Since the early 1980s, engineers and geologists have been unlocking the secrets of coal seam gas reservoirs. With time and technology advances, such as multi-lateral horizontal drilling, these reservoirs have contributed mightily to the Nation's gas supply. Many of these prolific reservoirs are maturing and field operators now look to improve incremental recoveries from these natural gas sources. One such method is through the use of carbon dioxide enhanced coalbed methane (CO2-ECBM).

CO2-ECBM is a process by which the gas is injected into a coal seam, it is preferentially adsorbed onto the coal, allowing incremental methane to desorb and be produced. This very unique characteristic of a coal allows it to serve double-duty as both a storage reservoir and the seal. As such, geologic sequestration of carbon dioxide in deep, unmineable coal seams may hold tremendous promise for long-term, secure storage of the greenhouse gases as well as providing incremental methane recovery.

However, with only a handful of CO2 injection pilots having been conducted, it seems more questions are being asked regarding the viability of the process than being answered. This paper will focus on the lessons learned from several large-scale and small-scale tests, framing these results against capacity and injectivity estimation and long-term suitability for various coal types/ranks.

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