Extraction and Multidimensional Characterization of Pore Fractures in Gradient Thermally Treated Shale Using Micro-CT

Abstract

Thermal stimulation is a cutting-edge technology for improving shale matrix permeability and achieving efficient shale gas development, as heating can reshape shale pore structures and enhance reservoir percolation capacity. Currently, numerous studies have revealed basic thermal-action laws and clarified the intrinsic relationship between temperature and shale reservoir structures. Nevertheless, most previous tests adopt several discrete temperature points, and quantitative descriptions of successive pore-fracture evolution in the high-temperature range under equal-interval temperature gradients are still lacking. This restricts theoretical support for optimizing field thermal-simulation parameters. To fill this gap, shale samples gradient-treated at 50–300 °C are investigated. Micro-CT scanning, ImageJ, FracLac, and Avizo are employed for two-dimensional statistics and three-dimensional reconstruction. Pore-fracture parameters, fractal dimension, and lacunarity are extracted. Complementary SEM observations at 100 and 250 °C corroborate CT-derived pore-fracture features at these two temperatures. Permeability curves covering 50–300 °C gradient series are further plotted, whose overall trend agrees well with pore-fracture structural variations captured by CT reconstruction. The results show that pore quantity and porosity decrease initially and then rise with increasing temperature. The maximum porosity appears at 300 °C, and the most complicated pore frameworks are formed at 200 °C. Fractal dimension effectively characterizes the spatial heterogeneity evolution of thermally modified shale pore networks, providing insights for shale gas thermal stimulation applications.