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| Development of an unified pipe-interface element method and its application in hydraulic fracturing simulation |
| YAN Xiao1，2，JING Hongwen1，SUN Zizheng3，YU Liyuan1，ZHANG Yiming4
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(1. State Key Laboratory for Geomechanics and Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. School of Civil Engineering，Tongji University，Shanghai 200092，China；3. School
of Qilu Transportation，Shandong University，Jinan，Shandong 250061，China；4. School of Civil and Transportation
Engineering，Hebei University of Technology，Tianjin 300401，China) |
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Abstract This paper proposes a novel method，named as unified pipe-interface element method(UP-IEM)，for modelling the hydraulic fracture propagation in a permeable porous medium. There are two unified processes including the combination of the fluid flow and the fracture propagation into 1D pipe element and the unification of the matrix pipe and the fracture pipe as a same pipe with different hydraulic conductivities for solving the fluid flow using the same mathematical equations. UP-IEM overcomes the difficulties to consider the rock matrix permeability of traditional discrete fracture network model. The interface element is introduced to simulate the fracture propagation. For UP-IEM which has high efficiency，neither local crack propagation criteria nor tracking algorithms are required compared with traditional FEM and DEM. The deformation of the rock matrix is described by poroelasticity theory and effective stress concept. The cohesive zone model is used to simulate hydraulic fracture propagation and the contact-frictional model is utilized to model closure and slip of natural cracks. Besides，the fluid flow in porous medium and fractures is solved using Darcy law. A semi-explicit frame is built to solve the hydro-mechanical coupling problems. Three typical examples，including Terzaghi's consolidation test，unsymmetric four-points bending test and KGD model，are simulated. The simulation results are compared with analytical solutions and experimental results，verifying the accuracy and applicability of UP-IEM simulating fluid flow，fracture propagation and hydraulic fracturing. Furthermore，the hydraulic fracturing in models with single natural fracture and complex fracture network is simulated，analyzing the interaction between hydraulic fractures and pre-existing fractures and discussing the influence of in-suit stresses on the fracture propagation path. These examples show that UP-IEM could effectively simulate the hydraulic fracturing in discrete fractured rock.
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2022, Vol. 41 
