Paper No. 30-5
Presentation Time: 9:20 AM
SEDIMENTARY CHARACTERISTICS OF LACUSTRINE STROMATOLITE LIMESTONE AND ITS PETROLEUM GEOLOGICAL SIGNIFICANCE IN QAIDAM BASIN
WU, Yinye, Petroleum Geology, Research Institute of Unconventional oil @gas Branch, CNOOC Ltd., Guobing Building Office, No21 Jiangtai, Chaoyang District,Beijing, Beijing, 100016, China, LV, Jialei, Petroleum Geology, RIPED of China, Main Building Office, P.O.Box910, No.20 Xueyuan Road,Haidian District,Beijing, Beijing, 100083, China, FANG, Xiang, Petroleum Geology, RIPED of China, Main Building Office247, P.O.Box910, No.20 Xueyuan Road,Haidian District,Beijing, Beijing, 100083, China, YANG, Zhi, Research Institute of Petroleum Exploration & Development, PetroChina, Beijing, 100083, China and WANG, Lan, Petroleum Geology, RIPED, PetroChina, No. 20 Xueyuan Rd., Haidian District, Beijing, 100083, China
A series of paleolakes developed in Miocene in northwestern China, and the sediments of inland lakes in the plateau are easily affected by climate fluctuations. The stromatolite with typical stacked laminas and shading layers can effectively record the information of climate oscillation. It is of great significance for the study of lacustrine stromatolites, which can be used to analyze paleogeography and paleoclimate, uplift of Qinghai-Tibet Plateau, hydrocarbon source rock, oil and gas reservoir and potential of conventional and unconventional resources. The main lithologic types of Miocene are marl, stromatolite limestone and algal reef limestone. Stromatolites are rich in various types, including wave-shaped, cone-shaped, columnar and their combination, which can be classified into the following three types: dome stromatolites, columnar stromatolites and layered (wave-like) stromatolites.
It is found that two development periods of stromatolites can be distinguished longitudinally in the coring section. The corresponding thickness from bottom to top is 2-3m and 1-2m.The sedimentary environments of each stage are mainly littoral shallow lake and semi-deep lake. The stromatolite may be exposed periodically, and there are more silty continental clasts in the same deposition period, which is supposed to be formed in the sedimentary environment of mixed rocks. When the lake level rises, the lacustrine water deepens, and the stromatolite limestone is transformed into marl, forming a lacustrine transgressive systems tract(TST).
The significance of petroleum geology lies in the development characteristics and scale of oil and gas reservoir as a guide to oil and gas exploration. Stromatolite limestone, reef limestone and clastic mixed sediments can form interlayer dissolved pores, fractures and intragranular dissolved pores. For example, the porosity in Qaidam basin is 0.6 ~ 7.1%, the buried depth is 2500 ~ 4000m, the porosity in Sichuan basin is 0.2 ~ 1.3%, and the buried depth is 1400 ~ 3200m. The tight oil ~shale oil reservoir is developed in these kind of strata.
Keywords: Stromatolite limestone, sedimentary microfacies, unconventional oil and gas, tight oil reservoir, petroleum geology
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