MULTIPHASE HYDROCARBONS FROM CARBONIFEROUS RESERVOIR ROCKS AND THEIR ORIGIN IN THE DONGHETANG AREA, WESTERN TABEI UPLIFT, TARIM BASIN, NW CHINA
Zhicheng Lei1,2,3, Huaimin Xu1, Tongwen Jiang4, Zhongchao Li2, Jingwen Li1, Weilu Li5, Yunbin Xiong2, Songze Li2,3, Junwei Zhao1
1Department of Geoscience, China University of Petroleum-Beijing, Beijing 102249, China
2Research Institute of Petroleum Exploration and Development, Zhongyuan Oilfield Company, Sinopec, Puang, Henan, 457300, China
3Post-Doctor Research Center, Zhongyuan Oilfield Company, Sinopec, Puyang, Henan, 457300, China
4Research Institute of Petroleum Exploration and Development, Tarim Oilfield Company, PetroChina, Korla 841000, China
5National Marine Data and Information Service, Tianjing 30071, China
Keywords: Multiple phase hydrocarbons, water washing, biodegradation, bacterial sulfate reduction, gas washing, evaporative fractionation, volcanic degassing, Tarim Basin
Abstract
The Carboniferous Donghe sandstone reservoir is the most important target in the Tabei Uplift of the Tarim Basin, which contains a range of hydrocarbon types, including bitumen, heavy oil, condensate oil, light oil, crude oil, and hydrocarbon gas, and has high contents of CO2 and N2. The origin of multiple phase hydrocarbons from Carboniferous reservoir rocks in the Donghetang area, Western Tabei Uplift, is documented in this paper based on integral analysis of the geochemistry, pyrolysis, and carbon isotopes of the bulk composition and light composition hydrocarbons. Oil-source correlations determined that the paleoreservoir hydrocarbons that formed from the Permian to the Triassic derived from the Lower Ordovician (O1) source rocks and that those of the present-day reservoir that formed in the Neogene derived from Middle-Upper Ordovician (O2-3) source rocks. During the uplift episode lasting from the Permian to the Triassic, the hydrocarbons in the entire paleoreservoir underwent water washing, biodegradation, and bacterial sulfate reduction (BSR), resulting in residual bitumen, heavy oil, H2S, and pyrites in the paleoreservoir. The high CO2 and N2 contents originated from volcanic degassing due to volcanic activity from the Permian to the Early Triassic. The present-day reservoirs underwent gas washing and evaporative fractionation due to natural gas charging that originated from oil cracking and kerogen degradation in the deeper reservoirs; this resulted in fractionation and formed condensate oil and light oil with a high wax content in the residual crude oil. Based on this research, it was concluded that the diverse hydrocarbon phases in the Donghetang area were primarily attributed to water washing, biodegradation, BSR, volcanic degassing, gas washing, and evaporative fractionation.
DOI: 10.15372/RGG2019037
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