Influence of Type and Concentration of Acid on Reaction Kinetics and Reservoir Permeability Enhancement in Tight Limestone Acidizing

This study investigates the acid–rock reaction kinetics and their implications for enhancing tight limestone reservoir stimulation through systematic experiments. Using 14 tight limestone cores, we evaluate the dynamic behavior of single-phase and gelled acids (12%, 15%, and 20% HCl) under controlled reservoir conditions (80 °C; 10–180 min). Three key findings emerge: (1) gelled acids initially exhibit higher reaction rates (0.897%/min) compared to single-phase acids (0.453%/min at 10 min), but their efficiency converges over extended durations; (2) reaction rates for both acid types follow the quadratic decay pattern over time (R2 > 0.95), contrasting with conventional linear assumptions; and (3) reaction time is identified as the primary factor governing permeability enhancement (up to 29,200% improvement), outweighing acid concentration and type. The results demonstrate that concentrations above 15% significantly enhance etching efficiency, while single-phase acids with moderate reaction rates achieve an optimal balance between penetration depth and surface integrity. By integrating gravimetric analysis with permeability–porosity mapping, this work provides a predictive framework for acidizing process design in low-permeability reservoirs. The findings offer practical insights for optimizing acid fracturing operations, emphasizing time-controlled strategies over traditional concentration-focused approaches.