Evaluation and analysis of brittleness and acoustic emission characteristics of tight sandstone under the influence of acid-treatment

Acid treatment has been proven to effectively reduce reservoir fracture pressure, but the variation pattern of sandstone brittleness after acid treatment remains unclear. To effectively evaluate the characteristics of brittleness changes, uniaxial compression tests were conducted on tight sandstone subjected to acid treatment for different durations, and a brittleness index evaluation method based on radial strain response was established. The results show that sandstone uniaxial compressive strength decreases stepwise with prolonged acid treatment. Elastic modulus decreases slowly initially, drops sharply after 24 h of acid treatment, and stabilizes between 120 and 168 h. Poisson’s ratio decreases linearly after 6 h of acid treatment. The brittleness index first increases and then decreases, peaking at 12–24 h of acid treatment—consistent with AE results showing more high-intensity signals during the elastic compression stage of axial stress-strain curves. After acid treatment, sandstone crack initiation stress first increases slowly, then gradually decreases, and finally drops rapidly. This is attributed to acid-rock reaction-induced dissolution of minerals and cementing materials, which detaches fine-grained matrix particles, increases porosity, and reduces crack initiation stress. The findings provide a reference for engineering design and construction of high fracture pressure tight sandstone reservoirs.