海底甲烷渗漏背景下自生矿物形成控制条件数值模拟研究

发布时间：2018-08-12 18:24

【摘要】：甲烷厌氧氧化反应是海底厌氧沉积物的重要生物地球化学过程,该反应显著地调控着全球甲烷收支平衡,在全球碳、硫循环中发挥着重要作用,同时与甲烷厌氧氧化反应伴生的生物地球化学特征也成为天然气水合物找矿的标志。已有的研究多是针对生物作用和生物能量学对甲烷厌氧氧化反应的控制,缺少综合考虑甲烷厌氧氧化反应、成岩作用和溶质运移来研究海底甲烷渗漏背景下自生矿物的形成。本文依托天然气水合物相关自生矿物形成项目,以南海北部陆坡台西南盆地为研究区,结合研究区的物性参数、生物地球化学条件,采用TOUGHREACT模拟软件,研究海底甲烷渗漏背景下自生矿物形成的控制条件。依据研究区实际物性参数,通过设置不同的模拟方案,研究不同的甲烷泄漏速率、水文地球化学条件情况下,硫酸盐-甲烷界面以及自生矿物形成的时间、空间变化特征。研究发现,甲烷泄漏速率对自生矿物的形成具有显著影响。甲烷泄漏速率越大,硫酸根-甲烷界面越浅,界面处甲烷厌氧氧化反应越剧烈,方解石沉淀量越大,界面处方解石的沉淀主要受控于甲烷厌氧氧化反应;当甲烷泄漏速率比基础方案增大20倍时(7.60×10-2 mmolcm-2 a-1),有文石的沉淀,甲烷泄漏速率越大,文石出现沉淀时间越早,沉淀位置越浅,沉淀量也越大,甲烷泄漏速率是文石生成的主要控制因素;硫酸根离子浓度对铁白云石的沉淀具有显著影响,硫酸根浓度越低,铁白云石的沉淀量越大,当硫酸根离子浓度减小3倍时,铁白云石的沉淀量能增大到3个数量级以上;钙离子浓度主要影响方解石、菱镁矿的沉淀,钙离子浓度比基础方案增大5倍时,方解石沉淀量比基础方案增大了0.16%,钙离子浓度比基础方案减小5倍时,菱镁矿沉淀量比基础方案增大约5个数量级,因此,低钙离子环境有利于菱镁矿沉淀;温度主要是从反应速率和平衡常数两个方面进行控制的,温度升高,奥长石、钾长石、钠蒙脱石、钙蒙脱石、绿泥石的溶解量增加,方解石、菱镁矿、黄铁矿的沉淀量增加。综上所述,在综合考虑生物作用、成岩作用和溶质运移来研究甲烷渗漏背景下自生矿物形成过程中,不同自生碳酸盐岩以及硫化物的形成能够指示不同的沉淀环境,因此在实际工作中结合沉积层矿物沉淀情况能够更好的指示底部存在天然气水合物的可能。
[Abstract]:Methane anaerobic oxidation is an important biogeochemical process of submarine anaerobic sediments, which significantly regulates the balance of global methane budget and plays an important role in the global carbon and sulfur cycle. At the same time, the biogeochemical characteristics associated with the anaerobic oxidation of methane have also become the indicators of gas hydrate prospecting. Most of the previous studies have focused on the control of methane anaerobic oxidation by biological action and bioenergy, and lack of comprehensive consideration of methane anaerobic oxidation, diagenesis and solute migration to study the formation of autogenous minerals under the background of methane leakage. In this paper, based on the natural gas hydrate related autogenic mineral formation project, taking the southwest basin on the northern slope of the South China Sea as the study area, and combining the physical parameters and biogeochemical conditions of the study area, the TOUGHREACT simulation software is used. The control conditions for the formation of autogenous minerals under the background of methane leakage on the sea floor are studied. According to the actual physical parameters of the study area, by setting different simulation schemes, the characteristics of the time and space variation of the sulfate methane interface and the formation of the autogenous minerals under different methane leakage rates and hydrogeochemical conditions are studied. It is found that methane leakage rate has a significant effect on the formation of authigenic minerals. The larger the rate of methane leakage, the shallower the interface between sulfate and methane, the more intense the anaerobic oxidation of methane at the interface, and the larger the amount of calcite precipitation. The calcite precipitation at the interface is mainly controlled by the anaerobic oxidation of methane. When the methane leakage rate is 20 times higher than that of the basic scheme (7.60 脳 10 ~ (-2) mmolcm-2 a ~ (-1), the larger the methane leakage rate is, the earlier the precipitation time is, the lighter the precipitation position is and the larger the precipitation amount is. Methane leakage rate is the main controlling factor for the formation of dolomite, and the concentration of sulfate ion has a significant effect on the precipitation of dolomite. The lower the concentration of sulfate is, the greater the precipitation amount of dolomite is, and when the concentration of sulfate ion decreases by 3 times, The precipitation capacity of dolomite can be increased to more than 3 orders of magnitude, and the calcium ion concentration mainly affects the precipitation of calcite and magnesite, when the calcium ion concentration is 5 times higher than that of the basic scheme. Calcite precipitation is 0.16% higher than that of base scheme. When calcium concentration is 5 times lower than base scheme, magnesite precipitation is increased by about 5 orders of magnitude. Therefore, low calcium ion environment is favorable for magnesite precipitation. The temperature is controlled mainly from two aspects: reaction rate and equilibrium constant. With the increase of temperature, the amount of precipitate of ordoclase, potassium feldspar, sodium montmorillonite, calcium montmorillonite, chlorite, calcite, magnesite and pyrite increase. In conclusion, the formation of different authigenic carbonate rocks and sulphides can indicate different precipitation environments in the study of the formation of authigenic minerals in the context of methane leakage, taking into account biological processes, diagenesis and solute migration, Therefore, the combination of sedimentary mineral precipitation in practical work can better indicate the existence of natural gas hydrate at the bottom.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P736.3

【相似文献】