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Collaborating Authors
Results
Evaluation of Leakage Potential Considering Fractures In the Caprock For Sequestration of CO2 In Geological Media
Lee, Jaewon (School of Mining Engineering, The University of New South Wales, Shahid Bahonar University of Kerman) | Min, Ki-Bok (Department of Energy Systems Engineering, Seoul National University) | Rutqvist, Jonny (Earth Sciences Division, Lawrence Berkeley National Laboratory)
ABSTRACT: In the context of Carbon Capture and Storage (CCS), the injection of CO2 induces a geomechanical change in the reservoir, which is an important issue for the stability of CO2 sequestration. The injection of CO2 makes the fluid pressure increase, resulting in ground heaving. In addition, the increased fluid pressure is expected to be a source of shear slip of fractures in the caprock, which leads to the leakage of CO2 and microseismicity. In this study, we conduct a multi-phase coupled thermo-hydromechanical analysis to investigate the geomechanical aspect of CO2 storage focusing on ground heaving and leakage of CO2. In order to describe the caprock, fractures are considered implicitly and explicitly. For the analysis using implicit fractures, the fracture orientations were generated using the Latin Hypercube Sampling (LHS) method. In order to investigate the effect of orientation of principal stresses, we considered three kinds of stress regimes with the pore pressure evolutions calculated using a TOUGH-FLAC analysis. Based on these generated fracture orientations and stress distribution information, the probability of fracture shear slip was examined using Mohr-Coulomb failure criteria. This study allows for a quantitative description of ground heaving and leakage potential induced by shear slip of fractures, which is an important parameter for performance assessment of CO2 reservoir. 1. INTRODUCTION For the geosequestration of CO2, fluid injection is the triggering force for the hydro-mechanical change of reservoir, and ground heaving and shear slip of fracture are critical issues for the stability CO2 reservoir. When a fluid is injected into the reservoir, the increased pore pressure makes the ground heave. For example, at the In Salah project in Algeria, approximately 5 mm/year of ground heaving was observed, with the affected area being several kilometers from the injection well [1].
- North America > United States (0.46)
- Africa > Middle East > Algeria (0.25)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Health, Safety, Environment & Sustainability > Environment > Climate change (1.00)
Probabilistic Analysis of Shear Slip of Fractures Induced By Thermomechanical Loading In a Deep Geological Repository For Nuclear Waste
Lee, Jaewon (Department of Energy Resources Engineering and Research Institute of Energy and Resources, Seoul National University, Seoul) | Min, Ki-Bok (Department of Energy Resources Engineering and Research Institute of Energy and Resources, Seoul National University) | Stephansson, Ove (GFZ German Research Center for Geosciences)
ABSTRACT: Various studies have shown that shear slip at existing fractures is an important mechanism for block sliding, increase of fracture permeability, and microseismicity. In the context of a deep geological repository for nuclear waste, the thermal stress generated by nuclear waste is expected to contribute to shear slip and dilation, which will eventually alter the fracture permeability in the region. In this study, the probability of the occurrence of shear slip at a fracture was examined by the Mohr- Coulomb failure criterion. The study was based on the fracture orientation generated by the Latin hypercube sampling (LHS) method, which can improve the efficiency of Monte Carlo simulations by the use of a more systematic approach for selecting the input samples. Statistical data of fracture orientations from the site investigation in Forsmark, Sweden, were used in this study. The historical assessment of thermal stress was based on three-dimensional finite element modeling (FEM) of a geological repository that measures 800 m by 2000 m and on a time scale up to 10,000 years. The results show that the probability of shear slip evolved differently at six selected points due to the difference stresses at each point. However, it was evident that the probability of shear slip was more than twice as large as the initial probability of failure. This increased probability of failure has implications for changes in permeability and microseismicity, which can be an issue during the initial operation of the repository. The study provided a quantitative assessment of the probability of shear slip at a fracture, which is an important parameter for assessing the performance of a geological repository. 1. INTRODUCTION Shear slip at a fracture is a critical issue for many applications of geological engineering, such as the design of an underground repository for nuclear waste, the enhanced geothermal systems (EGS), and the geosequestration of CO2. Shear slip can induce additional flow in the fracture, which results in the enhanced permeability of the region. Microseismic events that occur in the aforementioned applications are also explained by the mechanisms of shear slip in small fractures. There are various reasons for shear slip at existing fractures. When a fluid is injected into fractured rock, the increased pore pressure decreases the effective normal stress on the fracture. It is important to take this mechanism into account when injecting CO2 into a reservoir for carbon storage. This shear slip due to increased pore pressure is known to be an important mechanism for an enhanced geothermal system in which an artificial reservoir with greater permeability is generated by injecting cold water into hot, dry rock. In a deep geological repository for high-level nuclear waste, heat is emitted by the nuclear waste, and thermal stress is generated due to confined nature of the rock. This can be a source of shear slip and dilation in the geological repository [1]. The thermal stress alters the stress distribution throughout the rock mass, and, therefore, the condition for shear slip changes.
- North America > United States (0.28)
- Europe > Sweden (0.25)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource > Hot Dry Rock (0.34)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
ABSTRACT: A numerical simulator is developed to examine coupled thermal-hydrologic-mechanical-chemical (THMC) processes in fractured porous geological media. The simulator links the computational codes TOUGHREACT and FLAC3D, which individually model thermal-hydrologic-chemical (THC) and mechanical (M) processes, respectively. The coupled scheme is shown capable of representing undrained response of saturated media to mechanical loading. Embryonic mechanical and transport constitutive laws are developed which are capable of accommodating combined mechanical, thermal, and chemical effects. Initial characterizations note the significant anticipated influence of stress on chemical behavior. The coupled model is applied to examine the evolution of pore fluid pressures, stresses, and temperatures in a stimulated EGS geothermal reservoir where the effects of stresses on multiphase reactive flow are important. INTRODUCTION The deformability and transport characteristics of fractured rocks are intrinsically linked to the evolving fields of effective stress and chemical potential. In systems driven far-from-equilibrium the influence on mechanical and transport properties may be significant. This impact is amplified where the transmission of fluids is dominated by the fracture network, and transformations are sufficiently rapid that they may influence response, even on timescales as short as those of typical engineered systems. Observed linkages in chemical effects, mediated by stress, and mechanical effects, mediated by chemistry, are the focus of the special couplings explored in this work. A constitutive model is developed which defines both the evolution of the deformability of the cracked rock mass, and its fluid transmission behavior in terms of local effective stresses and chemical potential. This model is incorporated into linked mechanical and transport codes, and validated against appropriate cases for mechanically driven fluid flow, and with implications for fluid and thermally driven deformation. The applicability of these modeling techniques to other important contemporary problems driven far-from-equilibrium is highlighted. These include the evolution of fluid and thermal flow paths in geothermal reservoirs, in repositories for radioactive waste isolation, and in reservoirs for the sequestration of CO2.
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (0.55)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.51)
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