Numerical analysis of heat extraction efficiency in a multilateral-well enhanced geothermal system considering hydraulic fracture propagation and configuration

Abstract

Studying the effects of physical-based hydraulic fracture configurations on heat extraction performance in a multi-lateral enhanced geothermal system (EGS) can provide meaningful suggestions for in-situ operations. In this work, we proposed a 3D thermal-hydro-mechanical (THM) coupled numerical model that is capable to simulate both hydraulic fracturing and heat extraction in dual porous and fracture medium. Using this model, the exploitation of deep geothermal energy in a multilateral-well EGS from creation and configuration of hydraulic fractures, to thermal extraction was simulated and comprehensively studied. Based on the results, the following conclusions were drawn: 1) configuration of fracture pattern in a multi-lateral well EGS was affected by in-situ geological conditions (e.g. in-situ stress state) and operation strategies (e.g. sequence of hydraulic fracturing operation, position of perforation for hydraulic fracturing etc.); 2) different fracture configurations lead to great differences in heat production. The final thermal power of the worst configuration was 5.55 MW, while that of the best configuration was approximately 7.25 MW in this study; 3) a zipper fracture configuration is advantageous for homogeneously heat reduction in the geothermal reservoir that is preferable for efficient heat extraction; 4) stress shadow induced by simultaneous hydraulic fracturing can be used to create a non-connected zipper fracture pattern that can improve the heat extraction performance in the fractures at the toe side.