Theoretical Numerical Simulation of the Effect of Fracture Distribution Characteristics on EGS Heat Extraction

Abstract

The heat extraction from an enhanced geothermal system (EGS) strongly depends on the structure of fracture network of the reservoir. As the strong non-uniform distributed fracture networks are generally stimulated in EGS reservoir, a parallel multi-fracture non-uniformly distributed model is built to study the impact of fracture distribution characteristics on EGS heat extraction. Here, the concept of the preferential flow ratio and preferential thickness ratio are introduced to characterize the non-uniformity in fracture distribution. Theoretical simulation results show that the heat extraction performance for a non-uniformly stimulated reservoirs, will be co-affected by the number of fracture and the distribution characteristics of the fracture. The production temperature is in a loose positive relation to the number of fractures, and in a negative correlation to the preferential flow ratio and preferential thickness ratio. Moreover, it can enhance the heat extraction performance by blocking the preference fracture or narrowing the gap of fracture widths. To seal the inferior rock HTU or enhance the stimulation degree by increasing fracture number can also enhance the heat extraction efficiency. The results indicate that it is favorable to exploit the heat reservoir with the conditions of sufficient fractures and evenly distributed fracture width.