含气流体运移与天然气水合物成藏

Relationship Between Gas-Bearing Fluids Migration and Accumulation of Natural Gas Hydrate

含气流体运移是影响天然气水合物成藏的重要因素,包括流体运移方式、运移通道类型、运移效能等。基于全球典型海域天然气水合物勘探研究结果,围绕含气流体运移这一重要因素,系统回顾和总结了底辟构造、断层及裂隙和渗透层对天然气水合物形成与分布的影响。研究结果表明,以对流形式的运移是流体有效的运移方式,有利于烃类气体聚集及水合物成藏。已知水合物富集区内含气流体运移通道都不以单一形式存在,而是多种运移通道共同作用,呈复合型运移通道形式。在通道类型上,底辟构造、断层及裂隙、渗透层等都属于聚集型高通量流体运移通道类型,但这种通道类型与高饱和度、富集型天然气水合物藏并不存在一一对应的关系,其还与运移效能密切相关。因此有必要开展重点区域的流体运移的分析,揭示流体运移通道的展布以及运移规模,以达到更为准确预测和描述水合物藏的目的,并为水合物钻探站位部署提供有力依据。

Gas-bearing fluids migration, mainly including fluid migration pattern, migration pathway, and migration efficiency, is one of the important factors affecting natural gas hydrate accumulation. Based on the progress of global marine gas hydrate explorations and researches, focusing on gas-bearing fluids mi- gration, we mainly summarize several migration pathways, such as diapir structure, fault/fracture and permeable layer to understand their effect or impact on the formation and distribution of gas hydrate. Re- search results show that fluid convection is an effective migration pattern, which is beneficial for the hy- drocarbon gas accumulation and gas hydrate formation and concentration. Almost all known-natural gas hydrate occurrence zones develop multi-type migration pathways, not single-type pathway, and individual hydrate occurrence is commonly affected by various gas-bearing fluids migration pathways. In terms of pathway types, diapir structures, fault/fractures and permeable layers all belong to focused high-flux mi- gration pathway, conductive for hydrate formation and accumulation. However this focused high-flux mi- gration pathway type does not mean the existence of high saturation and enrichment of gas hydrate. The focused high-flux migration pathway does not have a one-to-one correlation with high saturation and en- richment of gas hydrate. As high saturation and enrichment of gas hydrate is still closely related to migra- tion efficiency. Therefore, it is necessary to analyze the gas-bearing fluids migration in key hydrate occur- rence areas, and then reveal the distribution of fluid migration pathways and the size of migration flux. With these analyses, the predictions and descriptions of hydrates would be more accurate, and they could also be reasons for site selections of marine gas hydrates.