Simulation experiment and result analysis on lost gas content of coalbed methane

ZHANG Qun; FAN Zhang-qun

doi:10.3321/j.issn:0253-9993.2009.12.012

Abstract：A hish pressure desorption apparatus was established.The pressure changes experienced by coal core during three stages of core recovery,exposed to atmosphere and sealed-in canister were simulated.Desorption ex-periments for five coal samples with three particle sizes from two rank coals were respectively performed under rapid drop pressure from approximate 8 MPa to ambient pressure.Volumes of simulated lost gas of methane were meas-ured.The desorption characteristics of methane gas from coal samples were revealed during the above three stages.Comparison between the measured volume of simulated lost gas and the volume estimated by USBM Direct method was made.The result shows that the curves shapes of methane desorption volume from coal samples all have the characteristics of three section pattern.Average desorption rates of methane in above three stages have great differ-ences,the rates in the former two stages are almost respectively 12～20 times and 6-8 times as large as in the laststage.Coal particle size also has much influence on desorption rate of methane gas from coal sample.The ratios ofaverage desorption rates of methane gas from the three distinct samples with 1～3 and 30～50 mm particle sizes andtk89 mm core size of the same coal are about 321.The measured volume of the simulated lost gas is much higher than one estimated by USBM Direct method,the former is 8～16 times larger than the later,and the smaller the particle size,their ratio is much more different.It is thought that the lost gas volume estimated by USMB Direct method is inaccurate,and much lower than the original one.This method needs to be modified by performing further research Work.