Study On Sedimentary Environment Of Shanxi Formation In The Period Of Coal Accumulating Of Zhongyu Coal Mine In Qinshui Basin Based On Seismic Sedimentation Method

The depositional environment before and after coal accumulation controls the spatial distribution of lithology and pore-permeability characteristics before and after formation of coal seams,and also controls the spatial distribution of coal seam thickness and coalbed methane deposition and storage conditions.Formed in the land surface and continental environment of the coal-bearing rock series,the rock facies,lithology lateral changes quickly,The traditional sedimentary facies analysis method based on geologic and drilling data can not solve the problems such as the sedimentary facies of the rock mass in the high frequency sequence and the prediction of the lithology characteristics in the favorable phase zone,And it is very important to study the fine characterization method of sedimentary facies during coal accumulation.Based on the modern sedimentary and high-resolution sequence stratigraphy,this paper introduces the seismic sedimentary interpretation technology into the sedimentary environment of coal-bearing rock series,and the sedimentary microfacies before and after the coal seams of No.2 coal seam of Shanxi Formation in Zhongyu area of Qinshui Basin were studied Using 90 ° phase conversion,stratigraphic sectioning,frequency division processing and seismic attribute interpretation techniques,The sandstone ratio of the sequence stratigraphy before andafter coal accumulation is predicted and reconstructed based on the seismic attribute of the smallest isochronous stratigraphic section,based on the intersection analysis method,the corresponding relationship between the sedimentary microfacies and the sand-land ratio is established,and the sedimentary microfacies such as the diversion channel,the natural embankment,the inter-bay and the flooded basins in the sequence stratigraphy of the Shanxi Formation in the study area are identified.The results show that the sedimentary environment of the No.2 coal seam in Shanxi Formation is the lower delta sedimentary environment,and the area of sand-land ratio of the underwater distributary channel and natural embankment in the lower section of Shanxi group is 0.5-1 and 0.3-0.5 respectively,less than 0.3 for the diversion bay;After the coal accumulation in the upper delta depositional environment,the area of sand-land ratio of the diversion channel and the natural embankment in the upper section of the Shanxi Formation is 0.6-1 and 0.4-0.6respectively,and the flood basin and the peat swamp microfacies are less than 0.4.The sand-land ratio of each microfacies in the upper Shanxi Formation is higher than that in the lower part of Shanxi Formation.The evolution rule of the sedimentary microfacies before and after coal accumulation in the No.2 coal seam in the study area is followed by the underwater distributary channel of the lower delta,underwater natural embankment,underwater diversion bay microfacies,peat swamp microfacies,onshore groundwater microfacies,land on the natural dike phase,flooded basins,peat swamp microfacies.The analysis of the relationship between the sedimentary facies and coal thickness and coal seam gas content before and after coal accumulation shows that the distribution of the sedimentary facies of coal seam 2 in Shanxi Formation has a certain control effect on the spatial distribution characteristics of coal seam thickness The influence of sedimentary facies after coal accumulation is not obvious.There are some control effects on the gas content of coal seams before and after coal accumulation,and the control effect before coal accumulation is more obvious,In general,the gas content of the river and natural embankment is relatively low,and thegas content in the area of the diversion bay,flood basin and swamp microphase is relatively high.