Experimental Study On Critical Desorption Pressure Of Coalbed Gas

As a kind of high-quality unconventional energy mainly stored in adsorbed state,CBM has a very good development prospect.The research on the desorption of CBM is directly related to the development of the CBM industry and the transformation of the future energy pattern.It has been found through research that most of the CBM research currently uses dry coal samples and neglect the actual conditions of coal reservoirs.The CBM desorption is critical.The determination of pressure is also mainly based on the isothermal adsorption curve.In order to better study the desorption of coalbed methane,this paper designs the coal-rock particle size,water,gas saturation and reservoir pressure on the coal seam according to the actual conditions of the coal seam.The effect of gas desorption.Based on previous research results and the characteristics of coal and rock structure,the experimental results were analyzed.Through the desorption experiments of coal samples with different particle sizes,it was found that the desorption of dry coal samples can be roughly divided into four stages.In the first stage,the pressure is greater than 2.2 MPa,which is the pressure propagation stage.There is almost no gas desorption at this stage,mainly the macropore and mesopores.The freedom in the air.In the second stage,the pressure is between 1.8 MPa and 2.2 MPa,which is the high-pressure desorption section.At this stage,pores and micropores with better connectivity begin to have gas desorption.In the third stage,the pressure is between 1.8 MPa and 0.6 MPa,which is the middle pressure desorption section.In this stage,the coal bed gas in the micro pores and pores with poor connectivity also begins to desorb.In the fourth stage,the pressure is less than 0.6 MPa,which is the low-pressure desorption section.At this stage,the coal bed methane in the micropores and pores will be largely desorbed.Comparing the cumulative desorption curves under different reservoir pressures,it was found that as the reservoir pressure increases,the desorption amount in the desorption section of the medium-pressure desulfurization stage shows a stepwise decline,and each step contains a certain pressure range.This phenomenon is related to the fracturing of coalbed methane.The design and evaluation of coalbed methane reservoirs have certain guiding significance;experiments on gas saturation and reservoir pressure have found that the decrease of gas saturation and the increase of reservoir pressure all result in a decrease in the ratio of temporary reserves.By observing the cumulative desorption curve of coal bed methane,the correlation between the cumulative desorption pressure and the initial desorption of coal bed methane was found,and the corresponding critical desorption pressure was obtained;in combination with different particle sizes of coal samples,When the desorption test of dry coal samples was analyzed,it was found that the size of the coal particle size had no influence on the critical desorption pressure;when analyzing the results of liquid desorption experiments on coal bed methane,the main pore space for the damage of coal to the coal rock was found to be mesoporous and After the detailed analysis of the coal rank changes and the desorption conditions of the experiments,the authors verified the previous researches.The coal ranks of the reservoirs are most conducive to the exploitation of coalbed methane in the middle and high ranks.Finally,it was observed that as the pressure decreased,coalbed methane was not immediately desorbed.Combining with previous studies,it was found that the equilibrium state of CBM adsorption could not be broken down by pressure reduction,but rather pressure needed to be reduced to a certain degree to break this.Adsorption equilibrium.