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SUMMARYThis paper describes a fully coupled finite element/finite volume approach for simulating field-scale hydraulically driven fractures in three dimensions, using massively parallel computing platforms. The proposed method is capable of capturing realistic representations of local heterogeneities, layering and natural fracture networks in a reservoir. A detailed description of the numerical implementation is provided, along with numerical studies comparing the model with both analytical solutions and experimental results. The results demonstrate the effectiveness of the proposed method for modeling large-scale problems involving hydraulically driven fractures in three dimensions.

SUMMARYGeomaterials such as soils and rocks are inherently anisotropic and sensitive to temperature changes caused by various internal and external processes. They are also susceptible to strain localization in the form of shear bands when subjected to critical loads. We present a thermoplastic framework for modeling coupled thermomechanical response and for predicting the inception of a shear band in a transversely isotropic material using the general framework of critical state plasticity and the specific framework of an anisotropic modified Cam-Clay model. The formulation incorporates anisotropy in both elastic and plastic responses under the assumption of infinitesimal deformation. The model is first calibrated using experimental data from triaxial tests to demonstrate its capability in capturing anisotropy in the mechanical response. Subsequently, stresspoint simulations of strain localization are carried out under two different conditions, namely, isothermal localization and adiabatic localization. The adiabatic formulation investigates the effect of temperature on localization via thermomechanical coupling. Numerical simulations are presented to demonstrate the important role of anisotropy, hardening, and thermal softening on strain localization inception and orientation.

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6This paper gives an overview of the advances made in the field of risk assessment and risk management 7 of geologic CO 2 storage (GCS) since the publication of the IPCC Special Report on Carbon Capture and 8Storage in 2005. Development and operation of a wide range of demonstration projects coupled with 9 development of new regulations for safe injection and storage of CO2 has led to development and 10 deployment of a range of risk assessment approaches. New methods and tools have been developed for 11 quantitative and qualitative risk assessment. These methods have been integrated effectively with 12 monitoring and mitigation techniques and deployed in the field for small-scale field tests as well as 13 large-scale commercial projects. An important development has been improved definition of risks, 14 which can be broadly classed as site performance risks, long-term containment risks, public perception 15 risks and market risks. Considerable experience has now been gained on understanding and managing 16 site performance risks. Targeted research on containment risks and induced seismicity risks has led to 17 improved understanding of parameters and processes influencing these risks as well as identifying key 18 uncertainties that need to be targeted. Finally, significant progress has been made to effectively 19 integrate communication strategies with risk management approaches to increase stakeholder 20 confidence in effectiveness of deployed risk management approaches to manage risks. 21

SUMMARYThe paper deals with the numerical solution of Biot's equations of coupled consolidation obtained by a mixed formulation combining continuous Galerkin finite-element and multipoint flux approximation finite-volume methods. The solution algorithm relies on the recently developed fixed-stress solution scheme, in which first the flow problem and then the mechanical one are addressed iteratively. We show that the algorithm can be interpreted as a particular block triangular preconditioning strategy applied within a Richardson iteration. The key component to the success of the preconditioner is the sparse approximation to the Schur complement based on a pressure space mass matrix scaled by a weighting factor that depends element-wise on the inverse of a suitable bulk modulus. The accuracy of the method is assessed, making use of well-known analytical solutions from the literature. Numerical results demonstrate robustness and low computational cost of the fixed-stress scheme in accurately capturing the two-way coupling between deformation and pressure.

Rainfall weakens an earth slope in a number of ways. It increases the degree of saturation of the soil, thereby breaking the bonds created by surface tension between the soil particles. When the volume of infiltrating water is large enough to mobilize fluid flow inside the soil matrix, the fluid exerts a downhill frictional drag on the slope, creating a destabilizing effect. When excess fluid can no longer infiltrate the slope due to increased saturation in the soil, it is discharged as a surface runoff and erodes the slope. In this paper, we present a physics-based framework for continuum modeling of a hydrologically driven slope failure similar to what occurred in a steep experimental catchment CB1 near Coos Bay, Oregon. We quantify the rainfall-induced slope deformation and assess the failure potential of the slope using finite element modeling that couples solid deformation with fluid pressure in an unsaturated soil. Results of the studies suggest that for a steep hillside slope underlain by a shallow bedrock similar to the CB1 site, failure would occur by multiple slide blocks with the failure surfaces emerging on the slope face. These results suggest that an infinite slope mechanism would be insufficient to represent the failure kinematics for a slope similar to CB1.

The focus of this work is efficient solution methods for mixed finite element models of variably saturated fluid flow through deformable porous media. In particular, we examine preconditioning techniques to accelerate the convergence of implicit NewtonKrylov solvers. We highlight an approach in which preconditioners are built from block-factorizations of the coupled system. The key result of the work is the identification of effective preconditioners for the various sub-problems that appear within the block decomposition. We use numerical examples drawn from both linear and nonlinear hydromechanical models to test the robustness and scalability of the proposed methods. Results demonstrate that an algebraic multigrid variant of the block preconditioner leads to mesh-independent convergence, good parallel efficiency, and insensitivity to the material parameters of the medium.