Fast Equivalent Micro-Scale Pipe Network Representation of Rock Fractures Obtained by Computed Tomography for Fluid Flow
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ORIGINAL PAPER
Fast Equivalent Micro‑Scale Pipe Network Representation of Rock Fractures Obtained by Computed Tomography for Fluid Flow Simulations Feng Xiong1,3 · Qinghui Jiang1,2 · Chaoshui Xu3 Received: 26 December 2019 / Accepted: 21 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Fractures in rocks often provide preferential fluid migration pathways and their geometrical properties are the main factors influencing the permeability of the rock mass. By taking into account the complex geometries of rock fractures, including tortuous features, highly variable fracture apertures, rough fracture wall surfaces and complex fracture intersections, a highly effective approach is proposed in this work to investigate the behaviour of fluid flows in laboratory-scale fractured rocks. The computed tomography (CT) scanning was used to capture the micro-structures of non-planar fractures in a sandstone specimen. An image processing method was then developed to extract the three-dimensional fracture network. The fractures and fracture network were represented using an equivalent pipe network model, taking into consideration the complex geometries mentioned above. The nonlinear flow is incorporated into the model through the consideration of a friction factor in the pipe flow method (PFM). The absolute difference of the derived permeability between PFM and finite volume method (FVM) is 3.45%, but the FVM needs 15 times more CPU computation time. Therefore, the proposed approach is better than FVM in terms of computational efficiency. In addition, the use of the friction factor was demonstrated to be effective and efficient to model nonlinear flow within the fracture network, where the flow nonlinearity is caused by high flow velocity and the formation of eddies in certain parts of the fracture network, leading to a decrease in the overall apparent permeability and an increase in the flow tortuosity. The proposed method was further validated against flow test data covering a wide range of linear and nonlinear flow regimes. Keywords Fractured rocks · Computed tomography · Equivalent pipe network model · Nonlinear flow simulation · Rock permeability
1 Introduction
* Qinghui Jiang [email protected] * Chaoshui Xu [email protected] 1
School of Civil Engineering, Wuhan University, Wuhan 430072, People’s Republic of China
2
Key Laboratory Safety Geotechnical and Structural Engineering Hubei Province, Wuhan 430072, People’s Republic of China
3
School of Civil, Environmental and Mining Engineering, University of Adelaide, Adelaide 5005, Australia
Fractures in geological systems in general have a dominant impact on the fluid flow through the system. Knowledge of their flow properties is essential for applications such as underground constructions, shale gas production, geothermal systems and in situ mineral recoveries (Pan et al. 2010; Lei et al. 2017; Ren et al. 2017; Xiong et al. 2018, 2019). Fractures and fracture network in general are the main pathways for flow through
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