Geochemistry of borehole cutting shale and natural gas accumulation in the deepwater area of the Zhujiang River Mouth-Qi
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Geochemistry of borehole cutting shale and natural gas accumulation in the deepwater area of the Zhujiang River MouthQiongdongnan Basin in the northern South China Sea GAO Gang1*, ZHANG Gongcheng2, CHEN Guo1, GANG Wenzhe1, SHEN Huailei2, ZHAO Ke3 1 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum (Beijing), Beijing
102249, China 2 Research Institute, CNOOC, Beijing 100020, China 3 Geophysical Exploration Research Institute of Huabei Oilfield Company, Renqiu 062552, China
Received 4 October 2016; accepted 19 May 2017 ©The Chinese Society of Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
The Qiongdongnan Basin and Zhujiang River (Pearl River) Mouth Basin, important petroliferous basins in the northern South China Sea, contain abundant oil and gas resource. In this study, on basis of discussing impact of oil-base mud on TOC content and Rock-Eval parameters of cutting shale samples, the authors did comprehensive analysis of source rock quality, thermal evolution and control effect of source rock in gas accumulation of the Qiongdongnan and the Zhujiang River Mouth Basins. The contrast analysis of TOC contents and Rock-Eval parameters before and after extraction for cutting shale samples indicates that except for a weaker impact on Rock-Eval parameter S2, oil-base mud has certain impact on Rock-Eval S1, Tmax and TOC contents. When concerning oil-base mud influence on source rock geochemistry parameters, the shales in the Yacheng/Enping, Lingshui/Zhuhai and Sanya/Zhuhai Formations have mainly Type II and III organic matter with better gas potential and oil potential. The thermal evolution analysis suggests that the depth interval of the oil window is between 3 000 m and 5 000 m. Source rocks in the deepwater area have generated abundant gas mainly due to the late stage of the oil window and the high-supper mature stage. Gas reservoir formation condition analysis made clear that the source rock is the primary factor and fault is a necessary condition for gas accumulation. Spatial coupling of source, fault and reservoir is essential for gas accumulation and the inside of hydrocarbon-generating sag is future potential gas exploration area. Key words: cutting shale, organic geochemistry, gas accumulation, deepwater area, Qiongdongnan Basin, Zhujiang River Mouth Basin Citation: Gao Gang, Zhang Gongcheng, Chen Guo, Gang Wenzhe, Shen Huailei, Zhao Ke. 2018. Geochemistry of borehole cutting shale and natural gas accumulation in the deepwater area of the Zhujiang River Mouth-Qiongdongnan Basin in the northern South China Sea. Acta Oceanologica Sinica, 37(2): 44–53, doi: 10.1007/s13131-018-1151-2
1 Introduction The Zhujiang River (Pearl River) Mouth and the Qiongdongnan Basins are important gas-bearing basins in the northern South China Sea, with a great deal of oil and gas having been discovered (Zhu et al., 2008; He et al., 2008; Zhang et al., 2009, 2010). A great number of existing research achievements for the structure, sedimentology, reservoir,
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