Study on Rock Damage Assessment Method Based on Crack Characteristic Analysis under CO2 Fracturing

Abstract

Carbon dioxide ( CO 2 ) fracturing is an effective new carbon neutrality technology for underground space excavation engineering. To address the quantitative evaluation problem of rock damage induced by CO 2 fracturing, a rock damage assessment method is proposed. A numerical model was established to obtain time-series images of rock crack propagation at borehole spacings of 1.4, 1.6, and 1.8 m. Crack binary images were obtained via sequential treatments of grayscale conversion, contrast enhancement, Gaussian smoothing denoising, adaptive threshold segmentation, and morphological optimization. Feature parameters of crack area ratio, crack length ratio, and crack number were extracted from the binarized images. Dimensionality reduction and weight calculation were conducted on the feature parameters combined with principal component analysis, and a rock damage evaluation method based on the cumulative damage factor model was established. The results show that the proposed crack damage assessment method can realize accurate measurement and quantitative assessment of the rock crack damage degree. This damage assessment method can classify the damage grades of different stages of crack propagation. Under the working conditions of three different borehole spacings, the crack damage factor for the 1.6-m hole spacing case ultimately reached the maximum value of 0.84059, and this spacing shows a more favorable CO 2 fracturing response under the test conditions. This provides an effective methodological support for the damage evaluation of rock under CO 2 fracturing and a quantitative basis for the borehole spacing optimization of CO 2 fracturing engineering.