Experimental Study Of Coal Bed Methane Displacement And Exploitation By Super Critical Carbon Dioxide Injection

Gas, as an additional energy source, is put a high value. At the same time,greenhouse effect makes us study how to reduce greenhouse gas emissions whilestoring CO2in coal has been considered a solution. Therefore, the study aboutCBM extraction and CO2-ECBM recovery has been done by many researchers.The purpose of this article is to study the permeability and adsorption ofsuper critical CO2in coal bed with natural cleats and fractures of large scale andcoal swelling during the ECBM process. A new experimental apparatus MCQ-Ⅱsuited for test of large coal specimen in size of100100200mm isdeveloped. It is found that：Permeability and adsorption tests were conducted for48,54and60MPaconfnements at50°C temperature. The permeability of super critical CO2increases with injection pressure rise and decreases with increasing confinementpressure and is among0.0066×10-3μm2~0.0312×10-3μm2. To study CO2 adsorption volume variation and its effect on permeability, accumulative supercritical CO2adsorption mole and actual super critical CO2volume are analyzed.The accumulative super critical CO2adsorption mole linearly increases withinfiltration pressure but actual super critical CO2adsorption volume decreaseswith injection pressure rise due to higher density, which contributes topermeability increase. Also, coal swelling is recorded and coal swellingvolumetric percentage linearly increases with the amount of CO2stored duringthe permeability measurement. Moreover, due to the anisotropic property of thecoal deformation, swelling volume in the plane perpendicular to the bed isgreater.Supercritical CO2was injected to coal samples adsorbing CH4, and moreCH4in specimen#1(weakly caking coal) desorbed than that in specimen#2(coking coal). However, the replacement ratio of carbon dioxide to methaneand the CO2storage rate are almost equal,4.01/4.16,20.05%/20.09%,respectively. Meanwhile, coal swelled after absorbing CH4and injecting CO2. Inaddintion, coal swelled faster after injecting supercritical CO2. The research isexpected to provide theoretical guidance for carbon dioxide geological storagein the deep coal seam.