Implicit and Explicit Fracture Shear Slip Analysis for Geological Storage of Carbon Dioxide and Nuclear Waste

Abstract

numerical analysis at the hypothetical CO2 storage reservoir, analytic solution at the reservoir with underground injection, and numerical analysis at nuclear waste repository. For the explicit fracture shear slip analysis, TOUGH-UDEC coupled code is developed and verified. After that, numerical analysis is conducted for the hypothetical CO2 storage reservoir with pre-existing fracture to investigate the effect of fracture shear slip on the leakage of CO2. With implicit fracture shear slip analysis and explicit fracture shear slip analysis, systematic quantitative analysis for the hydroshearing and thermoshearing is conducted. Techniques of leakage and reservoir geomechanics analysis that is developed in this thesis are essential for Carbon Capture and Storage (CCS) technology in view of selection investigation. The result of this analysis can provide a guideline for performance assessment of CO2 reservoir and can help to determine the critical injection pressure at a given reservoir condition and layout of the injection wells. Also the microseismic events which are expected to occur after the injection of CO2 can be reliably predicted. The prediction of ground heave in conjunction with monitored results can improve the confidence in the performance of CO2 reservoir and nuclear waste repository.

Shear slip at a fracture is a critical issue for many applications of geological engineering, such as the design of the geosequestration of CO2 and an underground repository for nuclear waste. Shear slip can induce mechanical instability and additional fluid 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 injecting CO2 into a reservoir for the carbon storage, the increased pore pressure decreases the effective normal stress on the fracture, and this is expected to induce fracture shear slip. 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. The thermal stress alters the stress distribution throughout the rock mass, and, therefore, the condition for shear slip changes. The phenomenon of shear displacement and dilation of fractures due to pore pressure change is termed hydroshearing and due to thermal loading is termed thermoshearing,The main focus of this thesis is to provide systematic quantitative analysis for the hydroshearing and thermoshearing. This thesis is divided into two parts

implicit fracture shear slip analysis and explicit fracture shear slip analysis. For the implicit fracture shear slip analysis, the probability of shear slip is evaluated considering a Coulomb failure analysis and the statistical fracture distributions from In Salah and Forsmark site. The calculation of stress evolution is divided into three parts