Formation Mechanisms of the Thick Conglomerate Reservoir in the Permian Jiamuhe Formation, Zhongguai Uplift, Junggar Basin

Thick conglomerate reservoirs possess substantial storage capacity and pronounced heterogeneity, yet their genesis remains debated. This study investigates the Permian Jiamuhe Formation thick conglomerate reservoir in the Zhongguai Uplift, Junggar Basin, utilizing full-diameter core analysis, cast thin-section petrography, X-ray diffraction, fluorescence microscopy, and heavy mineral assemblage analysis. The conglomerates exhibit low compositional and textural maturity, negligible clay matrix, and abundant magmatic lithic fragments. The pore system comprises predominantly detrital-grain dissolution pores (57.5%), followed by cement dissolution pores (25.1%) and microfractures (17.4%). Proximal Carboniferous volcanic rocks supplied plagioclase, pyroxene, and amphibole, providing labile constituents for subsequent acidic dissolution. Parent-rock weathering released Ca, Si, and Al, facilitating early zeolite and calcite cementation that reinforced grain-support frameworks and preserved primary porosity. Protracted leaching by acidic meteoric water during subaerial exposure was critical for reservoir enhancement. Steep paleotopography and the Jiamuhe–Wuerhe unconformity facilitated sustained fluid infiltration and extensive dissolution. In Well ZJ142, integrated petrophysical, mineralogical, and petrographic evidence indicates pronounced meteoric-water modification within the uppermost approximately 75 m beneath the weathering crust, with meteoric dissolution contributing up to a cumulative absolute porosity increment of 25.7 percentage points. Late faults and fractures provided pathways for deep acidic fluids interpreted to contain organic acids associated with source-rock maturation, promoting localized secondary dissolution during deep burial. The development of relatively favorable reservoir intervals was governed by a multistage process involving proximal supply of readily dissolvable volcanic fragments, early zeolite cementation, prolonged meteoric-water dissolution, and fault-assisted deep-fluid modification. Proximal soluble volcanic supply, early zeolite cementation, protracted meteoric dissolution, and fault-assisted deep fluid modification. These findings provide a robust theoretical basis for exploring deep thick conglomerate reservoirs in the Junggar Basin.