Numerical study on heat extraction performance of a multilateral-well enhanced geothermal system considering complex hydraulic and natural fractures

The complex fracture network is necessary to provide flow and heat transfer channels for working fluid of an enhanced geothermal system (EGS). It is significant to compare heat extraction performances of different complex fracture networks and to provide suggestions for fracturing operation of an EGS. Based on a 3D thermal-hydraulic-mechanical coupled model, this paper studies heat extraction performances of 11 different complex fracture networks with natural and hydraulic fractures for a multilateral-well EGS. Effects of natural and non-planar fractures on multilateral-well EGS performance are investigated. Influences of primary fracture stage quantity on multilateral-well EGS performance are studied. Contributions of primary and secondary fractures to heat extraction of multilateral-well EGS are compared. Results indicate that natural fractures should be considered when accurately estimating multilateral-well EGS performance. The model with planar fracture networks overestimates production temperature and thermal power of multilateral-well EGS. It is suggested that 3 stages of primary fractures are beneficial for multilateral-well EGS performance. Fracturing operation of multilateral-well EGS should focus on generating long fractures to connect natural fractures far from lateral wells rather than inducing numerous fractures around lateral wells. Simulation results provide significant suggestions for the fracturing operation of multilateral-well EGS. (C) 2019 Elsevier Ltd. All rights reserved.