海底泥火山特征及其与天然气水合物的成矿关系

海底泥火山与其周缘的天然气水合物矿体存在着紧密的关联,近年来成为深水天然气水合物勘探的重要对象之一。从泥火山形态及内部结构、喷发物岩石学特征、泥火山周缘热异常特征等3个方面分析认为,泥火山外部形态多样,依据泥火山顶部的形状可将其分为3种:圆锥型、平坦型和塌陷型;海底泥火山喷发物岩石学特征与半深海-深海沉积具有显著差异,喷出物组成混杂,且来源多样;泥火山作为一种流体逸散构造,其分布常常与构造断裂、底辟(泥底辟、盐底辟)的分布一致,且往往引起周缘地层热异常,从而影响水合物的形成和赋存。将与泥底辟相关的泥火山形成过程划分为龟背阶段、刺穿阶段、生长(喷发)阶段和塌陷阶段4个阶段。在前述基础上分析了泥火山与天然气水合物的成矿关系,指出泥火山对天然气水合物非均质性分布特征的控制作用、泥火山的形成与天然气水合物动态成藏、泥火山控制下的天然气水合物与常规油气资源共生机制将会是今后天然气天然气水合物研究的重点方向。

SUBMARINE MUD VOLCANO AND ITS RELATIONSHIP WITH GAS HYDRATE

The coexistence of submarine mud volcanoes and their periphery gas hydrates illustrates the close relationship between them. Submarine mud volcanoes have been regarded as important exploration targets for deep-water natural gas hydrate in recent years. This paper deals with deep-water mud volcanoes from three aspects including morphology and internal structure, petrology characteristics of eruptions and ambient thermal anomaly. The mud volcanoes may vary in shape, and three kinds can be classified according to the shape of mud volcano crest:cone type, pie type and collapse type. Petrology of mud volcanic eruptions, of which composition is complex due to diverse sources, is significantly different to the abyssal sedimentary environment. The distribution of mud volcanoes, as a fluid dissipation structure, is commonly associated with faults, diapirs (mud diapirs or salt diapirs). The mud volcanoes often cause geothermal anomaly, which would affect the formation and occurrence of gas hydrate. The formation process of mud volcano related to a mud diaper could be divided into four stages:turtle back, pierce, eruption and collapse. Based upon the discussion above, the relationship between mud volcano and natural gas hydrate is analyzed. The results of the study suggest that the controlling effect of mud volcano over gas hydrate heterogeneity distribution, gas hydrate dynamic accumulation and its relationship with mud volcanoes, the coexistence of gas hydrate and conventional hydrocarbon controlled by mud volcanoes will become the main directions in future natural gas hydrate research.