Logging Evaluation Of Geological Factors And Productivity Analysis Of CBM Wells In South Shizhuang Block

In this paper,taking No.3 coal reservoir of South Shizhuang Block in Qinshui Basin as object,the CBM in No.3 coal reservoir is rich and of commercial exploitation value.However,the heterogeneity of No.3 coal seam roof and floor,gas content and coal industry group is obvious,resulting in bigger difference on gas production for various coal-bed gas wells.Thus,it is vital to do further research on geological factors affecting productivity for latest development.The application of well logging data,combined with the experimental data of coal core,evaluates the geological factors,including coal seam host rocks,coal seam industrial components and coal gas content.Furthermore,multiple linear regression is applied to analysis how those factor have an effect on coalbed methane production.Results are as following:(1)The thickness of No.3 coal seam in South Shizhuang Block is 4.45~7.68 m,and the average thickness is 6.35 m.The depth mostly varies from 600 to 800 m,showing deeper depth from southeast to northwest,and the spatial distribution of No.3 coal seam is sloping from southeast to northwest,which is consistent with the tectonic background of the study area.(2)The average mudstone content,porosity and permeability of host rocks of No.3 coal in South Shizhuang Block are evaluated by the logging data.The average clay content of its host rocks is between 28%~60%,and is higher in west and low in east.The clay content of roof and floor is generally below 35% in eastern region,while between 40%~55% in the western region.The average porosity of roof and floor of No.3 coal is 3%~10%,which is greater than 7% in the eastern region and less than 6% in the western region,demonstrating higher in east and low in west.The average permeability of No.3 coal seam roof and floor is 0~0.7m D,showing higher permeability in east and lower in west.(3)There exists a good correlation between ash content and density log data of No.3 coal in study area,and so is fixed carbon with ash,volatile matter.The industrial composition of No.3 coal seam is assessed by density logging data.Results show that the content of ash,fixed carbon,volatile matter content and moisture in No.3 coal is 10%~20%,60%~80%,10%~16%,and 0%~2%,respectively.(4)The multiple linear regression equation betweem gas content and coal seam density,resistivity,gamma,buried depth of No.3 coal seam is built by multiple linear regression method to clarify the distribution of gas content of No.3 coal seam.On the whole,the gas content of No.3 coal seam in the North block of South Shizhuang Block is higher than that of the South,which is higher in the west than in the east.(5)The quantity of high-yield wells of No.3 coal seam in South Shizhuang Block is less,while that of stripper wells is much.Considering geological factors,it is proved by multiple linear regression fitting that No.3 coal gas production of South Shizhuang Block is mainly affected by the gas content,the average clay content of host rocks and ash content of coal.Favorable gas production areas in South Shizhuang Block are primarily located from Hu Jia Zhuang to Shan Tai Mountain area.(3)There is a good correlation between ash content and density log data of No.3 coal seam in South Shizhuang Block,and there is a good correlation between the fixed carbon and ash,and there is a good correlation between the fixed carbon and Volatile matter.The industrial composition of No.3 coal seam is evaluated by density logging data.The ash content of No.3 coal seam is 10%~20%,the fixed carbon content is 60%~80%,the volatile matter content is 10%~16%,and the moisture content is 0%~2%.(4)The multiple linear regression equation betweem gas content and coal seam density,resistivity,gamma,buried depth of No.3 coal seam is established by multiple linear regression method,and the distribution of gas content of No.3 coal seam is evaluated.On the whole,the gas content of No.3 coal seam in the North block of South Shizhuang Block is higher than that of the South and that of the west is higher than that of the east.(5)The high production CBM wells of No.3 seam in South Shizhuang Block are less and less production wells are much.In the geological factors,through multiple linear regression fitting,No.3 coal seam gas production of South Shizhuang Block is mainly affected by the gas content,the average of coal seam roof and floor clay content,ash content of coal seam.Gas production favorable areas of South Shizhuang Block are mainly located from Hu Jia Zhuang to Shan Tai Mountain area.