To control corrosion that can potentially occur in the completion equipment, wellhead valve trims and wetted parts of packers should be made of stainless steel, nickel, or Monel. Experiences with injection of supercritical CO2 have demonstrated the need for elastomers and seals resistant to swelling. Additionally, CO2 as a solvent will dissolve any hydrocarbon based material, therefore Teflon, nylon, and hardened rubber are effective materials for use in packing and sealing elements. These refinements made in the design of injection equipment for CO2—EOR can be applied to CCS such that these projects are technically safe and reliable.
Several decades of experience with CO2—EOR projects provide invaluable lessons about how to conduct CCS operations in a safe and technically sound way (Parker et al., 2009). Public perception of the safety risks associated with CCS is one of the major hurdles to wide scale deployment of this technology; CO2—EOR projects have stored over 600 million tons of CO2 without any significant safety endangerment events, thus the technologies and procedures employed in CO2—EOR ought to be emulated. In the CO2—EOR industry, improvements in the design of injection infrastructure can be applied to the design of the standard equipment used in CCS sites.— Shanna Hoversten
Parker, M., Meyer, J., Meadows, S., 2009. Carbon Dioxide Enhanced Oil Recovery Injection Operations Technologies. Energy Procedia 1, 3141–3148.
M. E. Parker from ExxonMobil and his partners at Contek Solutions, LLC. and the American Petroleum Institute, provide a synthesis of information on technical design improvements that have been made over years of CO2—EOR projects. An important caveat to these recommendations stems from the heightened potential for corrosion that takes place in CO2—EOR projects due to the use of the WAG (water alternating gas) process; because CCS uses CO2 that is essentially in a dry state, there is a smaller incidence for problems with corrosion as compared to CO2—EOR projects. Thus, Parker et al. proceed to detail recommendations based on CO2—EOR experience while recognizing that these measures are relatively cautious.
Parker et al. detail specific designs that should be employed to the wellbore and completion equipment to ensure safe injection of CO2. Wellbore elements include the casing, cement, and casing heads, and the completion includes the packer, tubing, and wellhead valves assembly. Casing should be made out of carbon steel, which is both economically feasible and technically sound, provided that it is coated in corrosive resistant material. Tubing strings exposed to wet CO2 can also be subject to corrosion, and thus should be coated with a protective liner of plastic, epoxy, or glass reinforced epoxy. Cement is important in anchoring the casing to the formation and providing a seal as well as structural stability. CO2—EOR suggests that Portland cement can be used effectively in spite of some presence of carbonic acid, despite laboratory data suggesting that the carbonic acid will compromise the integrity of the cement. However, in cases where carbonic acid is a more significant threat, adding materials such as fly ash, silica flour or other resistant materials can mitigate the risk of corrosion.