抄録
Tight sandstone reservoirs commonly experience rapid porosity loss during early diagenesis, followed by localized pore enhancement during later burial, forming a characteristic diagenetic evolution pathway of early densification–late-stage modification that fundamentally controls reservoir quality and tight oil accumulation. Using the Chang 8 Member in the Huanqing area of the Ordos Basin as a case study, this study investigates the evolutionary processes and controlling mechanisms of this diagenetic system through an integrated analysis of petrographic observations, scanning electron microscopy, cathodoluminescence, fluid inclusion analysis, three-dimensional lithofacies modeling, and diagenetic facies evolution. The results show that the reservoir underwent an initial densification stage dominated by mechanical compaction and early cementation, followed by late-stage pore enhancement driven by dissolution and microfracture development associated with organic matter thermal evolution, acidic fluid migration, and tectonic activity. These processes generated a spatially heterogeneous reservoir architecture characterized by strong directional and zonal variations in pore development. The evolution of the early densification–late-stage modification system exerts a fundamental control on pore structure evolution, reservoir–fluid coupling, and hydrocarbon enrichment, with high-quality tight oil reservoirs preferentially occurring where late-stage dissolution and microfracture systems are favorably superimposed. This study establishes a process-based diagenetic evolution framework that links early reservoir densification to late-stage pore modification and tight oil enrichment, providing a transferable genetic model for reservoir quality prediction and sweet-spot evaluation in tight sandstone systems.
