Abstract
Hydraulic fracturing has been used to accelerate removal of methane from coal seams ahead of underground mines. Originally, all of the gas that was produced was flared or vented. Over the past decade, however, there has been a growing awareness of the vast potential for recovery of methane gas from coal seams. This awareness is leading to the commercial exploration and development of coalbed methane reservoirs in many areas of the U.S.
Coalbed methane production is viewed as a new and significant energy source. Associated methane gas from coal is now the primary source of natural gas for the state of Alabama and is rapidly becoming a major source of natural gas in the San Juan Basin of New Mexico and Colorado.1–6 The natural gas industry is still learning how to complete wells and produce gas from coal-seam reservoirs. Compared to our knowledge of techniques for the completion and production of sandstone and limestone reservoirs, our knowledge in coal-seam reservoirs is minimal, at best.
The success achieved in producing gas from shallow coal has encouraged some operators to explore for gas trapped in deep coal seams that will never be mined. One area of significant activity is the San Juan Basin. To optimize recovery from most of the wells drilled into deep coal seams, hydraulic fracturing treatments are required. Experience has shown that the design and execution of fracture treatments in coal seams is not straightforward. High injection pressures, complex fracture systems, screenouts and the production of proppant and coal fines after the treatment are typical problems facing the operator.
