Abstract
Abstract. Enhanced Geothermal Systems (EGS) are widely used in the development and application of geothermal energy production. They usually consist of two deep boreholes (well doublet) circulation systems, with hot water being abstracted, passed through a heat exchanger, and reinjected into the geothermal reservoir. Recently, simple analytical solutions have been proposed to estimate water pressure at the abstraction borehole. Nevertheless, these methods do not consider the influence of complex geometrical fracture patterns and the effects of the coupled thermal and mechanical processes. In this study, we implemented a coupled thermo-hydro-mechanical (THM) model to simulate the processes of heat extraction, reservoir deformation, and groundwater flow in the fractured rock reservoir. The THM model is validated with analytical solutions and existing published results. The results from the systems of single fracture zone and multi-fracture zones are investigated and compared. It shows that the growth of the number and spacing of fracture zones can effectively decrease the pore pressure difference between injection and abstraction wells; it also increases the production temperature at the abstraction, the service life-spans, and heat production rate of the geothermal reservoirs. Furthermore, the sensitivity analysis on the flow rate is also implemented. It is observed that a larger flow rate leads to a higher abstraction temperature and heat production rate at the end of the simulation, but the pressure difference may become lower.
Highlights
The Increasing development of geothermal energy has become a central issue globally for its low-carbon generation and environmental friendliness (Sun et al, 2018)
An Enhanced Geothermal System (EGS) is a man-made reservoir created in the subsurface where hot rocks are available, but they are insufficiently permeable for the high flow rate circulation to be economical
Having the model verified with analytical solutions and published results, we studied the effect of different reservoir characteristics, e.g., single fracture zone compared to the complex system on heat production
Summary
The Increasing development of geothermal energy has become a central issue globally for its low-carbon generation and environmental friendliness (Sun et al, 2018). Zhou et al.: Thermo-hydro-mechanical modelling study of heat extraction cost-effective, i.e., the cost of injection and abstraction will be too high These two criteria are investigated in our study. A mathematical model capable of handling the thermal, hydraulic, and mechanical (THM) coupled processes was developed and implemented within different numerical simulators for the investigation of the performance of the geothermal reservoirs in EGS (e.g., Ogata et al, 2018; Pandey et al, 2018; Danko and Bahrami, 2012; Li et al, 2016). In this study, we investigate the THM effects induced by the fracture zone number and spacing on the overall pressure and temperature distributions at the injection and extraction wells by comparing the results successively among several sets of parallel fracture zones. A sensitivity analysis on the flow rate is implemented to investigate the role of flow rate in the heat production process in EGS
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