Research On Plugging Removal Technology Of CBM Well By Hydraulic Jet Washing In Qiyuan Mine Of Shanxi Province

Coalbed methane(CBM),commonly known as coalbed "gas",is an unconventional natural gas energy that coexists with coal.As the reservoir of CBM,the coal commonly has low mechanical strength and lose structure,and thus large amount of pulverized coals are easy to formed near the wellbore during the production of CBM,which may cause blockage of the wellbore of CBM well.The wellbore blockage by the pulverized coals is one of the key influcnes for gas production during the exploitaition of CBM.Targeting on study of the blockage of pulverized coals in the CBM development of Qiyuan Coal Mine in Jinzhong City,Shanxi Province,this thesis did experimental and in-field investigations to study the resevoir geological and mechanical characteristics,analyzed the cleaning techniques for CBM wells in the study area.The plug removal technology provids corresponding technical support for the development of CBM in the study area.The main achivements are summarized as follows:(1)The coiled tubing hydraulic jet well washing and plugging removal technology has the advantages of simple and convenient construction procedure,concentrated jet energy and large treatment depth.(2)The conical straight nozzle with contraction Angle of 30° and length-todiameter ratio of 4 is suitable for hydraulic jet well cleaning operation.This kind of nozzle has simple processing technology and concentrates jet energy.Compared with the domestic nozzle and the United States nozzle,the former is more suitable for single short time construction operations,the latter is more suitable for multi-layer or multi-segment long time continuous construction operations.(3)The rotating speed of the hydraulic jet well cleaning tool and the impact force of the jet on the casing wall will be affected by the change of pump pressure.With the increase of pump pressure,both of them will increase.However,when the pump pressure remains unchanged,the jet impact pressure will gradually weaken with the increase of the injection distance.(4)Rotating jet processing capacity is mainly affected by jet driving pressure,blockage strength and cleaning action time.Under the permission of ground equipment and operating pipe strings,increasing the displacement and pressure of the ground pump is conducive to improving the cleaning unblocking effect and treatment depth.(5)This process has been applied in Wells 1,3 and 8 successively.Through drainage observation,single well CBM production has been greatly improved compared with that before construction.The coiled tubing hydraulic jet well washing technology has a good effect on plugging of CBM Wells in Qiyuan coal mining area.