Numerical temperature prediction system in injection tubing, bottom hole and reservoir condition for supercritical CO₂ injection into deep coal seams

The Japan consortium to enhance the CO₂ sequestration into coal seams has carried out a project on CO₂ injection at Yuhbari City, Hokkaido. However, supercritical condition of CO₂ has not been satisfied due to heat loss along the deep injection tubing. The absolute pressure and CO₂ temperature at the bottom hole are approximately 15.5MPa and 28ºC. Therefore, it can be assumed that CO₂ is injected in liquid phase to the coal seam. The liquid CO₂ causes decreasing injectivity into the coal seam due to high viscosity and swelling of the coal matrix. This study has provided a numerical procedure to predict the CO₂ flow characteristics of pressure, temperature, supercritical or liquid in considering heat transfer from the injector to surrounding casings and strata. Present study has focused on the keeping supercritical CO₂ in the tubing because viscosity of supercritical CO₂ is 40% smaller than that of liquid CO₂. The CO₂ temperature has been successfully predicted in order to keep CO₂ in supercritical condition from the surface to the bottom for various CO₂ injection rates and electric heater power. Finally, Injected CO₂ is expected to be supercritical over 12ton/day of injection rate without any heating.