Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
Abstract: We have quantitatively analysed the influence of boundary constraint stiffness on stress heterogeneity modelling in fractured rock mass using the two dimensional (2D) combined finite-discrete element method (FEMDEM). We generalise the boundary constraints found in the literature to a four-plate boundary with variable stiffness. For a 1.5 × 1.5 m rock mass model subjected to boundary loading, the stress tensors induced in the model under various boundary stiffness conditions are extracted and their scatter calculated using Euclidean dispersion – a scalar value akin to standard deviation. The results show an overall decrease in Euclidean dispersion as the boundary stiffness increases. Our findings lead us to suggest that when undertaking stress heterogeneity analyses, a boundary constraint stiffness equal to the Young's modulus of rock should be used. Although this is only a preliminary investigation of stress heterogeneity simulation, it nevertheless suggests the importance of boundary constraints when conducting such numerical modelling in rock mechanics. Introduction In situ stress is an important parameter for a wide range of endeavours in rock mechanics, including rock engineering design, hydraulic fracturing analysis, rock mass permeability and earthquake potential evaluation (Amadei and Stephansson, 1997; Latham et al., 2013; Matsumoto et al., 2015; Zang and Stephansson, 2010; Zoback, 2010). Because of the inherent complexity of fractured rock masses in terms of varying rock properties and the presence of discontinuities, especially in highly fractured rock masses, stress often displays significant heterogeneity (Martin, 1990; Obara and Sugawara, 2003). The in situ stress measurement results shown in Fig. 1 exemplify the dramatic variation in terms of both principal stress magnitude and orientation that may be observed in a small zone (Obara and Sugawara, 2003). Studying stress heterogeneity is not only beneficial to understanding the complex nature of fractured rock masses, but also to supporting any rock engineering-related analysis. However, it is often not possible for stress heterogeneity to be thoroughly interpreted due to a lack of sufficient in situ stress data (Harrison et al., 2010). Due to implementation difficulties and budget limits, most rock engineering projects usually do not have the luxury to conduct a large number of in situ stress measurements, with the result that numerical simulation approaches need to be employed to investigate stress heterogeneity (Harrison et al., 2010; Hart, 2003).
- Europe (1.00)
- North America > United States > Texas (0.28)
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.68)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.69)
A Fluid-Solid Coupled Approach for Numerical Modeling of Near-Wellbore Hydraulic Fracturing and Flow Dynamics with Adaptive Mesh Refinement
Obeysekara, A. (Imperial College London) | Lei, Q. (Imperial College London) | Salinas, P. (Imperial College London) | Pavlidis, D. (Imperial College London) | Latham, J.-P. (Imperial College London) | Xiang, J. (Imperial College London) | Pain, C. C. (Imperial College London)
Stephansson, 2003] (a) hydraulic properties, (b) fluid Deformation, fragmentation, and fracturing is a common pressure at the boundaries and (c) the'void' geometry cause of weakness in rocks due to natural geological (fractures, porosity). The fluid flow properties of porous processes such as fault slips, and engineering driven rocks can be described using the widely used fluid flow activities such as drilling, blasting and hydraulic model for porous media, Darcy's Law.
Abstract: This paper presents a stress-induced variable aperture model to characterise the effect of polyaxial stress conditions on the permeability of a three-dimensional (3D) fractured sedimentary layer. The 3D fracture network is created by extruding a 2D outcrop pattern of a limestone bed that exhibits a ladder structure consisting of a “through-going” joint set abutted by later short fractures. Geomechanical modelling of the fractured rock is achieved by the 3D finite-discrete element method (FEMDEM), which can capture the deformation of matrix blocks, the variation of stress fields, the reactivation of pre-existing fractures and the propagation of new cracks. A joint constitutive model (JCM) is implemented to simulate the rough wall interaction behaviour of individual fractures associated with roughness characteristics. The combined JCM-FEMDEM model gives realistic fracture behaviour with respect to opening, closing, shearing and dilatancy, and includes the recognition of the important size effect. A series of 3D geomechanical simulations is conducted for the fractured rock under various polyaxial in-situ stresses. Fluid flow is further modelled for the stressed but static solid skeletons based on the hybrid finite element-finite volume method (FEFVM). The magnitude of the equivalent permeability varies significantly with respect to the change of stress ratio. Introduction Natural fractures are ubiquitous in crustal rocks in the form of faults, bedding planes, joints and veins over different length scales (Lei and Wang, 2016). These naturally occurring discontinuities often comprise complex networks and dominate the geomechanical and hydromechanical behaviour of subsurface media (Rutqvist and Stephansson, 2003). The understanding of the nontrivial effects of fractures on the overall behaviour of such highly disordered geological media has important implications for many engineering applications including geothermal energy, nuclear repository safety and petroleum recovery. Discrete fracture networks (DFNs) are often used to mimic naturally faulted or jointed geological structures (Dershowitz and Einstein, 1988). Compared to the conventional dual porosity model (Warren and Root, 1963) and analytical solution for mathematically idealised discontinuity networks (Oda, 1985), the discrete fracture approach possesses the advantage of explicit representation of fracture geometries together with specific description of hydraulic transmissivity (Herbert, 1996). Flow properties, such as the block or equivalent permeability tensor, of a finite-sized fracture system can be studied from steady state fluid flow modelling (Lang et al., 2014; Renard and de Marsily, 1997).