Genesis of high-quality ultra-thick glutenite reservoirs: coupled control of sedimentation and diagenesis

As a distinctive type of oil and gas reservoir, ultra-thick glutenite reservoirs are characterized by strong heterogeneity and complex diagenetic evolution, making the prediction of high-quality intervals particularly challenging. Previous studies have mainly emphasized either the “sedimentary facies control” or individual diagenetic processes, leaving the coupling mechanism between sedimentation and diagenesis in-sufficiently understood. Moreover, the quantitative relationship between sedimentary microfacies and microscopic pore structures within ultra-thick reservoirs remains poorly constrained. These limitations hinder the design of stratified water-injection strategies and the optimization of well pattern adjustments during the late stages of waterflood development. In this study, the ultra-thick glutenite reservoir of the Permian Lower Urho Formation in Well Block 530, Junggar Basin, was selected as the research target. Through the integration of core observation, thin-section petrography, petrophysical testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion capillary pressure (MICP) analyses, a multi-scale analytical framework linking macroscopic sedimentary microfacies, microscopic diagenetic minerals, and pore–throat structures was established to systematically investigate reservoir characteristics and the principal controls on high-quality reservoir development. The results indicate that pores in the Lower Urho Formation glutenite reservoir are dominated by intergranular and dissolution pores. Notably, the second member of the Urho Formation (P₂w₂) contains high-porosity, high-quality reservoir zones composed mainly of preserved primary pores with abundant secondary dissolution pores. The key conditions for the formation of these high-quality reservoirs are: ① strong hydro-dynamics within main and marginal channel microfacies, high contents of rigid com-ponents (e.g., granite fragments), and low argillaceous content, which collectively favor primary pore preservation; and ② The dissolution of analcime generates abundant secondary dissolution pores. Concurrently, the transformation of analcime into albite is accompanied by further dissolution and the development of extensive albite intercrystalline micropores, significantly enhancing reservoir quality. This study reveals that sedimentation—controlling the original pore framework at the macroscopic scale—and diagenesis—modifying pore structure at the microscopic scale—act in con-cert to govern reservoir quality evolution through a cascading “facies–mineral–pore–throat” mechanism. The findings advance understanding of pore evolution in ultra-thick glutenite reservoirs and provide a genetic model and theoretical foundation for predicting high-quality (“sweet spot”) reservoirs in the Junggar Basin and analogous depositional settings.