Abstract: Electricity is generated during the injection of a dense fluid through an injection well and into a subterranean formation having a connate fluid pressure less than the available downhole pressure of injection fluid in the injection well. A fluid engine/generator is positioned in the well to define upper and lower zones in the well; a level of dense fluid is established in the upper zone; and dense fluid is flowed from the upper zone through the fluid engine/generator and into the subterranean formation to thereby generate electricity, which is subsequently recovered. Control of the downhole fluid pressure is also achieved.