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Productivity mode and control factors of coalbed methane wells:a case from Hancheng region

SHAO Xian-jie1,WANG Cai-feng1,TANG Da-zhen2,SUN Yu-bo1,XU Hao1(1.Department of Petroleum Engineering,Yanshan University,Qinhuangdao 066004,China;2.School of Energy Resources,China University of Geoscience(Beijing),Beijing 100083,China)  
Based on the analysis of coalbed methane(CBM) wells production performance in Hancheng region,three aspects of production characteristics were summarized:the high water yield and long drainage period;the increasing gas yield with the increase of water-output;and the long stable production period.Four productivity modes of CBM wells including eight subclasses were built.Productivity is influenced significantly by coal layer thickness,permeability,gas content and hydrogeological conditions.Interlayer interference seriously affects the production performance of multiple completion wells.The higher the average discharge of pump and the frac sand volumes in fracturing process,the higher the gas yield after putting into production.Productivity of lower fracture pressure gradient well is higher than that of higher pressure gradient.Stress sensitivity takes a key role in yield rising and stable periods.Thus,a reasonable drainage and production method can be divided into four periods.The first is the water-draining and pressure-lowing period,water-output rate can be appropriately increased to get steady descent of dynamic fluid level and formation pressure.The second is the gas yield rising period,water-output rate can be reduced in order to realize gas yield rising steadily.The third is the stable production period.Displacement can be stabilized to spread pressure drop funnel steadily and lengthen stable production period.The fourth is the production decline period,displacement can be controlled properly to slow down gas yield decrease rate.
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