Abstract: An underground carbonaceous deposit containing other mineral values is burned in situ. The underground hot zone is cooled down to temperature below the boiling point of a leaching solution. The leaching solution is percolated through the residial ash, with the pregnant solution recovered for separation of the mineral values in surface facilities.

Abstract: Medium BTU gas is generated from coal in situ by establishing communication channels through the coal in part by projectiles and in part by burning. Oxygen is employed for reaction with the coal and reaction temperatures are controlled by injection of steam.

Abstract: An underground coal fire is smothered by sealing the overburden for a minimum depth over the coal deposit. Wells are drilled into the fire area and the underground reaction zone is pressurized. Using various combinations of injecting oxidizers and reducing agents the coal deposit is produced in situ to yield a variety of useful products. Wells are cased without cement and with the hermetic seal attained by a column of slurry between the casing and well bore.

Abstract: This invention relates to the production of combustible gases from coal in situ, in which one or more passages are established between the surface of the ground and an underground coal deposit. The coal is set afire and the fire is sustained by injection of an oxidizer for a period of time. Oxidizer injection is terminated, followed by injection of steam for a period of time into the hot coal bed. Produced gases are captured at the surface. Products of combustion from the burn cycle are saved at the surface, reconstituted by the addition of oxygen, then reinjected for subsequent burn cycles until the sulfur dioxide content is sufficiently high to warrant recovery in surface facilities. Condensible gases are cooled in surface facilities with liquids captured apart from noncondensible gases.