How do gas companies extract the methane from the coal seam?
Methane travels with the ground water being pumped from the coal from a well drilled and completed in a coal seam that contains methane and fixed with a water pump. Since methane has very low solubility in water it separates from the water in the well before the water enters the pump. The extraction of CBM involves pumping the available water from the coal seam aquifer in order to reduce the water pressure that holds the gas in the coal seam. CBM producers try not to dewater the coal seam. The goal is to decrease the water pressure (or head of water) in the coal seam to just above the top of the seam. However, sometimes the water level drops into the coal seam. Water moving from the coal seam to the well bore encourages gas migration toward the well. As this water pressure is released, the gas will rise and is separated from the water and piped away.
