南海沉积物中烃类气体(酸解烃)特征及其成因与来源

Geochemical Characteristics of Hydrocarbon Gases and Their Origin from the Sediments of the South China Sea

烃类气体是形成天然气和天然气水合物的物质基础,可通过顶空气、吸附烃和酸解烃等方法来探测。南海473个站位767件沉积物样品的酸解烃分析结果表明,甲烷含量为0.8~22153.6μl/kg,平均为335.8μl/kg,并可分成台西南—东沙、笔架南、琼东南—西沙海槽、中建南—中业北、万安—南薇西和南沙海槽等6大异常区,其中南沙海槽是异常最强烈的地区,台西南盆地次之。154件甲烷样品的碳同位素分析结果表明,其δ13C1值为-101.7‰^-24.4‰(PDB标准,下同),平均为-44.5‰,其中南沙海槽的δ13C1值明显偏低,为-101.7‰^-71.4‰,应是微生物气或是以微生物气为主的混合气,而南海其他地区的δ13C1值相对较高,为-51.0‰^-24.4‰,明显属于热解气。

Hydrocarbon gases from sediments are the resources to form natural gas and gas hydrate, which could be measured by headspace gas, absorbed gas, and ＂extraction＂ gas （which released by acid treatment of the sediments）. Total 767 samples of sediments from 473 stations were collected from the South China Sea, and were treated with acid to determine the concentrations of hydrocarbon gases. The methane concentrations range from 0. 8 to 22,153.6 μl/kg with averagely 335.8 μl/kg, and six anomalous areas of higher methane concentrations are subdivided in the South China Sea, including the Taixinan Basin and the Dongsha Islands, the Bijianan Basin, the Qiongdongnan Basin and the Xisha Trough, the Zhongjiannan Basin and Zhongyebei Basin, the Wan＇an Basin and Nanweixi Basin, and the Nansha Trough. However, the Nansha Trough is of the highest methane concentrations, and the Taixinan Basin is the secondly, respectively. Total 154 samples were been determined for carbon isotopic composition, whose δ^13C values of methane range from - 101.7‰ to -24. 4‰ with averagely - 44. 5‰（PDB）. Furthermore, lower δ^13C values of methane （ from - 101.7‰ to - 71.4‰） are observed in the Nansha Trough, which seem to be mainly microbial gas or mixed gas, whereas there are much more thermogenic gas in the other areas of the South China Sea, whose higher δ^13C values （from - 51. 0‰ to - 24. 4‰） are discovered, respectively.