海底甲烷渗漏区孔隙水及矿物组分变化数值模拟

Numerical simulation on variations of pore water chemistry and mineral composition induced by the submarine methane leakage

海底甲烷的渗漏(通常是底部天然气水合物的分解引起的)往往会伴随着浅表层沉积物中一系列的地球化学变化。文章以南海九龙甲烷礁地区为研究区,建立了一维垂直柱状模型,利用数值模拟方法定量分析甲烷渗漏背景下海底沉积层中孔隙水及矿物组分的变化。结果表明:HCO3-和HS-浓度在垂向上随深度的增加先增大后减小,在SMI(sulfate-methane interface)处浓度达到最大值;SMI的深度会随着底部甲烷泄露通量的增大而变浅;SMI界面处AOM-SR(Anaerobic oxidation of methane coupled to sulphate reduction)反应最为强烈,在界面附近生成了方解石和黄铁矿等自生矿物。该研究结果对于研究天然气水合物相关自生矿物的形成特征、海底地球化学异常探测与水合物勘探等具有重要的理论意义。

The submarine leakage of methane（usually due to the decomposition of the bottom gas hydrate） is often accompanied by a series geochemical variation in the shallow sediments. Based on the field measured data from Jiulong Methane Reef, Northern South China Sea, a 1-D vertical column model was built to represent the seabed sediment layer, and the variation in geochemical characteristics caused by methane leakage was analyzed using the numerical simulation method.The simulation results show that HCO3-and HS-concentrations increased first and then decreased with the depth. The depth of SMI decreased（close to the seabed） with increasing leakage flux of methane from deep sediments. Anaerobic oxidation of methane coupled to sulphate reduction（AOM-SR） was the most intensive at the SMI, where authigenic minerals, such as calcite and pyrite formed. The results of this study have an important theoretical significance for the further study of the formation characteristics of gas hydrate related minerals, and the combination of geochemical anomalies detection with the exploration of gas hydrate.