Pore Characteristics and Factors Controlling Lacustrine Shales from the Upper Cretaceous Qingshankou Formation of the Songliao Basin, Northeast China: A Study Combining SEM, Low-temperature Gas Adsorption and MICP Experiments

To investigate pore characteristics and the factors controlling lacustrine shales, geochemical, mineralogical and petrophysical experiments were performed on 23 shale samples from the Qingshankou Formation of the Songliao Basin, China. A comparison of mercury injection capillary pressure（MICP） and low-temperature N2 adsorption pore-size distribution showed that MICP has a higher pore-size distribution（PSD） line in its overlapping pore diameter range, which may be elevated by the higher pressure of MICP. Therefore, in the overlapping range, low-temperature N2 adsorption data were preferred in pore characterization. Negative correlations were observed between pore volumes and TOC content, indicating organic matter pores are not well-developed in the studied samples. This may be related to their low grade of maturity and type I kerogens. There existed negative relationships between pore volumes and S1, which illustrated that liquid hydrocarbons occupied some pore space. Micropore volume had a better correlation with S1 than mesopore and macropore volumes, which suggests that liquid hydrocarbons preferentially occur in micropores. No obvious relationships between pore volumes and quartz or feldspar were observed, while pore volumes increased with the increasing clay mineral content. These relationships indicate that intraparticle pores in clay minerals represent the principal pore type.