Geological characteristics and significance of micro pores in ultra-low permeability reservoir based on digital rock technology: a case study of the Bozhong F structure in the Bohai Sea area

Using emerging digital rock technologies of two-dimensional large-scale backscatter image stitching (MAPS), micro CT, focused ion beam scanning electron microscopy (FIB), and fully automatic digital slide scanning (AXIOSCAN), combined with conventional experimental methods of casting thin sections, the micro pores of the ultra-low permeability sandstone and conglomerate in the Bozhong F structure of the Paleogene Kongdian Formation in the Bohai Sea area were scanned at multiple scales and dimensions with high precision, and the storage significance of micro pores was systematically studied. The experimental results show that the types of micropores with pore radius less than 15 μm in the target area were mainly intragranular, intragranular micropores, and intercrystalline micropores. The uneven dissolution of feldspar-rich skeleton particles is the main cause of the intercrystalline micropores in the target area. The main distribution range of micropore radius is 0.2-14.8 μm, and the smaller the porosity of the reservoir section, and relatively the greater proportion of nano- and submicron-scale intercrystalline dissolution micropores. The average microporosity in the research area is 7.03%, which has significant storage significance. Some micropores also serve as storage spaces and throats, with strong fluorescence display, playing a key role in the connectivity between large pores.