Comprehensive Research On Hydrocarbon Source Rocks Of Harjiawu Formation In Late Carboniferous Of Santanghu Basin

Santanghu Basin is a small petroliferous basin, which is located in the northeast of Xinjiang. Although great breakthrough of oil and gas exploration has made in volcanic hydrocarbon reservoir of Carboniferous system, but the research of hydrocarbon producing substance and hydrocarbon potential are relatively low. This paper systematically study on the source rocks of Harjiawu Formation of Santanghu Basin in late Carboniferous.A preliminary study suggested that Harjiawu Formation and Batamayineishan Formation are the same lithostratigraphic unit and widely distributed in the whole basin. Harjiawu Formation contains basic volcanic rocks, pyroclastic rocks and sedimentary rocks. According to the research of lithofacies and palaeogeography conducted by previous researchers and biological marker, the paper further confirmed the semi-deep lacustrine, shallow lacustrine and limnetic facies of Haerjiawu Formation of Santanghu Basin in late Carboniferous.Variations of the drilling accumulative total thickness and single layer thickness of source rocks in Harjiawu Formation very rapid laterally, sandwiched between volcanic rocks, and pyroclastic rock as lenses. Thickness of source rocks is biggest in the malang depression and gradually thinned from northwest(Tiaohu and Hanshui depression) and southeast (Weibei uplift) of Santanghu Basin. According to the lithology, Source rocks of Harjiawu formation is divided into four types-black mudstone, tuffaceous shale, carbonaceous mudstone and coal rock. Geochemical component of source rock show its parent rock is acidic and mafic magmatic rocks, and mafic composition probably come from the strong volcanic activity during the sedimentary period of source rock in the studied area.Organic geochemical data show that organic matter abundance of hydrocarbon source rocks in Harjiawu Formation is high, but the plane heterogeneity of organic matter abundance is severe and the abundance of organic matter is gradually reduced from the southeast to northwest of Santanghu Basin. Rock pyrolysis hydrogen index, kerogen maceral and carbon isotope indicate that hydrocarbon source rocks of Harjiawu Formation mainly consists of kerogen of Ⅲ and Ⅰ type, mixed type in different proportions of Ⅲ and Ⅰ type. Biomarker compounds show that the source of organic materials is from mixed source of terrigenous higher plants and aquatic bacteria algae, which is formed in the weak oxidation-reduction and oxidation freshwater environment; Tmax, vitrinite reflectance and biomarker maturity indicators reveal that hydrocarbon source rocks are mainly in the mature stage, a few samples are in high maturity stage for the large buried depth. The maturity of hydrocarbon source rock is also gradually reduced from the southeast to northwest, which is consistent with paleogeothermal gradient on the previous studies. The above indexes demonstrate that the hydrocarbon source rock of Harjiawu Formation in Santanghu Basin is a good-excellent hydrocarbon source rocks, but difference of different sedimentary facies zone exists for different parent material type. Hydrocarbon generation potential of hydrocarbon source rocks is high and prospects of oil and gas exploration is great.