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Reversing the Gas Crisis: The Methane Hydrate Solution

 

Commercialization of methane recovery from coastal deposits of methane hydrates could head off an impending gas shortage.

Fortnightly Magazine - January 2005

are about 20,000 trillion cubic meters (706,293 Tcf) and correspond closely to the above-mentioned organic carbon in the form of hydrates assuming a composition of 100 percent methane. This compares with the upper bound of 20,000 Tcf of technically remaining recoverable conventional and unconventional natural gas resources, excluding, of course, methane hydrates. The other unconventional sources of natural gas-gas from tight formations, geopressured reservoirs, Devonian shales, extremely deep reservoirs, and coal beds-are now included in natural gas production, and reserve and resource statistics, such as the Dec. 31, 2003, proved global reserves value of 6,076.5 Tcf [5].

The U.S. potential is enormous-at least 100,000 Tcf-but significant commercial production has not been achieved. Hydrates production is possible using depressurization, thermal stimulation, and solvent injection (such as methanol). It is already quite apparent that the latter has unacceptable environmental impacts, and that thermal stimulation is too expensive. Depressurization is most feasible in deposits where, under a stable, non-porous sediment cap, there are sediments with increasing hydrate concentrations at increasing depth, bounded by a free gas zone. As the pressure in this free gas zone is reduced by production with suitably designed wells, increasing amounts of the overlying hydrates in the porous sediments decompose and can be produced without any environmental impact.

Note that 100,000 Tcf of methane would meet total U.S. primary energy requirements at the current rate for 1,000 years and that combustion of 69,000 Tcf of methane would emit only 1,000 billion metric tons of anthropogenic carbon in the form of carbon dioxide (CO 2). This is the upper bound of total anthropogenic emissions set by the Intergovernmental Panel on Climate Change (IPCC) from 1991 to 2100 to limit atmospheric CO 2 concentrations to 550 parts per million by volume, about double the pre-industrial concentration, and thereby limit projections of further increases in average global surface temperatures due to this CO 2 enrichment at mean climate sensitivities to between 1.6°C and 2.8°C [6,7].

Potential U.S. and Japanese Methane Hydrate Resources

U.S. methane resources in methane hydrates, according to an August 1998 study by the DOE's Office of Fossil Energy [8], are 112,000 Tcf at 95 percent probability, 676,000 Tcf at 5 percent probability, and a mean value of 320,192 Tcf, in 9 coastal plays and on a small 590 Tcf on-shore permafrost play in Alaska. In a 1995 study by the U.S. Geological Survey (USGS) cited by Timothy Collett [4], U.S. resources are 3,200 trillion m 3 (113,000 Tcf) at 95 percent probability and 19,000 m 3 (671,000 Tcf) at 5 percent probability in 10 coastal plays and one on-shore permafrost play in Alaska, with a mean value of 9,000 trillion m 3 (317,800 Tcf). How much of this wealth of methane resources is practically recoverable is not known, but even a relatively small percentage would greatly expand U.S. gas supplies. To pursue this objective, the U.S. government has budgeted $47.5 million from fiscal year 2001 through fiscal year 2005 (Public Law 106-193, May 2, 2000) for the Methane Hydrate Research and Development Act of 2000 (under the direction of the