Study on Multi-factor Coupled Mechanisms of Acid-Rock Reaction Kinetics in Ultra-High-Temperature Carbonate Reservoirs

This study systematically investigates the multifactor coupling mechanisms of acid-rock reaction kinetics in acid fracturing stimulation of ultra-high-temperature (160–180 °C) carbonate reservoirs in the Second Member of Dengying Formation, Penglai Gas Field. Through high-temperature and high-pressure rotating disk experiments, 3D laser scanning, and NMR/micro-CT characterization techniques, we quantitatively analyzed the acid-etching pore evolution patterns of different lithologies and compared the reaction kinetic characteristics of three acid systems: conventional HCl, gelled acid (viscosity 30–80 mPa s), and pH-sensitive diverting acid. The results show that: Algal-bound dolomite exhibited localized dissolution stagnation due to siliceous cementation (18%), leading to reduced reaction rates; Fine-crystalline dolomite demonstrated the highest reaction rate owing to well-developed intercrystalline dissolution pores (10–50 μm); When permeability increased from 0.001 mD to 1.87 mD, porosity showed an average enhancement of 500%, with high-permeability samples (1.87 mD) forming dendritic dissolution networks that achieved 800% porosity increase; Conventional acid created longitudinally dominant channels, while gelled acid (80 mPa s viscosity) inhibited mass transfer, reducing reaction rates by 15–20% compared to conventional acid; Diverting acid achieved branched dissolution pathways through dynamic rheological regulation; The established modified diffusion coefficient model showed excellent agreement with experimental data (90.7% for temperature and 93.53% for acid concentration), revealing that reaction rates follow quadratic exponential growth with temperature (40% increase per 15 °C), and under high-permeability conditions (50 mD), reaction rates can reach 14.91 times those in low-permeability rocks (5 mD).