The role of fracture networks randomness in thermal utilization of enhanced geothermal system

The construction of fracture networks is crucial to utilization of deep geothermal energy such as hot dry rock resources, which is benefit to build an engineered reservoir with high permeability for enhanced geothermal system. In present work, the supercritical carbon dioxide is used as working fluid, and the three-dimensional fracture networks with Python programs are established. The effects of randomness, groups, numbers, crossing angle, strike pitch and geometry of fracture networks on the production performance of EGS are numerically investigated. The results show that the initial discrete fractured model has a 22.5 years of high yield period, accounting for 45% of the total operation time, and the production temperature varies from 473.15 K to 436.82 K. It's found that the injection pressure decreases by 21.6% from 54.6 MPa to 42.8 MPa, which is derived from the fact that the permeability of fracture networks has increased by about 5 times. The results indicate that the maximum and minimum output thermal powers are 13.35 MW and 11.4 MW, respectively. Furthermore, the production temperature and injection pressure are more significantly affected by fracture length than that by fracture number does. When the fracture number is 200 and fracture length is 100 m, the production performance is better. The unordered fracture networks can cause a significant decline of 15.51% in thermal power. The longer fractures in thermal reservoir can decrease the injection pressure. The fracture density of 0.007 m(-1)-0.009 m(-1) is benefit to the discrete fractured enhanced geothermal system model. The heat recovery efficiency of the enhanced geothermal system can be improved by changing fracture strike.