Influence on Efficiency and Key Parameters of Liquid Co2-Ecbm Under the Different Pressure and Temperature: From Experimental to In-Situ Test

Abstract

A B S T R A C TTo study the influence on the efficiency and key parameters of liquid CO2 (LCO2) phase-transition to displace CH4 under the different temperature (Ti) and pressure (Pi), this paper focuses on investigating the efficiency of CO2 displacing CH4 in the coal under the optimal Ti and Pi, then an in-situ test is conducted on LCO2-ECBM in the high-gas coalbed. The results shown that low-temperature inhibits the movement activity of CO2/CH4 in the coal and a significant delayed effect is exhibited during CO2 displacing CH4, the maximum displacement efficiency (ηmax) is only 56.02%. As the Ti gradually increases, competitive adsorption effect of CO2/CH4 intensifies, ηmax increased to 84.13%. Moreover, CH4 desorption rate and migration dynamics in the coal exacerbates as the Pi raised, performing a sharp increasing of efficiency, ηmax is reached to 92.87%. In the 30.00 oC where CH4 exists in the coal, Pi appropriate increases the maximum replacement ratio (μmax) decreases from 1.60:1.00 to 0.40:1.00, indicating a higher efficiency. In-situ test of LCO2-ECBM show that the concentration and flow rate of methane extraction increased by nearly three times. Simultaneously CBM extraction standard time and boreholes layout number have been shortened by one-third and half, respectively, resulting in significant comprehensive benefits.

Keywords: CBM extraction, Liquid CO2, Pressure and temperature, Displacement efficiency, In-situ test