Prediction and control of hydraulic fracture trajectory in enhanced geothermal system

Abstract

ABSTRACT A new fully coupled numerical model is presented to analyze artificial fracture morphology and artificial fracture propagation during synchronous fracturing. The interaction mechanism between natural and artificial fractures is also considered in this new model. The new numerical solution, based on the boundary element method (BEM) and the finite difference method, is used to solve the problem of coupled rock deformation, fluid interference, stress interference, interface slipping, and opening and to investigate the effect of natural fractures and interference between fractures on fracture morphology during synchronous fracturing. An analysis of factors of influence showed that synchronous fracturing can be used to control the fracture trajectory and construct an effective enhanced geothermal system (EGS). Artificial fractures of two adjacent wells attract each other during synchronous fracturing, and eventually, the two fractures become connected, and the two wells become connected. The choice of well location also has an important influence on the successful establishment of an EGS. To establish an effective EGS successfully, the fracture spacing should preferably be no more than 20 m, and the well spacing should preferably be greater than 400 m. An EGS is easier to construct in a hot dry rock reservoir with a high natural fracture density and small natural fracture angles (preferably less than 30º).