Analysis for effects of complex fracture network geometries on heat extraction efficiency of a multilateral-well enhanced geothermal system

Abstract

The reservoir stimulation is important for the enhanced geothermal system (EGS), because it creates an effective fracture network to provide heat extraction channels for the working fluid to acquire commercial heat flow. Investigating heat extraction efficiencies of different fracture network geometries can provide suggestions for the EGS fracturing. This paper uses a 3D thermal-hydraulic-mechanical coupling model to study heat extraction efficiencies of 8 different fracture network geometries for a novel multilateral-well EGS. The effects of primary fracture stage quantity and position on the multilateral-well EGS efficiency are investigated. Contributions of primary and secondary fractures to the heat extraction of a multilateral-well EGS are compared. Heat extraction characteristics of a multilateral-well EGS with orthogonally intersecting fractures and bifurcated fractures are analyzed. Results indicate that the primary fracture stage quantity and fracturing position have significant effects on the multilateral-well EGS efficiency. A larger distance between the first stage fracture and lateral-well intersection is beneficial for the multilateral-well EGS efficiency. A multilateral-well EGS with bifurcated fractures has higher efficiency than orthogonal fractures. The fracturing operation of the multilateral-well EGS should focus on creating long secondary fractures to connect reservoir far from lateral wells rather than generating numerous fractures near lateral wells. Results provide significant suggestions for the fracturing operation of a multilateral-well EGS.