A Novices Introduction to Coal Bed Methane
Kimberly Robinson and Dr. Jim Bauder
A large component of natural gas is a substance called methane (CH4). Methane is a gas compound which is produed when organic material is geologically turned into coal. When the coal and methane conversion process occurs such that the resultant coal is saturated with water and methane is trapped within the coal, the result is "coal bed methane". Coal bed methane - CBM - is the same compound as natural gas - just derived from a different geologic situation. Since methane is lighter in weight than oxygen, methane will rise to the surface or atmosphere if a well is drilled into a coal seam which contains methane.
According to the CBM Association of Alabama, 13% of the land in the lower 48 United States has some coal under it, and nearly all of this coal contains methane - either in the form we know as natural gas or as CBM.
CBM exploration and extraction is not a new industry. In fact, CBM extraction has been done in many places - not just in the U.S., but throughout the world. It's just that CBM is now recognized as an easy-topget energy source and we are learning more each day about locations where CBM is relatively close to the land surface. CBM extraction an issue getting a lot of attention in Montana these days. The gas has a wide variety of energy-related uses, and with the current energy crisis and relatively high fuel prices, increased attention has been put on the development of this resource. Methane is generally considered a cleaner form of energy than traditional coal and oil. Exploration costs for coal-bed methane are low, and the wells used to extract CBM are cost effective to drill.
Development of the CBM industry is well underway in Wyoming, while development in Montana is on halt while an Environmental Impact Statement is being written and litigation is being addressed. The Powder River corridor in Montana and the Tongue River Valley in southeastern Montana are viewed as hot spots for future CBM development.
Extraction of coal bed methane is not without controversy. The extraction of CBM involves pumping large volumes of water from the ground in order to release the water pressure that is trapping the gas in the coal. The quantity, quality, and dispersal of the water that needs to be pumped is a source of much debate. Each well is expected to produce approximately 5 to 20 gallons of water per minute. If a well produced 12 gallons per minute, that would total 17,280 gallons of water per day for one well. The product water, although acceptable to drink or water livestock with, has a modestly high salinity hazard and often a very high sodium hazard based on standards used for irrigation suitability. When considered as an irrigation supply or when spread on the land, water of CBM quality could alter the soil physical and chemical properties; it could also limit the long-term productivity of sensitive rangeland species. On the positive side, if the right management practices and bioremediation processes can be defined, CBM product water can serve as a valuable supplement to existing irrigation water supplies, we are almost always in limited supply and undesirable quality by the middle of the summer in southeast Montana. Depending on soil type, the discharge water by itself is often not suitable for irrigation except with very rigorous management or on the most coarse soils.
Research underway at Montana State University-Bozeman is attempting to find the best ways to manage CBM product water. There are several directions that research here at the university is pursuing. The first aspect is to determine standards and criteria which discharge water must meet for discharge into waterways and land spreading. Research will focus on determining acceptable and sustainable guidelines of mixing rates of CBM water with irrigation water from the Powder River for summer irrigation flow periods. The second facet of MSU research is focusing on using artificial wetlands and specific plant communities for the mitigation of discharge water. From the data collected from this research a diagnostic and decision support tool (a user-friendly, Internet accessible and printed worksheet) will then be developed for irrigator use in determining suitability of CBM-impacted irrigation water for specific irrigated soil x crop combinations.