An in situ method of producing hydrocarbon fluids from an organic-rich
rock formation is provided. The method may include heating an
organic-rich rock formation, for example an oil shale formation, in situ
to pyrolyze formation hydrocarbons, for example kerogen, to form a
production fluid containing hydrocarbon fluids. The method may include
separating the production fluid into at least a gas stream and a liquid
stream, where the gas stream is a low BTU gas stream. The low BTU gas
stream is then fed to a gas turbine where it is combusted and is used to
generate electricity.