Quantitative Characterization of Coalbed Methane Desorption Hysteresis in High Rank Reservoir and Its Influence on Development

This paper proposes two quantitative characterization indexes, such as residual adsorption gas content and desorption hysteresis coefficient through theoretical reasoning. And the two indexes are verified by the isothermal adsorption and desorption experiments. On this basis, the influence of desorption hysteresis on CBM development is analyzed. The results show that the modified Langmuir adsorption model is suitable for fitting the isothermal desorption data of high rank coal reservoirs. Residual adsorption gas contents and desorption hysteresis coefficient can be used to characterize quantitatively the degree of desorption hysteresis. The residual adsorption gas content and desorption hysteresis coefficient of coal samples are affected by reservoir physical properties. The lower the porosity and permeability, the smaller the pore radius and the larger the specific surface area of coal samples, the greater the residual adsorption gas content and desorption hysteresis coefficient. The phenomenon of desorption hysteresis leads to the decrease of actual desorption pressure in coal reservoirs. It is necessary to use isothermal desorption curve to calculate the actual desorption pressure.