School of Earth Resources,China University of Geosciences(Wuhan),Wuhan ,China

In order to understand fluid drainage characteristics and controlling factors of multi-layer drainage in the CBM well,taking multi-layer drainage wells of the CBM in Zhengcun in the southern Qinshui Basin as the research object，through systematic analysis of multi-layer drainage wells about characteristics of drainage of gas,water and pulverized coal,we found influencing characteristics of the casing pressure,the flowing bottom hole pressures of No.3 coal reservoir and rate of its exposure.Firstly,the results show that deepening pump to No.15 coal reservoir will cause a certain impact on the fluid output in multi-layer drainage wells.Secondly,when casing pressure dropp in the early phase,decreasing rate of casing pressure should be controlled in 0.001 0～0.001 2 MPa/d.When the casing pressure drop or dump down 0.2 MPa in the later period,trends of producing gas will become falling from rising;when it goes up or jumps over 0.2 MPa,trends of producing gas will be changed from falling to increasing.Furthermore,No.3 coal reservoir’s exposure is not harmful definitely.The casing pressure is controlled above 0.2 MPa when No.3 coal reservoir is exposing,which can effectively resolve the questions that exposure of No.3 coal reservoir result in the gas output falling.At the same time,when the casing pressure is controlled in more than 0.2 MPa,exposing No.3 coal reservoir is contributed to increase multi-layer drainage wells gas production.