Mining Publication: Pressure Monitoring and Observed Effects of Mining at the Oak Grove, AL, Coalbed Degasification Pattern

The U.S. Bureau of Mines and the United States Steel Corporation evaluated the progress of methane drainage at the Oak Grove, Alabama, degasification pattern. Coalbed pressures were monitored between December 1981 and November 1985. Formation pressures, in the lower bench of the Mary Lee coalbed, were reduced from 400 lbf/in2(ga) in 1977 to 50 lbf/in2(ga) in November 1985. Gas contents of coal cores obtained from monitor wells were compared with coalbed gas contents measured in 1976. Data indicated a 48- to 56-pct reduction within the pattern and a 29-pct reduction at a point 500 ft outside the pattern. The effect of the advance of a section of the Oak Grove Mine on changes in gas and water production rates in the pattern was evaluated. Gas production increases were noted in 12 wells; water production decreases were noted in 6. The times of initial influence indicate the presence of a zone of high permeability within the pattern. This zone correlates well in orientation and location with a fracture zone mined through at the mine. The existence of such fracture zones could have a significant effect on productivity of individual coalbed methane wells.