Dissolution Kinetics and Porosity Development in Carbonates under Seawater-Assisted HCl Acidizing

Carbonate reservoirs account for nearly ۵۰% of global proven oil reserves, with ۷۰% in the Middle East occurring in fractured formations. Their heterogeneous pore structures and oil-wet surfaces limit recovery efficiency. Matrix acidizing is a well-established stimulation technique to improve productivity in carbonate reservoirs; however, its success is strongly influenced by acid composition, ionic strength of the carrier fluid, and surface wettability conditions. This study experimentally evaluates the effects of acid concentration (۱۵% and ۲۸% HCl), brine composition (distilled water vs. seawater), and surfactant pre-flush (CTAB) on the dissolution kinetics and porosity evolution of carbonate cores under both oil-free and oil-saturated conditions. Laboratory experiments were conducted on core samples at ۲۶ °C using controlled acid injection tests. The initial contact angle (~۱۴۰°) confirmed the strongly oil-wet nature of the untreated rock surface. Results revealed that seawater-based acid systems produced more stable wormholes, ۲۰–۳۵% higher porosity enhancement, and approximately ۱۵% lower sludge formation compared with distilled-water-based acids. The CTAB pre-flush significantly improved acid accessibility, reduced CO₂ bubble blockage, and enhanced dissolution uniformity, particularly under oil-saturated conditions. These findings demonstrate that combining seawater-based acids with surfactant-assisted pre-treatment provides a more sustainable, efficient, and field-applicable strategy for carbonate reservoir stimulation.

کلیدواژه ها:

Carbonate Reservoirs ، recovery efficiency ، Matrix Acidizing ، wormhole