Optimizing Geothermal Heat Extraction from End of Life Oil & Gas Wells Using a Transient Multiphase Flow Simulator

Oil and gas wells that have reached their economic end of life or have never been put into production for any reason may have potential for an alternate form of energy. Geothermal energy can be extracted from wells and is dependent upon numerous factors, but primarily by the thermal gradient of the region and the well depth. These two primary factors cannot be altered, however the design of the completion and production systems for extracting geothermal energy can significantly impact the amount of energy that can be extracted. This paper presents results from evaluating the rate of thermal energy that can be extracted under various completion scenarios using a transient flow simulator. This evaluation was conducted on closed loop systems whereby the fluids are contained within the well bore and surface facilities and do not involve any formation fluids. The results from the transient flow simulator show that the direction of flow circulation and insulation of the tubing string are crucial in evaluating assorted options to diminish thermal losses. There is an economic decision required for the decision on insulation type Results were also obtained for using the system to store energy in the upper regions of the well during time periods when there is no heat required from the system. This improves thermal recovery efficiencies when heat demand returns. Based on analyses of the simulations the two-stage storage/extraction processes significantly improved the technical, economic and environmental merits of the previously developed coaxial technology for heat generation. The use of a multiphase flow simulator for this study provides a roadmap for understanding the thermal energy potential, as well as the most important variables when considering extraction of geothermal energy from existing oil and gas wells.