深海甲烷电化学原位长期监测技术及其在海洋环境调查和天然气水合物勘探中的意义

深海溶解甲烷浓度数据连续获取的方法技术,对于海洋环境和天然气水合物开发过程中甲烷扩散作用及通量的动态监测,具有重要的科学意义和实际应用价值。本文较详细地介绍了依据"海水脱气、气体样品定量输入、电化学高精度检测"技术思路,采用"增压排液整机系统控制的海水循环、减压稳流、气液分离、烃类组分高精度检测技术改进"方法,研发"深海甲烷电化学原位长期监测技术"的关键环节和技术方法。结合原位传感器在胶州湾港口为期94天底水长期监测实验获取的数据成果,对原位传感器的技术性能、数据质量、地质效果进行了研究评价。结果表明:(1)原位传感器量程甲烷指标达到0.01～10 000 nmol/L,灵敏度达到0.01 nmol/L,对烃类组分检测具有较好的稳定性和选择性;(2)监测水域溶解甲烷数值范围19.01～106.87 nmol/L,正常甲烷背景32.41 nmol/L,局部异常甲烷背景80.60 nmol/L,资料显示异常与污水排放过程对海水环境污染有关;(3)实测甲烷数据成果地球化学特征与胶州湾海域海水环境以往调查研究成果符合,证明了实测数据的客观性和科学性;(4)海试监测试验成果证明,原位传感器测试性能可靠、结构设计合理、设计思路科学,基本具备了海洋科学调查中对海水甲烷浓度数据获取的能力,在未来海洋天然气水合物开发过程中对甲烷扩散作用的动态监测及深海甲烷浓度通量的长期监测中,具有实际应用价值和科学意义。

Deep sea methane electrochemical in-situ long-term monitoring technology and its significance in the ocean environmental investigation and gas hydrate exploration

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.