Abandoned Oil and Gas Wells as an Alternative Geothermal Energy Source: Current Practices and Way Forward

Abandoned oil and gas wells (AOGWs) are a prospective source of geothermal energy for sustainable development by opting for various geothermal energy systems (GTESs), viz., deep borehole heat exchangers and enhanced geothermal systems. In our opinion, the feasibility of utilizing AOGWs can be quantified by employing the yield of heat (YOH), defined as geothermal heat extraction efficiency, and the duration of heat extraction (DOHE). Both YOH and DOHE depend on the heat transfer mechanism(s) and changes that occur in the reservoir due to thermo-hydromechanical-chemical coupling. As such, some of the contemporary issues that need to be addressed for understanding YOH and DOHE are (1) optimizing an appropriate GTES for heat extraction, (2) analyzing the interaction between low-temperature working fluids, including water, organic fluids, and CO2, and the reservoir formation, and (3) evaluating the influence of various operational parameters, reservoir characteristics, and the thermal properties of both the reservoir formation and working fluid on the geothermal heat extracted. However, the prohibitive cost and time required for simulations, in situ experiments, and laboratory tests for understanding the mentioned contemporary issues are big deterrents to the growth of this niche area. Hence, it would be prudent if the interdependency of parameters and prevailing mechanisms could be established by synthesizing the data available in the literature before going for any pilot study. This review presents details of such an exercise, and it is believed that the findings would be useful in deciding upon the feasibility of the AOGWs as a source to harness geothermal energy sustainably.