Gas content prediction simulation of unsaturated low coalification coal cores

Abstract

In order to compare and analyze the on-site desorption performance and numerical simulation desorption performance of low coalification reservoir coal core, the on-site gas content of coal core of a coalbed methane (CBM) well in Xinjiang was measured, and a numerical model of coal core in undersaturated reservoir with adsorbed gas is established, and based on this, the loss gas content calculation method was analyzed. The results show that the loss gas, desorption gas and residual gas contents calculated by the desorption numerical model of the unsaturated coal core (adsorbed gas saturation 54.77%, 77.51%, and 99.79%, respectively) were close to the corresponding results measured in the field (error<10.12%), which could reflect the gas content composition of the unsaturated coal core. For the coal core numerical model of gas bearing saturated reservoir (both adsorbed gas and free gas are saturated), the regression analysis method of the square root of the sum of gas loss time and desorption time and the cumulative desorption gas volume at the initial stage of desorption had a large error in predicting the loss gas content, which was no longer applicable. Under the same gas loss time condition, the proportion of loss gas content of saturated coal core (18.64%) was higher than that of unsaturated coal core (11.95%), the proportion of desorption gas of oversaturated coal core (80.90%) was lower than that of unsaturated coal core (87.32%), and the proportion of residual gas of oversaturated coal core (0.46%) was lower than that of unsaturated coal core (0.63%).

Keywords

• coalbed methane
• gas content
• low coalification coal
• loss gas content
• coal core