Definition
Coal Bed Methane (CBM) is an unconventional form of natural gas found in coal deposits or coal seams. CMB is formed during the process of coalification, the transformation of plant material into coal. It is considered a valuable energy resource with reserves and production having grown nearly every year since 1989. Varied methods of recovery make CBM a stable source of energy.
CBM can be recovered from underground coal before, during, or after mining operations. It can also be extracted from “unminable” coal seams that are relatively deep, thin or of poor or inconsistent quality. Vertical and horizontal wells are used to develop CBM resources.Extraction requires drilling wells into the coal seams and removing water contained in the seam to reduce hydrostatic pressure and release absorbed (and free) gas out of the coal.
Context
CBM extraction continues to undergo research and development. Concerns include assessing the resource, identifying favorable geologic production areas, establishing efficient recovery schemes, demonstrating advanced drilling technologies and supporting capture and use of diluted gas streams.
The environmental impacts of CBM also continue to be assessed. Methane is a greenhouse gas emitted through CBM extraction. Global methane emissions from coal mines are projected to account for approximately 8 percent of total global methane emissions. Disturbance of lands drilled and its effect on wildlife habitats results in ecosystem damage. CBM production behavior is complex and difficult to predict in the early stages of recovery. Reservoir engineers and simulators must be employed to assess gas content, sportion time, thickness and reservoir pressure, among other factors. Though this is considered the optimum development strategy that could lead to economic recovery of CBM, any single factor can be affected by unpredictable nuances in a land’s profil. An increasing concern is the effect water discharges from CBM development could potentially have on downstream water sources. Disposal of the highly salinized water that must be removed in order to release the methane creates a challenge, as its introduction into freshwater ecosystems could have adverse effects. Land disputes have emerged regarding claimed effects of waters as well as the water damage that might arise in the future.
CBM development is a rapidly emerging industry and is considered an important source of energy. Communication links and information sharing between industry, government, non-governmental organizations, private developers and individual landowners will remain critical if this energy source is to be developed responsibly.
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