of gas generation and timing of gas migration. Enhanced log analysis techniques that can better predict the presence of gas in shaly rocks has facilitated the detection of gas-bearing strata that may have been by-passed during drilling.
Results of the multidisciplinary studies provide a background for reassessment of selected Cretaceous rock units that have the potential for additions to reserves in the next 30 years of shallow biogenic gas in Montana. We have defined four principal assessment units: Judith River Formation, Claggett Shale-Eagle Sandstone, Niobrara Formation-Carlile Shale, and Greenhorn Formation-Belle Fourche Formation. We will estimate ultimate recoveries of individual producing fields and then aggregate the fields within each assessment unit.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado