Coupled flow network and discrete element modeling of injection-induced crack propagation and coalescence in brittle rock


We present a numerical analysis on injection-induced crack propagation and coalescence in brittle rock. The DEM network coupling model in PFC is modified to capture the evolution of fracture geometry. An improved fluid flow model for fractured porous media is proposed and coupled with a bond-based DEM model to simulate the interactions among cracks induced by injecting fluid in two nearby flaws at identical injection rates. The material parameters are calibrated based on the macro-properties of Lac du Bonnet granite and KGD solution. A grain-based model, which generates larger grains from assembles of particles bonded together, is calibrated to identify the microscopic mechanical and hydraulic parameters of Lac du Bonnet granite such that the DEM model yields a ratio between the compressive and tensile strength consistent with experiments. The simulations of fluid injection reveal that the initial flaw direction plays a crucial role in crack interaction and coalescence pattern. When two initial flaws are aligned, cracks generally propagate faster. Some geometrical measures from graph theory are used to analyze the geometry and connectivity of the crack network. The results reveal that initial flaws in the same direction may lead to a well-connected crack network with higher global efficiency.

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This research is supported by the Earth Materials and Processes program at the US Army Research Office under grant contracts W911NF-14-1-0658 and W911NF-15-1-0581, Air Force Office of Scientific Research under grant contract FA9550-1186-17-1-0169, US Department of Energy Nuclear Engineering University Program under grant contract DE-NE0008534, National Science Foundation under grant contract EAR-1516300, Anhui Science and technology research projects (No. 1604a0802106), the Open Fund of the Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering, Ministry of Education, Wuhan University, the Open fund from state Key Laboratory of Water Resources and Hydropower Engineering Science, China (No. 2016SGG02), the Open Fund of the Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering, Ministry of Education, Wuhan University, Key Laboratory of Geological Hazards on Three Gorges Reservoir Area (China Three Gorges University), Ministry of Education (No. 2015KDZ03), and Chinese Universities Scientific Fund (No. JZ2016HGBZ1021). These supports are gratefully acknowledged. The first author is also grateful to the China Scholarship Council (CSC) for providing him with a scholarship during his study in the USA. These supports are gratefully acknowledged.

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Liu, G., Sun, W., Lowinger, S.M. et al. Coupled flow network and discrete element modeling of injection-induced crack propagation and coalescence in brittle rock. Acta Geotech. 14, 843–868 (2019).

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  • Brittle rock
  • Crack coalescence
  • Discrete element method
  • Flow network
  • Fluid-driven fracture