Changes to the dielectric and mechanical properties of coal by ECBM-relevant fluids

Injection of waste CO2 fluid may be used to displace and produce adsorbed methane from coal seams whilst removing CO2 from the Biosphere. Monitoring the progress of such displacement may require remote sensing by geophysical methods. In particular, by the use of electromagnetic (EM) methods such as Ground Penetrating Radar (GPR) and magneto-telluric soundings or direct resistivity measurements. Propagation of EM-waves and interpretation of GPR soundings are dependent upon dielectric properties of the coal/fluid system. Therefore, data on electrical conductivity and dielectric properties during the (ad/de)-sorption processes are required. The enhanced solvent properties of supercritical CO2 are also expected to affect the organic content of coal and possibly alter its mechanical strength and transport properties.

These two aspects form the basis of research by the HPT group at Utrecht University in collaboration with NITG-TNO, Netherlands. Preliminary experiments on the dielectric properties of powdered coal have been carried out under ambient conditions as a precursor to further experiments under ECBM production conditions. The role of humidity is found to be especially important due to the high dielectric constant of water (~80, c.f. ~1 for most other materials and gases). Apparatus is under development to extend these experiments to supercritical conditions and also to monitor compaction creep deformation with the presence of the same ECBM-relevant fluids.