中文摘要：

天然气水合物是一种具有广阔前景的清洁能源资源,但目前对海洋天然气水合物预测方法有多种,利用浅层沉积物孔隙水地球化学示踪沉积层深部天然气水合物的方法,可以为海域天然气水合物前期普查提供一个廉价有效的途径。利用南海北部东沙海域D-5、D-8和D-F站位沉积物孔隙水硫酸根离子、溶解无机碳、钙离子和镁离子在剖面上的分布特征,模拟了3个站位甲烷供给通量及天然气水合物可能的发育特征。计算结果表明,D-5、D-8和D-F站位到达甲烷-硫酸根氧化界面的甲烷通量分别为11.97?10–3mol/(m2·a)、5.98?10–3mol/(m2·a)和26.45?10–3mol/(m2·a),天然气水合物形成的最大温度梯度分别为0.058℃/m、0.020℃/m和0.149℃/m,计算的天然气水合物顶界深度分别为海底之下170~197m、378~386m和79~98m,甲烷通量对天然气水合物顶界影响大,温度对天然气水合物发育顶界影响较小。结合研究区似海底反射层发育特征判断,D-5和D-F站位深部沉积层中可能有天然气水合物,D-8站位应该没有天然气水合物发育。

英文摘要：

Gas hydrate is a potential clean energy resource,but no economic and efficient predication method for marine gas hydrate has been set up yet.The pore water geochemistry data of shallow sediments can be used to trace gas hydrate occurrence in subsurface and might provide a low-cost and efficient way for the preliminary stage of marine gas hydrate investigation.The methane flux has reached the sulfate-methane transition zone and possible occurrences of gas hydrates are simulated using the profiles of sulfate,dissolved inorganic carbon,and calcium and magnesium ions in pore water from cored sediments at sites D-5,D-8and D-F in the Dongsha area,northeastern South China Sea in this study.The calculations show that methane fluxes towards the seafloor at D-5,D-8and D-F are11.97?10-3mol/(m2·a),5.98?10-3mol/(m2·a)and26.45?10-3mol/(m2·a),respectively.And only when the geothermal gradients are less than0.058℃/m,0.020℃/m and0.149℃/m for sites D-5,D-8and D-F,the gas hydrate will occur and the top occurring depths of gas hydrate are calculated to be170-197mbsf,378-386mbsf and79-98mbsf,respectively.Our study also shows that the influence of methane flux on the top occurrence of gas hydrate is significant,but the impact of temperature is slight.By considering the depth of bottom simulation reflector occurring on seismic profiles in the study area,the gas hydrate might only occur at sites D-5and D-F.