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Pau, France

Nguyen S.T.,Euro Engineering | Nguyen S.T.,Duy Tan University
Journal of Applied Geophysics | Year: 2014

The objective of this work is to employ the micromechanical approach for the modeling of the electrical resistivity and of the conductivity of sandstone. This type of rock is considered as a mixture of solid mineral and porous space filled fully or partially by conductive water. The Eshelby's solution of a spheroidal inclusion in a homogeneous matrix is employed. The differential effective medium model (DEM) with different concepts of the microstructure is developed for the calculation of the resistivity. The parametric study clarifies the impact of the microscopic parameters on the macroscopic electrical properties. The simulations are compared with the classical empirical and theoretical approaches as well as with the laboratory measurements. The results show a strong impact of the microstructure (the shape of the pore, the presence of non-conductive fluids in the pore space, the connectivity of conductive fluid) on the macroscopic resistivity and conductivity of sandstone. This approach gives a link between the microscopic physical parameters of the rock and the macroscopic electrical parameters such as the cementation exponent and the electrical formation factor. © 2014 Elsevier B.V. Source

Nguyen S.T.,Euro Engineering | Nguyen S.T.,Duy Tan University | Dormieux L.,Laboratory Navier
International Journal of Damage Mechanics | Year: 2016

The aim of this paper is to model the viscoelastic properties of micro-cracked materials based on the homogenization micro-macro approach. The isotropic case with random orientation distribution of micro-crack in Burgers non-ageing linear viscoelastic solid was previously modeled. However, in many cases, micro-cracks appear to be parallel and the macroscopic behavior is transversely isotropic. An alternative effective transversely isotropic Burgers model is developed to model the behavior of such materials for the cases of open cracks. For this anisotropic case, the Burgers model for the macroscopic viscoelastic behavior of the micro-cracked materials depends on 20 viscoelastic parameters which are functions of the damage parameter and of the viscoelastic properties of the solid phase. In this study, the evolution of all 20 damage viscoelastic parameters as functions of the crack density is detailed based on a dilute-stress homogenization approach. The use of the same Burgers viscoelastic model as non-cracked material to model the viscoelastic behavior of micro-cracked material is an approximation. This approximation is carried out in short- and long-term behaviors. However, the comparison of this approximation with the exact solution in the case of 1D traction loading showed an excellent validation of this approach in transient situation. © The Author(s) 2015. Source

Nguyen S.T.,Euro Engineering | Nguyen S.T.,Duy Tan University | Vu M.-H.,Duy Tan University | Vu M.N.,Duy Tan University
Journal of Applied Geophysics | Year: 2015

This study is devoted to model the elastic and the sonic properties of sandstones. The main difficulty in modeling granular materials like sandstones is the effect of grain-to-grain contacts. A new concept of an equivalent porous medium (EPM), which is a porous medium of a continuous solid matrix and pore-inclusions with an equivalent porosity that is higher than the porosity of the initial medium, is proposed to avoid this difficulty. A combination of the classical Hashin-Shtrikman (HS) approach and EPM provides an efficient simulation of the elastic properties of aggregate materials like sandstones, in comparison with experimental and numerical data in literature. The porosity of EPM of clean sandstones, that is calibrated using laboratory data, is about two times greater than that of the initial medium. The effects of clay and organic contents in shaly sandstones are also taken into account by introducing a notion of an un-supporting soft-phase. Similarly to the case of clean sandstones, the volumetric fraction of the soft-phase of EPM is about two times greater than that of the initial rock. The stress sensitivity and a comparison of this model to the heuristic modified Hashin-Shtrikman model are also discussed at the end of the paper. A power law is proposed for the dependence of the volumetric fraction of the EPM's soft-phase on the effective confining pressure. The proposed concept of EPM is proved to have many practical applications for the interpretation of sonic and seismic data of reservoir rocks. © 2015 Elsevier B.V. Source

Fressard M.,University of Caen Lower Normandy | Thiery Y.,Euro Engineering | Maquaire O.,University of Caen Lower Normandy
Natural Hazards and Earth System Sciences | Year: 2014

This paper aims at assessing the impact of the data set quality for landslide susceptibility mapping using multivariate statistical modelling methods at detailed scale. This research is conducted on the Pays d'Auge plateau (Normandy, France) with a scale objective of 1 / 10 000, in order to fit the French guidelines on risk assessment. Five sets of data of increasing quality (considering accuracy, scale fitting, and geomorphological significance) and cost of acquisition are used to map the landslide susceptibility using logistic regression. The best maps obtained with each set of data are compared on the basis of different statistical accuracy indicators (ROC curves and relative error calculation), linear cross correlation and expert opinion. The results highlight that only high-quality sets of data supplied with detailed geomorphological variables (i.e. field inventory and surficial formation maps) can predict a satisfying proportion of landslides in the study area. Source

Nguyen S.-T.,Euro Engineering | Nguyen S.-T.,Duy Tan University | Thai M.-Q.,University of Transport and Communications | Vu M.-N.,Duy Tan University | To Q.-D.,University Paris Est Creteil
Mechanics of Materials | Year: 2016

The aim of this paper is to model the effective linear non-ageing viscoelastic properties of porous media based on a micromechanical approach. A porous medium is modeled as a mixture of a viscoelastic matrix and pore inclusions. The Generalized Maxwell (GM) viscoelastic model is employed for both the solid matrix and the porous medium. The effective parameters of the viscoelastic GM rheology of the porous medium, which are functions of the porosity and the viscoelastic properties of the solid phase, are derived considering the short and long term behaviors in Laplace–Carson space (LC). They are validated against exact solutions obtained from the inverse LC transform for a simple configuration. The proposed method allows avoiding the complexity of the inverse LC transform in general condition. An application for cement with assumption of spherical pore is considered to illustrate the powerful of this method. © 2016 Elsevier Ltd Source

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