非常规天然气成藏体系

Unconventional natural gas accumulation system

有别于常规天然气,非常规天然气在成藏条件、富集机理、分布模式、预测方法及勘探应用技术等方面都具有明显的特殊性。从成藏系统的角度分析非常规天然气成藏过程和主控因素,对于非常规天然气评价和预测具有重要的意义。为此,基于成藏机理和分布模式,将非常规天然气成藏体系划分为页岩气、煤层气、致密碳酸盐岩气、致密砂岩气、水溶气及天然气水合物共6种主要类型;按照成藏体系“元素—功能—结构”的研究思路和“气源岩—输导体系—成藏分布”的组配关系,将非常规天然气成藏体系划分为6类“源—位结构”关系,分析了除天然气水合物以外的其余5种类型非常规天然气成藏体系的特点。研究结果表明:①页岩气、煤层气、致密碳酸盐岩气均属于源内型非常规天然气成藏体系,具有生供气能力强、无输导体系、缺乏二次运移、生储盖一体、原地成藏等结构特点;②致密砂岩气和水溶气属于源缘型非常规天然气成藏体系,具有生气类型多样、邻层近源聚集、储层内部运移、就近成藏富集等结构特点;③盆地演化、沉积环境和后期构造运动控制了非常规天然气成藏体系的类型。结论认为,我国南方古生界海相沉积有利于页岩气和致密碳酸盐岩气成藏体系的形成;南、北方上古生界海陆过渡相沉积则有利于煤层气、页岩气及致密砂岩气成藏体系的发育;中、东部中新生代深水陆相沉积有利于深层致密砂岩气和页岩气成藏体系,浅水陆相盆地则对煤层气、致密砂岩气及页岩气成藏体系的形成更为有利;水溶气则广泛见于新生代富有机质浅层区或邻近气源岩的高压储层中。

Different from the conventional,unconventional natural gas accumulations have obvious particularity in reservoir forming conditions,enrichment mechanism,distribution modes,prediction method and exploration technology.Analyzing the reservoir forming process and main controlling factors of unconventional natural gas accumulations under guide of the hydrocarbon accumulation system theory is of great significance for unconventional natural gas reservoir evaluation and prediction.Based on the reservoir forming mechanism and distribution mode,the unconventional natural gas accumulation systems are divided into six types,including shale gas,coalbed methane,tight carbonate gas,tight sandstone gas,water-soluble gas and gas hydrate.According to the concept of"element–function–structure"in the hydrocarbon accumulation system theory and the relationship of"gas source rock–migration system–accumulations distribution",the unconventional gas accumulation system is divided into six"source–location"types.The characteristics of the other five types of unconventional gas accumulation systems except gas hydrate are analyzed.The following results were obtained.(1)Shale gas,coalbed methane and tight carbonate gas belong to an intra-source type unconventional gas accumulation system,characterized by intense gas supply capacity,the lack of either a transport system or secondary migration,integration of source,reservoir and caprock,in-situ accumulation,and so on;(2)Tight sandstone gas and water-soluble gas belong to a source marginal type unconventional gas accumulation system,characterized by diverse gas origin,near source accumulation in adjacent layers of source rock,internal migration within reservoirs,and so on.(3)Basin tectonic evolution,sedimentary environment and late tectonic events control the types of unconventional gas accumulation systems:The Paleozoic marine sediments in South China are conducive to the formation of shale gas and tight carbonate gas accumulation systems;The marine–continental transitional facies deposits of Upper Paleozoic distributed in the South and North China are conducive to the development of coalbed methane,shale gas and tight sandstone gas accumulation systems;In the Middle and East China,Mesozoic–Cenozoic deep-water continental deposits are more conducive to the deep tight sandstone gas and shale gas accumulation systems,while shallow water continental basins are more conducive to the formation of coalbed methane,tight sandstone gas and shale gas accumulation systems.Water-soluble gas is widely found in the Cenozoic shallow-buried areas rich in organic matter or high-pressure reservoirs adjacent to gas source rocks.