A novel method for examining the influence of molecular and structural properties of the asphaltene fraction on the wettability change of the calcite surface

Abstract

Asphaltene deposition in the porous media of the reservoir during the production life causes serious challenges with significant economic cost. From the point of view of proactive action to prevent the formation of such precipitates, today asphaltene inhibitors are widely used in the oil industry. The successful performance of inhibitors strongly depends on molecular structure of asphaltene. This study investigates the effect of molecular-structural properties of asphaltene in four crude oil samples on calcite surface wettability. The wettability of the calcite surface is evaluated with contact angle test and micromodel. The crude oil properties are determined using DHA (Detailed Hydrocarbon Analysis) and FTIR (Fourier Transform Infrared Spectroscopy) tests, while the molecular-structural properties of asphaltene are assessed using elemental analysis, FESEM (Field Emission Scanning Electron Microscopy), NMR (Nuclear Magnetic Resonance), and FTIR techniques. Based on FTIR analysis of oil samples, the higher polarity of samples B and G compared to samples F and A can be attributed to the presence of C = O carboxylic acid stretches. In addition, DHA analysis indicates that sample B, which contains heavier compounds comprising 27.4220 % of the C14+ compounds by weight, exhibits distinct characteristics. The FESEM images demonstrate a uniform and smooth spread surface morphology of the asphaltene samples. However, the elemental analysis does not establish a correlation between the heteroelement ratios of N/C, O/C, and S/C and asphaltene adsorption tendency. FTIR and NMR analyses suggest that the wetting properties observed on the surface are mainly attributed to the high aromatic and aliphatic compounds present in the asphaltene of sample B, while the polar compounds are less influential. The results reveal that crude oil sample B exhibits the highest percentage of damage to the porous medium caused by asphaltene deposition, with a rate of 36.18 % and a contact angle of 163.53 degrees. This indicates a wetter surface of the oil compared to other samples. Samples G and A follow with contact angles of 157.34° and 153.60°, respectively. On the other hand, sample F shows the lowest wettability change on the calcite surface with a contact angle of 144.77° and only 0.08 % damage to the porous medium.