TITLE:
Research on Reservoir Characteristics of the Shanxi Formation in the Eastern Yanchuan Area and Their Geological Significance
AUTHORS:
Qiyu Gao, Meng Wang, Tianchao Guo, Xiao Yang
KEYWORDS:
Shanxi Formation, Reservoir Characteristics, Pore Structure, Petrophysical Evaluation, Eastern Yanchuan Gas Field
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.11,
November
19,
2025
ABSTRACT: The sandstone reservoir of the Shanxi Formation serves as a key exploration and development target in the eastern Yanchuan gas field of the Ordos Basin, where its physical properties and pore structure directly govern the enrichment and distribution of hydrocarbons. This study systematically examines the petrological features, pore types, throat structures, and petrophysical parameters of the Shanxi Formation sandstone reservoir using core observation, thin-section identification, cast thin-section and scanning electron microscopy analyses, mercury injection porosimetry, and conventional petrophysical testing. Results indicate that the reservoir predominantly comprises fine- to medium-grained sandstones, dominated by lithic sandstones, lithic quartz sandstones, and quartz sandstones as the primary lithofacies assemblages. Detrital components are chiefly quartz and metamorphic rock fragments, with cementation primarily of the pore-filling type and common siliceous and carbonate cements. Dominant pore types include dissolution pores in volcanic lithics, residual intergranular pores, and minor intercrystalline pores and microfractures. Porosity is generally low, averaging less than 6%, with permeability ranging from 0.001 to 5.577 mD. Mercury injection experiments reveal that throat sizes are predominantly small, exhibiting poor sorting and limited connectivity, classifying the reservoir overall as an ultra-low-porosity, tight type, though locally high-quality sandstone intervals are developed. Integrated analysis highlights pronounced heterogeneity in the Shanxi Formation reservoir, wherein pore preservation and dissolution processes exert significant enhancement on reservoir quality, while microfractures play a pivotal role in hydrocarbon migration and accumulation. These findings offer valuable insights for reservoir evaluation and natural gas exploration and development in the Shanxi Formation of the eastern Yanchuan gas field.