Deep sea methane electrochemical in-situ long-term monitoring technology and its significance in the ocean environmental investigation and gas hydrate exploration
1. School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, China 2. No.5 Gold Geological Party of PAP, Xi’an 710100, China; 3. Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou 510075,China 4. Hunan Geo-sun High-Technology Co.,Ltd, Changsha 410208, China 5. School of Geosciences and Info-Physics of Central South University,Changsha 410083, China;
The continuous acquisition of dissolved methane concentration data in the deep sea has important scientific significance and practical application value for dynamic monitoring of marine environment and methane diffusion in gas hydrates development. This paper introduces key technologies of electrochemical in-situ long-term monitoring technology for deep sea methane in detail, which include the technical ideas of "seawater degassing, quantitative injection of gas samples, and high-precision electrochemical detection", the technical method of "sea water circulation controlled by supercharged drainage system, decompressed steady flow, gas-liquid separation, and improvement of high precision detection technology for hydrocarbon components". Based on the long-term monitoring experiment data obtained from bottom water in Jiaozhou Bay during 94 days, the authors studied and evaluated the technical performance, data quality and geological effect of the in-situ sensors. Some conclusions have been reached: (1) In-situ sensor has an index range of 0.01~10 000 nmol/L and sensitivity reaches 0.01 nmol/L. It has good stability and selectivity for the detection of hydrocarbon components; (2) The range of dissolved methane in the monitoring area is 19.01~106.87 nmol/L, the normal methane background is 32.41 nmol/L, and the local anomalous methane background is 80.60 nmol/L. These data show that abnormality is related to sewage discharge and seawater pollution; (3) The results of measured methane data are consistent with those obtained from previous investigation and study of seawater environment in Jiaozhou Bay, which proves that the measured data are objective and scientific; (4) The sea trial monitoring results show that the in-situ sensor is reliable in testing, reasonable in structure design and scientific in design ideas, and it basically has the capability for acquiring seawater methane concentration data in marine scientific investigation. It has practical application value and scientific significance in the dynamic monitoring of methane diffusion and long-term monitoring of deep sea methane concentration during the development of marine gas hydrate in the future.
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