Characteristics of Micropore Structure and Its Influence on Shale Oil Occurrence: A Case Study From the Second Member of Funing Formation, Subei Basin

To clarify the micropore structure characteristics of shales in the second member of the Funing Formation, Subei Basin and their influence on shale oil occurrence, various tests were conducted, including low‐temperature nitrogen adsorption (LTNA), scanning electron microscopy (SEM), rock pyrolysis, total organic carbon (TOC), and X‐ray diffraction (XRD) analysis. The organic matter, mineral compositions, and oil content of the shales were analyzed and the micropore structure and fractal characteristics were clarified. Additionally, factors influencing shale oil occurrence were disclosed. The results reveal that the mineral compositions of the studied shales are complex, comprising quartz, clay minerals, calcite, and dolomite. Pores at the edges of brittle mineral particles predominate. The LTNA curve exhibits an H2–H3 type, corresponding to a high specific surface area (SSA) and a low average pore size. Micropores (<25.00 nm) dominate, contributing significantly to the total pore volume (PV) and SSA. The pore size distributions (PSDs) are unimodal, peaking at approximately 3.00 nm. Fractal analysis identifies two stages, with fractal dimensions D 1 ranging from 2.46 to 2.58 (mean 2.53) and D 2 from 2.52 to 2.83 (mean 2.75). Pore structure and fractal dimensions are controlled by mineral compositions and organic matter. Higher quartz, calcite, and organic matter contents promote larger average pore sizes and lower fractal dimensions, indicating more homogeneous pore structures. Larger average pore sizes and simpler pore structures enhance free oil accumulation and production. Shales with TOC > 2.30% in the Funing Formation are most favorable for shale oil exploration and development. These findings provide insights for optimizing shale oil exploration in the Funing Formation, aiding the understanding of micropore structures and their role in oil accumulation.