Injection of carbon dioxide into deep coal seams has the potential to enhance coalbed methane recovery, while simultaneously sequestering a greenhouse gas. Analysis of production operations from the world's first carbon dioxide-enhanced coalbed methane (CO2-ECBM) pilot, a 4-injector/7-producer pattern in the San Juan Basin, indicates that the process is technically and economically feasible. To date, over 2 Bcf of CO2 has been sequestered with negligible breakthrough. Enhancement of gas production can be as high as 150% over conventional pressure-depletion methods. Dewatering of the reservoir is also improved. ECBM development may be profitable in the San Juan basin at wellhead gas prices above $1.75/Mcf, adding as much as 13 Tcf of additional methane resource potential within this mature basin.

The key reservoir screening criteria for successful application of CO2-ECBM include laterally continuous and permeable coal seams, concentrated seam geometry, and minimal faulting and reservoir compartmentalization. Operational practices for CO2-ECBM recovery are still being refined. Injection wells should be completed unstimulated, while production wells can be cavitated or hydraulically stimulated. CO2 injection should be continuous and concurrent with methane production to prevent lateral water encroachment. Apart from the San Juan basin, many other coal basins have significant CO2-ECBM potential. In the U.S., the Uinta and Raton basins are geologically most favorable, while additional potential exists in the Greater Green River, Appalachian and other coal basins. Coal basins in Australia, Russia, China, India, Indonesia and other countries also have large CO2-ECBM potential. When viewed from a commercial project viewpoint, the total worldwide potential for CO2-ECBM is estimated at approximately 68 Tcf, with about 7.1 billion metric tons of associated CO2 sequestration potential. If viewed purely as a non-commercial CO2 sequestration technology, the worldwide sequestration potential of deep coal seams may be 20 to 50 times greater.

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