Coalbed methane in Indiana
by Harper, Denver (Author) |
Harper, Denver, 1991, Coalbed methane in Indiana: Indiana Geological Survey Occasional Paper 56, 18 p., 7 fig.
INTRODUCTION: Methane is a tasteless, odorless, invisible, combustible gas (chemical formula: CH4) that occurs naturally in certain rock strata, including almost all coalbeds. Because it is lighter than air, methane accumulates in underground coal mines in pockets along the roof and in poorly ventilated areas. Miners sometimes refer to methane-rich atmospheres as "firedamp," which has been a dreaded hazard since the 17th Century. Methane explosions are especially destructive when they initiate explosions of coal dust that may propagate through long distances in dust-filled galleries. Tens of thousands of miners have been killed worldwide in explosions, and such tragedies stimulated some of the earliest enactments of social legislation, as well as some of the earliest examples of governmentally supported scientific research (Bryan, 1975). Although much progress has been made, the potential for disaster still exists wherever coal is mined underground. Even mines that have long been abandoned can contain pockets of methane that are a hazard to drilling operations that inadvertently penetrate them. But this menace to coal miners is also a potential resource. Methane is the principal constituent of natural gas, which is a clean-burning and highly desirable source of energy. In 1985, about 17.3 trillion cubic feet (Tcf) of gas were consumed in the United States (about 0.4 Tcf in Indiana) (American Petroleum Institute, 1987) - but almost all of that gas was derived from conventional petroleum and gas reservoirs, where it occupies pore spaces mostly within sandstones and limestones. During the 1970's, unusually severe winters (1977-1979) and perturbations of world energy prices caused by the Arab oil embargo (1973-1974) and the Iranian revolution (1978) stimulated interest for a time in unconventional sources of gas - including coalbed methane. With subsequent reduction of world energy prices and political resignation to reliance on imported energy, that interest has largely subsided in the United States. But the dual aspect of coalbed methane - both hazard and potential resource - still deserves consideration. The purpose of this report is to provide an overview of what presently is known (and not known) about methane in Indiana's coalbeds.
Keywords: coal, geochemistry, methane, coalbed methane, cbm
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