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Why Right-Sizing the Area of Review for Class VI Wells is Key to CCS Success

In the US, the number of Carbon Capture and Storage (CCS) projects in development is rapidly increasing, mainly due to government funding and tax incentives announced in 2022. For projects involving geological sequestration of CO₂in the US, a permit to drill a Class VI wells is required by the Environmental Protection Agency (EPA). One of the fundamental steps in the application process is determining the Area of Review (AoR).

In this article, we discuss why the size of the AoR is so important when planning and permitting a Class VI.

17 October 2023 | 2 min read

Grant Billings

What is a Class VI well?

Class VI is a new class of wells specific to the geological sequestration of CO₂. (The other classes of well are shown in the diagram below.)

Overview of the EPA Injection Permit Classes for CO2 injection

Why do we need an Area of Review?

The Area of Review refers to the region surrounding a CCS project where underground sources of drinking water (USDWs) could be affected by the injection of CO₂into deep geological formations.

Drinking water could be endangered if there is a vertical leakage pathway between the CO₂injection zone and the USDW.

Additionally, drinking water can be negatively impacted by the movement of CO₂through changes in pH or acidity, contamination by trace impurities, including mercury or hydrogen sulfide, or the leaching of metals and organics.

If non-potable water, such as brine, moves up into a USDW because of the increased pressure in an underlying geological formation (or reservoir) due to the injection of CO₂, the USDW could become contaminated.

What project considerations does the AoR impact?

The AoR sets the boundary area for Class VI permitting and will impact several factors.

Site characterization – Gathering extensive information about the proposed site’s local and regional geology and hydrogeology for feasibility studies and planning. Depending on the availability of existing studies, this data may be time-consuming and expensive to obtain.
Corrective action – Artificial penetrations such as active and abandoned wells in the AoR must be evaluated for potential leakage before authorization to inject is granted.
Testing and monitoring – During active injection, the area must be monitored regularly using 4D seismic and/or monitoring wells. The monitoring period can extend to 50 years after CO₂injection stops depending on the jurisdiction governing the proposed site.
Emergency and Remedial Response – The AoR will inform the Emergency and Remedial Response Plan for the project’s duration regarding notifications and reporting.

The permitting process for Class VI well - Used for carbon capture and storage

How is the AoR determined?

The area of review is delimitated and can be mapped using established methods based on the site information. Geologists and hydrologists use complex computer modeling to determine how all phases of the injected carbon dioxide stream (whether supercritical, liquid, or gaseous) and the fluids it displaces, will behave. The model must account for various physical and chemical properties of the CO₂, geological information, site characterization, monitoring, and operational data.

Why size matters – for an AoR

It’s important to talk about right-sizing for the AoR because this area will impact carbon sequestration projects for the entire project lifecycle. If the AoR is larger than necessary, more resources will be needed to characterize the site, more corrective action will be required, and there will be a broader area to monitor. The scope of the emergency and remedial response plan will also be affected.

Depending on the method used to calculate the size, the AoR could become too large, making the entire project unfeasible from a cost and operational perspective. On the other hand, a too-small area of review could mean that artificial penetrations, such as well bores into the reservoir that will be impacted by the CO₂/pressure plumes, are not properly assessed and sealed, resulting in a leak beyond the AoR boundary. Any leaks could potentially halt the injection process, resulting in negative consequences such as contract breach, costly remediation and reputational issues. Such incidents would obviously damage public and regulatory confidence and could slow down the widespread adoption of CCS.

A winning team

The permitting and technical team at TetraTech, RPS’ parent company, use their deep expertise in permitting oil and gas wells and applies it to Class VI wells. It comprises energy industry professionals with various backgrounds, including geology, geoscience, engineering, regulatory, and economics.

They collaborate with specialists from the environmental engineering, geology, reservoir engineering, and resource monitoring teams within TetraTech and RPS, a TetraTech company, to ensure successful project delivery.

Our approach

Using our experience from multiple fields, we support our clients throughout the regulatory process. We advise our clients with the project life cycle from pre-injection to post-operation in mind. We understand that details in the permit application will have long-term and potentially significant operational costs. Our aim when permitting is to set our clients up for success, not just in the application but until closure.

Experience matters

Many of our technicians have worked with produced water, a result of the oil and gas production, for over 15 years. Produced water is regulated under the Underground Injection Control Program. As a result, we already have deep expertise with this program. We apply the insights we’ve gained to deliver projects while regulatory regimes develop.

This team use their specialized experience to identify potential issues and mitigate environmental, financial, operational and reputational risks on these large-scale, long-term infrastructure projects.

Our experience in permitting Class VI wells

We have completed or are working on permit applications in Alabama, Colorado, Louisiana, Mississippi, North Dakota, Oklahoma, Texas and Wyoming. In addition, they have completed feasibility studies and reviews in Virginia, Pennsylvania, Alberta, and Columbia.

The team comprises energy industry professionals with various backgrounds, including geology, geoscience, engineering, regulatory, economics, and more. Using our experience from multiple fields, we support our clients throughout the regulatory process.

We advise our clients with the project life cycle from pre-injection to post-operation in mind. We understand that details in the permit application will have long-term and potentially significant operational costs. Our aim when permitting is to set our clients up for success, not just in the application but until closure.