Recovering coal bed methane from deep unmineable coal seams and carbon sequestration

Published data from nearly 2,000 coal samples comprising 250 coal beds from 17 states, representing many of the coal producing horizons in the USA, shows moderate correlation (0.7) between depth and methane content for high volatile coal ranks. Low-volatile rank coals average the highest methane content, 12.74 m3/ton (450 ft3/ton), subbituminous rank coals the lowest, <0.71 m3/ton (<25 ft3/ton). Experimentation under replicated in situ conditions of triaxial stress, pore pressure and temperature on Pittsburgh No. 8 coal indicate permeability decreases with increasing CO₂ pressure, with an increase in strain in the coal associated with its swelling.