Physicochemical characterization of asphaltenic fractions precipitated under high-pressure CO2 conditions in pre-salt reservoirs

In Brazil’s pre-salt oil reservoirs, elevated carbon dioxide (CO2) concentrations often lead to the precipitation of organic particles, particularly asphaltenes, presenting challenges to flow assurance in oil production. Several factors influence the characteristics of asphaltenes, including crude oil, the precipitating agent, and production conditions. To evaluate the behavior of this fraction, it is necessary to understand its physical–chemical structure. This study focuses on evaluating the physicochemical properties of asphaltenic fractions obtained under high-pressure conditions to elucidate the influence of CO2 on deposited asphaltenes. The adaptation of ASTM D6560 facilitated the extraction of heptane-insoluble fractions for comparison. During CO2 precipitation, a solids detection system (SDS) coupled with a high-pressure filtration apparatus enabled the collection of precipitated fractions under reservoir conditions (64 ºC and 600 bar). Characterization through elemental analysis (CHN), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) revealed that CO2-precipitated fractions exhibited greater aliphatic characteristics, while n-heptane-precipitated fractions displayed more aromatic behavior. This distinction is crucial, as asphaltene fractions with higher aromatic content exhibit greater self-association and surface adsorption capacity.