Fracture propagation characteristics and energy evolution law of deep coal seam containing gangue based on discrete lattice method Available to Purchase

Hydraulic fracturing is a key technology for the development of deep coal-rock reservoirs. Gangue, a common rock type within coal-bearing strata, significantly influences fracture morphology after fracturing. Understanding fracture propagation in coal-rock containing gangue and effectively controlling artificial fractures remain critical challenges in fracturing operations. To address this, the study investigates the coal-bearing strata of the Benxi Formation in the Daning-Jixian area of the Ordos Basin, characterized by the presence of gangue. A three-dimensional discrete lattice model was developed to analyze the effects of gangue-related factors, including the number, thickness, dip angle, and type, on hydraulic fracturing. The fracture propagation patterns and stimulation effects under these factors were systematically compared. Using node path tracking and post-processing techniques, the study identified the fracturing characteristics and fracture propagation modes at different stages. The findings indicate that gangue characteristics significantly impact fracture morphology and propagation paths. Specifically, an increase in the number of gangue layers enhances fracture complexity but reduces the effective stimulation ratio. Gangue thickness positively correlates with fracture tortuosity and inversely correlates with the effective stimulation ratio. The dip angle of gangue determines the direction of fracture propagation but has minimal influence on the stimulation area. The gangue type also affects fracture morphology; for instance, sandstone gangue leads to narrower fractures and more interface fractures at the sandstone–coal boundary compared to mudstone gangue. Fracture propagation, characterized by energy changes, can be divided into four distinct stages: Stage I (initial injection phase), Stage II (onset of fracture propagation), Stage III (fluid energy storage within gangue), and Stage IV (fracture penetration through gangue). These stages are marked by variations in fluid injection energy, fluctuation energy, surface energy, and strain energy as the fracture penetrates the layer, deflects, and forms horizontal fractures. The simulation of fracture network evolution in coal-bearing strata containing gangue provides significant theoretical guidance for understanding, predicting, and controlling fracture network morphology in coal reservoirs. These findings are instrumental for the efficient development of deep coalbed methane.