Glutenite reservoir characteristics and development model of Permian Upper Wuerhe Formation in Fukang Sag, Junggar Basin

The glutenites in the Permian Upper Wuerhe Formation in the Fukang Sag of the Junggar Basin possess great potential for oil and gas exploration. However, uncertainties in the reservoir characteristics and formation mechanisms of these glutenites seriously restrict their effective exploration. The study provides a compre- hensive analysis on the characteristics, main controlling factors, and development models of glutenite reservoirs of the Upper Wuerhe Formation in the Fukang Sag of the Junggar Basin using microscopic thin sections, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that: (1) Two types of interstitial materials are observed in the glutenites of the Upper Wuerhe Formation, where the spaces between gravels are primarily interstitially filled with coarser sandy components, and the cementation mainly occurs between these sandy components. (2) The glutenites generally exhibit low porosity, with minimal pore development within gravels, while the pores in sandy interstitial materials are more developed. The reservoir space is mainly composed of intercrystalline and secondary dissolution pores. (3) Diagenetic processes related to reservoir formation mainly occur within the coarse sandy interstitial materials between gravels, mainly involving aluminosilicate dissolution, which results in abundant dissolution pores. (4) In high-energy sedimentary microfacies, such as estuary bars and underwater distributary channels, reservoirs are more favorably developed, where the reservoir space is mainly associated with feldspar dissolution. Fractures and unconformities are the main channels for acidic fluid migration. (5) During the eodiagenesis, acidic fluids, mainly atmospheric water, infiltrated along unconformities, with more significant dissolution near the Beisantai arch. During the middle diagenetic period, dissolution was mainly attributed to organic acid. (6) Three types of reservoirs are developed in the glutenites: atmospheric acid dissolution reservoirs, organic acid dissolution reservoirs, and dual-source acid superimposed dissolution reservoirs. The distribution of these reservoir types determines the exploration strategies for oil and gas reservoirs of glutenites of the Upper Wuerhe Formation in the Fukang Sag of the Junggar Basin. Glutenites in the slope and sag areas and zones of superimposed fault development are the key objectives for oil and gas exploration of glutenite reservoirs of the Upper Wuerhe Formation in Fukang Sag.