Abandoned oil and gas wells exploitation by means of closed-loop geothermal systems: a review

In mature oilfields, decommissioned oil and gas wells with depths reaching approximately 5000-6000 metres represent good candidate structures for geothermal heat exploitation, as they can provide useful access to subsurface geothermal energy resources. Comprehending the possibility to economically harness geothermal energy by means of coaxial WBHEs is bound to the main features of the physical model, applied to estimate the amount of heat that can be gained from the borehole. Simultaneously, due to the continuous spatial variability of geological formations in oilfields, accurate and realistic estimates of the heat exchanger performances cannot be separated from a proper consideration of the thermophysical parameters of geological strata surrounding the hydrocarbon wells.