Product Summary

Technical Approaches to Stacked Storage

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. A stacked storage approach may include a colocated combination of dedicated storage in saline aquifers and storage associated with enhanced oil recovery in hydrocarbon-bearing intervals. However, this investigation was predominantly focused on dedicated storage in stacked saline aquifers. Advantages for using stacked storage include accessing more of the pore space available in a given area, which allows for a smaller project area and may result in a reduced area of review (AOR), which can minimize the number of legacy well penetrations needing review for containment assurance. The area requiring monitoring may also be reduced, which can result in significant cost reductions over the life of a project. A smaller project area may also reduce the number of landowners involved in the project and ease pore space leasing and unitization/amalgamation efforts. Using multiwell pads to access stacked storage can consolidate surface facilities and CO₂ distribution systems, which can minimize environmental risks and impacts. Stacked storage also creates some unique design and operational considerations. Some of the most significant considerations include the following: 1) Corrosion-resistant casing and cement across each of the storage intervals increases material costs. 2) The use of multireservoir injection well completions is much more complex, more expensive, and increases operational risks. 3) On-site equipment is necessary to support different injection pressures needed for each storage formation on a multiwell pad. 4) Stacked storage reservoirs with little vertical separation may be difficult to image separately with seismic monitoring methods. 5) Legacy wellbores within the AOR and unitized/amalgamated area for a stacked storage project will need to be assessed for compliance over each storage complex. 6) The potential geomechanical effects of injection in multiple intervals on interburden and on the cap rock of the uppermost injection interval are not well understood. Several sedimentary basins within the Plains CO₂ Reduction Partnership region contain multiple potential storage units that could be amenable for stacked CO₂ storage. A growing number of prospective CO₂ projects in the region are considering stacked storage scenarios.