Experimental Study On Imbibition Effect Of Gas-bearing Coal With Different Metamorphic Grade

This research intends to conduct an experimental study on the laws of imbibition effect of gas-bearing coal.An experimental devise is designed and built on the basis of the investigation of current relevant devices.The devise can effectively exclude the influence and interference of water injection pressure and volume,ensure that the pressure change in the coal sample tank can only result from the imbibition effect promoting the gas desorption in gas-bearing coal.Besides,the devise is equipped with high precision pressure sensor,which can monitor and record the pressure changes in the coal sample tank during the process of the imbibition effect.The briquette was chosen as the experimental coal type after compared with coal particles on the capacity of spontaneously absorbing water under atmospheric pressure.The appropriate briquette height and coal water content are investigated and determined which were adopted in the experiment.On the basis of the above research,a series of experiments of WYM,PSM,JM,QM were carried out under the conditions of the fixed adsorption equilibrium pressure with the water content varied and of the fixed water content with the adsorption equilibrium pressure varied respectively,and the gas imbibition amount,gas imbibiton rate,gas imbibition velocity change laws of WYM,PSM,JM,QM under different experimental conditions were discussed.Results show that moisture can displace the adsorbed gas by imbibition effect after natural invasion,which can effectively promote the gas desorption in gas-bearing coal.Under the fixed adsorption equilibrium pressure,the gas imbibition amount and the imbibition rate increases with the moisture percentages of the coal sample while the increase rate decreases,which all fits the function of Langmuir adsorption isotherm.The gas imbibition amount and imbibition rate reaches to the maximum when the water content stretches to the ultimate quantity of the water adsorption of the coal.Under the fixed moisture content condition,the gas imbibition amount increases with the increasing of the adsorption equilibrium pressure,which also fits the function of Langmuir adsorption isotherm,while the imbibition rate decreases with the increase of adsorption equilibrium pressure.The two experimental conditions of imbibition effect include three stages of "rapid imbibition-slow imbibition-terminated imbibition".The higher the moisture percentage is and the higher the initial adsorption equilibrium pressure is,the higher the initial gas imbibition velocity becomes during the early process of water invasion.Under the same experimental condition,the four kinds of coal(WYM,QM,PSM,JM)have different imbibition effects.In the terms of gas imbibition quantity and gas imbibition velocity,WYM is the biggest,QM and PSM are the medium,and JM is the minimal.In the terms of gas imbibition rate,QM is the biggest,WYM and JM are the medium,and PSM is the minimal.According to the theoretical analysis,the different wettability and pore structure characteristics of the four kinds of coal lead to the differences above.