Interfacial Stability of Acid–Crude Oil Emulsions in Matrix Acidizing of Carbonate Reservoirs

Matrix acidizing is a fundamental technique for enhancing oil recovery in carbonate reservoirs by injecting acidic solutions, typically 15% (w/w) HCl, to promote wormhole formation and bypass damaged zones. However, acid-crude oil interactions frequently result in stable emulsions, leading to formation damage, reduced hydrocarbon mobility, and excessive acid consumption. This study presents a systematic investigation of the Emulsion Stability Index (ESI) in acid-oil systems under carefully controlled laboratory conditions designed to simulate potential field scenarios, assessing the effects of temperature (30-80 °C), acid-to-oil volumetric ratio (0.2-0.8), and FeCl₃ concentration (0-3000 ppm). The experiments were conducted in triplicate to ensure reproducibility with no significant differences observed among replicates. The acid-to-oil ratio was identified as the most influential factor in mitigating emulsion formation. Lower ratios (e.g., 0.2) significantly reduced ESI values, particularly when combined with elevated temperatures and ferric ion concentrations. In addition, commercial additivesa demulsifier and a corrosion inhibitor, both characterized by high hydrophilic-lipophilic balance (HLB) and applied at concentrations of 1, 3, and 5 vol %were evaluated for their performance. The main findings indicate that lower acid-to-oil ratios combined with elevated temperatures, FeCl₃, and the presence of 3-5 vol % of these additives significantly reduce emulsion stability, enabling safer and more effective acidizing operations in carbonate reservoirs.