Heat transfer characterizations of water flow through a single fracture with integrating water dissolution effects for the Enhanced Geothermal Systems

The Enhanced Geothermal Systems (EGS) is the technology that generates connected fracture networks in the Hot Dry Rock (HDR) reservoir with the application of water as the working fluid for hydraulic fracturing and geothermal energy production. A good understanding of water flow behaviors in the single fracture is critically important because connected fracture networks are composed of individual fractures. It should be noticed that the dissolution reaction between the reservoir rock and the working fluid (water) will change the fracture surface directly and consequently affect the mass and heat transfer process of water through the rock fracture in the HDR reservoir. In this study, the heat transfer process of water flow in the single fracture by considering dissolution reactions between water and fracture surfaces of reservoir rock have been investigated under high pressure and temperature conditions. The experiments of dissolution reaction and convective heat transfer have been performed separately for different temperature conditions with the rock sample of 0.2 mm fracture aperture. The influences of reaction duration, mass flow rates and initial temperature have been presented and analyzed. It is found that mass flow rates and temperature have significant effects on measured temperature of fracture surfaces. The effects of dissolution reaction on fracture surface morphology exists but it is extremely small for heat transfer. Based on experimental and simulation data, a modified correlation that integrates reaction duration, mass flow rates and changes of thermophysical properties has been proposed and its maximum error that compares with experimental results is less than 7%. The results of this study provided an accurate correlation for simulations and characterizations of the Hot Dry Rock reservoirs, which is of great importance for geothermal energy production and optimization.