Experimental and modeling studies on high pressure methane adsorbed on coals
ZENG Quanshu, GAO Qingchun, WANG Zhiming
1 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum-Beijing, Beijing 102249 2 MOE Key Laboratory of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249
Coalbed methane (CBM) is mainly adsorbed within the coal matrix, accounting for 80%~90% of the total reserves.The adsorbed methane will desorb as CBM recovery processes, and the matrix will shrink, showing up as the opening of cleats and the improvement of cleat permeability. Based on gas adsorption isotherms, methane adsorption tests were conducted on several coal samples from different basins, and the influences of temperature, pressure, and proximate analysis results on adsorption capacity were further analyzed. The results show that the adsorption will decrease with temperature. The adsorption will first increase then decrease with pressure, and the maximum adsorption occurs at a pressure of around 10 MPa. In addition,fixed carbon is the effective component adsorbing methane, on the contrary, equibrilium water content will reduce the adsorption.The equation of state and potential energy function were evaluated to obtain the optimal simplified local density (SLD) theory,wherein three parameters should be determined by fitting the experimental results. The SLD theory can describe the methane adsorption at pressures up to 20 MPa with a reasonable accuracy, the average relative errors between the experimental and predicted results are all within 0.90%. These three parameters were then represented by the proximate analysis results of adsorbent,the average relative errors are 3.9%, 7.7%, and 18.9%, respectively. Based on these the SLD theory were generalized, the average relative errors between the generalized and SLD results are all within 20%.
Key words：
coalbed methane; adsorption experiment; simplified local density theory; application
ZENG Quanshu, GAO Qingchun, WANG Zhiming. Experimental and modeling studies on high pressure methane adsorbed on coals. Petroleum Science Bulletin, 2020, 01: 78-92.
