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%) N2/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.

Stable and non-stable contact angles of a synthetic flue gas and pure CO2 on an hvbB coal were determined in a pressure range between atmospheric to 16 MPa using a modified pendant drop cell at a constant temperature of 318 K.Figure optionsDownload high-quality image (87 K)Download as PowerPoint slideHighlights
► The wetting behavior was evaluated on a hvbB coal surface by synthetic flue gas and CO2 injection.
► Contact angle increases with pressure and surface becomes gas wet for CO2 injection.
► Wettability alters to intermediate wet for synthetic flue gas injection as pressure increases.
► Synthetic flue gas experiments show that mainly CO2 sorbs and not nitrogen.
► Experimental results are comparable to CO2 results at the same CO2 (partial) pressures.