Formation environment and origin of hydrocarbon-rich shales in Qingshankou Formation,northern Songliao Basin
Comprehensive research involving quantitative restoration of paleo-geotherm,paleo-geomorphology,sedimentary environment,and geological events were conducted to study the formation environment and genesis of hydrocarbon-rich shales in the Qingshankou Formation of northern Songliao Basin.The results show that the Ro of the hydrocarbon-rich shales in the Qingshankou Formation of Songliao Basin mainly ranges from 0.75％to 1.60％,with a high content of free hydrocarbons,mainly from 4 to 12 mg/g,formed under a high-temperature thermal basin background with a paleo-geothermal gradient of 50 to 70 ℃/km.Under the background of extensional geodynamics and thermal subsidence,shale layers controlled by densely fractured normal fault zones were formed.The paleo-ge-omorphology,characterized by two depressions and a protrusion,provided a conducive environment for the forma-tion and evolution of these shales.The warm and humid climate of the lacustrine environment,along with magmatic hydrothermal fluids,laid the material foundation for the proliferation of algae,which was crucial for the develop-ment of thick layers of hydrocarbon-rich shales.The semi-deep lacustrine with oxygen deficiency,deep lake reduc-tion,and strong reduction environment were conducive to the burial of organic matter.Comprehensive analysis indi-cates that the coupling effects of tectonics,lacustrine sedimentation,and paleo-geothermal conditions provided the tectonic background and thermodynamic conditions of hydrocarbon-rich shales.The warm and humid climate,anox-ic environment,and nutrients brought by volcanic hydrothermal fluids are important reasons for the formation of hy-drocarbon-rich shales.
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维普
