True triaxial experiment and FDEM simulation on the controlling effect of coal-measure rock interfaces on hydraulic fracture propagation
Jun-qiang Ma , Si-yuan Wei , Xue-hua Li , Guo-wei Dong , Qiang-ling Yao , Yu-xin Yuan , Hong-sheng Wang
Journal of Central South University ›› : 1 -24.
This study integrates true triaxial hydraulic fracturing experiments with FDEM numerical simulation to systematically investigate the control mechanisms of interface strength and inclination angle on hydraulic fracture propagation in coal measure strata under different in-situ stress conditions. The results indicate that the fracture propagation path at the rock interface is jointly controlled by the interface strength coefficient (η), the interface inclination angle (θ), and the vertical stress difference coefficient (k). When fractures propagate from soft rock to hard rock, the interface strength coefficient (η) plays a dominant role. The larger the η, the more likely the hydraulic fracture is to penetrate the interface along the direction of vertical stress. Conversely, when fractures propagate from hard rock to soft rock, vertical stress primarily controls the propagation path. A larger vertical stress difference coefficient promotes interface crossing, while a smaller coefficient tends to cause the fracture to extend laterally along the interface. The interface inclination angle (θ) influences the magnitude and direction of the vertical stress component along the interface. A smaller (θ) facilitates interface penetration by hydraulic fractures, whereas a larger (θ) leads to fracture propagation along the interface. The complexity of the hydraulic fracture network increases with higher (k) and (θ) values. Moreover, the complexity of hydraulic fracture morphology exhibits a non-monotonic trend, initially decreasing and then increasing with rising (k) and (θ). This research provides an important theoretical basis for the design and control of hydraulic fracturing in coal measure strata.
coal-measure strata / hydraulic fracturing / rock strata interface / fracture propagation / FDEM
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Central South University
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