白云凹陷天然气水合物成藏条件

针对珠江口盆地白云凹陷，应用地质勘探法、速度法及地震似海底反射（BSR）法对该凹陷的天然气水合物沉积进行了预测研究。结果认为，该凹陷具备有利于天然气水合物成藏的水深、温度、压力条件及配套地质条件：①发育两套主要的烃源岩（文昌组和恩平组），有机碳含量和镜质体反射率值都较高，以生气为主，生烃潜力极大，为天然气水合物成藏提供了充足的气源；②运移条件优越，有两类运移通道，一是沟通气源的断层，二是底辟作用所形成的通道；③运移模式有三种，一是单一断层运移，二是单一底辟构造运移，三是先底辟构造运移再断层运移。近期的实钻也在该凹陷首次发现了两类天然气水合物沉积：一是有地震BSR标志的天然气水合物，二是无BSR标志的天然气水合物。该凹陷不但存在单BSR天然气水合物沉积，而且还存在双BSR天然气水合物沉积。该凹陷天然气水合物沉积层厚度一般为250～450 m。初步预测认为，白云凹陷的天然气水合物资源潜力极大。

CONDITIONS OF ACCUMULATION OF GAS HYDRATE IN BAIYUN SAG

Various methods such as geologic exploration, velocity and seismic BSR are used to study and predict the gas hydrate deposits in Baiyun sag of the Pearl River Mouth Basin. It is revealed that this sag has favorable conditions of gas hydrate accumulations, including water depth, temperature, pressure, and geologic conditions. ① Two sets of major source rocks, including Wenchang and Enping formations, are developed in this sag. These source rocks are relatively high both in TOC and in vitrinite reflectance (Ro), are gas prone, and has huge gas generating potential, thus provide abundant gas source for accumulation of gas hydrate. ② The hydrocarbon migration conditions are favorable. There are two kinds of migration pathways, i.e., gas source linking faults and diapires. ③ There are three migration patterns, including single migration along faults, single migration along diapires, and complex migration first along diapires and then along faults. Recent drilling has discovered, for the first time, two kinds of gas hydrate deposits in this sag, i.e., gas hydrate with seismic BSR marks and that without seismic BSR marks. Both single BSR gas hydrate and double BSR gas hydrate occur in this sag. The thickness of gas hydrate deposits generally ranges from 250 to 450 m in this sag. Preliminary prediction results reveal that the resources potential of gas hydrate is huge in Baiyun sag.