Sub- and super-critical carbon dioxide flow behavior in naturally fractured black coal: An experimental study

Abstract

A proper understanding of super-critical carbon dioxide (CO2) flow behavior in coal is essential, as CO2 normally exists in its super-critical state in deep coal seams and studies are lacking. The main objective of this study is to distinguish the permeability behavior of coal for sub-critical and super-critical CO2 flows. Therefore, a series of triaxial experiments was conducted on naturally fractured black coal specimens. Permeability tests were carried out for 15, 20 and 25 MPa confinements at 33.5 °C temperature. Three test scenarios were conducted to investigate, (1) variation of the permeability behavior of coal with CO2 phase condition, (2) the swelling effect on sub- and super-critic..