The diagenesis and evolution of conglomeratic reservoirs in the Wutonggou Formation in the Yingyeer area

Abstract

The conglomeratic reservoirs of the Permian Wutonggou Formation in the Yingyeer area of the Turpan–Hami Basin are key petroliferous horizons, with enormous potential for hydrocarbon exploration. Existing studies on the conglomeratic reservoirs in this area mainly focus on the sedimentary environment and sand body distribution, while few of them concern the diagenesis and evolution of the conglomeratic reservoirs, leading to deficient knowledge about relevant mechanisms. By comprehensively utilizing the data from ordinary and casting thin section identification, the x-ray diffraction analysis of whole rock and clay, scanning electron microscopy, and other analyses and assays, this study analyzed and investigated the petrological characteristics, diagenetic types, and characteristics, and diagenetic evolutionary stages and mechanisms of the conglomeratic reservoirs of the Permian Wutonggou Formation in the Yingyeer area. The study results are as follows. Under the influence of sedimentary provenances, tectonic evolution, and paleogeomorphology, the conglomeratic reservoirs of the Permian Wutonggou formation have low clastic grain maturity and low structural maturity, suggesting proximal provenances. The reservoirs are subjected to various diagenesis, including carbonate cementation, which fills pores and throats; compaction as a major factor leading to poor reservoir quality, and dissolution, which significantly improves the reservoir properties. The conglomeratic reservoirs in the Wutonggou formation are generally in substage A of the middle diagenetic stage. The diagenetic evolution of the reservoirs generally underwent early mechanical compaction, calcite precipitation, secondary quartz overgrowth, the injection of organic fluids, the dissolution of feldspars and lithic grains, the transformation of clay minerals, and calcite cementation in sequence. Hydrocarbon charging mainly occurred during the late Middle Jurassic and was greatly influenced by early compaction and dissolution.