A calculating method of indirelt absorbedgas content of Low-rank Couls based on isothermal adsorption experiments under different temperatures and pressures

In order to systematically analyze the sorption gas content of low-rank coals,methane isothermal adsorption experiments on moisture-equilibrated coals were performed under different temperatures.In total 8 low-rank coal samples’ methane adsorption experiment data on 25℃ and 45℃ were collected and analyzed while 2 of those were conducted,based on which a indirect adsorbed gas content calculating method was proposed.The results showed that adsorbed gas content in low-rank coals decreased as temperature increased.The relationship between methane adsorption decrement and pressure was not linear over a wide range,but was better described by a logarithmic form.Based on the calculating method,four low-rank coal samples of Hailar Basin in Inner Mongolia and drilled coal seam of F1 well in Fukang mining area of sourthern Junggar Basin were evaluated under in-situ conditions of reservoir temperature and pressure.The results showed that the adsorbed gas content in these low-rank coal reservoir increases but not obviously with increasing burial depth from 600 to 1400m.These characteristics are quite different from that of middle or high rank coal reservoir and the calculating method was validated to be correct by the comparative analysis between calculating results and actual test results of F1 well.Findings in this work are helpful to further understand the adsorbed gas content and improve evaluation of the coalbed methane reserve of low-rank coal reservoirs.