Hydrocarbon-generating potential of the Middle Permian Lucaogou source rocks in the Gucheng Sag, Junggar Basin, China

Abstract

A billion-ton mega shale oil field has been discovered in the Jimsar Sag, located in the Eastern Uplift of Junggar Basin, which reveals the good hydrocarbon-generating potential of the source rocks in the Middle Permian Lucaogou Formation. This paper systematically evaluates the hydrocarbon-generating potential and formation environment of the Lucaogou source rocks in the Gucheng Sag, which is adjacent to the Jimsar Sag, and draws the distribution range of the source kitchen, and compares them with those of the Lucaogou source rocks in the Jimsar Sag. The results show that the kerogen type of Lucaogou source rocks in the Gucheng Sag is mainly of type II/III–III, dominated by good–excellent source rocks, and the type and abundance are slightly inferior to those in the Jimusar Sag. In the Middle and Late Jurassic, the Lucaogou source rocks in the Gucheng Sag entered the hydrocarbon-generating threshold, and now, the area entering the main oil-generating window reaches 212 km². Although both of them are lacustrine deposits, the Lucaogou source rocks in the Gucheng Sag have slightly higher Pr/Ph, Ts/(Ts + Tm), C₁₉/C₂₁ tricyclic terpane, C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane ratios, and somewhat lower C₂₈ regular sterane content than the Jimsar Sag, suggesting that Lucaogou source rocks were deposited in an oxidizing–reducing transitional environment of a specific salinity in the Gucheng Sag. There was a certain amount of terrestrial higher plant input in addition to the contribution of algal and microbial biota in the Lucaogou source rocks in the Gucheng Sag^. The Lucaogou source rocks have developed four centers with a thickness greater than 160 m in the Gucheng Sag, covering a total area of about 420 km². In the southern part of the sag, three hydrocarbon-generating centers with an oil-generating intensity greater than 2000 × 10³ t/km² have developed, covering a total area of 130 km². The research results further strengthen the resource base of the Middle Permian petroleum system in the Junggar Basin and lay the foundation for the next step of petroleum exploration in the Gucheng Sag.