Gob Wells—Is There a Way to Predict Water Makers?

Vertical gob wells are an efficient method of methane extraction from an actively mined longwall coal panel. These vertical wells are used for degasification of the gob area after mining. They are drilled above the predicted gob area before commencing with mining of the panel to within 50 feet of the top of the coal and become active once the face of the longwall travels far enough past the drilled well for the gob roof to fall and allow for methane to flow into the well from the gob area. The methane then travels up the well to the surface to be collected or vented to the atmosphere. At Coronado’s Buchanan mine in Buchanan County, VA, these wells are drilled through 1,500–2,500 feet of overburden. These wells can penetrate up to two previously mined coal seams and are cased below the elevation of the lowest seam. There are approximately 20 vertical gob wells drilled per panel at intervals of about 500 feet. This method of degasification seems to work well for this mine’s requirements. A typical well can initially produce methane at a rate of 1.50 MMcf/day at a volume concentration of 83%.