In-situ method of coal gasification

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 boreholes being an injection borehole;
• providing each of the substantially horizontally disposed boreholes with remotely controlled valve assembly for selectively closing off and establishing fluid communication between selected substantially horizontally disposed borehole and the substantially vertically disposed borehole;
• actuating the remotely controlled valve assemblies so that the at least one substantially horizontally disposed fracturing borehole is in fluid communication with the at least one substantially vertically disposed borehole and the at least one substantially horizontally disposed injection borehole and the at least one production boreholes are closed off from 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 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;
• actuating the remotely controlled valve assemblies so that the at least one substantially horizontally disposed fracturing borehole is closed off from the substantially vertically disposed borehole and the at least one substantially horizontally disposed injection borehole and the at least one production boreholes are in open communication with the substantially vertically disposed borehole;
• introducing an effective amount of an oxidant and stream into the network of fractures in the subterranean formation containing a coal seam to support combustion of the coal;
• igniting the coal so as to produce resulting hot, pressurized gases containing methane, hydrogen, carbon monoxide and carbon dioxide which travel upwardly through the formation to the at least one production borehole;
• and
• recovering the resulting hot, pressurized gases from the least one production borehole.