Study On Heterogeneity Of Coal Reservoirs In Fukang Mining Area On The Southern Margin Of Junggar Basin

Taking Fukang coal reservoir in the southeastern margin of Junggar Basin as the research object,this paper selects coal samples from different coal fields?CS,ShaGou,Baiyanghe,FK?and different main coal seams?39,41,42,44?in the mining area,based on borehole data analysis,experimental testing and theoretical reference.The spatial distribution of coal reservoirs and the vertical distribution characteristics of material composition are studied.It is clear that the trend of coal seam thickness is thinner in the West and thicker in the east.The variation coefficient of coal seam thickness in each section of the plane increases gradually from west to east.Vertical heterogeneity is stable;burial depth is deep on both sides of the East and west,shallow in the middle;macroscopic coal and rock types are dominated by semi-bright coal and semi-dark coal;the distribution trend of micro-coal and rock components in plane is that vitrinite is high in the East and west,low in the middle,inertinite is low in the East and west,high in the middle,the crustal group gradually decreases from west to east,and there is no uniform change rule in vertical coal seams;in plane,vitrinite is not uniform.The non-variation coefficient of inertinite and crustal groups is strong,and the variation coefficient of micro-coal and rock components increases first and then decreases along the vertical direction.The distribution characteristics of coal quality are as follows:water content is higher in the West and lower in the east,mainly low ash coal,volatile matter is higher in the East and west,and lower in the middle;water variation coefficient is lower in the plane,and heterogeneity is weaker;ashes and volatile matter heterogeneity increases gradually from west to east;water,ash and volatile matter heterogeneity decreases gradually in the vertical direction;Ro,Max increases gradually from west to east,and distributes vertically.Gradually increasing,the coefficient of variation in plane is smaller,the heterogeneity is weaker,vertical,the coefficient of variation is higher in shallow part and lower in deep part.The pore characteristics,permeability,gas-bearing and heterogeneity of coal reservoir are characterized in detail.It is revealed that the porosities show a trend of low in the West and high in the east,and increase first and then decrease in the vertical direction;the porosities show a trend of low in the West and high in the East in the heterogeneity plane,with little change in the vertical direction;the pore develops from micropore to macropore,mainly transitional pore and macropore,with good connectivity.On the permeability plane,the distribution trend is low in the West and high in the east;on the whole,the permeability of the main vertical coal seams decreases gradually from top to bottom;and the heterogeneity increases gradually from west to east.The adsorbability of coal reservoir increases gradually along the vertical direction.The average methane concentration and carbon dioxide concentration were 78.10%and 15.46%respectively.The heterogeneity characteristics were similar,and the coefficient of variation was higher in Shagou well field,while the overall heterogeneity was weaker in other areas.Combining with the structural characteristics,sedimentary evolution,coal seam burning and high concentration H₂S in the study area,this paper reveals the control mechanism of geological structure,coal-forming environment,coal seam burning and high concentration H₂S on the spatial distribution,metamorphism degree,pore characteristics,permeability and gas-bearing heterogeneity of coal reservoirs.The syncline structure in the area is most favorable for the enrichment of CBM;the migration of coal accumulating center results in the heterogeneity of coal seam thickness and ash content,the filling capacity of minerals in pore decreases gradually,and the sealing ability of reservoir roof and floor increases;coal seam burning results in the increase of ash content in shallow seam and the replacement of CO₂ with CH₄,which reduces the concentration,increases the pore and fracture,and forms water reservoir,which is beneficial to deep seam.Secondary biogas is enriched,and the mineral composition filled in H₂S dissolution pore enlarges the gas storage space.The research results of this paper have theoretical and practical significance for well location selection and drainage horizon determination of CBM wells under complex reservoir conditions in Fukang mining area.