Coupling Analysis Of Depressurization And Gas Production In The Horizontal Well Of The CBM In Dafosi

The depressurization and production is an important means for the development of CBM.With the decrease of reservoir pressure,the adsorbed CH4 in the coal reservoir is transformed into free state,which is transported to the ground through the wellbore.This is the CBM drainage.In this process,people can only adjust the reservoir pressure through the drainaging,so how to make reasonable drainage has become an important work of CBM production capacity.It has certain guiding significance for the later CBM development and construction.Based on the geological data of the Dafosi mine and the field data of CBM horizontal wells,combined with related experiments,the characteristics of coal and coal reservoirs in the Dafosi mine are studied.At the same time,the division method of the CBM well production stage is optimized.The six stage method is used to divide the horizontal wells in the study area,and the relationship between the depressurization and the gas production is quantitatively calculated.By using the two order derivative theorem of the curve,the change of water production before gas production is analyzed in the study of cumulative water production and cumulative gas production.Combined with CBM geology and groundwater dynamics theory,the gas production area of the target horizontal well in the study area is determined,and the change of gas content in the coal reservoir is studied.Then I determined the total amount of coal bed gas resources and the volume of gas volume in the gas production area of the cuboid.Finally,I predicted the production service life of production horizontal wells by studying the change of gas content.The analysis results are applied to the study area for CBM horizontal wells drainage work advice:appropriate to extend the pre-drainage time,at the same time in the gas ascent to strictly control the depressurization rate,prevent gas production growth too quickly lead to a large amount of coal dust caused by frequent outburst card pump,workover.There is a sudden change in the curve of cumulative water production.The change of water yield at the early stage of production is ahead of the change of gas production.At the same time,the service life prediction of the target horizontal well is given,and it is hoped to provide some reference for the construction of the horizontal well in the later period.