Abstract
Chemical inhibition of asphaltene deposition is considered a cost-effective way to prevent the harsh consequences of asphaltene instability in the produced crude. Thus, a careful screening of asphaltene inhibitors is crucial for an efficient prevention. However, the characteristics of asphaltenes such as their acid–base properties will influence the selection of an asphaltene inhibitor and the inhibition mechanism. Therefore, improved knowledge on asphaltene acidic and basic fractions is important. In this work, the separation of asphaltenes into acid, base, neutral, and amphoteric fractions was performed. Among the existing techniques to fractionate asphaltenes, the method of Ramljack was adopted and applied on a light oil extracted asphaltene. However, this oil was sampled from one of the wells in the Hassi Messaoud field in Algeria that experienced a recurring deposition of asphaltenes. The results of asphaltene fractionation reveal that the half composition of this heavy part of crude oil is active functions gathered acid and base components. However, the main contribution is reported to the neutral fraction. The characterization results of infrared and elementary analyses show that both active fractions are aromatic and polar. Moreover, the acid fraction contains in its structure carboxylic acids, phenols, sulfoxide groups, and aliphatic chains, while the structure of the base fraction contains amines, sulfoxide groups, and aliphatic chains.
Highlights
Asphaltene deposition can occur when changes in the thermodynamic conditions and the chemical composition upset the chemical equilibrium of the crude oil components, so the system loses its ability to disperse asphaltene particles, and as a result, these carbonaceous components precipitate out of solution.[1]
The crude oil was sampled from the wellhead of the selected well, and it was characterized to define some of its physicochemical properties according to specific standard methods as follows: density at 20 °C (ASTM D4052-11 and ISO12185-96), kinematic viscosity at 20 °C (ASTM D445-06 and ISO 3104-94), total acid number (ASTM D974-04 and ISO 661897), sulfur content (ASTM D4294-10 and ISO 8754-03), base sediment and water (ASTM D96 and ISO 9030-90), water content (IP 356), salinity (ASTM D6470), flash point (ASTM D56-05), pour and freezing points (ASTM D97), and metal content (ASTM D6728)
It was reported that acidity of crude oil may arise from two different sources: high sulfur content or the presence of carboxylic acids in crude oil.[25]
Summary
Asphaltene deposition can occur when changes in the thermodynamic conditions and the chemical composition upset the chemical equilibrium of the crude oil components, so the system loses its ability to disperse asphaltene particles, and as a result, these carbonaceous components precipitate out of solution.[1]Depending on the thermodynamic and hydrodynamic conditions, the asphaltene deposits can occur at any part of the production system.[2]. Asphaltene deposition can occur when changes in the thermodynamic conditions and the chemical composition upset the chemical equilibrium of the crude oil components, so the system loses its ability to disperse asphaltene particles, and as a result, these carbonaceous components precipitate out of solution.[1]. There are three methods to treat or mitigate the deposition of asphaltenes: mechanical (scrapers), thermal (hot oil, downhole heater, and heat liberate chemicals), and chemical (solvents, dispersants, and inhibitors).[5] The first two methods are usually applied after the deposition has occurred, while the chemical intervention can be employed before or after the deposition of asphaltenes
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