Reservoir characteristics and sweet spot prediction of mixed tight oil reservoirs in the saline lacustrine Lucaogou Formation, Jimusaer Sag, Junggar Basin, China

Sweet spot prediction in saline lacustrine mixed tight oil reservoirs is challenging. This study evaluates the P2l22-3 (PL23) member of the Lucaogou Formation in the Jimusaer Sag using organic geochemistry, XRD, thin sections, FE-SEM, core analysis, and NMR logging. The three sub-layers share similar source-rock conditions (good–excellent TOC, type I–II kerogen, mature), implying organic geochemistry does not cause reservoir-quality differences. Reservoir heterogeneity is controlled by lithofacies, clay mineral assemblages, and pore connectivity. Sub-layer 2 is the best interval, with highest movable porosity (4.63%), oil saturation (79.14%), superior NMR permeability, and good pay continuity. High-quality porosity comprises intergranular, dissolution, and microfracture pores in silty-fine sandstone and dolomitic siltstone. In contrast, smectite enrichment and poorly connected nano- to submicron pores reduce sub-layer 3 quality. Movable porosity is key; a classification integrating movable fluid parameters, type I movable pay thickness, and movable oil reserve abundance supports well placement.