Research On The Conditions Of Hydrocarbon-generating And The Correlation Of Oil And Source Rock From The Jiuxi Depression

Based on the principles of petroleum geochemistry and organic petrology, the author collected and analyzed the works of the former researchers, and use methods of advanced geochemical experiment and analysis to deal with the comprehensive evaluation of the conditions on hydrocarbon- genenrating of the lower Cretaceous source rocks and research on thermalevolution. On the basis of these works, the correlation of crude oils with source rocks and the migration direction of petroleum have been discussed using biomarkers in this thesis. The following conclusions are obtained.1. For the first time, the algae laminae with strong fluorescence are found out in the Cretaceous source rocks through the research of organic petrology. The development of algae laminae greatly enhanced the hydrocarbon-generating ability of source rocks in the research area. The discovery has important theoretical and practical values on understanding enrichment conditions and mechanism of the crude oils from the Jiuxi depression.2. The organic abundance of the Cretaceous source rocks is high and most of them belong to the better source rocks, in which the source rocks of the Chijinpu formation rank the best, and almost all of them reach the criterion of better source rocks, the Xiagou formation is the second and the Zhonggou Formation is the last one. The organic types of the hydrocarbon-generating materials belong to transitional type, in which the proportion of â…¡₁ and â…¡₂ keeps balanced, and some of them are Type I and Type III organic matter.3. The threshold depths of each subsag in the research area are determined by several methods such as the evolutionary characteristics of soluble organic matter. The Qingnan subsag ranges from 4000m to 4100m, the Shibei subsag is about 3000m and the Dahongquan subsag varies from 3200m to 3300m. The Zhonggou formationalmost lies at the stage of immaturity, the Xiagou formation ranges from immaturity to maturity, and the Chijinpu formation varies from low maturity to high maturity.4. Applying the Easy-Ro(%) model to the hydrocarbon generating history research of the lower Cretaceous source rocks shows that the main oil-generating period is from late Tertiary to Quaternary, and does not exist the second hydrocarbon-generating event during the geological time. The lower part of Xiagou Formation and the upper part of Chijinpu Formation are the main potential source rocks.5. The natural gases belong to typical oil-type gases. It is mainly composed of methane whose average content is 75.81%, and the average content of heavy hydrocarbons is 20.34%. The C1/C1-5 ratios range from 0.75 to 0.87 which attributes to typical wet gases. The 6 13Ci values lie in the range from -45.3%o to -4O.2%o, and5 I3C2 values range from -31.1 %o to -28.4%o. In addition, the carbon isotope values of hydrocarbons reveal an abnormal order which maybe results from the mixture of different mature typical oil-type gases.6. Synthetical correlation of oils and source rocks using multiple factors of biomarkers are studied in this dissertation. The results show that oils from the Jiuxi depression are very similar, which suggest their organic matter sources are high plant and planktonic algae and the sedimentary environment is a reductive one with some saltiness. The geochemical characteristics of source rocks not only have some generality but also evident difference which reveals stronger heterogeneity. The good relationship between the source rocks of the lower part of Xiagou Formation and the upper part of Chijinpu Formation with crude oils reveals that they are the potential contributors of the crude oils from Jiuxi depression.7. According to the regular change of carbazole compounds and the physical properties of the oil in the distance of petroleum migration, the direction of migration is from west to east. That is to say the oils migrated from Qingxi oil field to Ya'erxia oil field , then to Laojunmiao oil field and Shiyougou oil field. In the same reservoir, the direction of migration is from down to up.