Wettability determination by contact angle measurements: hvbB coal-water system with injection of synthetic flue gas and CO2

Geological sequestration of pure carbon dioxide (CO2) in coal is one of the methods to sequester CO2. In addition, injection of CO2 or flue gas into coal enhances coal bed methane production (ECBM). The success of this combined process depends strongly on the wetting behavior of the coal, which is function of coal rank, ash content, heterogeneity of the coal surface, pressure, temperature and composition of the gas. The wetting behavior can be evaluated from the contact angle of a gas bubble, CO2 or flue gas, on a coal surface. In this study, contact angles of a synthetic flue gas, i.e. a 80/20 (mol%) N-2/CO2 mixture, and pure CO2 on a Warndt Luisenthal (WL) coal have been determined using a modified pendant drop cell in a pressure range from atmospheric to 16 MPa and a constant temperature of 318 K. It was found that the contact angles of flue gas on WL coal were generally smaller than those of CO2. The contact angle of CO2 changes from water-wet to gas-wet by increasing pressure above 8.5 MPa while the one for the flue gas changes from water-wet to intermediate-wet by increasing pressure above 10 MPa. (C) 2011 Elsevier Inc. All rights reserved.