Study progress of permeability dynamic variation in drainage process of coalbed methane well

in the drainage process of the caled methane wel.the dynamic variation of the permeabiliy would determine the migration and cutput of the coalbedmnethane and woud be the key factor to conrol the production capacityof the coalbed metrane well n the drainage process.an analysis was conducted on the dynamic variation factors aff cted to the permeatility the dynanic vaiation law of the pemeablity and other aspects.The paper summarized the general understanding and new progress on the dynanic variation of the permeability at home and abroad and pointed out the problems existed in thestudy proces and thelatedevelopment tendency.The effective stess.cal matix shrinkage and Kinkenberg effect were mainly affeced to the coalbed metiane well inthe drainage pro.es and could cause the permeatiliy to genesally have an asymmetric U type variaton with reduction frst and then rising. /n combinaton with the unitary emphasis acion stage neglected,bias thery to the model hanged and othe problems existed in the study proc.ss the paper held that in a further conbination with the actual drainage data to fine the diferent action stage of each ifluence facto to stess the anal ysis on the efifctive permeatilit rate and the relevant permeability variation law affected to the gas and water capacity an to improve the dynanic seepage process ofthe reservoir in dinension could provide the rliable theoretical support to the fine and quantitative drainage control and would be the late study emphasis.