Controlling Factors Of Productivity Difference Of Coalbed Methane Wells In Eastern Yunnan And Western Guizhou

The coalbed methane(CBM)resources are abundant in eastern Yunnan and western Guizhou,but large-scale commercial development has not yet been achieved.High production wells are mainly distributed in the Yangmeishu syncline and the Agong syncline in the western Guizhou.The production of single wells in eastern Yunnan has not been able to achieve breakthroughs in industrial gas flow.In view of this,the geological conditions of CBM development in eastern Yunnan and western Guizhou were analyzed,the influencing factors of CBM productivity were discussed,the fundamental reason for CBM productivity differences were revealed,and the high productive pattern of CBM wells under the cooperative control of geology and engineering was established.The innovation findings of this thesis were summarized as follows.Firstly,a geophysical identification method for coal body structure was established,and the geological control factors for the abnormal fracture of the coal body structure in Laochang anticline were revealed.Based on the coal seam logging data and drilling coring data of the development wells,four conventional logging curves(GR,DEN,DT and CNL)were selected,the first principal component was extracted by principal component analysis,the coal seam gangue and the interference information in the logging data were eliminated,and the geophysical identification method of coal body structure was established.With the increase of coal seam thickness,the proportion of type I coal(primary undeformed coal and cataclastic coal)in the main coal seam of Laochang anticline development wells showed a decreasing trend of power function.Overall,the distribution characteristics of coal body structure in the main coal seam of Laochang anticline were the result of the combined effects of the coal thickness,goaf,tectonic type and tectonic stress field.Secondly,the concept and inversion model of the initial permeability after stimulation and the permeability before gas production were proposed for the first time to characterize the effect of reservoir stimulation and drainage of CBM wells,and the development technology of CBM wells was optimized.In this thesis,the pressure drawdown well test analysis method was introduced into the field of CBM drainage,and the inversion model of coal reservoir dynamic permeability in the saturated water single-phase flow stage was established based on the assumption that the water production in the saturated water single-phase flow stage is constant for five consecutive days.The average permeability in the first5 days of initial drainage stage was defined as initial permeability after stimulation,and the average permeability in the first 5 days of gas production was defined as the permeability before gas production.In order to ensure that CBM wells can obtain commercial development gas flow,the initial permeability after stimulation should be greater than 2.4m D.For this purpose,the volume of the fracturing fluid per meter should not be less than220m~3/m and the volume of fracturing sand per meter should not be less than 14m~3/m during hydraulic fracturing.Finally,a high productive pattern of CBM wells under the cooperative control of geology and engineering was established,and the reasons for the low production of CBM wells in eastern Yunnan were revealed.By using grey correlation analysis method,the gas saturation and permeability before gas production were extracted as the main controlling factors that affected the productivity of CBM wells.Based on this,the high productive pattern of CBM wells under the cooperative control of geology and engineering was proposed.The gas saturation of high production wells should be greater than 60%,and the permeability before gas production should be greater than 0.7m D.The gas saturation of the middle production wells should be greater than 40%,and the permeability before gas production was 0.3-0.7m D.The permeability before gas production of low production wells was less than 0.3m D.The buried depth of coal seam floor in Enhong syncline was more than1000m,and the coal body structure of Laochang anticline was abnormally broken,leading to the permeability before gas production of other development wells in eastern Yunnan was less than 0.09m D,except well YW-04(0.119m D),which was the fundamental reason for low production of CBM wells in eastern Yunnan.There are 71 figures,25 tables and 203 references in this thesis.