Study On Gas Controlling Mechanism And Coupled Accumulation Of Deep Coal Measure Gases In Qinshui Basin

Coal measures deposited at the unique marine–terrigenous depositional environment is characterized by lithological diversity and cyclic superposition which is served as the potential basics for coupled accumulation and co-exploration/development of coal measures gases(CMGs).Thus,more innovative efforts are needed to carry out for having insight into the coupled accumulation mechanism of deep CMGs.The main aims of this thesis include three aspects: comprehensively determining the development characteristics and geological controls of the transport system within coal measures gases reservoirs(CMGRs);studying on CMGs transport mechanism and occurrence behaviors considering with coupled geological factors;and revealing the coupled accumulation mechanism of deep CMGs and the geological selection processes of effective gas-bearing sections.Hence,this thesis selected Taiyuan–Shanxi formations as the target coal measures and taken coupled accumulation mechanism of CMGs and geological selection processes of effective gas–bearing sections as the core scientific issues.By using data investigations,field explorations,experimental tests,numerical simulations,demonstration project analyses,and theoretical sublimations,systematic researches were conducted.Followings are the main achievements and conclusions:(1)Basic geological conditions for CMGs coupled accumulation were fully evaluated.The kerogen types of the source rocks in target coal measures are predominantly with type III and their thermal evolution degree is mainly in the high– to over–mature stages,dominantly in the thermogenic generation stage.Total organic matter content(TOC)is a key parameter in determining hydrocarbon generation potential.Coals as a typical aggregated organic matter material with high TOC contents have stronger hydrocarbon generation potential and better physical characteristics,and thus play a decisive role for CMGs coupled accumulation.The transport system is significantly controlled by discrepant organic–inorganic fabric within CMGRs.Based on the pore connectivity for different scale pores/fracture systems,full–scale transport/pore system(TPV)of CMGRs were subdivided into immovable pore system(IPV)and movable pore system(MPV),and the latter significantly determines CMGRs' permeability.(2)Gas controlling mechanisms and geological control effects of CMGRs were deeply explained.The variable pore compressibility model was proposed for effectively describing transport system geological responses of deep CMGRs.A comprehensive transmission model considering different factors was also constructed for expounding CMGs transmission mechanism.Gas content is one of the most important parameters determining the potential resources and recovery of CMGs.The in–situ gas contents of various CMGRs were estimated by both direct and indirect methods based on the canister desorption results and methane sorption isotherms.Further,the geological controls on in–situ gas content were analyzed,and the performance behaviors of CMGs were then clarified in detail.Additionally,the gas controlling mechanisms and geological controls on CMGRs were proposed based on related results.(3)Geological evolution process and its effect on coupled accumulation CMGs were analyzed in detail.The whole geological evolution process of the target CMGs included five periods: source rocks–reservoir system superimposed matching period,primary hydrocarbon generation period,generation stagnation–reservoirs adjustment period,secondary hydrocarbon generation period,and readjustment and finalization period,accompanied by two key periods for CMGs coupled accumulation.Moreover,the transport system evolution models were established which were then applied to quantitatively determine the geological evolution characteristics of CMGRs' transport capacities.Based on these findings,CMGs coupled accumulation mechanisms were clearly analyzed.(4)Coupled accumulation assemblages and their geological selection processes were identified in detail.The key indexes for determining spatially effective gas–bearing sections within coupled accumulation CMGs were identified,and the dominant coupled accumulation assemblages were then divided into shale gas dominated coupled accumulation type,CBM dominated coupled accumulation type,and multiple CMGs coupled accumulation type.It is clear that the effective gas-bearing sections need the appropriate combination of source,reservoir and cap: coal development directly controls the distribution of effective gas–bearing section,burial conditions restrict the possibility of an effective gas-bearing section,and both organic-inorganic fabric and physical characteristics limit the potential of effective gas–bearing sections.It was proved that various CMGs' accumulations have the same gas source and the effective gas–bearing section distribution performed differentiated geological selection responses during the geological evolution process.There are 226 figures,19 tables and 300 references in this thesis.