Geochemical Characteristics Of Soluble Organic Matter And Shale Oil In Permian Lucaogou Formation Shale Of Santanghu Basin

Santanghu Basin is located in the northeast of Xinjiang Uygur Autonomous Region,which has abundant oil and gas resources.Since unconventional oil and gas breakthrough,large-scale exploration and development of shale oil began in Santanghu basin.In this paper,the soluble organic matter of shale and the saturated hydrocarbon and aromatic hydrocarbon components of crude oil in the Lucaogou Formation of Malang Sag and Tiaohu Sag in Santanghu Basin were systematically studied,and their geochemical characteristics were analyzed.The crude oil was divided into groups to compare the oil sources within the source.Combined with previous research results,the migration and accumulation mechanism of shale oil was discussed.1.The sedimentary organic matter types of the two sags are similar,mostly mixed with low aquatic organisms and terrestrial organisms.However,some biomarker parameters,such as the distribution characteristics of tricyclic terpanes,show that the contribution of aquatic organisms in the two sags is different.2.The sedimentary environments of the two sags are weak oxidation-weak reduction saline water-saline deep lake-semi-deep lake environment.The average Ga/C₃₀H ratio in Tiaohu Sag is 0.53,while the average Ga/C₃₀H ratio in Malang Sag is0.33,indicating that the salinity of shale sedimentary water in Tiaohu Sag is higher than that in Malang Sag.3.Most of the source rock samples in the two sags are in the low maturity-maturity stage,and a few samples are immature.However,the average value of C₂₉ regular sterane??/(??+??)in Tiaohu sag is 0.49,and the overall maturity is slightly higher,and the average value of this ratio in Malang sag is 0.30.The first and second Lu samples were in the immature–mature stage,and the third Lu sample was in the immature stage.4.The composition characteristics of saturated hydrocarbon and aromatic hydrocarbon show that the composition of crude oil in the two sags is slightly different.The distribution range of n-alkanes carbon number of crude oil in the two depressions is wide,showing a single peak.The main peak carbon is mostly n C₂₅,without obvious odd-even advantage,and Pr/Ph is between 0.68 and 1.08.However,the distribution of tricyclic terpanes in crude oil in Tiaohu Sag shows a'tail upwarping'pattern,with high C₂₄Te T/C₂₆TT ratio and high gammacerane index,which characterizes the saline water with rich aquatic biological sources.The ratios of Ts/Tm,C₂₉ sterane??/(??+??)and trimethylnaphthalene are higher and the maturity of crude oil is higher.The tricyclic terpane series of crude oil in Malang Depression showed an inverted'V'pattern with C₂₃ as the highest peak,and the C₂₄Te T/C₂₆TT ratio was low.The gammacerane index was 0.26,indicating that its aquatic biological contribution and water salinity may be lower than that of Tiaohu depression.The ratios of Ts/Tm,C₂₉ steroidal??/(??+??)and trimethylnaphthalene were low,indicating that the maturity of crude oil was also relatively low.5.The oil source correlation analysis of Tiaohu sag shows that the crude oil comes from Lu 1 and Lu 2.There is also the same oil source law in Malang sag,and crude oil has the highest affinity with Lu 1 and Lu 2.