A portion of the captured CO₂ can be reused by the food and chemical industries. However, the needs of industry fall far short of the quantities potentially recoverable.

Although the various possible options for geological storage are at different stages of maturity, all solutions will have to store the CO₂ at sufficient depth (more than 800 meters) in order for the gas to reach the supercritical state and thus occupy the smallest possible volume.

Storage in depleted oil and natural gas reservoirs

This type of storage offers numerous advantages, the most significant being that the cap rock is impermeable and well known. Indeed, natural reservoirs have proven their capacity to contain hydrocarbons for several million years. Moreover, CO₂ storage in this type of formation is a practice which, although not widespread, is at least known to the oil and gas industry, which already injects CO₂ into oilfields to reduce crude oil viscosity, improve mobility and thereby boost the recovery rate – a technique known as Enhanced Oil Recovery (EOR). Finally, some of the infrastructure in place for exploration and production of crude oil (such as pipes and wells) can be reused for CO₂ storage operations, thereby helping to control costs.

However, reservoirs are not always located near the source of CO₂ emissions; nor is the available storage capacity sufficient to meet all needs.

Storage in unminable coal beds

In this option, the coal bed is not used as a reservoir, but stores the CO₂ by absorption of the gas. Provided the coal bed is adequately covered over by impermeable cap rock, this technique would allow not only storage of CO₂ but also methane recovery (ECBMR – Enhanced Coal Bed Methane Recovery).

However, present understanding of this type of storage is still incomplete.

Storage in saline aquifers

There are numerous such aquifers located in sedimentary basins, with areas of up to several thousand square kilometers. They can be either offshore or onshore. Formed of porous, permeable rock often saturated with brackish water or brine that is unfit to drink, these aquifers are potential storage sites for considerable quantities of CO₂, provided they are at a sufficient depth (> 800 meters) and have overlying impermeable layers.

However, extensive work is still needed to gain better knowledge of these aquifers.

Diagram of carbon dioxide storage types