天然气水合物系统特征及其对我国水合物勘查的启示

Characteristics of Gas Hydrate System and Its Enlightenment to Gas Hydrate Exploration in China

油气资源在能源结构中具有举足轻重的作用,其成因机制及勘探思路已发展出了完善的系统理论--含油气系统理论,而天然气水合物作为潜在替代清洁能源,其勘探理论尚处于探索阶段。借鉴含油气系统理论,注重与常规油气成藏的差异性分析,在系统分析全球已发现天然气水合物主要研究区的天然气水合物特征基础上,从气体来源、气体运移通道、有利储层等方面对天然气水合物成藏机理进行了系统梳理,以探究天然气水合物系统特征。提出天然气水合物系统应包括气源、储层和天然气水合物稳定带3个基本要素以及气体生成-运移过程和天然气水合物形成过程2个基本作用;冻土带内气体来源以热解气为主,海洋环境中则以生物气或热解气和生物气的混合气为主;气体运移通道主要为流体底辟、气烟囱、大尺度断层、裂缝、滑塌构造及高渗透性地层等;天然气水合物储层在冻土带以砂岩为主,在海域则以黏土质粉沙及粉沙质黏土为主;综合全球各区域天然气水合物成藏特征,提出了9种类型天然气水合物系统,同时以我国神狐海域天然气水合物系统为例总结出了天然气水合物系统成藏事件表。

Oil and gas resources play an important role in the energy structure.The theory of Petroleum System,has been established for hydrocarbon genetic mechanism and exploration.For a potential alternative clean energy source,the exploration of gas hydrate is still in the exploratory stage.Drawing lessons from the theory of Petroleum System and focusing on the analysis of the differences between gas hydrate and conventional oil and gas,this study systematically analyses the characteristics of the main hydrate study areas in the world.Moreover,it systematically combs the mechanism of gas hydrate accumulantion from the aspects of gas source,gas migration pathway and favorable reservoir,explores the characteristics of gas hydrate system.This study suggests that gas hydrate system should include three basic elements:gas source,reservoir and gas hydrate stability zone,as well as two basic functions:gas generation and migration and gas hydrate formation process.The gas sources in the permafrost zone are mainly thermogenic gas,while the gas sources in the marine environment are mainly biological or mixed gas.Gas migration pathways in hydrates include fluid diapirs,gas chimneys,large-scale faults,fractures,slump structures and high permeability formations,etc.The lithology of hydrate reservoir is mainly sandstone in permafrost zone,and clayey silt or silty clay in the marine environment.Finally,this study proposes 9 types of gas hydrate systems based on comprehensive characteristics of gas hydrate accumulation in various regions of the world,Taking gas hydrate system in the Shenhu area for example,the study summarizes accumulation events of gas hydrate system.