FEASIBILITY STUDY OF HEAT EXTRACTION FROM A CLOSED-LOOP FRACTURED GEOTHERMAL RESERVOIR; A MULTIPHYSICS PROBLEM

Geothermal energy is recognized as an attractive, alternative energy resource to generate electricity in some parts of the world. Production of greenhouse gases in geothermal plants is significantly lower than fossil-fuel plants. In general, geothermal systems can be identified as either open- or closed-loop. There are several challenges during heat extraction from the open-loop systems. For instance, Loss of working fluid, affecting total cost of the generated electricity, is a common issue. However, the drawbacks are not limited to loss of working fluid. Surface subsidence, formation compaction, and induced seismicity are other disadvantages of heat extraction from the open-loop geothermal systems.

To address the indicated issues, a closed-loop geothermal system can be considered as an alternative solution. A closed-loop geothermal system has negligible environmental hazard compared to an open-loop system. For instance, produced water form the open-loop system contains high level of sulfur, salt, and radioactive elements. However, in a closed-loop system, none of these in-situ materials are produced with working fluid as there is no contact between working fluid and geofluid.

In the US, significant numbers of abandoned oil or gas wells exist which theoretically can be transferred into the geothermal wells to produce electricity. This study tries to show the feasibility of electricity production from these wells, using a closed-loop configuration to minimize the environmental hazards. To improve the heat extraction from these wells, we show how the presence of induced hydraulic fractures can affect the heat extraction in these wells. To consider multiphysics nature of heat extraction from such a system, comprehensive analysis of this problem requires simultaneous modeling of interaction between fluid flow, heat transfer and rock deformation. A numerical thermos-poro-elastic finite element model is developed to couple the interaction indicated parameters. Following result provides a brief description of specified problem.