(413b) Stacked Storage: Technical Considerations and Examples of Potential Reservoirs

When two or more CO₂ storage targets are present in the subsurface at the same geographic location, a CO₂ storage project may pursue a stacked storage approach. This investigation was predominantly focused on dedicated storage in stacked saline aquifers. A collocated combination of dedicated storage in saline aquifers and storage associated with enhanced oil recovery in hydrocarbon-bearing intervals is also a possibility.

Stacked storage has advantages that include accessing more pore space within a given surface area footprint, which allows for a smaller project area and, possibly, a reduced area of review (AOR). A smaller project area can minimize the number of legacy well penetrations needing review for containment assurance, reduce the number of landowners involved in pore space leasing efforts, and realize significant cost savings over the life of a project due to a smaller monitoring area. Multiwell pads to access stacked storage can consolidate surface facilities and CO₂ distribution systems and minimize environmental risks and impacts.

Stacked storage may require special design and operational considerations. Significant considerations include the following:

Corrosion-resistant casing and cement across each of the storage intervals may increase material costs.

• Multireservoir injection well completions are more complex, more expensive, and increase operational risks.
• On-site equipment to support different injection pressures for each storage formation may be needed.
• Legacy wellbores within the AOR and CO₂ storage project area will need to be assessed for integrity across each storage complex.
• The geomechanical effects of injection into multiple intervals on interburden and on the cap rock of the uppermost injection interval will need to be evaluated.

Several sedimentary basins within the U.S. Midwest and Mountain West regions contain multiple potential storage units that could be amenable for stacked CO₂ storage. Several prospective CO₂ projects in the region under development are considering stacked storage scenarios.