Pore structure dynamic evolution of coal during hydraulic intrusion based on NMR

Low-field nuclear magnetic resonance (LF-NMR) technology is a non-invasive measurement method, that provides a fast, direct, and nondestructive tool for characterizing complex pore structure. To reveal the evolution law of pore structure and stress sensitivity during hydraulic intrusion, this paper adopts LF-NMR monitoring and in-situ hydraulic intrusion technology to carry out the hydraulic intrusion test on both pre-drilled and un-drilled coal. The quantitatively characterizes the variation patterns of pore structure, compressibility, and other parameters, revealing the dynamic mechanism of pore structure evolution Three dynamic evolution laws of pores were obtained through experimental data analysis. The mechanism of dynamic evolution of pore structure was determined from the perspective of pore compressibility and effective stress. Based on the measurement results, LF-NMR is an efficient non-destructive method for quantifying pore size distributions of the coal.