A Novice's Introduction to Coal Bed Methane
Kimberly Robinson and Dr. Jim Bauder (2001)
Graduate Research Assistant and Professor, respectively
A large component of natural gas is a substance called methane (CH4). Methane is a gas compound produced when organic material is geologically turned into coal. When the coal and methane conversion process occurs such that the 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. 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 development of this resource.
Methane is generally considered a cleaner form of energy than traditional coal and oil. Exploration costs for CBM are low, and wells used to extract CBM are cost effective to drill. Because methane is less dense than oxygen, it rises to the surface as water pressure is reduced within the coal seam by pumping.
CBM exploration and extraction is not a new industry. In fact, CBM extraction has occurred worldwide for many years. However, the U.S. has only recently recognized CBM as an easy-to-get energy source, and exploration is underway in many parts of the nation to find CBM relatively close to the land surface. According to the CBM Association of Alabama, 13% of 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.
Development of the CBM industry is well underway in Wyoming, while development in Montana is on hold 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. Thus, CBM extraction is an issue getting a lot of attention in Montana these days.
Extraction of coal bed methane is not without controversy. CBM extraction involves pumping large volumes of water from coal seams in order to release water pressure that traps gas within the coal. The quantity, quality, and dispersal of this water 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 soil physical and chemical properties; it could also limit 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, as irrigation supplies are almost always in limited supply and of undesirable quality by the middle of the summer in southeast Montana. Depending on soil type, discharge water alone is often not suitable for irrigation except with very rigorous management or on the most coarse soils.
Multifaceted research underway at Montana State University-Bozeman is attempting to find the best ways to manage CBM product water. The first goal 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 mitigation of discharge water. From the data collected from this research a diagnostic and decision support tool (a user-friendly, Internet accessible, printable worksheet) will then be developed for irrigator use in determining suitability of CBM-impacted irrigation water for specific irrigated soil x crop combinations.