南海北部神狐海域GMGS1和GMGS3钻探区天然气水合物运聚成藏的差异性

为了探究南海北部陆坡神狐海域GMGS1与GMGS3天然气水合物(以下简称水合物)钻探区的钻探结果存在差异的原因,在分析区域地质背景的基础上,基于高分辨率准3D地震资料,结合实际钻探结果,从"水合物运聚体系"的角度,对上述两个钻探区含气流体运移疏导通道类型、发育演化特点及其对水合物成藏的控制和影响等方面进行了对比研究。结果表明:(1)两个钻探区相距甚近且地质背景相同,但含气流体运移通道类型、组合样式、发育演化特点和运移效能却存在着差异,使得二者气体来源不同;(2)GMGS1钻探区以气烟囱模糊带和中小尺度断层作为主要运聚通道系统,缺乏沟通古近系烃源岩与浅层水合物稳定域的沟源断裂,深部热成因气运移效能低,水合物气源以浅层生物气占绝对优势;(3)GMGS3钻探区靠近白云凹陷东部泥底辟及断层发育区,通道运移效能较高,源自深部古近系烃源岩的热成因气能够通过疑似泥底辟、气烟囱模糊带及断层垂向运移至水合物稳定域,热成因气对其水合物成藏的贡献要大于前者。结论认为,含气流体运聚通道的差异可能是使得上述两个钻探区水合物气体来源及运聚富集程度等出现较大差异的重要原因。

Differences in natural gas hydrate migration and accumulation between GMGS1 and GMGS3 drilling areas in the Shenhu area,northern South China Sea

In order to investigate why the drilling results of GMGS1 and GMGS3 natural gas hydrate (hereinafter "hydrate" for short) drilling areas in the Shenhu area, northern South China Sea, are so different, we analyzed their regional geological settings, and from the perspective of "hydrate migration and accumulation system", then comparatively analyzed these two drilling areas in terms of the types of gas bearing fluid migration and conduction pathway, the development and evolution characteristics and their control and effect on hydrate accumulation based on high resolution quasi-3D seismic data, combined with practical drilling results. And the following research results were obtained. First, GMGS1 and GMGS3 drilling areas are geographically close with the same geological settings, but they are different in the types of gas-bearing fluid migration pathway, the combination style, the development and evolution characteristics and the migration efficiency, so their gas sources are different. Second, in the GMGS1 drilling area, gas chimney fuzzy zones and middle-small faults act as the main migration and accumulation pathways, and there is no any big fault that connects the Paleogene hydrocarbon source rocks with the hydrate stability zone in the shallow layers, so the migration efficiency of deep-seated thermogenic gas is low and the shallow biogenic gas is absolutely the predominant gas source of hydrate. Third, the GMGS3 drilling area is adjacent to the mud diapir and fault development zones in the eastern Baiyun sag, so the efficiency of migration pathway is higher and the thermogenic gas derived from the deep Paleogene source rocks can migrate vertically to the hydrate stability zone through suspected mud diapirs, gas chimney fuzzy zones and faults. Obviously, the contribution of thermogenic gas to hydrate accumulation in the GMGS3 drilling area is greater than that in the GMGS1 drilling area. In conclusion, the difference of gas bearing fluid migration and accumulation pathway may be an important reason for the obvious difference of gas source and migration and accumulation degree of hydrate between GMGS1 and GMGS3 drilling areas.