中文摘要：

南海北部陆坡神狐海域是我国海洋天然气水合物勘探开发研究的重点靶区，独特的水合物成藏特征，难以利用当前观测到的沉积速率和流体流动条件对其成藏机理进行解释和量化说明，对其形成演化模式和控制因素尚不明确．本文构建了海洋天然气水合物形成演化过程的动力学模型，模型的主控参量为海底沉积速率和水流速率，以此计算了神狐海域天然气水合物聚集演化过程，并与饱和度的盐度测试值进行对比．最后，在研究神狐海域地质构造活动和水合物成藏动力学基础上建立了神狐天然气水合物形成演化模式．认为神狐海域当前的天然气水合物是在上新世末一更新世早期断裂体系水合物基础上继承演化而来的，神狐海域天然气水合物形成演化具有典型的二元模式．第一阶段水合物形成发生在距今1．5Ma之前构造活动形成的断裂体系中，高达50m／ka的孔隙水流动携带了大量的甲烷进入水合物稳定带，导致了水合物的快速生成，在4万年内形成了饱和度达20％的甲烷水合物；第二阶段发生在1．5Ma以来，泥质粉砂沉积使沉积体渗透率骤减，0．7m／ka的低速率水流使甲烷供给不足，在海底浅层新沉积体中无法生成水合物，仅在水合物稳定带底部有缓慢的水合物继承增长，并因此形成了神狐海域当前观测到的水合物产出特征，而且水合物资源量仍在减少．

英文摘要：

The Shenhu area on the northern continental slope of the South China Sea is considered as a promising target for gas hydrate exploration and exploitation. Its special hydrate occurrence makes it difficult to explain and quantitatively describe its formation mechanism by using the deposition rates and fluid flow conditions at present. Its formation evolution mode and controlling factors are unclear yet. In this paper a dynamic model for the hydrate accumulation is constructed with two controlling parameters, i.e. the sedimentation rate and fluid water flow rate. The model is used to simulate the hydrate accumulation in the Shenhu area and testified with saturation data derived from salinity. Finally, a hydrate formation pattern in the Shenhu area is built based on the investigation of tectonic activities and the dynamics of hydrate accumulation in the area. The model indicates that Shenhu hydrates were developed from the hydrates formed in late tectonic activities during the late Pliocene Epoch-early Pleistocene Epoch. The gas hydrate formation in the Shenhu area has a typical dual pattern. In the first stage the hydrate grew in fractured sediments formed by tectonic activities 1.5 Ma. The water flow rate was up to 50 m/ ka, and abundant methane gas was carried into the hydrate stability zone and led to a rapid hydrate formation. The hydrate saturation went up to 20% in the duration of 40 ka. In the second stage of the following 1.5 Mas, permeability of the sediment reduced sharply due to the sedimentation of clay silts. Fluid flux was 0.7 m/ka and methane supply was inadequate. Thus hydrates could not form in shallow sediments and only grew slowly on the base of the hydrate stability zone, and then formed the feature of hydrate occurrence observed currently in the Shenhu area. And also the resource amount of hydrate continued reducing.