Analysis of Pore Types in Lower Cretaceous Qingshankou Shale Influenced by Electric Heating

Shale encompasses a variety of pore types, possessing distinct microstructures and surface attributes. In situ electric heating can modify the pore structure, potentially enhancing hydrocarbon recovery. However, limited research has been conducted on how the proportion and distribution of shale pore types change with increasing electric heating temperatures. The inefficiency of manually identifying and classifying pore types has constrained progress in this area. This study introduces a method that integrates grayscale images with mineral distribution maps to automate pore-type identification, significantly improving efficiency. Furthermore, the incorporation of multiple theoretical approaches provides a more detailed characterization of the complex structures of different pore types. In this study, Qingshankou shale was selected for electrical heating experiments at various temperatures, followed by scanning electron microscopy and energy dispersive X-ray spectroscopy analyses on both natural and heated samples. Image processing techniques were employed to detect and quantitatively assess seven distinct pore types, and multifractal theory was applied to examine the heterogeneity within each type, ultimately exploring the alterations in the pore structure throughout the heating process. The findings indicate that the natural Qingshankou shale predominantly consists of organic pores, intercrystalline pores, intergranular pores, and intergranular cracks. Organic pores exhibit the most complex structures, followed by intercrystalline. Intergranular and intraparticle pores display simpler structures. As the temperature increases, the surface porosity of shale rises, with intercrystalline and intergranular pores becoming dominant. The thermal dehydration and dissolution processes of clay lead to a more intricate pore structure in intercrystalline and intraparticle pores. When the heating temperature reaches 500 °C, the intergranular pore network becomes significantly more complex due to clay dehydration, greatly enhancing the permeability of oil and gas.