Improved In-Situ Detection Technology For Dissolved Methane In The Ocean And Long-Term Monitoring Of Bottom Water

In marine fluid geochemistry,the hot scientific issues and technical requirements involved in the high-precision detection of dissolved methane in-situ by ocean bottom water are mainly reflected in two aspects.First,the dynamic detection of ocean greenhouse gas(including methane)values.Through the measured values and distribution of active methane emissions,the locations of methane leaks and submarine cold springs are calibrated to provide data support for research on marine environmental protection and the relationship between cold springs and hydrates.Second,dynamic monitoring of trace methane leakage in sea water near drilling in the development of marine hydrates.Through the changes in the value of methane in seawater,we understand the effect of solid-state methane expansion and gasification during the development of hydrates,and discover that dissolved methane geochemical anomalies in seawater can provide data support for the development of hydrate safety and seawater geochemical characteristics.The testing and monitoring technologies for methane and other hydrocarbons in seawater are classified into the category of fluid geochemistry.Compared with traditional shipborne CTD and laboratory fluid geochemistry methods,both domestic and foreign scientific research results show that methane in-situ testing technology equipped with sensor equipment is more real,accurate,fast,and accurate than the data obtained by conventional CTD methods.It is an inevitable trend for the development of marine fluid geochemistry,and the national high-tech plan has given a high degree of attention for a long time.In 2014,under the support of the “12th Five-Year Plan” National 863 Program,China University of Geosciences(Beijing)undertook the research task of “Dissolving methane in situ sensing technology for ocean bottom water”.The paper completed the following work:(1)Developed a low-power pressurization and drainage device for long-term monitoring of the internal and external seawater demand in deep sea high-pressure environments.(2)Forhigh-precision long-term detection and data acquisition of seawater dissolved gas samples,gas-liquid separation and gas sample detection devices were improved and perfected to ensure continuous and correct detection of methane concentrations in the dissolved gas in seawater samples.(3)Research on deep-sea environmental testing,performance indicators testing,and in-situ long-term monitoring tests of ocean bottom water in Jiaozhou Bay was conducted for the “in situ methane sensor” research and development.For the applicability of the in-situ sensor to complex sea conditions,the accuracy,stability,and practicality of the results of the dissolved methane indicators in seawater were tested and evaluated.The results of the thesis prove that the design idea of the in-situ sensor is scientific and reasonable,and it basically has the ability to acquire the seawater methane concentration data in the marine scientific survey.In the future,the dynamic monitoring of methane diffusion during the development of marine gas hydrates and the long-term monitoring of deep-sea methane concentration flux have practical application value and scientific significance.