Abstract
Hydraulic fracturing is usually employed to create a complex fracture network to enhance heat extraction in the development of an enhanced geothermal system. The heat extraction depends on the heat conduction from the rock matrix to the flowing fractures and the heat convection through a complex fracture network. Therefore, the geometries of the fracture network have important influences on the thermal breakthrough. In this paper, a hydro-thermal coupling mathematical model considering a complex fracture network is established. The embedded discrete fracture model is adopted to explicitly model the individual fracture on the mass flow and heat transfer. The model is validated by analytical solutions. Fracture network parameters are changed systematically to investigate the effects of fracture network distribution including regular and complex shape on the thermal production performance. The results show that the increase of producing pressure differential, fracture number, and conductivity will cause an early thermal breakthrough. The strong variation in fracture conductivity, as well as spacing and orientation, will cause thermal flow channeling and decrease the efficiency of heat extraction. A modified connectivity field is proposed to characterize the spatial variation of fracture network connectivity, which can be used to infer the thermal flow path.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
A non-traditional geothermal system refers to an enhanced geothermal system (EGS) in which the working fluids is injected via injection wells and the energy transfers from hot dry rock (HDR) by the way of heat conduction due to the absence of hot fluids in dry rocks [6,7,8]
In this paper, based on embedded discrete fracture model (EDFM), a mathematical model considering the main mechanisms in the mining of EGS and complex fracture networks is developed and the influences of fracture network properties on heat transfer are systematically investigated to instruct the development of EGS
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Employed marked point processes to develop a new computer code for discrete fracture network modeling In their studies, fracture geometries and properties are modeled by their respective probability distributions. Gan and Elsworth [32] coupled discrete fracture network modeling and optimized the heat production strategies for EGS geothermal reservoirs. They found that the fracture orientation played an essential important role in influencing the simulation results. The numerical simulation accounting for a densely arbitrary distribution of fracture networks coupling mass flow and heat transfer has not been well established. In this paper, based on EDFM, a mathematical model considering the main mechanisms in the mining of EGS and complex fracture networks is developed and the influences of fracture network properties on heat transfer are systematically investigated to instruct the development of EGS
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