Characteristics and genesis of Permian deep tight sandstone reservoirs in southern Dagang exploration area

Key words: 
• reservoir forming mechanism /
• diagenetic evolution /
• sandstone reservoirs /
• Permian /
• southern Dagang exploration area

Abstract: Utilizing core observations, thin section examinations, cathode luminescence analysis, scanning electron microscopy, fluid inclusions, carbon and oxygen isotope, hydrogen and oxygen isotope, electron probe analysis, situ laser ablation inductively coupled plasma mass spectrometry analysis, and various other analytical techniques, the diagenesis evolution and genetic model of Permian reservoirs in the southern Dagang exploration area were studied. By combining these results with the histories of burial evolution and hydrocarbon accumulation, it was revealed that the Permian sandstones in the South Dagang area possess high compositional maturity, characterized by quartz sandstones and sublithic sandstones. The high-quality reservoirs are dominated by secondary intergranular pores and kaolinite intergranular pores. The reservoir underwent an early exposure-open to late burial-closed environment, experiencing both meteoric freshwater leaching and deep burial dissolution under the control of tectonic movement. The formation of high-quality reservoirs is influenced by numerous factors. High maturity of medium coarse sandstone is the material basis for their formation. Stratum uplift causes sandstone to be leached by meteoric freshwater, forming a significant number of secondary pores, which is the key to the development of high-quality reservoirs. Early hydrocarbon charging and inhibition of cementation are conducive to the preservation of secondary pores. Reservoirs currently present in the slope and depression zone, but formed in an area of atmospheric water leaching and injection, represent a potential exploration targets. This model's establishment can be used as a reference for pre-drilling prediction of Permian reservoirs in other areas of the Bohai Bay Basin.