“源-储-输导系统”联控煤系气富集成藏机制——以鄂尔多斯盆地东缘为例

Mechanism of coal measure gas accumulation under integrated control of“source reservoir-transport system”:A case study from east margin of Ordos Basin

煤系气资源丰富,如何系统认识煤系多种非常规天然气富集成藏机制,是实现气藏有效开发的关键。从“源-储-输导系统”时空耦合配置角度,阐明煤系生烃—运聚—成藏的关键过程和主控因素,建立煤系气富集序列,丰富煤系气综合成藏内涵。稳定烃源岩是煤系气富集的基础,沉积微相宏观上控制优势储层展布,储层物性微观上决定成藏有效性,在输导体系影响下动态调整构成煤系综合含气系统。输导系统和储集系统受控于构造、沉积和成岩作用,生烃强度和生烃演化过程直接影响气体运移和聚集,输导系统转换是界定源内滞留和源外富集成藏的关键因素。输导系统转换界面之下,以煤系煤层和页岩内部发育的微纳米孔喉网络作为储集系统,煤系气在其中不运移或短距离运移;界面之上以砂体、裂缝和断层作为输导系统,煤系气就近或远距离运移。在此基础上,提出煤系气综合成藏序列,包括原位滞留型(包括太原组和山西组煤层气及页岩气)、近源充注型(包括山西组和下石盒子组致密气)和远源调整型(包括上石盒子组、石千峰组砂岩气和马家沟组灰岩气)的煤系气综合聚集模式,借此分析了华北地台煤系气富集规律和勘探方向,为煤系多气多层综合开发提供借鉴。

Coal measure gas resources are abundant.Systematical understanding on the mechanism of multiple unconventional natural gases accumulation in coal measures is the key for effective development of gas reserves.From the perspective of the time-space coupling of source rock,reservoir and transport system,this paper clarifies the key processes and controlling factors of coal measure hydrocarbon generation,migration and accumulation,builds the coal measure gas accu-mulation series,and enriches the coal measure gas reservoiring connotation.Stable source rock is the basis of coal measure gas accumulation.Sedimentary microfacies control the distribution of main reservoirs,and physical properties microscopically determine the effectiveness of reservoir.The comprehensive coal measure gas system is formed under the dynamic control of transport system.The transport system and the reservoir system are both influenced by structure,sedimen-tation and rock diagenesis.The hydrocarbon generation intensity and evolution directly affect gas migration and accumulation.The transformation of transport system is the key factor to define the accumulation of inside source kitchen retention and the outside source kitchen accumulation.Below the transfer interface of the transportation system,the micro-nano pore throat network developed in the coal measure source rock is the main gas storage system,and coal measure gases generally do not migrate or migrate in a short distance.Above the interface,sand bodies,fractures and faults can all play a role as the transport system,with gas migrating either nearby or by a long distance.Then,the comprehensive coal measure gas accumulation series,including in-situ retention type(e.g.,coalbed methane and shale gas in the Taiyuan Formation and Shanxi Formation),the close source charging type(e.g.,tight gas of in Shanxi Formation and the Xiashihezi Formation),and the near source adjustment type(e.g.tight gas of Shangshihezi and Shiqianfeng Formation and carbonate gas of Majiagou Formation),are proposed.Based on this,the enrichment law and exploration directions of coal measures on the North China platform are analyzed,providing support for the co-production of multi-gases in multi-layers within coal measures.