松辽盆地南部深层致密砂岩气储层形成机制及成藏主控因素

Formation Mechanism and the Main Controlling Factors of Deep Tight Sandstone Gas Reservoir in Southern Songliao Basin

为了加快松辽盆地南部(简称松南)深层致密砂岩气勘探开发进程,开展致密砂岩储层形成机制及成藏主控因素研究。通过对松南深层致密砂岩的分析,根据致密砂岩岩性组合特征将已发现的深层致密气类型划分为稳定厚层砂型、砂泥互层型、泥包砂型3种类型,储层物性普遍差,孔隙度多小于6%,渗透率主体<0.10×10^(-3)μm^(2),属于特低孔、特低渗储层。通过对松南典型致密储层矿物成分与微观特征的分析发现,致密砂岩有效储层形成主要受3个方面因素控制:一是早成岩期发育绿泥石包壳,有效抑制成岩中后期粒间钙质胶结、硅质胶结的发生,保护原生残余粒间孔隙;二是富火山岩岩屑溶蚀形成次生孔隙;三是生烃增压产生大量微裂缝,改善储层渗流特征。在此基础上总结出松南致密砂岩气成藏控制因素,即充足气源提供物质基础、斜坡古沟谷与断裂控砂、次生溶蚀与微裂缝控储、断裂活动与稳定盖层控富。

In order to accelerate the exploration and development process of deep tight sandstone gas in the southern Songliao basin,the formation mechanism of tight sandstone reservoir and the main controlling factors of reservoir formation are studied.At present,the discovered deep tight gas can be divided into three types:Stable thick sandstone,sandstone-mudstone interbedding,and muddy wrapped sandstone according to the petrological characteristics of tight sandstone.The physical properties of the reservoir are generally poor,the main porosity is below 6%,and the main permeability is less than 0.10×10^(-3)μm^(2),which belong to ultra-low porosity and ultra-low permeability reservoir.Based on the mineral composition and microscopic characteristics of typical tight reservoirs,it is found that the formation of effective reservoirs of tight sandstone is mainly controlled by three factors:First,chlorite enclaves are developed in the early diagenetic stage,which effectively inhibit the occurrence of intergranular calcareous cementation and siliceous cementation during the middle and late diagenesis,and protect the original residual intergranular pores;Second,secondary pores are formed by the dissolution of volcanic rock debris;Third,hydrocarbon generation pressurization produces a large number of micro fractures,which improves the seepage characteristics of the reservoir.The controlling factors of tight sandstone gas reservoir formation are summarized as followings,the sufficient gas source,the sandbody controlled by slope paleo-valley and fault,the reservoir controlled by secondary dissolution and microfracture,the enrichment controlled by fault activity and stable cap rock.