Instability Analysis of Supercritical CO2 during Transportation and Injection in Carbon Capture and Storage Systems

Captured CO 2 is in a subcritical state, whereas CO 2 deep underground is in a supercritical state because of the high geothermal heat and pressure. The properties of CO 2 can change rapidly at the critical point and in the near-critical region during the transportation and injection process. This study aims to identify the instabilities in the CO 2 flow in these regions, along with the causes and effects, during the transportation and injection process, and propose relevant design specifications. Thus, the critical points and near-critical region of CO 2 flow were numerically analyzed. The unstable region is presented in terms of temperature and pressure ranges, and the changes in the CO 2 properties in this region were analyzed. In the unstable region, the sudden change in density was similar to the density wave oscillation of a two-phase flow. The CO 2 stability map we obtained and the stability map of supercritical water show similar trends. Flow instability was also found to occur in standard CO 2 transportation pipelines. We demonstrate that flow instability in CO 2 transportation and injection systems can be avoided by maintaining the proposed conditions.