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Theses

Investigations into Asphaltenes Destabilization, Aggregation and Deposition

Abstract : Asphaltenes have been known, since decades, to occasionally cause severe industrial problems during crude oil extraction and during its transport. Petroleum fields are apprehensively developed with oversized and costly prevention approaches due to the limited understanding on asphaltenes deposition in conditions of oil production.Previous fundamental researches provided extensive descriptions of asphaltenes properties in good solvents, such as aromatic solvents. The incompatibility of asphaltenes with alkanes induces their destabilization, their aggregation and their deposition. The aggregation and the mass transfer behavior of asphaltenes have been explained by theoretical concepts for oil + liquid alkane systems. The amount of destabilized asphaltenes and their aggregation rate both increase as the volume fraction of the anti-solvent increases. Quantitative laboratory measurements have been accordingly developed for liquid systems at atmospheric pressure. However, risks related to the instability of asphaltenes are only qualitatively understood during the primary production of crude oils. In the oil fields, the pressure decrease of the oil causes the light constituents, such as methane or carbon dioxide, to increase their volume fraction in the liquid phase. Experimental determination of theoretical parameters related to asphaltene deposition under pressure is therefore a key.The first part of this dissertation addresses the understanding of bulk behavior (destabilization and aggregation) related to asphaltenes in oil-heptane systems. Analytical equations are proposed to distinctly model both phenomena. Numerical results obtained by combining both equations provide excellent agreements with experimental measurements. The study reconciles the continuum consideration of asphaltene molecules in crude oils with the notion of flocculation "onset" by distinguishing the destabilization and the aggregation kinetics. A reasonable match is found between the transition of the theoretical and the adjusted colloidal stability ratio, indicating that underlying physics are captured by considering simultaneous destabilization and aggregation kinetics.A fully immersed quartz crystal resonator is used to record the mass of deposit on solid surfaces in contact with varying liquid solutions. The deposition rate of asphaltenes is studied during continuous addition of heptane. A diffusion-limited model, designed for studied geometry, can explain experimental results and agrees with previous research on different apparatus. The mass transfer relationship reveals that primary unstable aggregates of asphaltenes mainly contribute to the deposition process and have an average hydrodynamic radius of 7 nanometers (± 50%). A linear relationship is found between the generation rate and the deposition rate of unstable asphaltenes in the investigated conditions. However, the initial presence of large suspending unstable aggregates slows down the asphaltenes deposition process.In the last phase of this work, the validity of defined concepts for the destabilization, the aggregation and the deposition induced by heptane additions is verified for oil-methane systems. The rate of change of solution properties is found to be the predominant variable affecting the deposition of asphaltenes. The effect of methane is significantly more pronounced than liquid alkanes on the asphaltene deposition.For the first time, the bulk concentration of unstable asphaltenes and their deposition rate can be quantitatively measured during the depressurization of live oils (light constituent dissolved). Although first tendencies are de-rived from this work, the effect of the anti-solvent nature still needs further research with the identified variables in order to fully elucidate the thermodynamic driving quantity which controls the amount of destabilized asphaltenes.
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Mohamed Saidoun. Investigations into Asphaltenes Destabilization, Aggregation and Deposition. Fluid mechanics [physics.class-ph]. Université de Pau et des Pays de l'Adour, 2020. English. ⟨NNT : 2020PAUU3020⟩. ⟨tel-03459429⟩

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