2007 Volume 123 Issue 11 Pages 518-523
A national project on a carbon dioxide (CO2) sequestration has been carried out from 2002 by injecting CO2 into one of the Ishikari coal seams located at the Minami Ishikari Coal Field in Hokkaido, Japan. The coal seam lies at 890 m under the surface with in-situ conditions of 29°C in temperature and 11MPa in static stress. Even if super critical CO2 over 70°C and 8 MPa is supplied at the surface, it becomes liquid CO2 with 29°C and 15MPa at the bottom of injector due to heat loss to low temperature strata and creates a problem of coal seam permeability reduction around the injector. Thus, coal characteristics for liquid CO2 injection are very important to carry out the project. However, measurements of permeability and coal swelling factor for liquid CO2 has not been presented and visualized clearly.
In this study, the permeability and swelling of a core sample drilled from the coal seam has been investigated. Furthermore CO2 adsorption/desorption properties of the coal have been measured using with a volumetric method with comparisons of coal samples mined from the Kushiro Coal Mine.
As a result, the swelling of the coal matrix has been observed clearly by visualization pictures of crushed coal sample and a hole drilled in the coal core sample sunk in CO2 liquid. The ratio of its area reduction by the swelling in liquid CO2 was 7% during 78hours.