Reservoir Physical Properties And Superimposed Accumulation Model Of Coal Measure Gas In Central-south Qinshui Basin

Taking the coal measure gas in Central-South Qinshui Basin as the study object,the substance composition,the source rocks geochemical property,the porosity-permeability,the gas bearing potential of coal measure gas reservoir were characterized and the test analysis of fluid inclusion,water chemistry and isotope were conducted.The main outcomes of this investigation are summarized as follows: the reservoir combination types of coal measure gas,coalbed methane and shale gas and the favorable horizons of coal seam and roof-floor mudstone in study area were defined combining the burial history,thermal evolutionary history,hydrocarbon generating history and hydrocarbon expulsion history models of coal measures;the secondary hydrocarbon generation characteristic and contribution were analyzed.In addition,the physical property,the heterogeneity,the anisotropism and their control mechanisms of low porosity-permeability coal measure gas reservoirs were systematic studied;the integrative classification scheme of pore-fracture network dividing pores into obstruction,semi-connected and connected type was established according to the adsorption-desorption curve shape of low temperature liquid nitrogen experiment,the pore distribution feature of mercury injection porosimetry,the T₂ spectrum of low field nuclear magnetic resonance and the spatial distribution characteristics swept by micro-CT;the methods of identifying the water formation based on water chemistry,stable isotope,129 I age and 14 C age of coal measures were established,the age of coal measures water was estimated and corrected in to 1.51²0.61 Ma,which reveals that the water in coal measures at the present stage is the mixture of a litter paleo sedimentary water and massive modern meteoric water;moreover,the coal measures reservoir type in study area is deemed to adjusting gas reservoir,which was based on the tectonic evolution of coal measure gas reservoir,the commonly higher nitrogen content and lower methane carbon isotope in coalbed methane composition,and the source and age of coal measure water;the formation reservoir period of coal measure gas is Late-Jurassic to Early-Cretaceous and Eearly-Cretaceous to Cenozoic respectively,which was deduced by the simulation of thermal evolution and the homogenization temperature of fluid inclusion;finally,the accumulation process of coal measure gas was simulated and the “source-reservoir adjacent type” superimposed accumulation model of coalbed methane and shale gas was constructed according to the burial history,thermal evolutionary history,hydrocarbon generating history and hydrocarbon expulsion history and the source and age of coal measure water;which reveals the accumulation mechanism of coal measure gas reservoir controlled by the “sedimentary-thermal event-tectonics-hydrodynamic force”.Achievements in this paper possess major theoretical significance and actual value for revealing the accumulation mechanism,guiding the co-exploration and co-exploitation of coal measure gas.