Fracture spacing in horizontal well multi-perforation fracturing optimized by heat extraction

Abstract

Multi-perforation fracturing in horizontal wells is the key procedure in the operation of enhanced geothermal system (EGS). However, two questions remain unclear: 1) what are the similarities and differences between three fracturing methods; and 2) how to optimize fracture spacing (FS)? Here we established a three-dimensional hydraulic fracturing model to unveil fracture initiation and propagation mechanisms. The fractures obtained by hydraulic fracturing were subsequently embedded in a geothermal mining model. Heat extraction was used as an evaluation indicator to optimize FS and geothermal mining. We found that the initiation pressure in multi-perforation fracturing is higher than that in single-perforation fracturing. The stress shadowing increases with increasing time and decreasing FS. FS not only changes the complex fracture network, but also affects the low-temperature area of hot dry rock. Quantitative analysis of heat extraction shows that the optimal FS in simultaneous, sequential,and alternate fracturing are 30 m, 40 m, and 50 m, respectively. Our study benefits fracturing method selection and construction parameter optimization in EGS operation.