In a typical carbon capture and storage project, it is important to maximise residual and dissolution trapping to minimise the risk of leakage. In this project, a techno-economic analysis of residual and dissolution trapping for the SW Hub Project was carried out.
The methodology used technically feasible engineering designs to optimise both of the above trapping mechanisms in the Perth Basin storage formation by determining the most feasible injection schemes. The aim was to estimate the relative economics of different injection schemes with different trapping results. The project did not assess the overall profitability of injection in absolute terms.
Continuous CO2 injection is usually preferred for carbon capture and storage (CCS) projects. However, the literature shows that this option does not necessarily maximise residual and dissolution trapping. The project chose to analyse the engineering and economic effects of several injection schemes. Some injection schemes and processes, such as foam injection, carbonated water injection and fines migration, were ruled out early on because they are believed to be extremely costly. As a result, the options that were analysed included –
- Vertical injection wells
- Horizontal injection wells
- Vertical injection wells and production wells for pressure relief
- Water Alternate Gas (WAG) wells and production wells for pressure relief
- Simultaneous Water Alternate Gas (SWAG)
- Most of the injection designs tested in this study show that injecting through perforations starting at the upper-middle of the Wonnerup Member provides the greatest potential for residual trapping, dissolution trapping and injectivity.
- In order to minimise CO2 production for the vertical CO2 injection and water production well scenario, it is advantageous to locate the perforations in the middle of the formation.
- Horizontal and SWAG well scenarios show the least injectivity because layers in the formation have very low permeability.
- Vertical wells are the most economically attractive and show intermediate overall trapping benefit.
- Although WAG wells are the least economically attractive, they do show the highest overall trapping benefit, especially early in the injection period.
Plan view of saturations for different depth layers of the CO2 plume after 100 years of observation.