Quantitative characterization of shale pore connectivity and controlling factors using spontaneous imbibition combined with nuclear magnetic resonance T2 and T1-T2

Shale oil can be extracted from shale by using interconnected pore networks. The migration of hydrocarbon molecules within the shale is controlled by pore connectivity. However, assessing the pore connectivity of shale oil reservoirs is uncommon. To characterize pore connectivity and clarify its controlling factors, this study used spontaneous imbibition (SI) combined with nuclear magnetic resonance (NMR) T 2 and T 1 -T 2 technologies on shale oil reservoirs selected from the Shahejie Formation in the Dongying Sag, Bohai Bay Basin. According to the findings, the SI processes of shales include fast-rising, slow-rising, and stable stages. The fast-rising stage denotes pore connectivity. The shales studied have poor connectivity, with lower imbibition slopes and connected porosity ratios, but large effective tortuosity. During the SI process, micropores have the highest imbibition saturation, followed by mesopores and macropores. Furthermore, n-dodecane ingested into micropores appears primarily as adsorbed, whereas n-dodecane appears primarily as free states in mesopores and macropores during the SI process. The pore connectivity of the shales under study is primarily controlled by inorganic minerals. Quartz and feldspar develop large and regular pores, resulting in better pore connectivity, whereas clay minerals and calcite with plenty of complex intragranular pores do not. Organic matter negatively influences pore connectivity because the dissolution of calcite by organic acid produced during hydrocarbon generation leads to a more complex and heterogeneous pore structure. This study sheds light on the pore connectivity and controlling factors of the shale oil reservoir and aids in the understanding of shale oil mobility.