Abstract: Research on the microscopic pore-throat characteristics and classification of the Shahejie Formation reservoirs in the Bozhong Oilfield is limited,failing to provide findings and insights with guiding significance for exploration and development.To address this issue,based on the analysis of high-pressure mercury injection (HPMI),oil-water relative permeability,and core NMR experimental results,the macroscopic physical properties,microscopic pore structure,and seepage capacity of low-permeability reservoirs in the Bozhong Oilfield were finely characterized and classified through single-factor discussion;reservoir comprehensive classification and evaluation were achieved using parameter optimization,comprehensive classification index calculation,K-means clustering,and other technical methods.The results indicate that the low-permeability reservoirs of the Shahejie Formation are a set of low-porosity, low-permeability reservoirs dominated by fine-grained feldspathic lithic sandstone with small pores and fine throats,with an average porosity of 11.40% and an average permeability of 1.90 mD;the reservoir space types are mainly secondary intergranular dissolved pores and intragranular dissolved pores,primarily developing sheet-like and curved sheet-like throat types.According to the comprehensive evaluation method and comprehensive classification index system, the low-permeability reservoirs are divided into three classes:Class Ⅰ are high-quality reservoirs with good reservoir quality and seepage capacity,Class Ⅱ are medium reservoirs,and Class Ⅲ are relatively poor reservoirs.This evaluation scheme is significant for predicting favorable reservoir areas and formulating development plans.

Key words: microscopic pore structure, seepage characteristics, reservoir evaluation, Shahejie Formation low-permeability reservoir, Bozhong Oilfield