Abstract: A method for utilizing the inner energy of an aquifer fluid includes geothermal thermal water mixed with gas and optionally crude oil in a closed cycle to obtain an environmentally-neutral, carbon-dioxide-free utilization of the aquifer fluid and an environmentally-friendly supply of electric and thermal energy. An aquifer fluid is removed from an aquifer by means of a removal device, gas is separated by degassing the aquifer fluid in a gas-separation device, optionally crude oil is separated if necessary, the heat energy of the thermal water is utilized in at least one system for utilizing the thermal energy, the extracted gas and the optionally separated crude oil is com busted in at least one combustion device and the inner energy of the gas is utilized by operating a generator, the CO2 being removed from the waste gas and recycled into the aquifer.