Patent ID: 8596356

Claim:
A method of producing synthesis gas by the underground gasification of coal from a coal seam comprising: (a) cementing casing string in a production well and an injection well which penetrates the coal seam by pumping into the wellbore a cementitious slurry having a density between from about 7.0 ppg to about 23.0 ppg, the cementitious slurry comprising a cement mix which comprises: (i) between from about 10 to about 70 weight percent of a cementitious material selected from the group consisting of Portland cement, pozzolan cement, fly ash cement and silica fume; (b) between from about 5 to about 70 weight percent of graphite; and (c) between from about 5 to about 70 weight percent of an aluminum silicate, and allowing the slurry to set to form a cement sheath in the wellbore; (b) igniting the coal in the coal seam; (c) introducing oxidant gas into the injection well; and (d) generating syngas as a combustion front in the coal seam and advancing the combustion front through the production well, wherein the temperature of the combustion front is greater than or equal to 800° C. and further wherein the heat from the combustion front is distributed along the cement sheath in the wellbore.