Hydrocarbon-generating potential of the Middle Permian Lucaogou source rocks in the Gucheng Sag,Junggar Basin
A billion-ton shale oil field was discovered in the Jimsar Sag,located in the East Uplift of Junggar Ba-sin,revealing the favorable hydrocarbon-generating potential of the source rocks developed in the Middle Perm-ian Lucaogou Formation.In this study,the hydrocarbon-generating potential and sedimentary environment of the Lucaogou source rocks in the Gucheng Sag,neighboring to the Jimsar Sag,were evaluated systematically,and the distribution range of the source kitchen was depicted.In addition,the characteristics of the Lucaogou source rocks in the Gucheng Sag were compared with those in the Jimsar Sag.The results show that the Lucao-gou source rocks in the Gucheng Sag are characterized by kerogen types Ⅱ/Ⅲ-Ⅲ and are good to excellent source rocks whose organic types and abundance are slightly inferior to those in the Jimsar Sag.In the Middle to Late Jurassic,the Lucaogou source rocks in the Gucheng Sag generally entered the hydrocarbon-generating threshold,and the area entering the main oil-generating window reaches 212 km2 at present.Although they were both deposited in a lacustrine environment,the ratios of Pr/Ph,Ts/(Ts+Tm),C19/C21 tricyclic ter-penes,C24 tetracyclic terpenes/C26 tricyclic terpenes in the Lucaogou source rocks in the Gucheng Sag are slight-ly higher than those of the Lucaogou source rocks in the Jimsar Sag,and the relative content of C28 regular ster-anes is slightly lower.This indicates that the Lucaogou source rocks in the Gucheng Sag were deposited in an oxidation-reducing transitional brackish environment with a certain number of terrigenous higher plant inputs in addition to the contribution of algae and microorganisms.Four thickness centers of the Lucaogou source rocks with more than 160 m thickness were developed in the Gucheng Sag,covering a total area of 420 km2.Three hy-drocarbon-generating centers with an oil-generating intensity greater than 200×104 t/km2 were developed in the southern part of the sag with a total area of 130 km2.The research results have further consolidated the resource potential of the Middle Permian petroleum system in the Junggar Basin and laid a foundation for future petro-leum exploration in the Gucheng Sag.
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