Thermal-fluid coupled fracture behavior of fissured granite in a 3D crystal model

Abstract

The discontinuous geological structures and crystalline characteristics of granite reservoirs drive hydraulic fracturing behavior, significantly influencing the process and effectiveness of reservoir stimulation. This paper introduces an improved three-dimensional thermo-hydro-mechanical coupled peridynamic crystal model (THM-PDCM) incorporating thermal cracking, nonlinear mechanics, and hydraulic effects. A polycrystalline microstructure model was developed based on the “crystal growth algorithm.” Within this framework, the effects of temperature, fissure dip angle and loading conditions on the hydraulic fracture propagation mechanism in granite were systematically investigated. Results show that THM-PDCM accurately captures thermally induced damage, fluid-driven fracture, and mechanical interactions. Grain boundary effects significantly influence the initiation and propagation of fractures. High temperatures induce microcracks that reduce the fracture toughness of the rock, alter crack propagation directions, and increase propagation instability. Thermally induced cracking combined with cold-water diffusion accelerates fracture growth, prompting transitions through crossing, propagation, deviation, and blocking as pressure declines.