Optimizing heat mining strategies in a fractured geothermal reservoir considering fracture deformation effects

Abstract

A coupled thermo-hydro model is developed for optimizing heat mining strategies in a fractured geothermal reservoir by incorporating material compressibility and fracture deformation. Governing equations for the three-dimensional fluid flow and heat transmission processes in terms of local thermal non-equilibrium concept are discretized using a unified pipe network method. The influence of fracture deformation on the distribution of fluid temperature is investigated using a near-wellbore reservoir model. The development optimization of a geothermal reservoir at Groβ Schönebeck is performed by evaluating heat production over 60 years. Several strategies are designed that involve changing the arrangement of a new horizontal wellbore and hydraulic stimulations. Simulation results for the different strategies, including the outlet fluid temperature drawdown, thermal breakthrough time, and net heat extraction rate, are analysed. Strategies with poor fracture connections feature relatively low flow rates and accumulated thermal production. Strategy 3 to Strategy 6 greatly improve the accumulated thermal production by enhancing fluid circulation in fracture-connected systems. Heat mining efficiency can be improved if a new wellbore is designed in the high-permeability formation and the discontinuities maintain high hydraulic connectivity for fluid circulation. This study provides a numerical method for optimizing geothermal development strategies in terms of economic benefits.