Assessment of Natural Gas from Coalbeds by Geologic Characterization and Production Evaluation
Raoul Choate, John P. McCord, Craig T. Rightmire, 1986. "Assessment of Natural Gas from Coalbeds by Geologic Characterization and Production Evaluation", Oil and Gas Assessment: Methods and Applications, Dudley D. Rice
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The relative attractiveness of coalbeds as source rocks and potential gas reservoirs are functions of the amount of methane generated by coal and the amount of methane retained in coal* The amount of methane gas generated during the coalification process depends primarily on the thermal maturity (rank) of the coal and the volume (thickness and lateral continuity) of coal present* The retention of methane gas in a coalbed reservoir will depend on a combination of factors including depth (i.e., fluid pore pressure), temperature, coal rank, and the hydrogeologic environment. Given a coalbed with the proper combination of methane generation and storage, the final and most critical factor is the production potential of the reservoir. Experience has shown that short duration testing (drill stem testing) does not provide the necessary data to address this issue. The production case histories presented here suggest that long duration production testing is the only way to adequately assess economic potential.
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There is a continual need to update estimates of oil and gas resources remaining to be discovered, and also to refine the methodologies for making these assessments. In 1974, AAPG sponsored a research conference dealing with the above topics, and many of the papers presented there were published in AAPG Studies in Geology 1. As a follow-up to that volume, a U.S. Geological Survey workshop was held in 1983, and many papers from talks presented there, in addition to several other papers, are contained within this volume. The 22 papers have been grouped into two types: those describing methodologies for evaluating resources and those presenting assessments of both conventional and unconventional resources.