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Fluid Injection-Induced Fracture Evolution and Breakdown Pressure in Naturally Fractured Rocks with Ultra-Low Permeability Matrix
Shahrzad ROSHANKHAH, Shivesh SHANDILAYA
[University of Utah, USA]
The energy geosystems that involve fluid injection into geological formations, such as shale oil and gas and enhanced geothermal systems (EGS), are increasing in number and importance every day. To improve efficiency and ensure the sustainability of these geosystems, one must understand the mechanisms and factors that govern the evolution of the induced fracture network in naturally fractured ultra-low-permeability rock masses. Previous studies have demonstrated that natural fracture characteristics strongly influence both the hydraulic and mechanical responses of such formations. In this study, a combined finite–discrete element method (FDEM) is employed to investigate coupled hydromechanical fracture processes during fluid injection, with particular emphasis on the role of natural fracture (NF) density. The results show that NF density significantly influences near-wellbore fracture initiation behavior, with rock matrix–natural fracture interlocking controlling the breakdown pressure at high NF density relative to homogeneous media. Following fracture initiation, NFs promote pressure dissipation along preferential pathways, thereby increasing the stimulated rock volume and reducing peak pressure within the primary hydraulic fracture. Increasing NF density further amplifies lateral pressure redistribution and distributed fracture opening away from the wellbore, while the hydraulic fracture may cross or deviate, depending on local stress-state redistribution. These findings indicate that increasing NF density modifies both the local near-wellbore stress state and its redistribution along the propagating hydraulic fracture. Understanding these will provide insights into implementing effective strategies for safer, more sustainable fluid injection practices in EGS.
Topic: Enhanced Geothermal Systems