Coalbed Methane is a natural gas produced from coal seams or adjacent sandstones. In 1994, U.S. coalbed methane reserves were 9.38 trillion cubic feet (Tcf), which was ~6% of the domestic natural gas reserves. Production in 1994 was 777 billion cubic feet(Bcf), or 4% of the natural gas production of the lower 48 states. Commercial production occurs in approximately 10 U.S. basins; the major producing areas are the San Juan, Black Warrior, and Central Appalachian Basins. The coalbed methane play is now international with tests or pilot projects in ~15 countries.
Coal is both the source rock and the reservoir for coalbed methane. As organic material (peat) is buried, temperature and pressure increase, and methane, water, and other volatile substances are liberated. As these fluids are released, the coally matter contracts and fractures in a distinctive manner. The fractures align themselves according to the existing stress fields in the earth. These fractures are called cleat and they provide permeability pathways through which the fluids may pass. Some gas may escape the coal. However, if formation pressure is sufficient, quantities of methane are retained in the pressurized coal matrix in an adsorbed state. To produce the methane, wells are drilled into the coal and pressure is reduced by removing formation water. Pumps are generally required to dewater the formation. This allows methane to desorb and pass into its gaseous state, so that it may be produced in the conventional manner into a pipeline. It is usually necessary to compress the gas before it may be put into the collection system.
Coalbed methane activity is increasing in the U.S., the world leader in reserves and production, due to recent high gas prices and dwindling conventional gas supplies. In 1999, U.S. coalbed methane production was 1.25Tcf (trillion cubic feet) (5% > than in 1998), and coalbed methane reserves were approximately 13.2 Tcf, or about 8% of the U.S. total dry gas reserves. Coalbed gas production from low-rank coal in the Powder River Basin is the most active natural gas play in the U.S., in terms of numbers of wells drilled, and it has resulted in new exploration models that have stimulated evaluation of coalbed gas in other low-rank coals. Elsewhere, coalbed methane is produced in Queensland, Australia, and the U.K., and pilot projects are underway in China and India. Independent operators are the most active coalbed gas exploration companies in the U.S. Internationally, both majors and independents are actively seeking to expand the industry. Capital is being spent for leasing, exploration, and development. In the San Juan Basin, for example, a major in-fill drilling (down-spacing) program is in progress north of the Fruitland fairway.
Today, coalbed gas research is limited in comparison to a decade ago when the Gas Research Institute (now Gas Technology Institute) championed the technology development that supported today’s successes. However, enhanced coalbed gas recovery research is being conducted in pilot projects by BP Amoco and Burlington Resources, and the U.S. Department of Energy is supporting studies of the feasibility of carbon dioxide sequestration in coals, which could be coupled with enhanced recovery.
For a complete version of the above, see the Committee’s Annual Report (May 2013) on the EMD Members Only page (log-in required).
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