Abandoned petroleum wells as sustainable sources of geothermal energy

A reliable heat transfer model was developed to determine the performance of a double pipe heat exchanger retrofitted to an abandoned petroleum well. The proposed model is compared against an analytical heat transfer model and two numerical models, in order to determine the reliability and accuracy of the proposed model. Rock mass properties and well dimensions are based on realistic averages, with the geothermal gradient and depth of the well based on an abandoned well in the Persian Gulf. The proposed model makes use Fourier's diffusion law coupled with terms to account for the unsteady state of the model and the convective heat transfer. These three properties are coupled with the energy conservation equation and simulated with the finite element modeller FlexPDE. The proposed model was developed with a constant inlet temperature and a constant power configuration. The constant inlet temperature model is used to ascertain the effects of insulation, inlet fluid temperature, mass flow rate, thermal conductivity of the rock mass, geothermal gradient, and vertical groundwater flow. The constant power model is better suited to direct use and heat pump applications due to the requirement of a stable power source.