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

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.