The Critical Element in Coal Bed Methane – Permeability

Tedesco, Steven¹, Trent Green^1
1 Atoka Coal Labs, Englewood, CO
² Pinnacle Technologies, Englewood, CO

The majority of literature and exploration programs focus on gas content and thickness of coals as a prerequisite to determine the viability of any basin for coal bed methane. Many of the coal basins developed in the 1980s and 1990s had a combination of permeability and gas contents that allowed them to overcome in general any reservoir limitations and thus be successful. In recent years basins that were considered less perspective in the past, such as Arkoma, Alberta, Cherokee, Piceance, Forest City and Illinois have become increasing the focus of exploration and development. While the gas contents in these basins have varied, the greatest stumbling block for their development has been finding completion and drilling methods that enhance or connect what is generally considered low permeability reservoirs. The use of horizontal drilling has overcome to some degree the low permeability reservoir characteristics of coals in the Arkoma and parts of the Appalachian basins. However, in other basins low gas contents prohibit the use of these directional methods. Therefore, measuring permeability in these basins is critical to determine the potential area of drainage for a wellbore and ultimate resource recovery. Permeability can be measured during the exploration phase of any program via injection fall off tests. This type of test allows for a measure of relative permeability and reservoir boundaries. This paper will present several examples how permeability is measured and what it implies for the viability of various coal seams as an economic resource in certain basins.