Formation mechanism of high-quality reservoirs in the Shanxi Formation of the Qingyang gas field in a meandering river delta setting

As global energy demand rises, unconventional gas resources, particularly tight gas reservoirs, have become increasingly important for future energy supply. Located in the southwestern Ordos Basin, the Qingyang gas field is a newly discovered deep tightgas field with proven geological reserves exceeding 31.8 × 109 m3 and has become a strategic focus for deep-gas exploration in China. Despite rapid appraisal that delineated several stable gas-bearing zones, a comprehensive understanding of the sedimentary architecture, diagenetic transformation, and enrichment mechanisms of high-quality reservoirs in the Permian Shanxi Formation remains incomplete. Focusing on the Shan 1 Member (hereafter referred to as Shan 1), we integrate core description, well-log interpretation, petrographic analysis of casting thin sections, scanning electron microscopy, and production-test data to classify sedimentary microfacies, quantify pore-structure attributes, establish diagenetic sequences, and interpret the spatial configuration of low-amplitude structures. The sandstones were deposited in a shallow-water meandering river delta system exhibiting pronounced lateral zonation and vertical stacking, which are common characteristics of meandering river delta front environments. Subaqueous distributary channels and mouth bars constitute the dominant reservoir microfacies. Reservoir lithology is dominated by medium- to fine-grained feldspathic lithic sandstones in which intergranular and intragranular dissolution pores impart marked heterogeneity. Reservoir quality is governed by the coupled evolution of compaction, cementation, and dissolution, with diagenetic timing exerting first-order control. Highenergy, laterally persistent sandbodies provide favorable primary conditions, while late-stage structural inversion governs sandbody amalgamation and migration. Low-amplitude structures further modulate the distribution of productive zones, with high-yield wells preferentially occurring on structural highs and in sandbody overlap areas. These results refine the genetic model for tight-sandstone reservoir formation in Shan 1 and provide geological guidance for high-resolution prediction and deployment of favorable targets in deep-gas exploration.