Patent ID: 7264049

Claim:
A method for enhancing in-situ coal gasification of subterranean coal by providing a network of fractures in a subterranean formation containing seams of the coal, the method comprising the steps of: providing a substantially vertically disposed borehole; providing a plurality of substantially horizontally disposed boreholes in fluid communication with the substantially vertically disposed borehole, at least one substantially horizontally disposed boreholes being a fracturing borehole, at least one substantially horizontally disposed boreholes being an injection borehole and at least one substantially horizontally disposed borehole being a production borehole; providing each of the substantially horizontally disposed boreholes with a remotely controlled valve assembly for selectively closing off and establishing fluid communication between the selected substantially horizontally disposed borehole and the substantially vertically disposed borehole; introducing an initial quantity of liquified gas into the at least one substantially horizontally disposed fracturing borehole such that the liquified gas communicates with the formation; allowing the quantity of liquified gas to vaporize in a portion of the at least one substantially horizontally disposed fracturing borehole whereby a resulting increase in pressure in the at least one substantially horizontally disposed fracturing borehole forms fractures in the formation; introducing an additional quantity of liquified gas into the at least one substantially horizontally disposed fracturing borehole; allowing the additional quantity of liquified gas to vaporize in the at least one substantially horizontally disposed fracturing borehole whereby a resulting increase in pressure in its at least one substantially horizontally disposed fracturing borehole forms additional fractures in its formation.