PROJECTS AND REFERENCES

Transient large heat advection in fractured rock: a zero-thickness interface formulation In a fractured rock mass, the existence of discontinuities may generate preferential paths where the hydraulic flow velocities are frequently much higher than in the porous mèdium and heat advection tends to dominate over heat diffusion. In these cases, the standard Galerkin FEM method leads to oscillatory results and requires the use of stabilization methods. Thus, the current paper introduces a 3-D formulation to solve the large advection problem for zerothickness interface elements –which may be used to discretize fractures in a FEM context–, based on a pre-existent Characteristic method. A verification example is presented, showing that the formulation exhibits a good performance to represent the heat transport by the fluid along zero-thickness interface elements.

In Proc. of the XVI International Conference on Computational Plasticity. Fundamentals and Applications, COMPLAS 2021 by Adrià Pérez, Ignacio Carol and Pere Prat.

Application of zero-thickness interface elements to sanding prediction analysis A computational micromechanical analysis based on zero thickness interface elements for modelling solid prediction in hydrocarbon reservoir sandstones is presented. The model is capable of modelling localization of deformation, disintegration and cracking of cemented rock formation that leads to initiation and continuous sand production during hydrocarbon production and reservoir depletion. Using only few physical parameters, the model is calibrated at the macroscale by reproducing the typical behaviour of geomaterials in compression element tests that is characterized by transition from brittle dilatant to ductile compactant behaviour with increasing confining stress. In the presented application presented, the model was calibrated first using the results of two triaxial tests performed on samples that were recovered from a deep well and then a sand production analysis was carried out. The model predictions are compared well with the experimental results of thick wall cylinder tests. The proposed methodology is very promising as it can predict not only the initiation of sanding, but also the continuous produced sand volumes under geometry changing conditions which is still a challenging research problem.

In Journal of Petroleum Science and Engineering 190, 2020 by Daniel Garolera, Ignacio Carol and Panos Papanastasiou.

Modeling acid attack of oil well cement exposed to carbonated brine: effect of specimen geometry on experimental results In recent years, the authors and co-workers have developed a diffusion-reaction model for the degradation process of oilwell cements exposed to carbonated brines in the context of CO2 capture and storage in abandoned oil reservoirs [1]. The model considers two main diffusion/reaction field variables for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field variables for chloride and alkalis concentrations. The volume fractions of solid constituents evolve according to the chemical kinetics and chemical equilibrium equations of the reactions involved, determining the diffusivity properties of the material. In this paper, in the framework of an experimental campaign in preparation, this model is used for assessing the effect of different specimen geometries on the kinetics and extent of the acid attack. The results obtained will help to optimize the experimental setup and to the interpretation of the results obtained.

In Proc. of XV International Conference on Computational Plasticity. Fundamentals and Application, COMPLAS XV, 2029. By Lucía Barandiarán, Joaquín Liaudat, Carlos María López and Ignacio Carol.

Micromechanical analysis of sand production We present a micromechanical approach based on zero-thickness interface elements for modelling advanced localization and cracking states of cemented granular materials, such as reservoir sandstones. The proposed methodology is capable of reproducing the complex behaviour of intergranular and intragranular localization, cracking, and fracturing of rock formation that leads to sanding in hydrocarbon production. The model is calibrated at the macroscale, using only a few physical parameters, by reproducing the typical behaviour of compression element tests. The model exhibits clear transition behaviour from brittle dilatant to ductile compactant behaviour with increasing confining stress. The methodology is implemented for sand production prediction analysis based on the simulation of 2D micromechanical models of hollow cylinder cross sections. The obtained results are compared well with published experimental data from hollow cylinder tests characterized by strong scale effect in the range of small perforations.

In International Journal for Numerical and Analytical Methods in Geomechanics, 43:1207–1229, 2019. By Daniel Garolera, Ignacio Carol and Panos Papanastasiou.

Modelling acid attack of oilwell cement exposed to carbonated brine. A diffusion-reaction model for the carbonation process of oilwell cement exposed to carbonated brine under CO2 geological storage conditions is presented. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field equations for chloride and alkalis concentrations, and by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. The model is used to simulate experimental tests performed by Duguid and Scherer (2010), leading to promising results indicating that the fundamental aspects of the phenomenon are captured.

In International Journal of Greenhouse Gas Control 68 (2018) by Joaquín Liaudat, Ariadna Martínez, Carlos María López and Ignacio Carol.

‘Onion-peel’ cracking and spalling in coupled meso-mechanical analysis of External Sulfate Attack in concrete using zero-thickness interface elements. External Sulfate Attack (ESA) is a chemical degradation process that may affect concrete structures exposed to sulfate-rich environments. The ingress of sulfate ions causes chemical reactions leading to the formation of secondary ettringite, with significant volume expansion and subsequent characteristic cracking. The model proposed combines a diffusion-reaction model with a meso-mechanical model in which the larger aggregates are represented explicitly and pre-inserted fracture-based zero-thickness interface elements represent potential cracks. In the model, opening cracks also become preferential diffusion paths for sulfate penetration, which brings in chemical-mechanical coupling in a staggered scheme. By exploiting improved calculation capabilities, significant extensions of previous 2D results and new 3D calculations have been obtained. The new results demonstrate the model’s effectiveness in realistically replicating “onion-peel” cracking and spalling patterns observed in experiments, as well as to sulfate ion penetration profiles.

In Construction and Building Materials, 455, 139011 (2024) by Caterina Biscaro, Ariadna Martínez, Adrià Pérez, Giovanna Xotta, Carlos María López and Ignacio Carol.

Numerical modeling of rock spalling around a tunnel using visco-plastic interface elements and a rock removal strategy.  Rock spalling is a brittle failure process that occurs around tunnels excavated in hard rock under high in-situ stress states. In nuclear waste disposal, spalling in fractured crystalline rock could create connected fractures, potentially providing pathways for radionuclides. Robust numerical models are therefore needed to evaluate the extent of rock spalling so that the design and layout of a prospective deep geological repository can be optimised and made fit for purpose. With this motivation in mind, this study proposes a methodology for the numerical analysis of rock spalling based on zero-thickness interface elements with a visco-plastic-fracture constitutive law, combined with a workflow for finite element removal/excavation. To simulate spalling, zero-thickness interface elements are pre-inserted along a sufficient number of mesh lines with random orientation within the rock mass. A uniform initial stress state is generated and the excavation of the circular tunnel is performed by removing the corresponding elements, which leads to stresses in excess of the elastic limit in some of the interfaces, and subsequent viscoplastic fracture openings. A criterion for excavation of the finite elements around the tunnel is established when a block which is totally surrounded by failed interfaces is totally detached or can slide off the mesh following a kinematically admissible path. The excavation of blocks causes a stress redistribution around the tunnel and this leads the need for new excavation steps, until a new equilibrium configuration is reached. The proposed methodology is applied to assess rock spalling in the Mine-by Experiment at the Atomic Energy of Canada Limited’s (AECL’s) Underground Research Laboratory in the massive Lac du Bonnet granite. The focus of the analysis is to understand the mechanisms and the influencing factors that lead to brittle failure, and to calibrate material properties to reproduce both the final stress state of the tunnel and its spalling depth.

In International Journal of Rock Mechanics and Mining Sciences (accepted, in Press). Laura Crusat, Daniel Garolera, Ignacio Carol, Paolo Trinchero, Andrés Idiart, Miguel Calpe and Diego Mas-Ivars.