Research And Application On Methane Adsorption Characteristic Under Equilibrium Water Condition

Under coal reservoir conditions, coal-methane-water exists together, and the presence of water has a significant impact on the methane adsorption. Isothermal adsorption experiments with dry coal samples distorts the real condition, but current study with them are still a lot, the applicability of dry coal samples experiments remains to be discussed. By using the knowledge of interface physical chemistry, this paper quantitatively analyzes the interaction forces among the three-phase molecules and reveals the physical and chemical mechanism of methane adsorption. Comparing the isothermal adsorption experiments with dry and quilibrium water coal samples,this paper studys the methane adsorption characterastic; Combining physical and chemical interaction analysis, this paper discusses the applicability of experiments with dry and equilibrium water coal samples.The total forces between coal and water molecules is larger than that between coal and methane molecules. There exists competitive adsorption between water molecules and methane molecules, which seizes the adsorption vacancy space on coal's surface;The blocking effect of water decreases the methane adsorption amount, the presence of water will affect the coal reservoir methane adsorption. But the water content of dry coal sample differs greatly from that of coal reservoir. Due to the lack of water, the adsorption space which should be occupied by water will be occupied by methane molecules, which makes the adsorption capacity of dry coal sample higher than the real condition.Calculating the methane pressure with different adsorption models, this paper finds that compared the exponential function, logarithmic function and power function adsorption models, the calculated methane pressure with Langmiur equation is closer to the actual measured value. According to the isothermal adsorption experiments with equilibrium water coal samples, calculating the methane pressure with Langmiur equation has practical significance.