Gas Well Conversion to Geothermal: A Case Study for Oklahoma

Abstract

Natural gas wells in Oklahoma’s Anadarco Basin are as deep as 25000 ft with an average gradient of 0.8-1.1°F/100ft. As many of these wells mature, it’s water to gas ratio continuously increases till it becomes non productive and is consequently shut in. This paper aims at providing a solution for the latter stages of a gas well initially using the gas as a fuel source for electricity and the hot production water later as a fuel source for the binary geothermal plant. Electricity generated from this produced water increases life of the well as well as increases dependency on geothermal energy. The system uses gas microturbines for electricity production with natural gas as a fuel. These low investment and low maintenance devices can be efficient up to 80% with waste heat recovery included. These turbines generate 25-500 kW depending on its size. Keeping economics in mind, it will take only 100 gas wells to produce 50 MW of energy at 500kW each. These devices can also work in a cogeneration system in which natural gas can be burnt to heat the produced water to generate steam for running the turbines. In later stages of the well, when water production completely dominates, the system can switch over to a standalone binary power plant that utilises the water to heat a power fluid to run the turbines. The water is then re-injected to complete the loop. This mechanism is very feasible in a state like Oklahoma that ranks third in total volume of water produced in the nation as shown by a study in 2012, owing to its large number of mature wells.