Abstract This study presents hollow-cylinder testing, a representative experimental approach for investigating borehole stability problems, using three-dimensional bonded-particle discrete element model (DEM) to identify failure mechanisms along the open hole by considering the effect of rock anisotropy. A transversely isotropic model was reproduced as an intact rock model embedding a smooth-joint contact model of which microparameters were calibrated against the laboratory results acquired from triaxial tests on overburden shale. A series of hollow-cylinder tests were performed on this transversely isotropic models that have five different inclined bedding planes, which were then compared to the laboratory observations. The result obtained from three-dimensional bonded-particle DEM model was able to capture the instability of the inner hole, i.e., a considerable reduction of effective confining pressure when the hole axis is sub-parallel to bedding planes. Furthermore, the DEM model manifested the overall failure patterns in the vicinity of the hole such as shear failure or spalling, which highly depend on the inclined angle of bedding planes. 1. Introduction Rock anisotropy is an important consideration in various engineering rock mechanics, e.g., borehole instability in shale formation especially when drilling sub-parallel to bedding planes (Økland et al., 1998). Thus, care must be taken when performing wellbore stability analyses on highly anisotropic rock formations. Of many forms of anisotropic models, a transversely isotropic model, which is pertinent to representing laminated rock formations (Jaeger et al., 2007), was adopted in this study. Recent studies have showed that the two-dimensional bonded-particle discrete element model (DEM) can effectively simulate the elastic and strength behavior of transversely isotropic rocks (Chiu et al., 2013; Duan and Kwok, 2015; Park and Min, 2015; Wang et al., 2016). However, two-dimensional modeling is not sufficient to capture stress distributions and associated failures observed in near borehole, which is relied upon heavily to the degree of bedding inclination. Therefore, three-dimensional modeling is needed for a true representation of anisotropic rock. The objective of the study is the three-dimensional bonded-particle DEM modeling of transversely isotropic rock to investigate the validity of hollow-cylinder test results by comparing the laboratory observations with the numerical results.

Abstract In this study, oil-water two phase flow was examined and the replacement process was visualized and analyzed by X-ray CT method. Here, porous rock samples were fully saturated by oil and water is pushed into the sample. As a porous sample, Berea sandstone was applied. Since the density difference between oil and water is very small for X-ray CT inspection, 10% of KI solution was used instead of water. It was found that the replacement process progressed gradually in the rock sample and that this process was clearly visualized as X-ray CT images. Moreover, the procedure to evaluate replacement ratio from CT image data was also newly introduced and the replacement ratio was estimated. It was found that the approximately 40% -50% of oil in pores were replaced by KI solution. 1. Introduction In the projects, such as oil productions, CCS and geothermal energy development, the analysis of multi flows in rocks is necessary. Among the projects, oil-water two phase flow is the representative two phase flow in the rock engineering (Stephan (2005), Wang (2016)). In this study, one dimensional oil-water two phase flow is examined and the replacement process is visualized by X-ray CT scanner system. Here, one-dimensional flow tests are conducted toward the porous rock sample which are initially filled with oil. As is well known, X-ray CT scanner is the system to visualize density distribution in the materials (Khalid (2010), Veerle (2013)). However, the density difference between oil and water is not large enough to visualize by X-ray CT scanner, and 10% concentration of KI solution is pushed into the rock sample instead of water for clearer visualization. Here, the procedure to obtain density difference due to the oil-KI solution replacement is firstly introduced. Then, the method to evaluate replacement ratio from CT data is induced, and the replacement process is analyzed through the evaluation of replacement ratio.

ABSTRACT: This paper is a numerical study on the HE-D experiment within the Opalinus clay formation at the Mont-Terri underground rock laboratory (Switzerland) using a self-developed code, i.e. a 3D Elasto-Plastic Cellular Automaton (EPCA 3D ),in which the unsaturated fluid flow, transient heat conduction and anisotropic model have been implemented. The temperature-dependent water viscosity was considered during the simulation. The simulated temperature evolution and the consequences on pore water pressure and rock deformation for Opalinus clay were well consistent with experimental data. It indicated that, the temperature distribution, pore pressure and mechanical behavior are greatly influenced by the anisotropic characteristic of Opalinus clay in HE-D. 1 INTRODUCTION Deep geological repository of high-level radioactive wastes is one of the most promising options to isolate wastes from the human environment. High-Level radioactive Waste (HLW) produces heat due to the continuous decay of radionuclide. Thus the geological disposal of HLW will impose a temperature increase upon the surrounding rock. Argillaceous rocks have a lower heat conductivity compared to granite or salt resulting in higher temperatures around the waste canister for a given heat loading. Moreover, the rock reacts sensitive to high temperatures. The increasing temperature will also influence the pore water pressure and might induce deformation of the rock, which again changes the pore water pressure. Various in-situ heating tests (Gen et al. 2007) have been performed involving the observation of the response of natural sedimentary clay. For instance, in the Hades laboratory the following experiments have been performed: the CACTUS test (Picard et al. 1994), the ATLAS test and the CERBERUS test (Bernier & Neerdael 1996, Bruyn & Labat 2002). A comprehensive understanding of coupled thermal, hydraulic and geo-mechanical processes (THM) will be a key element for the design of deep geologic repositories. Therefore, based on a self-developed numerical code, i.e. a 3D Elasto-Plastic Cellular Automaton (EPCN 3D ) (Pan et al. 2009a, 2009b), this paper presents a numerical study on the coupled THM processes in Opalinus clay in HE-D test.