Diagenesis and Reservoir Characteristics of Upper Triassic Chang 6 Sandstone in Panlong Area, Ordos Basin: Implications for Hydrocarbon Exploration

ABSTRACT

The extreme microstructural heterogeneity of tight sandstone reservoirs poses a significant challenge for accurately predicting fluid flow and optimizing hydrocarbon recovery, as conventional petrophysical models often fail to capture complex, multi‐scale pore architectures. To address this, this study investigates the diagenetic evolution and reservoir characteristics of the Upper Triassic Chang 6 tight sandstone in the Panlong area, Ordos Basin. By integrating fluid inclusion micro‐thermometry, scanning electron microscopy (SEM), and multi‐scale fractal geometry (utilizing the Frenkel–Halsey–Hill [FHH] model and high‐pressure mercury injection), we systematically quantify how specific diagenetic processes dictate pore geometry. Petrographic analysis reveals the reservoir is predominantly composed of mature arkosic sandstone, where primary porosity (ranging from 0.4% to 17.8%) has been severely diminished by intense mechanical compaction and pervasive authigenic cementation, including calcite, chlorite, and illite. The reservoir pore system exhibits highly heterogeneous, bimodal fractal behavior. Although nanoscale pores (<30 nm) maintain relative structural uniformity, fluid‐governing meso‐ and macropores demonstrate extreme tortuosity strictly driven by diagenetic facies. Specifically, compaction and carbonate cementation exponentially increase fractal complexity and capillary resistance, whereas feldspar dissolution zones yield secondary porosity networks with reduced structural tortuosity. Fluid inclusion data indicate that primary liquid hydrocarbon charging occurred between 100°C and 170°C, coinciding with early‐to‐middle diagenetic cementation. Ultimately, these findings demonstrate that quantitative multi‐scale fractal evaluation is essential for targeting secondary dissolution sweet spots, providing a robust theoretical framework for enhanced exploration strategies in tight continental basins.