Autogenous Solid Acid for Acid Fracturing in Deep Carbonate Reservoirs

Aqueous hydrochloric acid (HCl) systems suffer from high corrosivity and limited effective penetration depth, posing major challenges for acid fracturing in deep carbonate reservoirs. A novel autogenous solid acid, SA-G, was developed through anhydride-amine nucleophilic substitution to overcome these limitations. SA-G was systematically analyzed through high-temperature dissolution experiments, rotating disk corrosion tests, and fracture conductivity evaluations. SA-G exhibits a solubility of 70.3 g/100 mL at 25 °C. A 25 wt % SA-G solution generates acid continuously for 2.5 h at 180 °C, equivalent to a 14.36 wt % HCl concentration, with an etching efficiency of 91.14% at 95 °C. The dynamic corrosion rate at 180 °C is 61.97 g/(m2 h), and the acid-rock reaction kinetic rate is as low as −3.75 × 10–4 mol/(s cm2), demonstrating ultraslow-release characteristics at ultrahigh temperatures. Alternating injection of SA-G and gelled acid at 10 mL/min effectively etched rock plates, achieving a fracture conductivity of 17.67 D cm under 30 MPa closure stress. In field applications, SA-G was continuously delivered via a fracturing blender truck at a pumping rate of 9–10 m3/min, enabling acid fracturing in a 140 °C reservoir with reduced fracturing pressure and enhanced communication with natural fractures. SA-G overcomes the limitations of conventional liquid acids in equipment corrosion and penetration depth through its in situ slow-release acid-generation mechanism, providing a safe and deeply penetrating technical solution for efficient stimulation of ultrahigh-temperature carbonate reservoirs.