Coal Reservoir Sedimentary Characteristics Of Shanxi Formation In Southern Qinshui Basin

Based on the field outcrop observation of the Permian Shanxi Formation in Fucheng area, according to the xishan area, by using the methods of sample analysis,slice observation, particle size analysis, analyzing drilling and logging data of the study area, and so on, the sedimentary characteristics of coal reservoir, sedimentary evolution and the relationship between sedimentary microfacies and coalbed methane content,sedimentary microfacies and coal thickness in the southern Qinshui basin were studied.The results show that:(1) The Shanxi Formation in the Qinshui basin is mainly fluvial-dominated delta deposits affected by two big river of northeast and southwest. The sedimentary facies can be further divided into two subfacies( deltaic plain subfacies and delta front subfacies) and seven microfacies(branch channel microfacies, onshore natural levee microfacies, swamp microfacies, underwater distributary channel microfacies,underwater natural levee microfacies, branching mouth bars microfacies and tributary bay microfacies).(2)Accompanying with the sea regression occurred from northwest to southeast during the sedimentary period of Shanxi Formation in the research area, sedimentary environment transforms from delta front to delta plain sedimentary. The evolutions rules of sedimentary microfacies are via branch debouch bar microfaciesâ†'underwater distributary channel microfaciesâ†'underwater natural levee microfaciesâ†'distributary bay microfaciesâ†'swamp microfaciesâ†'branch channelâ†'onshore natural levee microfaciesâ†'swamp microfacie; On the plane, from the the northwest and southwest of the basin to the center of the basin, the evolution of the sedimentary environment is form upper delta plain,interdistributary bay to lower delta plain.(3)The sedimentary microfacies of the roof and floor of 3# coal seam most is distributary bay microfacies; The coal facies types is given priority to overlying water forest swamp and wet forest swamp facies, followed by low level swamp(reed) and dry forest swamp facies; the relationship between thickness of coal seam and sedimentary environment of shanxi formation is relatively close : along with the change of sedimentary environment, from the the northwest and southwest of the basin to thecenter of the basin, coal thickness increases gradually; so is the relationship between sedimentary environment and coalbed methane content. And sedimentary environment decides to coal seam coal facies, coal facies control the ability of coal rock to produce and save coalbed methane.In this paper, the research is helpful to reveal coal accumulating environment and coalbed methane accumulation rule of Shanxi Formation of Permian in the Qinshui basin and guide the reasonable development and utilization of coal and CBM resources in the Qinshui basin.