Phase field model of fracture propagation and pressure evolution induced by fluid injection considering the effect of initial stress field in power generation test project of Gonghe Basin, China

Abstract

Hydraulic stimulation technology is widely employed to enhance the permeability of geothermal reservoirs. Nevertheless, accurately predicting hydraulic fracture propagation in complex geological conditions remains challenging, thereby hindering the effective utilization of existing natural fractures. In this study, a phase field model was developed utilizing the finite element method to examine the influence of fluid presence, stress conditions, and natural fractures on the initiation and propagation of hydraulic fractures. The model employs Biot's poroelasticity theory to establish the coupling between the displacement field and the fluid field, while the phase field theory is applied to simulate fracture behavior. The results show that when σ_x0/σ_y0 < 3 or q_f < 20 kg/(m³·s), the presence of natural fractures can alter the original propagation direction of hydraulic fractures. Conversely, in the absence of these conditions, the propagation path of natural fractures is predominantly influenced by the initial stress field. Furthermore, based on the analysis of breakdown pressure and damage area, the optimal intersection angle between natural fractures and hydraulic fractures is determined to range from 45° to 60°. Finally, once a dominant channel forms, initiating and propagating hydraulic fractures in other directions becomes increasingly difficult, even in highly fractured areas. This method tackles the challenges of initiating and propagating hydraulic fractures in complex geological conditions, providing a theoretical basis for optimizing Enhanced Geothermal System (EGS) projects.

Keywords

Hot dry rock permeability / Enhance geothermal system (EGS) / Hydraulic stimulation / Phase field model / Fracture propagation / Breakdown pressure / Power generation test / Clean energy geological survey engineering

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