CO2 Injection Wells: Class II vs. Class VI Wells
Understanding the Regulatory and Well-Construction Differences Between CO₂-EOR and CO₂ Storage Injection Wells — Worldwide
Planning a CO₂-EOR project today, but want to keep CO₂ geologic sequestration options open for tomorrow? A&A's well-integrity consultants can help your company understand — and plan for — the differences between Class II and Class VI well requirements before they become a costly surprise.
Avasthi & Associates, Inc. (A&A) is an independent petroleum engineering and well-integrity consulting firm. A&A does not sell tubulars, cements, wellhead equipment, or workover services — our only business is expert technical consulting, which means our guidance on well classification is never influenced by a stake in any particular vendor, material, or technology.
More and more companies are evaluating mature oil fields, around the world, for their potential for CO₂ enhanced oil recovery (EOR) and/or CO₂ geologic sequestration projects. Under the U.S. EPA's Underground Injection Control (UIC) Program — or the equivalent regulatory framework outside the U.S. — the well classification required depends entirely on the injection objective, and the two classes that matter most for CO₂ projects carry very different construction and regulatory standards.
Class II Wells — CO₂-EOR Service
Class II wells are the classification required for CO₂ enhanced oil recovery (EOR) service. They fall under the same regulatory framework historically used for oil & gas-related injection (produced-water disposal and other enhanced-recovery injection), and their construction and monitoring requirements, while rigorous, are less stringent than those imposed on Class VI wells.
Class VI Wells — CO₂ Storage (Geologic Sequestration)
Class VI wells are the classification required for CO₂ storage (geologic sequestration) projects, where the objective is permanent, long-term containment of CO₂ rather than pressure support for oil recovery. Class VI construction and regulatory requirements are considerably more stringent than Class II, with heightened emphasis on materials of construction (tubulars) and CO₂-resistant cements — reflecting the long-term corrosive characteristics of CO₂ over a project's multi-decade injection and post-injection monitoring period.
Why the Distinction Matters for Your Project
Although a well-evaluation project's objective at present may be limited to CO₂-EOR service only, it is worth evaluating candidate wells against both standards from the outset. A company may later want to pursue CO₂ storage (geologic sequestration) objectives in the same field — and wells qualified only to Class II standards will not automatically qualify for Class VI service. Identifying that gap early, rather than after a CO₂-EOR project is already underway, can materially change the economics of a later storage decision.
How A&A Can Help
The high-level, seasoned well-integrity consultants of the A&A Consulting Team can evaluate your candidate wells against both Class II and Class VI construction and regulatory requirements, identify which wells already meet which standard, and flag the gap-closing work needed if your company wants to keep its options open for a future CO₂ storage project.
Related A&A Service: For a full description of A&A's life-cycle well-integrity due-diligence services — well status evaluation, workover assessment, and new-well program development, applicable across all well types and classifications — please see A&A's Well Integrity Consulting Services page.
To find out how A&A's well-integrity consultants can help your company navigate Class II and Class VI well requirements for your CO₂-EOR and/or CO₂ storage project, please contact us (Contact@AvasthiConsulting.com) or click here.
