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The stability of integration is essential to numerical simulations especially when solving nonlinear problems. In this work, a continuum damage mechanics model proposed by the first author is implemented with an integration method named cutting plane algorithm (CPA) to improve the robustness of the simulation. This integration method is one type of return mapping algorithm that bypasses the need for computing the gradients. We compare the current integration method with the previous direct method, and the result shows that the cutting plane algorithm exhibits excellent performance under large loading rate conditions. To enhance accuracy of the new method, a control procedure is utilized in the implementation of the algorithm based on error analysis. Thereafter, the theory of poromechanics is utilized with the damage model to account for the effects of fluid diffusion. Laboratory tests simulated with finite element method illustrate distinct behaviors of shale with different loading rates and indicate the development of microcrack propagation under triaxial compression. Copyright © 2016 John Wiley & Sons, Ltd.

Summary: Using the extended finite element method, faults can be introduced into a three‐dimensional reservoir‐geomechanical model without meshing to assess the potential for fault reactivation associated with industrial activities such as disposal of CO2 or fluid extraction. The residuals to the governing equations include basis functions formed from the enrichment functions for strong and weak discontinuities. The traditional spatial integration scheme is based on an algorithm that partitions each enriched element into a collection of subtetrahedra, which is time and storage intensive. To avoid element partitioning, we adopt the homogeneous numerical integration scheme (referred as HNI hereafter) where the integration of homogeneous monomials over each polyhedron is converted into the integration of the same monomials over the one‐dimensional edges of the polyhedron by using Stokes's theorem and Euler's homogeneous function theorem. The integrands for the strong and weak discontinuities are derived to implement the integration scheme in the three‐dimensional reservoir‐geomechanical model. An example of a jagged fault is presented to reveal the advantages of HNI scheme over the standard element partitioning approach. Several other examples that involve fluid flow, fault sliding, and fault sliding triggered by injection pressure are also presented to demonstrate that accurate and efficient computations are realized by the new integration scheme. [ABSTRACT FROM AUTHOR]

We propose and analyse a unified reactive transport model for leaching of cement paste in brines, with and without CO 2 . We investigate the impact of the boundary conditions on the rate of propagation of the reaction. In agreement with experiments, we observe distinct mechanisms as a function of the pH and the CO 2 concentration of the leaching brine. In particular, clogging is observed at intermediate concentration of CO 2 while higher concentration accelerates the reaction. In addition, we leverage the flexibility of the simulator to explore the impact of different models on the simulations. In particular, aqueous species, phase assemblage and diffusion coefficient model are varied. We demonstrate that in order to be able to obtain quantitative predictions, it is important to accurately capture the feedback between chemical reactions, microstructure and macroscopic transport parameters. [ABSTRACT FROM AUTHOR]

Abstract: Deep saline aquifers are promising candidates for long-term CO2 storage, provided they don’t leak. However, injection of CO2 causes pressure buildup and affects the geomechanical stresses in the caprock. If CO2 is injected at a temperature different from the temperature in the aquifer, additional stresses develop due to thermal expansion/contraction. Our work addresses the question whether these stresses are capable of fracturing the caprock and causing leakage. Using a fully coupled thermo-poromechanical model we simulate 10 years of continuous injection of CO2 at different temperatures. We use the geomechanical parameters for aquifer on Krechba (In Salah, Algeria) including recently published data on initial in situ stresses. We found that when CO2 is injected at temperature 40-50°C the stresses in the caprock become tensile and even overcome the tensile strength causing fracturing of the caprock. After initiation the fractures begin to propagate, driven by high fluid pressure in the reservoir. We estimate the fracture length to be 50 m within the first 10 years of propagation. [Copyright &y& Elsevier]

Abstract: Subsurface fluid injection results in a pore pressure increase, which induces geomechanical stresses. Additionally, if there exists a difference between the ambient formation temperature and the temperature of injected fluid, thermal stresses can develop. Herein we study the effect of CO2 injection temperature on caprock integrity using coupled thermo-poromechanical multi-phase simulations. Calculations show that when CO2 is injected within several years at a temperature below the ambient value in the formation, the stresses above the horizontal injection well lead to tensile or shear failure of the caprock. We study the sensitivity of resulting stresses to the injection temperature, caprock density and initial in situ stresses. We also show that the caprock failure can lead to propagating fractures, which may serve as pathways for CO2 leakage. Based on the results of our simulations we estimate the rate of fracture propagation and study the effect of caprock permeability on this rate. Our results show that injection of CO2 at temperature close to the ambient value in the aquifer significantly reduces the risk of caprock fracturing and, therefore, of possible leakage. [Copyright &y& Elsevier]