Effect of Temperature on Asphaltenes Precipitation: Direct and Indirect Analyses and Phase Equilibrium Study

Abstract

Asphaltenes precipitation is still a challenge for the petroleum industry during crude oil production and processing. Pressure, composition, and temperature variation can induce asphaltenes destabilization and aggregation, leading to fouling and flow blocking in pipelines and wellbore pores. The present work aims to investigate the effect of temperature on asphaltene precipitation using n-heptane as the precipitant alkane. Three different Brazilian crude oils, here named BR1, BR2, and BR3, were studied at temperatures of 5, 25, and 50 °C, using two different asphaltene yield and precipitation onset analyses, defined as direct and indirect methods. It has been found that when temperature rises, there is a decrease in the asphaltenes precipitation yield, together with an increase in the precipitation onset, which could be related to the increase in the asphaltenes solubility. Temperature effects on the onset seem to be influenced by crude oil properties, being less significant for more stable asphaltenes. Asphaltenes precipitation phenomenon was properly modeled by the intermediate of the Regular Solution Model, showing a low molecular weight asphaltene distribution when temperature rises. When indirect method is used, it has been seen that new fractions of heavy compounds aggregate and precipitate at a second precipitation stage under an n-heptane excess.

Long-Time Kinetic Impact on Key Factors Affecting Asphaltene Precipitation

“…However, the growth of particle sizes decreased after reaching its peak MED of 11.54 μm for the first 300 min in the 70 °C model oil system. The sharp decrease in the particle size was probably due to the enhancement of asphaltene solubility upon increasing temperature . In contrast, the particle sizes of the 50 °C model oil system maintained a consistent buildup for 2880 min reaching an MED of 13.39 μm.…”

“…The sharp decrease in the particle size was probably due to the enhancement of asphaltene solubility upon increasing temperature. 17 In contrast, the particle sizes of the 50 °C model oil However, after 2880 min, a sharp decline in the MED from 2880 to 7200 min was noticed. The confocal experimentation confirmed the accumulated yield experiments, which implied that asphaltene precipitation yielded more regarding decreasing temperature.…”

“…However, the extent to which time impacted the precipitation ability of these parameters was often neglected in the literature. Most studies investigating asphaltene precipitation by thermodynamic parameters were conducted under short-time scales ranging from 1 to 2880 min. , Recent studies over the past two decades hinted at the over-prediction of asphaltene precipitation by several short-time kinetic experimentations . Beck et al indicated that asphaltene yields would gradually increase as long as the medium is observed.…”

“…15,16 Recent studies over the past two decades hinted at the over-prediction of asphaltene precipitation by several short-time kinetic experimentations. 17 Beck et al 18 indicated that asphaltene yields would gradually increase as long as the medium is observed. The lack of long- time asphaltene precipitation experimentations highlighted a significant area for research to holistically understand the mechanisms of asphaltene precipitation.…”

Asphaltene Precipitation from Heavy Oil Diluted with Petroleum Solvents

“…Several thermodynamic models including cubic equations of state, the cubic plus association equation of state, statistical associating fluid theory, and regular solution theory have been applied to asphaltene precipitation from heavy oils diluted with pure n -alkanes. ,− Reviews of the performance of thermodynamic models with pure solvents can be found elsewhere. , In this study, only the regular solution approach is considered because it was specifically designed to model asphaltene precipitation from mixtures of heavy oil and solvents.…”