A system and method is disclosed for treating a mixture of hydrocarbon and carbon dioxide gas produced from a hydrocarbon reservoir. The system includes a gas power turbine adapted to burn the produced gas mixture of hydrocarbon and carbon dioxide gas with oxygen as an oxidizing agent and a capture system to collect the exhaust gas from the power turbine. An inlet compressor receives exhaust gas from the capture system and compresses the exhaust gas for injection of the exhaust gas into a hydrocarbon reservoir and for recycle to the power turbine. The system may further include a membrane system that preferentially removes carbon dioxide and hydrogen sulfide from the produced gas stream before said stream is used as fuel gas in the power turbine. The carbon dioxide and hydrogen sulfide removed by the membrane system is combined with the exhaust gas, and the combined gas is injected into a hydrocarbon reservoir.