Numerical temperature prediction system in injection tubing, bottom hole and reservoir condition for supercritical CO 2 injection into deep coal seams

Abstract

The Japan consortium to enhance the CO 2-ECBM has carried out a project on CO 2 injection at Yuhbari City, Hokkaido. The targeted coal seam at Yuhbari is located about 900 m below the surface. However, supercritical condition of CO 2 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 CO 2 temperature is about 28 °C before the injecting into the coal seam. Therefore, it can be assumed that CO 2 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 CO 2 critical temperature. The liquid CO 2 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 CO 2 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 CO 2 in the tubing because viscosity of supercritical CO 2 is 40 % smaller than that of liquid CO 2. The CO 2 temperature has been successfully predicted in order to keep CO 2 in supercritical condition from the surface to the bottom for various CO 2 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 CO 2 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 CO 2 using ECLIPSE. Finally, numerical predictions of CH 4 production against CO 2 temperature injected in the coal seam including supercritical CO 2 have been presented.