Prior to determining the optimal operating parameters for CO2 injection, conditions for both injection wellbore and storage formation should be evaluated; the build-up pressure induced by the CO2 injection could promote fractures in the storage formation, even collapsing the wellbore. In this study, a hybrid optimization methodology, which combined the proxy modeling and multi-objective optimization, was engaged in searching appropriate operating conditions for CO2 injection. The study utilized a fully coupled wellbore-reservoir (WR) model to simulate the CO2 injection scenarios. Three responses, such as pressure, temperature, and CO2 mass flow rate at the bottom-hole of injection wellbore, were investigated. To reduce the computational cost, the statistical proxy models were developed for approximating three responses. The developed fine-tuned proxy models revealed four influential factors; wellhead pressure, injected CO2 temperature, wellbore diameter, and permeability of a storage formation were significant in predicting three responses. Among these four influential factors, permeability was treated to be an uncertainty factor, while the other three factors were treated as tuning factors. According to acquired optimal solution sets, the optimum values for wellhead pressure and injected CO2 temperature were distributed around 10.0 MPa and 35 °C, respectively. For the wellbore diameter, its mean of optimal solutions was 0.1 m, and more solutions were concentrated at this mean value with a decrease in permeability.
Bibliographical noteFunding Information:
This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education [project number 2016R1D1A1B01008715]; by the Korea Environmental Industry and Technology Institute [project number 2018002440003]; by the Demonstration-Scale Offshore CO 2 Storage Project in Pohang, Basin, Republic of Korea , funded from Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) which was granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea [project number 20162010201980].
- CO injection
- Pareto-optimal solutions
- coupled wellbore-reservoir model
- multi-objective optimization
- proxy modeling