A new pore-scale numerical simulator for investigating special core analysis data

The study presented in this thesis addresses various pore-scale phenomena related to the oil industry by implementing new numerical models capable of simulating a wide range of multiphase flow processes such as depressurisation, water flooding, gas injection and various EOR techniques. The aim is not to produce quantitative predictions per se but rather to examine the effect of key petrophysical parameters on oil recovery when different production protocols are applied to specific rock analogues. In order to facilitate this, a new pore-scale process simulator is developed – numSCAL (numerical Special Core Analysis Laboratory) – with different modules associated with different mechanisms. A steady-state depletion model is described first and used to investigate the impact of numerous parameters on solution gas drive. We show that parameter combinations that increase bubble density can lead to delayed gas breakthrough and can result in high critical gas saturations. The model is extended to support three-phase flow by incorporating concepts from graph theory. Simulation results highlight the interaction between the underlying phase saturations, spreading conditions and wetting films and emphasise the competition among mechanisms acting in three-phase systems. Two unsteady-state models are also presented to study water flooding processes in porous media – the first mainly applied to simulate drainage processes and the second used to study the onset of ganglia mobilisation. Results show that parameters affecting the capillary number and viscous ratio play a crucial role in determining the observed invasion regime and final oil recoveries. Conditions required for ganglia mobilisation are derived and used to predict the likelihood of mobilisation at different parts of the reservoir. The dynamic drainage model is then extended to simulate low salinity (LS) water flooding and polymer injection – secondary and tertiary effects are shown to depend on interactions amongst several key flow parameters (including initial reservoir wettability, flow rate and viscous ratio). In addition, a positive synergistic effect is identified, where the combined injection of LS brine and polymer leads to increased recovery in several scenarios. The study concludes with an application of the pore-scale modelling technique in a novel research area. A new approach is presented to model drug perfusion surrounding Glioblastoma Multiform (GBM) tumours. Results show that blood flow, transmural transport and tissue diffusion have a direct impact on the average drug concentrations that develop in the vascular network and the surrounding tissue

La pertinence des cash-flows d'exploitation et de l'information financière traditionnelle dans la prévision de la détresse financière des entreprises tunisiennes

L'objectif de cet article est de valider la pertinence des cash-flows d'exploitation dans le domaine de prévision des difficultés financières. Il s'agit de vérifier si l'information renseignant sur les cash-flows d'exploitation prévoit mieux la cessation de paiement que l'information comptable basée sur les accruals. L'étude empirique ainsi menée sur 278 observations, a permis de se prononcer sur la supériorité des modèles LOGIT basés sur les cash-flows, par rapport à ceux basés sur l'information financière traditionnelle en terme de prévision de la cessation de paiement, et ce par la simple référence à leurs pouvoirs prédictifs. Toutefois, cette supériorité n'a été statistiquement validée par le test de Davidson & Mackinon (1981) que pour la prévision deux et trois ans à l'avance.Cash-flows; information financière; détresse financière

A Multiagent Architecture for Mobile Robot Navigation Using Hierarchical Fuzzy and Sliding Mode Controllers

The challenge of this work is to implement an algorithm which enables the robot to achieve independent activities in the purpose of achieving a common goal, which consists in autonomous navigation in a partially unknown environment. The use of multiagent system is convenient for such a problem. Hence, we have designed a structure composed of four agents dedicated to perception, navigation, static, and dynamic obstacle avoidance. Those agents interact through a coordination system

Sorption of Phosphorus, Nickel, and Lead from Aqueous Solution Using Manganese Oxide-Coated Materials

Manganese oxide-coated sand (MOCS) and manganese oxide-coated crushed brick (MOCB) were prepared and characterized and employed for the removal of phosphorus ions (PO4 3−) and Pb(II) and Ni(II) ions from aqueous solution. To study the surface properties of the adsorbents, scanning electron microscopy (SEM), X-ray diffraction (XRD) methods, and BET analyses were used. Adsorption was investigated by batch experiments. The estimated optimum pH was 7 for Ni(II) and 5 for all other ions retention by the two considered adsorbents. Both the Freundlich and Langmuir isotherms provided a reasonable fit to the experimental data for the adsorption. The adsorption capacities of the coated adsorbents at a considered pH value and a temperature of 20°C were 1.96 and 2.08 mg/g for PO4 3−, 2.4 and 3.33 mg/g for Ni(II), and 6 and 6.25 for Pb(II) onto MOCS and MOCB, respectively. The pseudo-first-order and pseudo-second-order equations as well as the intraparticle diffusion model were determined to test the adsorption kinetics and the rate constants derived from the three kinetic models being calculated. The pseudo-second-order kinetic model was better appropriated. Results obtained from this study confirm that the manganese oxide-coated sorbent is considerably considered like suitable for the removal of anions and cations from aqueous solutions

Etude et réalisation d’un Convertisseur A/N d’architecture Sigma Delta à courants commutés

The two step current cell memory can be considered as an operator fulfilling the functions of inversion, summation and delay. While using this operator, it is possible to develop basic circuit architectures (integrator). The object of our work is to design a second order Sigma Delta modulator. This modulator is based on a new differential integrator S2I. Fist, we had modelled the cell memory S2I. The finality of this work is to determine a model allowing the behavior of the Sigma Delta modulator. Then, we integrated the modulator on silicon in technology AMS 0.6μm triple level of metal. Then, various experimental measurements were carried out with using characterization system CANTEST. Secondly, we designed the chain of decimation which restore the signal delivered by the modulator (bitstream) on 13 bits at a frequency close to Nyquist. The simulation of the decimation filter at is realized with MATLAB then on software SPW (Signal Pocessing Workstation) which is a tool of fixed point system design, the VHDL code is generated by compilation. The third part of the thesis, consists in testing all the chain of analogue to digital conversion by gathering the modulator and the decimation filter.La cellule mémoire S2I de courant peut être considérée comme un opérateur réalisant les fonctions d’inversion, de sommation et de retard. En se basant sur cet opérateur, il est possible de développer des architectures de circuits élémentaires (intégrateur...). Le but de notre travail est de réaliser un modulateur Σ∆ d’ordre deux à base d’une nouvelle architecture d’intégrateur différentiel doublement échantillonné, S2I. Dans un premier temps, on a modélisé la cellule mémoire S2I. La finalité du travail consiste a déterminer un modèle permettant d’étudier le comportement du modulateur Σ∆. Ensuite, on a intégré le modulateur sur le silicium en technologie AMS 0.6μm triple niveau de métal. Puis, les diverses mesures expérimentales ont été réalisées avec le système de caractérisation CANTEST. Dans un seconde étape, on a conçu la chaîne de décimation qui permet de restituer le signal délivré par le modulateur sur 13 bits à une fréquence proche de Nyquist. La simulation du filtre de décimation à été réalisée avec MATLAB puis sur le logiciel SPW (Signal Pocessing Workstation) qui est un outil de conception de système, le code VHDL est généré par compilation. La troisième partie de la thèse, consiste à tester toute la chaîne de conversion analogique numérique en rassemblant le modulateur et le filtre décimateur