Abstract:
Geothermal energy is considered as an attractive alternative source of energy in some parts of the world. In general, geothermal systems can be identified as either open- or closed-loop. In an open-loop system, fluid is produced from the subsurface, while there might be some concurrent fluid injection into the reservoir. The loss of working fluid, surface subsidence, formation compaction, and induced seismicity are major shortfalls of the open-loop systems. To address the indicated challenges, closed-loop geothermal systems can be considered as an alternative option. In this method, a working fluid with low boiling point is circulated through the coaxial sealed pipes to extract the stored heat from the formation rock and fluid. To improve the heat extraction from closed-loop wells, we introduce a highly conductive hydraulic fracture to the system to improve the rate of the heat extraction from the surrounding rocks. Considering the multiphysics nature of the heat extraction from such systems, a comprehensive analysis of this problem requires simultaneous modeling of the interactions between fluid flow, heat transfer and rock deformation. A numerical thermo-poroelastic model is developed using the finite element methods to simulate this problem. The numerical results suggest that fractured wellbore has significantly larger thermal power and cumulative extracted heat than the unfractured wellbore in the proposed closed-loop configuration.
Introduction
Geothermal energy is referred to as an attractive energy resource to address the increasing electricity demand in various parts of the world. This energy resource is derived from the decay of the radioactive materials, such as uranium, thorium, and potassium, or the stored heat in the earth core during the formation of planet Earth. Armstead (1983) showed that the total heat content of the earth is in the order of 12.6 × 1024 MJ from which we only harvest a small portion. Geothermal energy is weather-independent compared to wind or solar energy and is environmentally friendly in comparison to the fossil fuels. Production of electricity from geothermal resources places it third among other renewable resources. Cumulative electricity production from the geothermal reservoirs is higher than the solar and wind resources, however less than the hydroelectricity and biomass. Geothermal resources in the US have the capacity to supply 10 percent of current national electricity consumption by 2050 (Giardini, 2009). Williams et.al (2008) showed that US can economically produce 100 GWe from the enhanced geothermal systems by 2050.
