Hydro-mechanical coupling in damaged porous media containing isolated cracks or/and vugs: model and computations

In this paper we present the development of the macroscopic model describing the hydro-mechanical coupling of damaged porous media containing cracks or/and vugs, by using the asymptotic expansion method. The analysis starts at the mesoscopic scale at which we assume a generic microstructure and the validity of the Biot model in the micro-porous domain saturated by a fluid. In the crack/vug domain the Stokes equation is assumed. After estimation of orders of magnitude of different terms, the description is rendered non-dimensional and the homogenization process is carried out. It leads to an extended Biot model that possesses the same mathematical structure as the initial Biot model. However, the macroscopic poro-elasticity and the macroscopic Darcy conductivity are modified. In order to illustrate the performance of the model, numerical computations of a macroscopic boundary value problem were performed. The results show practical importance of modifications introduced in the Biot model

Numerical computations of rock dissolution and geomechanical effects for CO 2 geological storage

International audienceThe paper is motivated by the long term safety analysis of the CO 2 geological storage. We present a methodology for the assessment of the ge-omechanical impact of progressive rock dissolution. The method is based on the use of X-ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution pro-cess is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited

Experimental evidence of the double-porosity effects in geomaterials

International audienceDouble-porosity is an important characteristic of microstructure in a large range of geomaterials. It designs porous media with connected fissures/fractures or aggregated soils. The origin of double-porosity can be natural or/and it can result from mechanical, chemical or biological damage. The presence of double-porosity can significantly affect the behaviour of geomaterials. In this paper we provide an experimental evidence of the double-porosity effects by performing laboratory experiments. Series of tracer dispersion experiments (in saturated and unsaturated steady-state water flow conditions) in a physical model of double-porosity geomaterial were carried out. For the comparative purposes , experiments of the same type were also performed in a single-porosity model medium. The results clearly showed that the double-porosity microstructure leads to the non-Fickian behaviour of the tracer (early breakthrough and long tail) in both saturated and unsaturated cases

About non-Fickian hyperbolic diffusion

Fick's law expresses the proportionality of solute flux with respect to concentration gradient. Similar relations are Darcy's law for the fluid flow in porous media, Ohm's law for the electric flux and Fourier's law for heat transfers. When introduced in the corresponding balance equations, these flux laws yield diffusion equations of parabolic character. Different attempts have been made to obtain hyperbolic equations so as to point out propagative phenomena. This was done by adding a time derivative flux term to the flow law. In the paper we focus on solute transport. Two possible non-Fickian diffusion cases are addressed. We firstly investigate diffusion in fluids by a mechanistic approach. Secondly, we study the macroscopic diffusion law in composite materials with large contrast of diffusion coefficient. We show that the obtained diffusion law yields hyperbolicity for drastically small characteristic times or non-propagative waves, respectively

The effect of Covid-19 on consumer behavior in Poland : preliminary research results

PURPOSE: The purpose of this paper is to present the results of preliminary research on the impact of restrictions during the Covid-19 pandemic in Poland on consumer behavior. In the research we tried to demonstrate that the pandemic restrictions and austerity have changed individual consumers' behavior in their daily shopping and to what extent.DESIGN/METHODOLOGY/APPROACH: In this research we used survey research method, i.e., CAWI (Computer Assisted Web Interview) technique. The surveyed population consisted of 214 respondents. The research was conducted in the second half of 2020. The sample selection was random.FINDINGS: The results indicate that certain consumer behaviors changed during the lockdown period, indicating the impact of the Covid-19 pandemic on consumer behavior.PRACTICAL IMPLICATIONS: The research results obtained can become guidelines for changes in individual customer service. Indeed, it should be kept in mind that the change in consumer behavior under the influence of Covid-19 has three implications for management. First, business must also learn to improvise and become more flexible during a pandemic crisis. The second managerial implication is the matching of demand and supply. The third managerial effect is the occurring likelihood that consumers will not return to their old buying habits unless the technology they learn to use does not bring about significant changes in their lives.ORIGINALITY/VALUE: Presented results, complement previously conducted research on the impact of the Covid -19 pandemic on the behavior of Polish consumers. The research was designed to address, to some extent, the research gaps identified by others, in examining the effects of Covid-19 on consumer consumption and behavior.peer-reviewe

DOUBLE-POROSITY SOILS WITH HIGHLY CONDUCTIVE INCLUSIONS: MODELING OF WATER FLOW IN UNSATURATED CONDITIONS

Summary The homogenization method by asymptotic expansions was used to study water flow in a double-porosity soil. The gravity effect is included. The macroscopic flow model was found to be a single diffusion-type equation with two effective parameters. The effective conductivity tensor is defined as depending on the solution of a local boundary value problem within a period. The effective specific water capacity is found to be the volumetric average. Both parameters are functions of the capillary pressure head. A numerical example of water infiltration into initially dry soil is presented. The results of homogenization show good agreement with the reference fine scale solution

Etude expérimentale de la dispersion dans un milieu à double porosité

Les milieux poreux naturels forment souvent des structures hétérogènes, qui dans le cas où il existe un fort contraste entre les tailles caractéristiques des pores, sont appelés « milieu à double porosité ». On observe alors le transport préférentiel dans les macropores avec des interactions/échanges avec les micropores qui contribuent à la propagation des solutés dans les conditions de non équilibre local. Dans cette étude, une compagne d'expériences 1D de la dispersion du traceur NaCl en échelon est réalisée en conditions d'écoulement saturé et insaturé sur trois milieux : sable, argile solidifiée et sol à double porosité, formé de billes d'argile arrangées périodiquement dans la matrice de sable. Les courbes de percée dans le milieu à simple porosité et à double porosité sont comparées pour mettre en évidence le comportement non Fickien, en fonction du degré de saturation