Evaluation Technology of Pore Mobilization Lower Limit in Low-Permeability Reservoirs Based on Multiscale Information Fusion

In response to the challenges of complex pore structures and low recovery rates in shale oil reservoirs of an offshore oilfield, this study investigates the evaluation technology for the lower limit of pore mobilization based on multiscale information fusion. Dynamic imbibition physical simulation experiments were conducted on core samples, and nuclear magnetic resonance (NMR) technology was employed to obtain T₂ spectra at various imbibition stages, enabling the analysis of fluid distribution within the pores. Pore throat structures were characterized using high-pressure mercury intrusion (HPMI) and low-temperature nitrogen adsorption (LTNA) experiments. A conversion relationship between the NMR relaxation time (T₂) and pore radius was established, achieving quantitative translation of electromagnetic signals into fluid mobilization behavior. The results indicate that the reservoir is dominated by micropores, small pores, and medium pores, with large pores and microfractures comprising a smaller proportion, reflecting significant heterogeneity. Initially, oil production primarily originates from large pores. As imbibition progresses, the contribution of small and medium pores gradually increases, and in later stages, mobilization across all pore scales tends to balance, with small pores playing a crucial role in overall productivity. The lower limit of pore mobilization in the cores ranges between 18.85 and 25.19 nm, indicating that a considerable portion of oil in small pores remains difficult to extract effectively. The findings provide a theoretical basis and technical support for the efficient development of offshore shale oil resources.