Acides naphténiques hydrates de gaz (influence de l'interface eau/huile sur les propriétés dispersantes d'un brut acide.)

Actuellement, les compagnies pétrolières sont amenées à exploiter des gisements de bruts situés à des profondeurs sous-marines de plus en plus importantes. Dans ces conditions de production (hautes pressions et basses températures), se pose le problème du bouchage des conduites pétrolières par les hydrates de gaz, composés cristallins constitués d'eau et de gaz. Il a été montré que certains bruts asphalténiques forment des émulsions eau dans huile (E/H) stables sur plusieurs mois et évitent la formation des bouchons d'hydrate. Dans le cadre de cette thèse, les propriétés "anti-hydrates" d'un brut acide AH provenant d'Afrique de l'Ouest sont étudiées. Ce brut comporte des acides naphténiques, composés hydrocarbures de formule brute RCOOH réactifs au pH et à la salinité de la phase aqueuse. Dans un premier temps, les propriétés émulsifiantes du brut AH ont été explorés. Il a été montré que la stabilité des émulsions E/H avec ce brut provient principalement des résines lourdes et des asphaltènes. Les naphténates RCOO-, forme basique des acides naphténiques, diminuent la stabilité des émulsions E/H. L'étude du brut AH vis à vis des hydrates de gaz a montré que ce brut présente des propriétés anti-agglomérantes modérées grâce aux résines lourdes et aux asphaltènes. Par contre, les naphténates RCOO- favorisent la formation des bouchons d'hydrate. D'autre part, il a été relevé que l'agglomération des particules d'hydrate accélère la cinétique de formation des hydrates et favorise le cassage des émulsions E/H. Un mécanisme d'agglomération par contact particule/gouttelette est proposé pour interpréter ces comportements. Enfin, nous proposons un modèle des équilibres physico-chimiques des acides naphténiques dans le mélange binaire eau/brut AH, afin de transposer les résultats obtenus en laboratoire aux conditions réelles.Nowadays, the development of offshore oil production under increasing water depths (high pressures and low temperatures) has led oil companies to focus on gas hydrates risks. Hydrates are crystals containing gas and water molecules which can plug offshore pipelines. It has been shown that some asphaltenic crude oils stabilise water-in-oil emulsions (W/O) during several months and exhibit very good anti-agglomerant properties avoiding hydrate plugs formation. In this work, we have studied the anti-hydraté properties of a West African acidic crude oil called crude AH. This oil contains naphthenic acids, RCOOH hydrocarbons which are sensitive to both the pH and the salinity of the water phase. The emulsifying properties of the crude AH have firstly been explored. It has been shown that heavy resins and asphaltenes are the main compounds of the crude AH responsible for the long term stability of the W/O emulsions whereas the napthenates RCOO- lead to less stable W/O emulsions. Dealing with hydrates, the crude AH exhibits moderate anti-agglomerant properties due to the presence of heavy resins and asphaltenes. However, the naphthenates RCOO- drastically increase the formation of hydrate plugs. Moreover, it has been pointed out that hydrate particles agglomeration accelerates the kinetics of hydrate formation and enhances the water/oil separation. In order to explain these behaviours, a mechanism of agglomeration by "sticking" between a hydrate particle and a water droplet has been proposed. Finally, we have developed a model which describes the physico-chemical equilibria of the naphthenic acids in the binary system water/crude AH, in order to transpose the results obtained in the laboratory to the real oilfield conditions.PAU-BU Sciences (644452103) / SudocSudocFranceF

A Theoretical and Experimental Approach for Electronic Structure Characterization of BN Isosteres of Anthracene.

COMInternational audienc

A new reduction method for phase equilibrium calculations

International audiencePhase equilibrium calculations require the most important computational effort in many process simulators and in reservoir compositional simulations. In this work, a new reduction method for phase equilibrium calculations is proposed. A new set of independent variables (and the related set of error equations) is introduced, based on the observation that, under certain conditions, the equilibrium ratios can be related only to some component properties (elements of the reduction matrix) and to equation of state parameters. The new formulation leads to simpler expressions of the elements of the Jacobian matrix. Some important features are presented, and an interesting and useful link with classical flash calculation methods is revealed. The reliability and efficiency of the proposed method are tested on several synthetic and reservoir hydrocarbon mixtures. The proposed method proves to be robust and it performs in all cases better than previous reduction methods. Finally, it is discussed how the new set of independent variables can be used for a variety of phase equilibrium calculations

Application de la luminescence à l’étude des changements de structure moléculaire, avec la température, de l’éthanol vitreux ou surfondu

Lorsqu’on élève de 80 à 150 K la température de l’éthanol d’abord vitreux, puis surfondu, des changements de structure à courte distance se produisent dans le domaine de la transition vitreuse (90, 100 K) et dans celui de la nucléation (110, 130 K). Ils peuvent être décelés et précisés à partir de l’étude de la luminescence d’un colorant (ici la fluorescéine) ou d’un carbure aromatique (ici le phénanthrène d10) dissous dans l’éthanol.Dans le cas de solutions étendues de fluorescéine (10-6 g/cm3), les mouvements libérés des molécules d’éthanol se traduisent par une dépolarisation de la fluorescence directe (S* → S). Dans le cas de solutions concentrées (10-2 ML-1) de phénanthrène d10, ces mouvements entraînent des « flambées » d’intensité de la fluorescence retardée, qui résulte de l’annihilation de l’énergie électronique de deux molécules de soluté dans l’état triplet de plus basse énergie

From established trends to the conceptualization of BN-aromatics.

COMInternational audienc

Formation/dissociation d'hydrates de gaz en milieu poreux (effet de la capillarité sur les conditions d'équilibre P/T.)

Les hydrates de gaz sont des composés solides qui pourraient être utilisés comme indicateurs thermiques des gisements d'hydrocarbures qu'ils surplombent. Pour cela, il est nécessaire de connaître avec précision leurs conditions d'équilibre P/T en milieu poreux. Le travail rapporté dans ce mémoire est une contribution à l'étude de ces conditions. Nous avons mis au point deux montages expérimentaux. Le premier, muni d'une cellule transparente, permet de visualiser et de mesurer les conditions d'équilibre des hydrates jusqu'à 0,5 MPa. Le second, muni d'une cellule sans fenêtre, permet de mesurer les conditions d'équilibre des hydrates jusqu'à 60 MPa. Nous avons vérifié que, en l'absence de milieu poreux, l'introduction d'un tensioactif (SDS) accélère la formation des hydrates. Leurs conditions d'équilibre mesurées et calculées sont en bon accord avec les données de la littérature sur l'intervalle 0,2 0,5 MPa pour l'hydrate de propane et 3 20 MPa pour l'hydrate de méthane. Nous avons amélioré la connaissance, tant expérimentale que théorique, des conditions d'équilibre de l'hydrate de méthane entre 20 et 53 MPa. Nous avons également vérifié que seuls des milieux mésoporeux (billes de silice, argile) ont une influence sur les conditions d'équilibre des hydrates. Ils produisent des décalages vers les plus basses températures et les plus hautes pressions, d'autant plus grands que les tailles des mésopores sont plus petites. Sur la base d'un modèle de van der Waals et Platteeuw modifié, nous avons montré que les décalages mesurés peuvent être attribués à la distribution de tailles des mésopores.Gas hydrates are solid compounds that could be used as a thermal tracer for the oil or gas fields they recover. In order to do it, the P/T equilibrium conditions must be known accurately in porous medium. The work presented in this report is a contribution to the study of these conditions. Two experimental set-ups were built up. The first one, provided with a transparent cell, allows to visualize and measure equilibrium conditions of gas hydrates up to 0.5 MPa. The second one, provided with a cell without any windows, allows to measure equilibrium conditions of gas hydrates up to 60 MPa. We checked that, in a bulk system, the use of a surfactant (SDS) accelerated hydrate formation. Their equilibrium conditions, measured and calculated, were in good agreement with literature data in the ranges 0.2 0.5 MPa for propane hydrate and 3 20 MPa for methane hydrate. We determined equilibrium conditions of methane hydrate, experimentally and theoretically, between 20 and 53 MPa, which completed literature data. We also checked that only mesoporous media (silica gels, clay) had an influence on equilibrium conditions of gas hydrates. They are shifted to lower temperatures and higher pressures and the smaller the mesopores, the higher the shift. On the basis of a modified van der Waals and Platteeux model, we demonstrated that shifts depended on the pore size distribution of the mesoporous systems.PAU-BU Sciences (644452103) / SudocSudocFranceF

Hydrate plug prevention by quaternary ammonium salts

International audienceThe use of low-dosage inhibitors is an alternative to thermodynamic inhibitors to prevent gas hydrates from plugging oil production pipelines. In this work, quaternary ammonium salts (QAs) with different structures were tested as hydrate plug inhibitors on model systems containing 1/1/4/X proportions (by weight) of water/THF/oil/QA systems. The experimental results suggest that the presence of both small (CH3) groups in their polar moiety and two long alkyl chains in their hydrophobic part has a beneficial effect on their ability to adsorb onto the hydrate surface and form a steric barrier around the hydrate crystals, which limits their agglomeration to larger masses. Above a minimum concentration, the concentration of the double-tailed QAs has no appreciable effect on their ability to prevent hydrates from plugging, Their effectiveness as hydrate plug inhibitors is not dependent on the chain length of the oil

Formulation of model cutting-oil water emulsions using paraffinic oil and ionic/nonionic surfactant mixture

International audienceCutting-oil emulsions are marketed under the shape of concentrates that the user has to dilute. More often these concentrates are monophasic microemulsions. We show that this kind of microemulsions may be obtained while relying on the generalized concept of Winsor, which guides the manipulation of three formulation parameters, which in turn rationally modify the surfactant interactions with the oily and the aqueous phases. The model concentrates that we have formulated contain six constituents. The oily phase is constituted of paraffinic oil and normal decanol. The aqueous phase is a solution of monoethanolamine borate in water whose hardness is fixed at 40°f. The active mixture contains a hydrophilic surfactant borate in water whose hardness is fixed at 40°f. The active mixture contains a hydrophilic surfactant and a lipophilic surfactant. We have formulated concentrates presenting an excellent ability to dilution, a very good stability to the hardness of water and pHs in agreement with the cutting fluid specification sheets, while identifying the formulation parameters to the mass ratio of normal decanol in the oily phase, to the mass ratio of monoethanolamine borate in the aqueous phase and to the mass ratio of the hydrophilic surfactant in the active mixture. Cutting-oil emulsions are marketed under the shape of concentrates that the user has to dilute. More often these concentrates are monophasic microemulsions. We show that this kind of microemulsions may be obtained while relying on the generalized concept of Winsor, which guides the manipulation of three formulation parameters, which in turn rationally modify the surfactant interactions with the oily and the aqueous phases. The model concentrates that we have formulated contain six constituents. The oily phase is constituted of paraffinic oil and normal decanol. The aqueous phase is a solution of monoethanolamine borate in water whose hardness is fixed at 40°f. The active mixture contains a hydrophilic surfactant and a lipophilic surfactant. We have formulated concentrates presenting an excellent ability to dilution, a very good stability to the hardness of water and pHs in agreement with the cutting fluid specification sheets, while identifying the formulation parameters to the mass ratio of normal decanol in the oily phase, to the mass ratio of monoethanolamine borate in the aqueous phase and to the mass ratio of the hydrophilic surfactant in the active mixture

Modelling of the surface tension of binary and ternary mixtures with the gradient theory of fluid interfaces

International audienceThe gradient theory of fluid interfaces is applied to compute the surface tension of various binary and ternary mixtures made up of a gas (carbon dioxide, nitrogen or methane) and hydrocarbons. The inputs of the theory are the Helmholtz energy density of the bulk homogeneous fluid and the influence parameters of the interfacial inhomogeneous fluid. The volume corrected Peng-Robinson equation of state (PR-EOS) is used to determine both the Helmholtz energy density and the bulk properties. The adjustable parameters of the equation of state are used to improve the description of vapour-liquid equilibria (VLE). The influence parameters are obtained from a correlation presented in a previous paper. It is shown that the geometric mixing rule for the influence parameters is the most efficient. This rule is used without any adjustable coefficients, which makes the method predictive. For carbon dioxide/hydrocarbon and methane/hydrocarbon mixtures, the predictions are in very good agreement with the available experimental data. The poorest estimates are obtained for the nitrogen/hydrocarbon mixtures (AAD ∼ 10%). However, even in that case, the gradient theory remains highly superior to existing traditional methods that can be used for such systems

Modeling of the surface tension of multicomponent mixtures with the gradient theory of fluid interfaces

International audienceThe gradient theory of fluid interfaces is for the first time applied, without any lumping, to complex mixtures of more than three components, here made up of hydrocarbons and of a high proportion of carbon dioxide, nitrogen, or methane. It is combined with the volume-corrected Peng-Robinson equation of state. No adjustable parameters are used in the influence parameters mixing rule, which allows use of the gradient theory in a predictive manner. It gives very good estimates of the surface tension of the complex mixtures studied. In any case, it is found to be much superior to the traditional parachor method. The gradient theory is also used to compute the density profiles of the mixture components in the interface; it confirms that the low interfacial tensions of the systems studied are principally induced by a local accumulation of carbon dioxide, nitrogen, or methane in the interface