The Diagenetic Characteristics of Chang4+5 Formation in Southwest Ordos Basin

As major layer series of development in southwest Ordos Basin have been developed, the Chang 4+5 reservoir in the area is a main and stable production supersede layer. However, there are few studies on the diagenesis of the reservoir in the layer, which affects the exploration and evaluation of high-quality reserves. The petrological characteristics of Chang 4+5 reservoir in southwest Ordos Basin area were systematically studied by using thin sections of rock samples, scanning electron microscopy, analysis and other methods, the diagenetic stages and evolutionary sequences were summarized, and the diagenetic characteristics were defined. The results show that the rock types of Chang 4+5 reservoir in the area are mainly medium-fine feldspar lithic quartz sandstone. The diagenetic types are mainly constructive dissolution and destructive compaction and cementation. The diagenetic evolution of Chang 4+5 reservoir in the area is mainly in the middle diagenetic stage A to middle diagenetic stage B, during which a large amount of oil and gas were filled, and the illite cementation-feldspar dissolved pore facies zone and kaolinite weakly dissolved-chlorite thin film facies zone are favorable diagenetic facies zone of Chang 4+5 reservoir in the area, which is conducive to oil and gas accumulation and integration.