海洋底水原位探测技术与中国南海天然气水合物勘探

In-situ detection of ocean floor seawater and gas hydrate exploration in the South China Sea

在分析研究国内外海洋底水原位探测技术的前提下,详细阐述了自主研发的"海水溶解气甲烷原位探测技术成果"的研发思路、关键技术和与国外技术的区别;结合该技术在我国南海北部水合物赋存区获得海洋底水原位甲烷测试数据以及现有分层海水技术在南海北部表层海水和台西南盆地底层海水中甲烷测试数据,进行了水合物勘探中分层海水甲烷指标地球化学特征和不同海水测量方法技术在天然气水合物勘探中指示作用的研究和评价,旨在为天然气水合物中海水地球化学勘探方法的选择和发展方向提供参考依据。结果表明:(1)表层海水溶解气甲烷异常在区域水合物远景区中具有10~50nmol·L^(-1)的绝对甲烷浓度和面积较大(上千km^2)的区域地球化学特征;(2)底层海水甲烷异常背景值一般具有100nmol·L^(-1)以上的绝对甲烷浓度和面积较确定的局部地球化学异常特征;(3)海洋底水原位甲烷地球化学异常数据在水合物赋存区上的异常具有300~800nmol·L^(-1)的绝对甲烷浓度并具有高衬度异常特征。勘探技术成果显示:(1)常规技术和CTD技术获取的表层海水异常能够筛选水合物勘探远景区;(2)底水原位技术和台湾的岩心钻探技术(core top water)获取的底水地球化学异常与地下烃类聚集体渗漏相关,并有以生物成因气为主的同位素特征,因此该异常能够显示与水合物相关的甲烷渗漏地,为水合物赋存区段的识别提供依据。海水原位地球化学勘探技术在水合物海水地球化学勘探中具有广阔的应用前景。

Based on the analysis of in-situ detection technology of ocean floor seawater in China and abroad, this article introduces a self-developed product used in the in-situ measurement of water-soluble methane, and elaborates on the research idea, key technical points and differences from technology used abroad. We have collected a large amount of data of water-soluble methane in the north of the South China Sea, including in the surface and bottom seawaters, and irvsitu exploratory data by our own product. Aimed at providing a reference for the geochemical prospecting of marine gas hydrate, we have compared the geochemical characteristics of stratified seawater-mainly about methane concentration, analyzed different seawater detection technologies and evaluated their significance when used as important indicators in gas hydrate exploration. The results show that： （1） there is a medium level methane concentration of about 10 - 50 nmol · L-1 and a large area of methane geochemical anomaly （〉1000 km2） of surface seawater in the gas hydrate prospect areas; （2） the bottom seawater has a certain regional methane geochemical anomaly and the methane anomaly background value is above 100 nmol · L-1 ; and （3） the in-situ detection of bottom seawater has an extra-high level methane concentration of about 300 - 800 nmol · L-1 in the hydrate bearing area. The achievements of the exploration technologies in fluid geochemistry reveal that.. （1） the methane anomaly obtained from surface seawater by the conventional techniques and CTD are helpful for finding the exploration prospect areas of gas hydrate; and （2） the methane anomaly of bottom seawater detected by in-situ online and core top seawater has a strong correlation with hydrocarbon seepage below the seafloor, and the isotopic characteristics indicate that we can seek out and identify methane seepage zone related to gas hydrate through biogenic methane. We believe the in-situ geochemical exploration technology has a promising prospect of application in finding marine gas hydrate.