Channel Sandstone Architecture of the Shanxi Formation in the Northeastern Ordos Basin: Evidence from Fugu Outcrop in Shaanxi

Key words: 
• Key words: Sandbody architecture /
• channel /
• Shanxi Formation /
• Fugu outcrop /
• Ordos Basin

Abstract: Abstract: [Objective] Tight gas sandstone within the Shanxi Formation is a significant gas-producing zone in the northern Ordos Basin. However, the variations in the vertical stacking patterns and lateral distribution of sandbodies across different intervals of the Shanxi Formation pose challenges for development well placement and gas production area selection. [Methods] This study establishes a three-dimensional digital outcrop model of the Shanxi Formation through measured stratigraphic sections and drone oblique photography modeling. Based on lithofacies classification and hierarchical bounding surface identification, sandbody architecture analysis was conducted. [Results]The results demonstrate that:①The Shanxi Formation represents a delta plain depositional environment, where sandbodies primarily correspond to the braided distributary channel microfacies. Under warm and humid climatic conditions, well-developed vegetation restricted crevasse formation, with overbank flooding (splay deposition) being the dominant process instead.②Four main types of sandbody architecture are identified: longitudinal bar, transverse bar, incised channel, and laminated sandstone.③The vertical succession of sandbody architectures within the Shanxi Formation, from base to top, is characterized by: composite longitudinal bars and laminated sandstones in the lower part, transverse bars in the middle part, and incised channels in the upper part. [Conclusions]The systematic variation in fluvial channel sandbody architecture within the study area records the gradual closure of the northern Solon Ocean and coeval tectonic uplift in the Ordos Basin's north. This uplift drove the evolution of distributary channels from an initial wide and shallow form, through a wide and deep intermediate stage, to a final narrow and deep, incised morphology. Our study elucidates the response mechanism linking channel evolution, architectural differentiation, and reservoir heterogeneity under coupled tectonic-climatic controls, offering a novel perspective for research on the Shanxi Formation reservoirs in the northeastern Ordos Basin.