南海东北部陆坡天然气水合物富集特征及成因模式

南海东北部陆坡具有良好的天然气水合物(以下简称水合物)成藏条件,其水合物资源的成因模式明显不同于2007年在神狐海域钻探发现的分散型水合物成矿区。为探讨前者的成藏特征与成因模式,利用钻探区的地震、测井、现场钻探取心及测试分析等资料进行了综合研究,以期加深对南海东北部陆坡水合物富集规律的认识。研究结果表明:(1)在纵向上,该区发育浅、中、深3套水合物层,构成既相对独立又有一定成因联系的成藏系统,区内存在扩散型、渗漏型和复合型3种成因模式的水合物矿藏;(2)扩散型水合物呈层状分布在稳定域底部,其底界与海底反射界面(BSR)分布吻合;(3)渗漏型水合物呈块状、脉状等形式充填在沉积物裂隙或裂缝中,在稳定域不同部位形成多个矿体;(4)复合型水合物矿藏兼具扩散型和渗漏型水合物的成藏特征,在稳定域底部发育扩散型水合物矿层,而在稳定域上部发育渗漏型水合物体,共同构成复式成藏系统。结论认为:南海东北部陆坡是目前中国水合物资源最为丰富、成藏地质条件最为复杂的成矿区之一。

Accumulation characteristics and genetic models of natural gas hydrate reservoirs in the NE slope of the South China Sea

The northeastern slope of South China Sea has favorable conditions for the accumulation of natural gas hydrate (NGH), and its genetic model of NGH is significantly different from the diffusion-type NGH reservoir discovered in the Shenhu sea area in 2007. The accumulation characteristics and genetic models of NGH in the NE slope of the South China Sea are investigated based on a comprehensive analysis of the seismic, well logging, core and testing data of this area . According to the results, three NGH reservoirs (shallow, medium and deep) are vertically developed in this area, and their accumulation systems are relatively independent, but genetically related. In this area, there are three genetic models of NGH reservoirs, i.e., diffusive model, seeping model and complex model. In the diffusive model, NGH presents lamellar distribution at the bottom of the stability zone, and its bottom boundary is coincident with the distribution of bottom simulating reflector (BSR). In the seeping model, NGH fills sediment cracks or fractures in the form of block and vein, and constitutes multiple mineral ores in different parts of the stability zone. The complex NGH reservoir has the accumulation characteristics of both diffusive and seeping NGH reservoirs. In this model, diffusive NGH is developed at the bottom of the stability zone, seeping NGH is developed in the upper part of the stability zone, and they jointly constitute a complex accumulation system. To sum up, the northeastern slope of the South China Sea is one of the areas with the richest and most complex NGH reservoirs in China.