Potential Issues and Costs Associated with the Conversion from UIC Class II EOR to Class VI CO2 Storage Wells

The U.S. Environmental Protection Agency (EPA) has promulgated requirements for geologic storage of CO₂, establishing a new class of wells -- Class VI -- under authority of the Safe Drinking Water Act’s Underground Injection Control (UIC) Program. In a separate rulemaking, EPA also established reporting requirements under its Greenhouse Gas Reporting Program (GHGRP) for facilities that inject CO₂ underground; Subpart UU applies to CO₂ injected to enhance hydrocarbon recovery; Subpart RR to CO₂ injected for geologic storage.

CO₂ enhanced oil recovery (CO₂-EOR) is a long-standing practice, and CO₂-EOR wells are regulated as Class II wells under the EPA UIC program. For current CO₂-EOR operations injecting anthropogenic CO₂, some could be converted to permanent geologic storage or qualify for CO₂ storage during EOR operations. Recent guidance issued by EPA confirms that CO₂-EOR operations can result in stored CO₂, and a conversion to Class VI is not required for assuring CO₂ storage. This guidance implies that for a CO₂-EOR operation to get “credit” for stored CO₂, reporting under Subpart RR may be required, but a complete conversion from Class II to Class VI operations may not be necessary.

The presentation characterizes the potential issues and estimated costs associated with converting a CO₂-EOR project to a CO₂ storage project, or for adapting a CO₂-EOR project to enable it to get “credit” for stored CO₂. This characterization is based upon technical requirements and published guidance in the EPA Class VI rule and for GHGRP Subparts RR and UU. Estimated costs are based, in part, on cost analyses developed as a part of these rulemakings.  In addition, costs take into consideration the actual costs incurred at DOE-funded CO₂ storage research projects. 

Consideration of the issues and costs for a Class II to Class VI conversion will include those associated with well construction (or rehabilitation), existing well abandonment, well operation, testing and monitoring, post-injection site care, and site closure.  Two scenarios are considered for a full Class II to Class VI conversion:

• A Base Case assumed to meet the minimum requirements in the Class VI rule, where existing CO₂-EOR injection wells are “grandfathered” and utilized as the injectors for CO₂ storage; additional shallow wells will be drilled for use as monitoring wells; and a Class VI monitoring, reporting, and verification (MRV) plan is sufficient for Subpart RR.
• A High Case which assumes that a Class VI Program Director requires more than the minimum requirements; assuming new injection wells will be constructed to Class VI standards; a more extensive suite of monitoring methods, including various seismic methods; and additional monitoring under Subpart RR.

A fundamental question is: can a CO₂-EOR operator report under subpart RR to get credit for stored CO₂, and if so, what exactly is the role of Subpart RR?  In other words, is Subpart RR reporting purely just a GHG accounting/reporting responsibility, or will the Subpart RR program  need to accept some (or most) of the responsibilities associated with the UIC Class VI program?

To consider this, two levels of reporting requirements under subpart RR are considered:

• A Low RR Monitoring Case assuming that Subpart RR is merely a GHG reporting program, with minimal incremental requirements for assuring integrity of the reservoir into which CO₂ in injected and stored.
• A High RR Monitoring Case representing the high end of the possible range of EPA requirements, comparable to Class VI MRV plan requirements.

Transitioning CO₂-EOR operations to CO₂ storage may also proceed through one or more phases: (1) conventional CO₂-EOR; (2) CO₂-EOR with credit for stored CO₂; (3) transition from CO₂-EOR to CO₂ storage, and (4) CO₂ storage post-CO₂-EOR operations (Class VI).  Phases 1 through 3 may still represent, for the most part, traditional CO₂-EOR/Class II well operations. However, in Phases 2 through 4, additional MRV activities may be necessary and/or required to verify the volumes of CO₂ stored for which credit is desired.

For Phase 3, there will likely be a rationale to “prepare” the reservoir for CO₂ storage, prior to the end of CO₂-EOR operations, in order to “re-optimize” the oil field for storage.  This may be particularly important for reservoirs that have undergone a water-alternating-gas (WAG) CO₂-EOR process, to reduce reservoir pressure, improve injectivity for CO₂, and increase storage capacity. The logic associated with the need for carrying out this transition will be presented.

Finally, the potential scenarios are applied to several fields currently undergoing CO₂-EOR operations to approximate a “real world” implementation of this strategy.