--> Abstract: Estimation of Coalbed Methane Contents from Geologic Data, by R. R. Charpentier and B. E. Law; #90987 (1993).

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CHARPENTIER, RONALD R., and BEN E. LAW, U.S. Geological Survey, Denver, CO

ABSTRACT: Estimation of Coalbed Methane Contents from Geologic Data

Appraisal of coalbed methane resources is dependent on an accurate estimation of methane content per unit volume of coal. For those cases where desorption measurements are not available, it would be very useful to make methane content estimates using available data, such as depth to the coalbed, rank, and coal quality. Although relationships have been previously established for such estimation, they have not quantified the

uncertainty. Appraisals of gas resources are of much greater utility when given in a probabilistic format that expresses the uncertainty.

We have compiled a database of approximately three thousand coalbed desorption measurements and have used it to assess the uncertainty in the estimations of gas content. These data were collected from public and private sources and include, when available, location information, proximate analyses, vitrinite reflectances, and gas analyses.

Coalbed gas content can be estimated by a function that increases linearly with depth. Gas content also increases with increasing rank, and separate linear estimation functions for each rank were developed. Importantly, the uncertainty of these estimations can also be quantified. For example, the estimate of gas content for high volatile bituminous coals is generally within +/- 3 cc/g. For higher rank coals the uncertainty of the gas content estimate increases, and for lower rank coals this uncertainty decreases. Further analysis also shows how other geologic characteristics, such as ash content, affect the coalbed methane content.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.