Kevin, Just read your idea of underground coal gasification. How do you plan to control the release of the hydrogen and co2? I remember hearing of under ground fires in coal mines that were sealed because they could not put them out and just left to burn and it caused a VERY big health problem for the people above the mines that were still burning. It would be better to forget about those seams and just pipe the co2 from coal burning plants and feed it to algea growing systems built next to the power plants now and in the future. This would reduce the co2 released into the air and provide a fuel source at the same time.
If is too deep to mine, it is probably too deep to provide a control release of the gases made by the fire