Abstract: A borehole packer used with the water infusion system to control the movement of methane gas in an underground coal mine. A non-sparking plastic pipe or mandrel is mounted in each of a series of previously drilled generally horizontal boreholes. Normally this pipe is sealed by an encircling packer in the form of an expandable envelope. The mandrel and envelope are put in each borehole to a depth of about 110 to 185 feet with about 15 feet near the end away from the borehole entrance being opened. The flexible expandable envelope extends along almost all of the length of the hollow mandrel. In the volume between the outer surface of the mandrel and the envelope a hardenable fluid grout under pressure is pumped. As the grout fills this cavity the packer's flexible surface expands within the borehole until it forms a tight seal therewith. Because the grout is in an initial fluid state, it is flowable when forced into the packer and it can flow around irregular borehole surfaces.