TITLE:
Petrographic Characteristics and Pore Structure Analysis of Benxi Formation Sandstone Reservoirs in the Yanchuan East Block, Ordos Basin
AUTHORS:
Qiyu Gao, Meng Wang, Tianchao Guo, Xiao Yang
KEYWORDS:
Ordos Basin Yanchuan East Block, Benxi Formation, Sandstone Reservoir, Petrographic Characteristics, Pore Structure, Diagenesis
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.11,
November
19,
2025
ABSTRACT: This study investigates the Benxi Formation sandstone reservoirs in the Yanchuan East Block of the Ordos Basin, employing an integrated approach that includes core observation, thin-section analysis, scanning electron microscopy, high-pressure mercury intrusion, and petrophysical testing to systematically evaluate reservoir petrographic features and pore structures. Results reveal that Benxi Formation sandstones predominantly comprise quartz sandstones, lithic quartz sandstones, and lithic sandstones, characterized by high quartz content, widespread volcanic lithic fragments, moderately well-sorted grains, and complex cement types. Pore types are dominated by residual intergranular and dissolution pores, with minor intracrystalline pores and fractures; overall porosity ranges from 0.17% to 9.07% (average 4.74%), and permeability from 0.01 to 6.05 mD, classifying them as ultra-low porosity and tight reservoirs. High-pressure mercury intrusion indicates microfine throats as the primary structure, divisible into four distinct types. Diagenetically, compaction and cementation are the main drivers of primary pore loss and reservoir tightening, whereas late-stage dissolution partially ameliorates pore networks. Overall, Benxi Formation sandstone reservoirs exhibit pervasive densification but localized favorable pore assemblages and connectivity, facilitating hydrocarbon migration and accumulation. These findings advance understanding of Upper Paleozoic tight sandstone reservoir characteristics and aid in predicting sweet spots.