Investigations of Water Flow Behaviors Induced by Local Temperature Variations through a Single Rough Fracture for the Enhanced Geothermal Systems

In recent years, Enhanced Geothermal System (EGS) technologies have been applied to the geothermal resources production in the Hot Dry Rock (HDR). The core of EGS technologies is to adopt hydraulic fracturing in the reservoir to create a connected network of discrete fractures with the consideration of water as a working fluid for hydraulic fracturing and heat production. This paper investigates the characteristics of water flow behaviors through a single rough fracture under different temperature and pressure conditions. A single fracture model with rough fracture surfaces is constructed and then characterized, and influences of the anisotropic factor on the average tortuosity and frictional resistance coefficient of water flow through a single fracture with rough surfaces have been compared and analyzed. With consideration of other impacting factors (temperature, pressure, fracture roughness), the impact of mass flow rate has also been presented. Numerical simulation results present that changes of average tortuosity for water flow through a single rough facture are mainly affected by temperature. It can be observed that higher temperature leads to larger average tortuosity but the frictional resistance coefficient shows an opposite trend. As for pressure conditions, it is found that effects of pressure on average tortuosity and frictional resistance coefficient is very small, which can be neglected under high pressure conditions. Furthermore, the average tortuosity shows a progressively linear relationship with the mass flow rate. On the contrary, the frictional resistance coefficient has a negative relationship with the mass flow rate. It is revealed that when the mass flow rate reaches a critical point, the influences of temperature on the frictional resistance coefficient will be negligible. Comparisons of single rough fractures with different anisotropic factors show that values of average tortuosity and frictional resistance coefficient have positive relationships with the increase of anisotropic factors.