Substoichiometric combustion of low heating value gases using different platinum catalysts

The in situ combustion process for recovering liquid hydrocarbons from subterranean formations which comprises injecting a stream of combustion air into at least one injection well leading to a combustion zone in said subterranean formation, producing liquid hydrocarbons and combustion gas from at least one production well, separating the liquid hydrocarbons from the stream of combustion gas whereby a separated stream of flue gas is obtained having a heating value between about 15 Btu/scf and about 200 Btu/scf and containing at least one aliphatic hydrocarbon having from one to about seven carbon atoms, passing said flue gas stream admixed with air for combustion through two combustion zones in series comprising a first combustion zone and a second combustion zone in contact with an oxidation catalyst in the first combustion zone comprising from about 0.2 to about ten weight percent platinum on an inert support and in contact with an oxidation catalyst in the second combustion zone comprising from about 0.05 to about five weight percent platinum on an inert support, the ratio of the concentration of platinum on said oxidation catalyst in the first combustion zone to the concentration of platinum on said oxidation catalyst in the second combustion zone being between about 1.2:1 and about 20:1, at a temperature in each combustion zone which is high enough to initiate and maintain combustion of said gas stream, the total amount of combustion air being sufficient to provide an overall air equivalence ratio between about 0.30 and about 0.80, expanding the gas stream in a gas turbine following said catalyzed combustion, and driving an air compressor with said gas turbine to compress and inject said stream of combustion air into the said subterranean combustion zone.