Adaptive Management Approach

Are sufficient data available to characterize the storage site or will new data from exploratory fieldwork be required?

What strata combination will define the storage complex? This may consist of a single reservoir and overlying seal or multiple reservoir and seal layers.

How many CO₂ injection wells will be necessary to inject the expected quantity of CO₂ at the rate it will be delivered to the site? Where should these wells be placed and to what depth?

What surface infrastructure will be necessary to transport and process the CO₂ before injection (e.g., size and length of pipeline, CO₂ cleanup needs, compression needs, etc.)?

What is the overall footprint of the storage complex, including the area of review (AOR)?

Is it necessary to secure pore space or negotiate access agreements to a portion of the storage site from affected property owners?

What are the applicable state and/or federal regulations and permitting requirements for the construction and operation of the storage system, including MVA? What data are needed to meet these regulatory and permitting requirements? Who is liable for the stored CO₂ following the cessation of active CO₂ injection?

What environmental risks exist at the site, e.g., potential leakage through legacy wellbores that could impact sensitive environmental receptors?

What project cost estimate, including additional site-characterization activities (e.g., seismic surveys, additional exploration wells, etc.), is required to finalize the facility design or secure required construction and operation permits?

What are the detailed requirements of the necessary surface infrastructure, and what are the costs to deploy and operate the surface infrastructure?

How many CO₂ injectors are needed? Where should they be placed, and how must they be constructed?

What MVA-specific elements are necessary to meet the operating and regulatory permitting requirements?

What type of surface and subsurface measurements are needed to implement the MVA program? Where should monitoring instrumentation be placed, and how often should the monitoring data be collected and analyzed?

Are deep monitoring wells required to meet the MVA program requirements? If so, how should they be constructed, and where should they be placed?

What are the costs to deploy and operate the MVA technologies?

What are the major areas of technical risk associated with the storage operations, and can they be managed within acceptable risk limits?

Is the injected CO₂ securely contained within the storage complex and conforming with model predictions?

Have any unexpected operational issues been observed, e.g., unusual pressure buildup?

Has the project risk profile changed based on field observations and the collected monitoring data?

What level of information ensures regulatory agencies that the CO₂ has been safely stored at closure and will remain in the storage complex during the postclosure period?

Is the risk profile of the site at acceptable levels? What mitigation actions will be enacted if risk levels are exceeded?

How frequently should the site risk profile be updated during the postclosure period?

Static geocellular models representing the subsurface, as well as dynamic simulations predicting the effects of injecting and storing CO₂, are important for designing a CO₂ storage system, assessing the project risks, and designing and interpreting the results of an MVA program. A primary challenge in this stage is balancing the complexity and detail of a geocellular model with the computing power and time needed to generate predictions based on that model. Modeling typically begins early in the development of a project and continues throughout the operation of the site, with precision and complexity increasing over time. For example, preliminary static models with little or no dynamic simulation may adequately meet the needs of the screening phase of the project. However, as the project moves through feasibility toward a final design, running CO₂ injection simulations becomes critical in defining the AOR and developing a better understanding of CO₂ migration risks and subsurface pressure effects. If field production or injection data exist before the start of CO₂ injection, as is often the case for CO₂ enhanced oil recovery (EOR) or depleted field sites, then simulation models can be history-matched for improved reservoir performance predictions. Because of the inherent uncertainties in the data that are used to create the static and dynamic models, they should be frequently assessed and, if necessary, revised as operating and MVA data are gathered during the operations phase of the project to allow history matching at regular intervals. Moving into the closure/postclosure phase of a project, the resulting calibrated models should be sufficient to continue supporting the interpretation of MVA data collected.

The identification and assessment (qualitative or quantitative) of the potential risks to the success of a CO₂ storage project occur early in the development of a project and are refined as more characterization, operational, and monitoring data become available. While a high-level risk assessment may be performed at the site-screening phase using generic lists of risks associated with the geologic storage of CO₂, initial risk assessments are usually conducted during the feasibility phase to create a site-specific risk register, which can be updated during subsequent phases of the project based on refined predictions of the system performance. Design-phase risk assessments are especially important since making changes in the storage system configuration and planned operations to eliminate potentially unacceptable risks is still relatively easy.

Conducting risk assessments will continue through the operation and closure/postclosure phases of the project based on data collected through the MVA program. Continuation of these efforts in latter phases of the project is important to demonstrate to the public, federal and state regulators, and other stakeholders that the risk profile of the subsurface storage of CO₂ is being continuously monitored and remains at an acceptable level.

All CO₂ storage projects require MVA activities to track the migration of injected CO₂ and confirm that the surface and subsurface environments are not negatively impacted by injection activities. MVA data have multiple uses, the primary goal to verify that the injected CO₂ and other formation fluids are contained within the target storage complex. In addition, regulatory requirements governing the storage system may require measurement of the total mass of CO₂ injected into the subsurface. These monitoring data also provide valuable information to support the other technical elements of the AMA such as the continued refinement of models and simulations and the site-specific risk assessment.

Other than baseline monitoring activities, which may be performed during the feasibility, design, or construction/operation phases of the project, MVA activities are primarily implemented during operations and will continue through closure/postclosure. Technologies including surface, near-surface, and deep-subsurface monitoring techniques will be employed as part of the MVA activities at a CO₂ storage site. Many of these techniques, e.g., geophysical logging and seismic surveys, are identical to those used during site characterization; however, the data use is different. During site characterization, data are used to gather new information and/or verify existing data related to the static geologic storage system prior to CO₂ injection. In contrast, as part of the MVA program, data are used to monitor the dynamic response of the system during active CO₂ injection and document the containment of the CO₂ in the storage complex during operation and through the closure/postclosure period.