Pore-Structure Differences and CO2 Storage Potential of Laminated and Bedded Qingshankou Formation Shales

Abstract Geological CO2 storage has attracted increasing attention as a strategy for reducing anthropogenic carbon emissions. Organic-rich shales may have considerable potential for geological CO2 storage, but their storage effectiveness is strongly controlled by the pore structure and lithofacies. This study focuses on organic-rich shales from the upper Cretaceous first member of the Qingshankou Formation (K2qn1) in the Central Depression of the northern Songliao Basin. We combined argon-ion-polished scanning electron microscopy, low-temperature N2 adsorption, and high-pressure mercury intrusion porosimetry to compare pore-structure characteristics between laminated and bedded shales and to evaluate their implications for potential CO2 storage. Laminated shale contains abundant organic matter pores and bedding-parallel microfractures, with pore systems dominated by micro- to fine mesopores. Bedded shale contains more abundant interparticle and dissolution pores, higher porosity, and a distinct fine-throat, coarse-pore architecture. Fractal analysis indicates that laminated shale has a more complex fine-pore network, which may favor CO2 retention in micro- to nanoscale pores. Bedded shale shows stronger macropore domain heterogeneity and may provide comparatively more pore space for free-phase CO2 occurrence. Burial-stage analysis further indicates that the intermediate burial stage may provide relatively favorable pore-structure conditions for potential CO2 storage.