Hydrocarbon Generation And Evolution History And Main Controlling Factors Of Carboniferous Source Rocks In The Eastern Qaidam Basin

The Qaidam Basin is one of the three major oil and gas bearing basins in northwestern my country.The Carboniferous is the fourth set of oil and gas be aring systems in this basin,with great potential for oil and gas resources.The hydrocarbon generation history of source rocks is the basis for analyzing the dynamics of hydrocarbon generation,migration and accumulation.Taking the Carboniferous in the e astern Qaidam Basin as the research object,based on ground investigation,drilling,2D seismic equilibrium profile,paleotemperature scale inversion,etc.,analyzed the thermal history of the eastern Qaidam Basin;combined with the organic geochemical characteristics of source rocks,studied the burial history,hydrocarbon generation and evolution history and main controlling factors of the Carboniferous.The research shows that the eastern Qaidam Basin has experienced a gradual cooling process as a whole,with a geothermal gradient ranging from 22.1 to 41.5°C/km.The geothermal gradient has been in a slow cooling stage since the Late Carboniferous.The paleothermal gradient in the eastern Qaidam Basin in the late Paleozoic was 38-41.5°C/km,and the average geothermal gradient was 39°C/km;the early Paleogene was29-35.2?/km,the average value is about 33.0?/km,the geothermal gradient increased again at the end of the Paleogene,and then entered the cooling stage again.T he Carboniferous to the Early Jurassic,the Oligocene period,and the Miocene strata were rapid burial periods,the Early Jurassic to the Oligocene,the late Oligocene to the Miocene,and the Miocene strata were uplift suffers from denudation periods.The source rocks of the Carboniferous Kruike Formation in the eastern Qaidam Basin entered the hydrocarbon generation threshold around the Early Permian and entered the early hydrocarbon generation stage,with a burial depth of about 1500 m and a hydrocarbon generation threshold temperature of about 90 °C.Until the early Jurassic hydrocarbon generation stopped,the Paleocene Carboniferous source rocks reached the hydrocarbon generation temperature again,mainly producing gas.The thermal evolution history of the Carboniferous source rocks in the eastern Qaidam Basin is mainly characterized by early hydrocarbon generation and late hydrocarbon generation and secondary hydrocarbon generation.The second hydrocarbon generation stage is the main hydrocarbon generation period.The history of hydrocarbon generation of Carboniferous source rocks in the eastern Qaidam Basin is closely related to regional tectonic movements and thermal history from the Late Paleozoic to the present.Among them,the Hercynian movement,the late Indosinian Movement,the late Yanshan Movement and the early and late Himalayan Movement had a greater impact on it.