I did a consulting job for a guy, at least 15 years ago on this. Old gas wells, producing water from below the old producing gas zone. He was intending to power the pumps for reinjection using energy from the well.
Wells are my expertise but using sophomore engineering and physics, he needed more energy than the well was going to produce.
Be careful and so your "sums" and how much energy will you produce and how much do you need for operations!
BTW, the guy never paid me!
Doug White
Sugar Land