Evaluation On The Characteristics Of The Deep Permian Source Rocks In The East Part Of The Junggar Basin

The vast area in the east part of the Junggar Basin is a virgin area to be explored in hydrocarbon exploration.The Permian source rocks are one of the main source rocks in the Junggar Basin,however,their characteristics and space distribution in the east part of the basin are almost unknown.Based on the abundant geochamical data,the charactertistics of the Permian source rocks,namely,their abundance,types of the organic matter,and maturity,are systmatically and statistically analyzed.Then their space distribution are illustrated in combined with well logging,coring and seismic profiles that covering the east part of the Junggar Basin.The following conclusions can be drawn:(1)There are two sets of argillaceous source rocks developed respectively in the Lower Permian Jingou Formation and the Middle Permian Pingdiquan Formation.(2)The distribution of Permian source rocks is characterized by north-south zoning and east-west blocking.This pattern is controlled by Permian dextral tensioning caused by final delamination of the oceanic crust due to the subduction and closure of the northern Tianshan ocean and the Kelamei ocean.(3)Space distribution of the source rock maturity is controlled by late-stage tectonic movement and characterized by higher maturity in the west and lower in the east,higher maturity in the south and lower in the north.Comprehensive thermal evolution model shows that the Permian source rocks enter the threshold of hydrocarbon generation at burial depth of 2000 m and reach the peak of hydrocarbon generation at burial depth of 3000m;Simulation results of the thermal evolution indicate that the Permian source rocks entered the threshold of hydrocarbon generation at the end of Jurassic and reached the peak of hydrocarbon generation at the end of Cretaceous.(4)The criteria for high quality Permian source rocks is established and their space distribution are revealed.High quality source rock is most often black or gray shale and mudstone formed in deep lake environment indicated by its thickness greater than 100 m.High quality source rock is most often characterized by type II organic matter with the total organ carbon(TOC)greater than 1%.Based on the above criteria,high quality source rocks are mainly developed in the middle Permian Pingdiquan Formation from the faulted and folded zone of Zhangbei District,the Jimusar Sag and the northern Mulei Sag.Research results have theoretically illustrated for the first time the charateristics and space distribution of the Permian source rocks and will practically guide the hydrocarbon exploration in the east part of the Junggar Basin.