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天然气水合物分解释放的甲烷向上逸散与孔隙水中硫酸盐发生甲烷厌氧氧化—硫酸盐还原反应。深海沉积物有机质氧化也可驱动硫酸盐还原反应。针对甲烷渗漏背景下硫酸盐还原的不同驱动模式,对沉积物中总有机碳、总硫、酸可挥发性硫(AVS)、δ34Spyrite及孔隙水中的SO2-4等进行了测试,结果表明:1总硫在390cm、610~890cm处为0.3%~0.7%,此含量高于相邻层位;2AVS含量在表层较低,于610~868cm区间缓增至565μmol/g,898cm处AVS含量激增至9 315μmol/g;3δ34Spyrite值由浅至深逐渐增大,由-44.4‰升至17.9‰,后回落到12.6‰;490~900cm区间的SO2-4含量逐渐下降,大于900cm则SO2-4含量变化不大。研究结果显示:研究区存在分别由有机质氧化和甲烷厌氧氧化驱动的2种硫酸盐还原模式;硫酸盐甲烷转换带以总硫、δ34Spyrite等指标为判定因素可分为上、下2部分;研究区SMI深度约为900cm,这一较浅的SMI预示着研究区深部可能存在天然气藏或天然气水合物藏;结合微生物研究结果发现,研究区地球化学特征和微生物的分布存在耦合现象,这对进一步研究甲烷水合物潜在区的生物地球化学循环具有一定的意义。
Upward Methane Release from Gas Hydrate Decomposition and Methane Anaerobic Oxidation to Sulfate Reduction in Sulfate in Pore Water. Organic matter oxidation in deep sea sediments can also drive sulfate reduction. According to different driving modes of sulfate reduction in the background of methane seepage, total organic carbon, total sulfur, acid volatile sulfur (AVS), δ34Spyrite and SO2-4 in pore water were tested. The results show that: The content of 2AVS in the surface layer is lower, it increases slowly to 565μmol / g in the range of 610 ~ 868cm, and the content of AVS in 898cm increases rapidly in the range of 390cm and 0.3 ~ 0.7% To 9 315μmol / g. The value of 3δ34Spyrite gradually increased from shallow to deep, from -44.4 ‰ to 17.9 ‰ and then to 12.6 ‰. The content of SO2-4 decreased gradually from 490-900 cm, while that of SO2-4 increased from 900-900 cm Not big. The results show that there are two sulfate reduction modes driven by organic matter oxidation and methane anaerobic oxidation in the study area, respectively. The sulfate conversion zone can be divided into upper and lower fractions with the determination factors of total sulfur and δ34Spyrite. The shallow SMI is about 900 cm deep. This shallow SMI indicates that there may be natural gas reservoirs or natural gas hydrate reservoirs deep in the study area. According to the results of microbiological research, there is a coupling phenomenon between geochemical characteristics and microbial distribution in the study area, It is of significance to study the biogeochemical cycle of methane hydrate potential area.