Computational Fracking: 3D Numerical framework for multiphysics modelling of propagating fractures in rock
Mechanics
Final Report Abstract
In this project, we presented a robust computational framework based on phase field model to study hydraulic fracture propagation through two and three dimensional layered rock media. In the numerical investigation, we considered two configurations, namely, the softtostiff and the stifftosoft, and also different inclination angles of the layer interface. The phase field characteristics of fluiddriven fracture in layered geological formations were systematically explored. In addition, the displacement and stress characteristics related to geological system stability were investigated. The relationship between the phase field (fracture pattern), the stiffness contrast and inclination angle of the geological formations, was also further revealed. Based on minimization of the energy functional, our simulations automatically revealed the three potential fracture scenarios in naturallylayered geological formations, i.e., penetration, singly deflected and doublydeflected scenarios. The phase field simulation in these studies deepened our understanding of crack patterns and their governing factors in layered geological formations. The successful application of PFM also showed its immense potential in modelling the interface crack between two layers and how cracks emerged in neighbour ing layers, which were not easily captured with conventional methods. Subsequently, an efficient framework was presented to simulate hydraulic fracture in spatially variable rock mass combined with random field theory and phasefield method. The random field theory and phasefield model were implemented in COMSOL Multiphysics to simulate the irregular propagation of cracks effectively. The influences of spatial variability of elastic modulus on peak fluid pressure, fracture area and fracture shape were systematically analysed based on the framework. Finally, to overcome the shortcoming of lack of consideration of the initial stress field and to investigate the hydraulic fracture propagation in naturally layered rocks, a PFM for simulating quasistatic hydraulic fracture propagation in naturally layered porous media subjected to stress boundary conditions was proposed. Since the horizontal well drilling technology was commonly adopted in hydraulic fracturing and the minimum horizontal stress was often the minimum principal stress, two limiting cases can be adopted as the initial hydraulic fracture scenarios: the transverse pennyshaped fracture and longitudinal fracture. The longitudinal fracture was analyzed in our study as the first attempt because it can be regarded as an extension of the 2D plane strain case. In our PFM, variational approach was used to obtain the governing equations for the displacement and phase fields by means of a new energy functional which considers the initial stress field. Besides, Biot poroelasticity theory was utilized to couple the fluid pressure field and the displacement field, with the phase field approximating the fluid properties from the intact domain to the fully broken domain. In addition, numerical simulations under different cases were performed to understand the influence of the initial stress field, stiffness contrast, and inclination angle of the interface on fracture patterns.
Publications
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On the hydraulic fracturing in naturally-layered porous media using the phase field method. Engineering Geology, 266, 105306.
Zhuang, Xiaoying; Zhou, Shuwei; Sheng, Mao & Li, Gengsheng
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Phase-Field Modeling of a Single Horizontal Fluid-Driven Fracture Propagation in Spatially Variable Rock Mass. International Journal of Computational Methods, 19(08).
Chen, Fuyong; Zhou, Shuwei; Zhuang, Xiaoying; Zhang, Wengang & Wu, Renjie
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Three-dimensional phase field feature of longitudinal hydraulic fracture propagation in naturally layered rocks under stress boundaries. Engineering with Computers, 39(1), 711-734.
Zhuang, Xiaoying; Li, Xinyi & Zhou, Shuwei
