Influence of structural damage on evaluation of microscopic pore structure in marine continental transitional shale of the Southern North China Basin: A method based on the low-temperature N2 adsorption experiment

Abstract

Structural damage from sample preparation processes such as cutting and polishing may change the pore structure of rocks. However, changes in pore structure caused by this structural damage from crushing and its effect on marine continental transitional shale have not been well documented. The changes of microscopic pore structure in marine continental transitional shale during the sample preparation have important research value for subsequent exploration and development of shale gas. In this study, the pore structures of transitional shale samples from the Shanxi-Taiyuan Formation of the Southern North China Basin under different degrees of damage were analyzed through low-temperature N2 adsorption experiments, combined with X-ray diffraction, total organic carbon, vitrinite reflectance analysis, and scanning electron microscopy. The results showed that (1) With increasing structural damage, the specific surface area (SSA) changed within relatively tight bounds, while the pore volume (PV) varied significantly, and the growth rate (maximum) exhibited a certain critical value with the crushing mesh number increasing from 20 to 200. (2) The ratio of SSA to PV can be used as a potential proxy for evaluating the influence of changes in the pore structure. (3) Correlation analysis revealed that the microscopic pore structure of marine continental transitional shale from the Shanxi-Taiyuan Formations is mainly controlled by organic matter and clay minerals. Clay minerals play a leading role in the development of microscopic pores and changes in pore structure.