Study On The History Of Maturity And Maturity Of Carboniferous In The Eastern Qaidam Basin Abstract

The eastern Qaidam Basin is one of the potential exploration areas in the Qaidam Basin.In recent years,researchers found more and more anthraxolite and oil sand in the Carboniferous of eastern Qaidam Basin,which indicated that the Carboniferous of that area has certain potentiality of oil and gas resources.However,the present geothermal field,thermal history and maturity evolution history of the eastern Qaidam Basin are not clear,which restricted the oil and gas resource potential evaluation.This study collected a total of more than 300 samples and tested more than 500 of the data and evaluated the characteristics of Carboniferous hydrocarbon source rocks in this area through organic matter abundance,organic matter type and organic matter maturity three aspects;used the temperature data of 56 wells to research present geothermal field of the eastern Qaidam Basin;tested,arranged and collected 18 fission track data and 178 vitrinite reflectance data,using paleothermometers method to reveal thermal history of the eastern Qaidam Basin;based on the characteristics of hydrocarbon source rocks and thermal history,using the advanced basin simulation technique to rebuild maturity history of the eastern Qaidam Basin.The study concluded that:(1)Organic matter abundance of hydrocarbon source rocks of Carboniferous in the eastern Qaidam Basin is high,kerogen types are ?1~? in high mature and over mature stages and the overall evaluation of medium to good hydrocarbon source rocks.(2)The present geothermal gradient and heat flow are 24.1°C/km and 53.1mW/m2 have characteristics of low temperature geothermal field of tectonically quiet region.(3)It has experienced 5 thermal evolution stages from Carboniferous: the sustained temperature increase stage of Carboniferous-Late Triassic,reached the peak of geothermal gradient in Middle Triassic and the maximum paleogeothermal gradient was 39.8°C/km;the uplift erosion temperature drop stage of Late Triassic-Early Jurassic;the sustained temperature increase stage of Early Jurassic-Early Crataceous;the continuous decline stage after transient temperature increase stage of Early Crataceous-Eogene;the sustained fast cooling stage of Neogene.(4)Maturity evolution process of Carboniferous strata of the eastern Qaidam Basin: hydrocarbon source rocks attained hydrocarbon generation threshold in Early Carboniferous and stayed in mature stage till the end of Permian;in Late Triassic,due to the influence of Indosinian Movement,the Qaidam Basin was uplifted and eroded and the hydrocarbon generation of Carboniferous stopped;in the end of Middle Jurassic,due to Yanshan Movement,the downfaulted basin of early and Middle Jurassic reversed and led to uplift and denudation;in Late Jurassic-Early Crataceous the basin subsided again and deposited the upper Jurassic and the lower Crataceous strata,temperature increased and Carboniferous stayed in middle mature stage in Late Crataceous;in the end of Cretaceous,due to Late Yanshan Movement,that region uplifted again,the hydrocarbon generating process of Carboniferous interrupted;in Cenozoic,the basin deposited Eogene,Neogene and Quaternary strata,hydrocarbon source rocks attained middle mature-high mature stage.(5)According to the characteristics of hydrocarbon source rocks of Carboniferous of eastern Qaidam Basin and thermal evolution history of maturity,considering that Carboniferous strata of the eastern Qaidam basin has hydrocarbon generation potential and oil-gas exploration should mainly carry out in the regions of Shihuigou-ChengqianggouMountain Oulongbulukeand Wanggaxiu coal mine.The research results of this paper can provide evidences for decision of the oil-gas exploration.