Numerical Temperature Prediction System in Injection Tubing, Bottom Hole and Reservoir Condition for Supercritical CO2 Injection into Deep Coal Seams

Abstract

Abstract The Japan consortium to enhance the CO2-ECBM has carried out a project on CO2 injection at Yuhbari City, Hokkaido. The targeted coal seam at Yuhbari is located about 900 m below the surface. However, supercritical condition of CO2 has not been satisfied due to heat loss along the deep injection tubing. The absolute pressure at the bottom hole is approximately 15.5 MPa and the CO2 temperature is about 28 °C before the injecting into the coal seam. Therefore, it can be assumed that CO2 is injected in liquid phase to the coal seam. Replacements of usual tubing pipes with thermal insulated tubings were carried out, however, the temperature at the bottom hole was still lower than the CO2 critical temperature. 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. The control map showing targetted injection rate against power of the line heater with a parameter of elapsed time has been presented in order to keep the supercritical condition at the bottom hole of the injection tubing. Injected CO2 is expected to be super critical over 12 ton/day of injection rate without any heating in the tubing. Furthermore, this study has provided numerical simulation results of temperature distribution of the coal seam after injection of CO2 using ECLIPSE. Finally, numerical predictions of CH4 production against CO2 temperature injected in the coal seam including supercritical CO2 have been presented.