Optimization of Well Placement and Operating Condition for Various Well Types in CO2 Sequestration in Pohang Basin, Korea

Since CO₂ emission of South Korea has continuously increased, the government started a pilot project for geological storage into an aquifer in Pohang basin in 2013. Pohang basin has geological characteristics of multi-layered reservoir and pre-existing faults which restrict CO₂ injection to a certain amount. To store a large amount of CO₂ and keep the storage security, it is needed to define the optimum injection well type, placement and the operating conditions.

This study applied various well types to improve the capacity by changing well trajectories and controlling the pressure build-up, with monitoring the injection and fault pressure. Single vertical injection well, two vertical injection wells, single horizontal injection well, and two vertical wells for pumping and injection have been employed and designed in the numerical simulation using a geological model of Pohang basin. To determine the optimum well location and operating conditions of each well type, the optimization process was conducted with a commercial optimizer, Designed Exploration and Controlled Evolution (DECE) of Computer Modelling Group (CMG).

The results showed two vertical wells for pumping and injection at the optimum location and fluid rate kept the security within the pressure boundary and allowed almost 8 times larger volume of CO₂ to be stored compared to base case. When using a single well, vertical injection well injected 126 kton of CO₂ that was the largest, and horizontal well prevented the upward-migration of CO₂ for additional storage security. Through this research, it is expected to forecast the effect of various well types in the CO₂ sequestration in Pohang and propose the optimum well type and conditions for the largest storage capacity.