In order to achieve precise control of the process of rock breaking, the characteristics and evolution laws of coda wave signals indifferent rock fracturing stages were studied. The coda wave signal test of supercritical CO₂ fracturing sandstone under triaxial confining pressure was carried out, and the evolution characteristics and signal parameter changing law of coda wave signals during CO₂ fracturing process were analyzed. The sensitive nuclei function of coda wave extension based on probability density was established, and the characteristics and evolution law of coda wave signal in different fracturing stages were revealed. The results indicate that supercritical CO₂ fracturing rock can be divided into four stages: early stage, middle stage, late stage and post-failure stage. The relative change rate of coda wave velocity shows a downward trend as a whole, reflecting the rapid accumulation process of rock damage. The diffusion sensitive nuclei reveals that the rock damage gradually accumulates during the fracturing process, resulting in enhanced wave scattering inside the rock, increased energy loss and rapid development of coda waves.

Supercritical CO₂  /  Rock fracturing  /  Red sandstone  /  Coda wave interference  /  Time-frequency analysis