中国近海天然气水合物的研究进展

PROGRESS OF GAS HYDRATE INVESTIGATION IN CHINA OFFSHORE

南海、东海具有形成天然气水合物的良好动力学环境和丰富的烃类气体来源。根据卫星对海面增温异常的观测、底水气体地球化学、标志矿物和流体组成的研究表明 ,南海、东海海底存在强烈的烃流体活动和排气作用 ;南海南北陆坡区海底气体主要由CH4组成 ,前者多为微生物成因气 ,后者多为热解气 ;冲绳海槽热液沉积区的气体 ,主要为CO2 (86 % ) ,其次为CH4、H2 、H2 S(14 % ) ,分别来自岩浆流体及陆源有机质的降解 ,也属热解成因气。地震地球物理的研究主要集中于南海东北部、北部、南部陆坡区和冲绳海槽中南部 ,测线长度还很有限 ,虽然都有BSR标志的发现 ,但质量比较好 ,研究程度也比较高的还只有南海东北部主动陆缘和北部被动陆缘的一些海域。通过沉积物烃含量和热释光的研究 ,南海、东海共获得 6个地球化学异常区。在综合对比物化探、地热等项资料的基础上初步认为 :笔架南 (Ⅰ )、台西南—东沙 (Ⅱ )异常区是寻找水合物的最佳远景区 ;琼东南—西沙海槽(Ⅲ )、中建南—中业北 (Ⅳ )和冲绳海槽南部异常区是寻找水合物和常规油气藏的有利地区 ,但Ⅳ区更有利于寻找油气 ,其余 2区更有利于寻找水合物 ;南沙海域的研究程度总体上比较低 ,但在其中的南沙海槽 ,物化探异常标志均优 ,甲烷含量较其它地区高

In the South China Sea and the East China Sea, there exist favorable dynamic conditions and abundant hydrocarbon sources for forming hydrate. According to the long term observations of anomalously increased sea surface temperature scanned by satellite based thermal infrared, and the investigations of the gas geochemistry of bottom water, the authigenic minerals and the fluid composition, it was concluded that there exist strong degassing and hydrocarbon fluid activities in the submarine. The main composition of submarine gas in the southern and northern continental slopes of the South China Sea is CH 4, mainly biogenic for the southern slope and thermogenic for the northern slope. The gas of hydrothermal sedimentary region of the Okinawa Trough that is a part of the East China Sea, consists of 86% of CO 2 and 14% of CH 4, H 2, and H 2S; CO 2 is possibly from magma fluid and the other components are from decomposition activities of the land organic substance. The seismic geophysical studies were concentrated in northeastern, northern, southern slopes of the South China Sea and the southern Okinawa Trough. BSR marks show up in many places, but only for some areas of the northeast active continental margin and of the north passive continental margin the existence of BSR is rather credible and the investigation work has been done adequately. On the basis of studies of the hydrocarbon gases and the radioactive thermoluminescence in the sediments, the South and the East China Sea are divided into 6 geochemical anomalous regions. By synthetically comparing the geophysical, geochemical and geothermal data, we have preliminarily confirmed that: the Bijia'nan (Ⅰ), the Taixi'nan Dongsha (Ⅱ) anomalous regions are the most optimistically potential regions for gas hydrate formation; the Qiongdongnan Xisha Trough (Ⅲ), the Zhongjiannan Zhongyebei (Ⅳ) regions and the south part of Okinawa Trough (Ⅵ) are favorable for exploring hydrate, oil and gas; the Ⅲ and Ⅵ regions are more favorable for hydrate; the Ⅳ region is more favorable for traditional oil and gas. Generally speaking, the investigation work of Nansha area is far from adequate, but for the Nansha Trough Basin therein, the geophysical and geochemical anomalies are quite good for gas hydrate, which are worthy of further study. For the ODP 184 1144 site in the Taixi'n Dongsha potential region the depth of the gas anomaly and the pore water chlorinity anomaly are consistent with the BSR, which predicts the existence of gas hydrate.