Experimental evaluation of alterations in crude oil properties induced by hydrochloric acid, reservoir rock powder, and surfactants

This study investigates how hydrochloric acid (HCl) at different concentrations and reservoir rock powder (RRP), combined with two surfactants, cetyltrimethylammonium bromide (CTAB, cationic) and Tween 80 (nonionic), affect the physicochemical properties of crude oil. The parameters evaluated were interfacial tension (IFT), viscosity, emulsion droplet size, sludge formation, and chemical composition. Tests were conducted with HCl concentrations of 10%, 15%, 20%, and 28%, and with surfactants at the critical micelle concentration (CMC) and one-fifth of CMC. Higher acid concentrations promoted sludge, peaking at 28%. In acidic media, RRP induced asphaltene aggregation, which increased viscosity and IFT. FTIR confirmed chemical changes, showing growth of carbonyl bands linked to acid-oil reactions and polar asphaltene aggregation. These adverse effects were moderated by surfactants. CTAB at higher dosage (370 ppm) gave the greatest reductions in viscosity and IFT via strong electrostatic interactions, while Tween 80 achieved substantial reductions at lower dosage (100 ppm) through steric stabilization, with little added benefit at higher concentration. Emulsion stability was highest at 15-20% HCl, indicated by narrow, unimodal droplet size distributions with the lowest values. Between these, 15% HCl in seawater or diluted seawater offered the optimal balance by minimizing sludge, preserving interfacial properties, and enhancing emulsion stability. Overall, CTAB provided the strongest mitigation of RRP-induced effects under these conditions.