Study On Desorption Characteristics Of Coalbed Methane Wells Under Negative Pressure

In recent years,with the increase of mining years in many CBM fields,the proportion of inefficient wells has gradually increased.In view of the problems of difficult drainage and low production of low-efficiency wells,the application of negative pressure drainage technology can improve the production of low-efficiency wells and solve the problem of gas gathering and transportation.In order to explore how the negative pressure drainage technology can effectively improve the production of CBM wells,we conducted high pressure isothermal adsorption and desorption experiments on coal samples in Qinshui Basin and Ordos Basin,which deepened the understanding of the adsorption and desorption process.Using Langmuir formula as prototype,the empirical formula of desorption process was deduced by data analysis method,and the parameters of empirical formula were calculated.It was found that the parameters of empirical formula were related to coal rank.Through the negative pressure desorption experiments of coal samples with different water content,it is found that the desorption effect of all experimental coal samples in the negative pressure stage is more obvious than that in the conventional stage.Through the analysis of residual adsorption,unit pressure degradation absorption and desorption rate,it was found that water promoted desorption from low pressure zone to negative pressure zone.After the implementation of negative pressure drainage technology,the cumulative gas production of field low-yield well group J19 increased by 86,500 square meters compared with the six-month production situation.B4 well group increased production by 30% after applying negative pressure drainage technology.Negative pressure drainage technology has a good application prospect in the study area.Based on isothermal adsorption and desorption experiments,this study explored the desorption law of CBM in coal samples under negative pressure,filling in the blank of adsorption and desorption experiments in negative pressure.It provides a theoretical basis for the negative pressure drainage technology of coalbed methane in the eastern edge of Ordos.