Characteristics and controlling factors of Jurassic reservoirs in Chepaizi area, western Junggar Basin

We analyzed the characteristics of Jurassic reservoirs in the Chepaizi area in the western Junggar Basin using thin section microscopy, core description and physical property analysis. Combined with the study of petrophy-sical parameter cutoffs, we summarized the controlling factors of reservoirs, and divided reservoirs among types. The results showed that reservoirs in the study area mainly develop five lithofacies including matrix-supported conglomerate facies, particle-supported conglomerate facies, conglomeratic sandstone facies, sandstone facies and siltstone facies. The conglomerate reservoirs had limited reservoir space with very-low porosity and ultra-low permeability. The sandstone reservoirs develop comparatively more reservoir space, mainly primary pores, and show the characteristics of middle to high porosity and permeability. By the quantitative evaluation of diagenesis, we identified 11 diagenetic facies. The properties of reservoirs are mainly controlled by lithofacies, and diagenesis promoted the differentiation of reservoirs. Combined with petrophysical parameter cutoff and reservoir properties, three reservoir types are identified in this area. Type Ⅰ reservoirs are the combinations of (conglomeratic) sandstone facies and medium to strong dissolution diagenetic facies, and the reservoir properties are best. Type Ⅱ reservoirs are the combinations of siltstone facies and weak cementation, weak dissolution diagenetic facies, and the reservoir properties are poorer than type I. Type Ⅲ reservoirs are the combinations of conglomerate or sandstone facies and medium to strong cementation, dissolution diagenetic facies, and the reservoir properties are poorest.