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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

Nguyen S.-T.,Euro Engineering | Nguyen S.-T.,Duy Tan University | To Q.-D.,University Paris Est Creteil | Vu M.-N.,Duy Tan University | Nguyen T.-D.,Duy Tan University
Composite Structures | Year: 2016

This paper presents analytical solutions for the effective viscoelastic properties of composite materials based on a homogenization approach. The cases of spherical inclusions and cracks were recently developed. The objective of this paper is to use the same technique to deal with the case of periodic media containing cuboidal inhomogeneities. The viscoelastic behavior of both the matrix and the homogeneous equivalent medium is modeled by the Zener rheological model while inclusions are assumed to be linearly elastic. The viscoelastic Hill tensor required for the calculation of the effective viscoelastic tensors is obtained explicitly in the Laplace-Carson space in terms of Fourier series. The final expressions show that overall behavior depends on the viscoelastic properties of the matrix, the 3D dimensions of the inclusions and the thickness of the matrix layer between two nearby inclusions. Applications to masonry structures are presented to illustrate the theoretical results. © 2016 Elsevier Ltd

Nguyen S.-T.,Euro Engineering | Nguyen S.-T.,Duy Tan University | Pham D.-C.,Institute of Mechanics VAST | Vu M.-N.,Duy Tan University | To Q.-D.,University Paris Est Creteil
International Journal of Engineering Science | Year: 2016

This paper provides a new homogenization scheme, which is a combination of the theoretical and experimental approaches, for modeling effective transport properties of heterogeneous materials. Differ from the classical methods, this method considers a free conductivity of the reference matrix that is not a pre-defined parameter and can be calibrated based on an inverse analysis using available microscopic and macroscopic data. This technique is illustrated using experimental data of electrical conductivity of rocks published in literature. We show that the conductivity of the reference matrix can be approximated by linear or quadratic functions of the porosity. The proposed approach can be used to model materials containing highly contrast phases. © 2016 Elsevier Ltd. All rights reserved.

Nguyen S.T.,Euro Engineering | Hammad T.,University of Lorraine | Onaisi A.,Total S.A.
EAGE Workshop on Geomechanics in the Oil and Gas Industry | Year: 2014

The Eaton-Terzaghi concept offers an appropriate framework for pore pressure prediction under the conditions of compaction disequilibrium as major source of overpressure and constant clay rich silicoclastic lithology, provided that the normal compaction trend (NCT) is well calibrated. To deal with cases that are outside of the domain of validity of Eaton's approach, and also to make the definition of the NCT less user or calibration dependent, Total is developing and testing a new geomechanics based approach. The proposed method takes into account the heterogeneity of the lithology by considering the clay fraction and clay types. The porosity of the clay fraction is interpreted and is used for the calculation of pore pressure to avoid the impact of the other mineralogical components on the results. A Hydro-Thermo- Mechanical (HTM) coupled model in which the sediments behave as Elasto-Visco-Plastic material simulates the combined effects of temperature gradient, burial speed and complex loading/unloading scenario such as tectonic stresses, fluid expansion and hydrocarbon generation. Copyright © (2014) by the European Association of Geoscientists & Engineers All rights reserved.

Rambeau O.,Total S.A. | Alves M.-H.,Euro Engineering | Andreu N.,IPREM | Loriau M.,Total S.A. | Passade-Boupat N.,Total S.A.
Society of Petroleum Engineers - SPE EOR Conference at Oil and Gas West Asia, OGWA 2016 | Year: 2016

A side effect of EOR polymer flooding on topsides process chain is the generation of stable thin emulsion in viscous water phase. Both viscosity and severe emulsion impede the efficiency of water treatment technologies. The viscosity of the back produced polymer increases the time of clarification of oily water phase. The target of the water treatment specialist would be to collapse the viscosity of the produced water. The main concern is to decrease the viscosity of the produced water containing polymer back produced, acting on the degradation of the polymer without generating more severe oily emulsion. Shearing, a well known mode of degradation has been compared to other techniques such as chemical oxidation (bleach) and sonication. All the tests were performed with a high molecular weight polyacrylamide commonly used in EOR; at bench lab scale on synthetic viscosified produced water and on back produced water from field with cEOR flooding. Degradation efficiency was evaluated through viscosity measurements and polymer molecular weight analyses. This paper presents the results of the different investigations carried out to drop the viscosity of the produced water to an acceptable value for water treatment. Chemical oxidation using bleach has proved its efficiency on synthetic produced water. Different shearing conditions and different powers of sonication have also highlighted actions on the polymer and on the viscosity of the water phase. Even if all the tested degradations lead to a significant viscosity drop of the synthetic viscosified water, the improvements on water treatment were not equivalent. Analytical measurements of the molecular weight of the degraded polymer allowed initiating a scale of degradation efficiency. The efficiency, feasibility, difficulty, beneficial impact on water treatment and level of readiness of the technology have been estimated. An assessment of the different techniques for the polymer degradation in water treatment is presented at the end of this paper. The feasibility to decrease the viscosity of the back produced water would allow to simplify the water treatment process chain dedicated to polymer flooding case. Works continues on integrated water treatment process, including pre-degradation of the polymer back produced. Copyright 2016, Society of Petroleum Engineers.

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.

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.

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.

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.

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

We model the anisotropy of the electrical conductivity of geomaterials based on the micro-macro homogenization theory. These materials are considered as random mixtures of solid grains and pores filled by fluids, both are supposed to have ellipsoidal shapes with their long axes oriented in horizontal direction. The electrical behavior of such material is transversely isotropic. The classical Eshelby's concept of a mixture of an ellipsoidal inclusion in an infinite homogeneous matrix, that was developed to study elastic properties of heterogeneous materials, is extended to analyze the conductivity of rocks. A combination of the self-consistent and the differential effective medium techniques allows developing a theoretical formula for the simulation of conductivity of anisotropic heterogeneous materials. For particular isotropic cases, this formula is similar to the classical well-known solutions that are largely used in practice such as Archie's law, Bruggman's theory and Bussian's equation. When applying to geomaterials, the developed theory provides the conductivities in both horizontal and vertical directions. The anisotropy, defined as the ratio between these two conductivities, is a function of the porosity, the shapes and the conductivities of each phase of rocks. This paper, focusing on a purely theoretical approach, shows how the micromechanical parameters affect the macroscopic anisotropy of electrical conductivity and resistivity of anisotropic materials. © 2015 Elsevier B.V.

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