Gas hydrates distribution in the Shenhu area, northern South China Sea: comparisons between the eight drilling sites with gas-hydrate petroleum system

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	Gas hydrates distribution in the Shenhu area, northern South China Sea: comparisons between the eight drilling sites with gas-hydrate petroleum system
	Su, M.; Yang, R.; Wang, H.; Sha, Z.; Liang, J.; Wu, N.; Qiao, S.; Cong, X.
刊名	GEOLOGICA ACTA
	2016
卷号	14 期号:2 页码:79-100
关键词	Gas hydrate Variable distribution Gas-hydrate petroleum system Shenhu area Northern South China Sea
通讯作者	Sha, Z (reprint author), Guangzhou Marine Geol Survey, Guangzhou 510075, Guangdong, Peoples R China. ; Sha, Z (reprint author), China Univ Geosci, Fac Earth Resources, Wuhan 430074, Hubei, Peoples R China.
中文摘要	The results of the first marine gas hydrate drilling expedition of Guangzhou Marine Geological Survey (GMGS-1) in northern continental slope of the South China Sea revealed a variable distribution of gas hydrates in the Shenhu area. In this study, comparisons between the eight sites with gas-hydrate petroleum system were used to analyze and re-examine hydrate potential. In the Shenhu gas hydrate drilling area, all the sites were located in a suitable low-temperature, high-pressure environment. Biogenic and thermogenic gases contributed to the formation of hydrates. Gas chimneys and some small-scale faults (or micro-scale fractures) compose the migration pathways for gas-bearing fluids. Between these sites, there are three key differences: the seafloor temperatures and pressures; geothermal gradient and sedimentary conditions. Variations of seafloor temperatures and pressures related to water depths and geothermal gradient would lead to changes in the thickness of gas hydrate stability zones. Although the lithology and grain size of the sediments were similar, two distinct sedimentary units were identified for the first time through seismic interpretation, analysis of deep-water sedimentary processes, and the Cm pattern (plotted one-percentile and median values from grain-size analyses), implying the heterogeneous sedimentary conditions above Bottom Simulating Reflectors (BSRs). Based on the analyses of forming mechanisms and sedimentary processes, these two fine-grained sedimentary units have different physical properties. Fine-grained turbidites (Unit I) with thin-bedded chaotic reflectors at the bottom acted as the host rocks for hydrates; whereas, fine-grained sediments related to soft-sediment deformation (Unit II) characterized by thick continuous reflectors at the top would serve as regional homogeneous caprocks. Low-flux methane that migrated upwards along chimneys could be enriched preferentially in fine-grained turbidites, resulting in the formation of hydrates within Unit I. However, overlying fine-grained sediments related to soft-sediment deformation would hinder the further migration of gases/fluids, causing the extremely low methane concentration in Unit I. Three of the eight sites with hydrates from recovered core samples were located within sedimentary Unit I, and the other five sites were not. Because, the most significant difference between the eight sites is the nature and type of sedimentary deposits above the BSRs, it is suggested therefore that sedimentary conditions are the crucial factor controlling the formation and occurrence of gas hydrates in the Shenhu gas hydrate drilling area, northern South China Sea.
学科主题	Geology
内容类型	期刊论文
源URL	[http://ir.scsio.ac.cn/handle/344004/15601]
专题	南海海洋研究所_中科院边缘海地质重点实验室
推荐引用方式 GB/T 7714	Su, M.,Yang, R.,Wang, H.,et al. Gas hydrates distribution in the Shenhu area, northern South China Sea: comparisons between the eight drilling sites with gas-hydrate petroleum system[J]. GEOLOGICA ACTA,2016,14(2):79-100.
APA	Su, M..,Yang, R..,Wang, H..,Sha, Z..,Liang, J..,...&Cong, X..(2016).Gas hydrates distribution in the Shenhu area, northern South China Sea: comparisons between the eight drilling sites with gas-hydrate petroleum system.GEOLOGICA ACTA,14(2),79-100.
MLA	Su, M.,et al."Gas hydrates distribution in the Shenhu area, northern South China Sea: comparisons between the eight drilling sites with gas-hydrate petroleum system".GEOLOGICA ACTA 14.2(2016):79-100.