Study of Fracture Aperture Variation in a Fracture Network on Heat Production from an Enhanced Geothermal System (EGS)

Abstract

With the development of the Enhanced Geothermal System (EGS) technology, extensive geothermal energy applications have become feasible. To simulate fluid migration and heat propagation within a fractured geothermal reservoir, discrete fracture models (DFMs) of the TH processes are widely used. However, the variability of aperture size from one fracture to another is typically ignored in these models. In this work, a discrete fracture model considering variable aperture fractures is applied to investigate the performance of a geothermal reservoir in EGS. The fracture apertures are randomly distributed within the networks, but constant for one single fracture. The simulation results show that the heat production rate and outlet temperature can be divided into three stages based on the value of coefficient of variation of fracture apertures. The higher variability results in the low heat production rate but high outlet temperature. On the other hand, the average heat production rate is proportional to the fracture density. However, the effect of fracture density is reduced with an increase of coefficient of variation. Furthermore, the comparison between fracture aperture and density shows that, the increase in mean fracture aperture leads to a higher increase in average heat production rate than an increase in fracture density.