PSI - Issue 47

Ahmed Al-Mukhtar et al. / Procedia Structural Integrity 47 (2023) 938–944 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The permeable flow and porosity of a rock are interconnected by cracking. Hence, the injection of fluid into a borehole in the rock produces a fracture surface. Therefore, the velocity potential of this flow is simulated using FEM Liquid and Structural Analysis Software LISA (Anon 2013). LISA is a professional FEA program package with an integrated, modular, multithreaded solver and graphical post-processor supporting a full range of analysis types (Anon 2013). In addition, thermal analysis, Darcy, and storativity can be investigated using LISA. Different parameters and analyses can be investigated within LISA software. Velocity, permeability, and materials can be used as input parameters. However, the requirements for good conductivity between the two wells require a large surface area, which is produced by fracturing, LISA has no cracking simulator. Fracture Analysis Code Franc2D (Cornell Fracture Group 2010) simulates the crack, stress intensity, and facture toughness as based on the linear elastic analysis. Franc2D was validated for stress and fracture analysis in metal structures, see Refs. (A.M. Al-Mukhtar 2011; A. M. Al-Mukhtar 2020; Al-Mukhtar 2014, 2016; Al-Mukhtar et al. 2010), and for brittle materials, see Refs. (A. M. M. Al-Mukhtar 2020; Al-Mukhtar 2017; Al-Mukhtar and Merkel 2015; Al ‐ Mukhtar and Könke 2021). Therefore, the comparison between Franc2D and LISA will be presented. 2. Models and Simulations This work focuses on the modelling of fluid flow in porous materials like rocks, where the capability to simulate systems to circulate the fluid is needed. Therefore, the boundary conditions were investigated with respect to time. The geometry of the model is a 2D block of rock at a uniform initial ambient pressure with the flow from the central hole, see Fig. 1a. The fluid loading is simulated directly by assuming a constant fluid velocity on the wall of the bore toward the continuum material. The ambient pressure, material density, and Young’s modulus were selected to be equal to 10 5 Pa, 2710 Kg/m 3 , and 85.12E09, respectively. The hole diameter was 0.02 m, and the block dimensions were 0.80 × 0.80 m 2 , see Fig. 1.

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(b)

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Fig. 1. Geometry, mesh distribution, and elements of a rock block with a hole, LISA.

In the quarter geometry, the fluid will flow from the right to the left, see Fig. 1(b, c). The fluid is injected at a uniform velocity potentially. However, LISA program has no multi-physics options; but right now, the results are satisfactory. The model assumes that the rock is porous and subject to uniform pore pressure. Fine meshes are recommended for realistic results. In general, the finer meshes are needed only in a certain location, which is expected to have meaningful behaviour to avoid the time consuming, and difficulties of running. The results have been benchmarked. The velocity potential and flow rate were applied only to the nodes around the hole, see Fig. 1. The boundary elements remain free to consider the case of a complete block of rock where the flow is in four directions. In this