Geochemical Characteristics Of Palaezoic Hydrocarbon Source Rocks In Delingha Area Of Qaidam Basin

Based on previous results made by other researchers, analysis of crop samples which are from Palaezoic strata in Delingha Area of Qaidam Basin and vast amounts of data, this thesis comprehensively analyses depositional environment, abundance, types and maturity of organic matters of Palaezoic hydrocarbon source rocks in Delingha Area in order to reveal the geochemical characteristics and exploration potential of those resources. The organic geochemical method was mainly adopted in this study: organic abundance evaluation of source rock based on the analytical data of TOC, thermal decomposition and chloroform extract; restoration of organic types based on data analysis of thermal decomposition, structureless organic matter composition, biomarker character, microscopic examination of kerogen, carbon isotope composition of structureless organic matter, et al. Furthermore this study evaluates the maturity of Palaeozoic source rock from biomarker and the characters of maturity, and finally the method of organic carbon analysis was used to make quantitative evaluation of hydrocarbon volumes generated by Palaeozoic source rock.Comprehensive evaluation reveals that sedimentary environment in Delingha Area was shore in Middle-Late Cambrian and meanwhile it was at early stage of transgression, which was not conducive to organic preservation. So during this period the organic content was very low and there was no source rock. But, from Lower Ordovician to Middle Ordovician, the overall sedimentary environment changed from shallow to pelagic and hemipelagic that was thrive and flourish with living beings and sediment were widely distributed, which was also conducive to organic sediment and preservation, so the organic abundance and types are excellent. Thus, there is source rock in Ordovician. To Late Carboniferous, coming with another early stage of transgression, sedimentary environment became shallow and low energy, which was also conducive to organic sediment and preservation. Bed thickness and distribution are steady, which is rich in organic material from aquatic life, wherefore the organic abundance and types are preferable. Until Early Permain, regression happened and sedimentary environment was shoreland or swamp, which belonged to paralic environment. In this transitional environment, energy was low, which was also conducive to part of mixed-source organic sediment and preservation going together with deposition of mudstone. Based on the organic evaluating conditions, Lower Permian dark mudstones are preferable source rocks in Wanggaxiu section, but on the other hand the dark gray carbonaceous slate are poor source rock or invalid in north Delingha section.From the microscopic analysis, biomarkers'characters also prove that types of source rocks are sapropel type kerogen or partial sapropel in Middle-Lower Ordovician, Late Carboniferous and Lower Permian, Delingha Area, which belongs to reducing environment or slight reducing environment. At the same time, the data also indicates that organics of all source rocks have come to late stage of maturity. Comparatively speaking, source rocks of Upper Carboniferous have higher maturity index, Lower Permian the second and Lower Ordovician the least. Manifold methods are used to evaluate the hydrocarbon volumes generated by Cambro-Ordovician source rocks in study area. The oil-forming quantities of the type of hydrocarbon source rock through a estimated evaluation of organic carbon analysis methods are in the sequential decrease as: Middle Ordovician Shihuigou formation has the highest hydrocarbon volumes generated about 425 hundreds of millions of tons, Lower Ordovician Duoquanshan formation the second about 121.5 hundreds of millions of tons, and Cambrian the least. Therefore, there is exploration potential in Middle-Lower Ordovician. The evaluation result shows Palaeozoic source rocks of Delingha Area are quality and have a rosy future in exploration.