Hydrocarbon Generation Conditions Of The Lower Jurassic Kangsu Formation In The Southeast Depression Of The Tarim Basin

The Jurassic stratum in the Southeastern Depression of the Tarim Basin is distributed in the narrow strip between the Altyn foothill fault and the South Uplift of the Tarim Basin.The exploration degree is low,the seismic data quality is poor,and the distribution of main source rocks and hydrocarbon generation potential aren’t clear enough,which restrict the exploration of oil and gas.It is confirmed that the Jurassic Yangye Formation and the Kangsu Formation have certain hydrocarbon generation potential in field work.In this study,the coal-bearing source rocks of the Kangsu Formation with relatively high maturity were selected.Through field geological survey,profile measurement,sample collection and geochemical tests were carried out,combined with drilling data and sample analysis data of Ruocan 1,Ruocan 2 and Qiedi 1 wells,the lithology of the source rocks,sedimentary environment,spatial distribution characteristics,geochemical characteristics and hydrocarbon generation potential of the Lower Jurassic Kangsu Formation in the southeastern part of the Tarim Basin was carried out by means of elemental geochemical analysis,total organic carbon content prediction via well logging,and single well hydrocarbon generation history simulation.The source rocks of this formation were systematically evaluated and compared with other areas on the periphery of the Tarim Basin,which provides a strong basis for the Jurassic oil and gas exploration of the Southeastern Depression of the Tarim Basin.The results obtained are as follows:The deposition period of the Kangsu Formation is generally in a warm and humid climate with weak oxidative-weak reduction environment.The sedimentary center of the Washixia Sag has a shallow water depth with freshwater-slurry water.The climatic conditions are conducive to the growth of ancient vegetation and have a certain preservation effect on the hydrocarbon-forming parent material in the sediment.The deposition thickness of Kangsu Formation is about237.0⁸55.6m,and Kangsu Formation developed two sedimentary centers,which are located in the deep recessed area of southeast of Ruocan 1 and the frontal depression area of the Hongliugou Old Coal Mine and Qigeleke.The source rocks of this formation are mainly dark mudstones and carbonaceous mudstones,with a thickness of about 60¹40m,accounting for25%of the thickness of the formation.The organic matter abundance of source rock is high in the Ruocan 1 and the Hongliugou Old Coal Mine,the organic carbon content of the dark mudstone is 1.2⁴.4%,carbonaceous mudstone is 5.0³9.6%,kerogen type is II₂-III,and the source rock is mainly in the stage of low maturity-maturation.Compared with the source rocks at the same sedimentary time around the basin,the hydrocarbon generation potential of the source rocks in the Washixia Sag of the Southeastern Depression of the Tarim Basin is relatively lower than that of the Kuche Depression in the north of the Tarim Basin,while are slightly better in the northeast and southwest profiles of the Tarim Basin.The source rocks of the Kangsu Formation in the depression are now at the peak of hydrocarbon generation,with certain hydrocarbon generation potential and exploration prospects.