Abstract
Natural fractures usually develop in shale reservoirs. Thereby, in the process of hydraulic fracturing, it is inevitable that hydraulic fractures will intersect with natural fractures. In order to reveal the interaction mechanism between hydraulic-induced fractures and natural fractures, a two-dimensional fracture intersection model based on the extended finite element method (XFEM) is proposed, and the different types of intersecting criteria reported in the literature are compared. Then, the effects of natural fracture azimuth, fluid pressure in hydraulic fracture, and in situ principal stress difference on hydraulic fracturing are studied in detail. The results show that the fracture morphology is different under different criteria and working conditions. And the stress concentration phenomenon mainly concentrates on the tip in the obtuse angle side of natural fracture. Meanwhile, different fluid pressures in hydraulic fracture can also induce different intersection patterns. The obtained results in this work are of great benefit to understand the intersection mechanism between hydraulic fractures and natural fractures.
Highlights
Shale reservoirs have very low porosity and permeability. us, hydraulic fracturing technique is widely employed to generate hydraulic/induced fractures and enhance the productivity of shale reservoirs. ere are many discontinuities in shale reservoirs, such as natural fractures/cracks, bedding planes, and faults [1]
Natural fractures have production capacity only when they are activated by induced fractures [3]. us, understanding the interaction mechanism between hydraulic fractures and natural fractures is of great significance for the stimulation of shale reservoirs
A linear elastic and isotropic block is considered with Young’s modulus of 25 GPa and Poisson’s ratio of 0.20, and the tensile strength T0 is 1.0 MPa. e in situ principal stress difference is set as 2.0 MPa, and fluid pressure in hydraulic fracture is 10 MPa
Summary
Shale reservoirs have very low porosity and permeability. us, hydraulic fracturing technique is widely employed to generate hydraulic/induced fractures and enhance the productivity of shale reservoirs. ere are many discontinuities in shale reservoirs, such as natural fractures/cracks, bedding planes, and faults [1]. Ere are many discontinuities in shale reservoirs, such as natural fractures/cracks, bedding planes, and faults [1]. Us, understanding the interaction mechanism between hydraulic fractures and natural fractures is of great significance for the stimulation of shale reservoirs. Extensive theoretical works have been conducted to investigate the interaction mechanism between hydraulic fractures and natural fractures based on experiments [2, 4,5,6]. Compared to theoretical and experimental methods, numerical methods can simulate the interaction process under more complex geological conditions. Zhang et al [12] investigated the interaction mechanism between hydraulic fractures and natural fractures with a hybrid discrete-continuum method. The full coupled multiscale numerical model has been introduced to investigate hydraulic fracturing complexity in naturally fractured rock masses [15]. Belytschko and Black [16] presented a minimal remeshing finite element method for crack growth, which is referred to as the extended finite element method (XFEM)
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