Geological Storage of Carbon Dioxide: The Role of Sedimentary Basins

Abstract

Sedimentary basins, occuring throughout the world, are thick piles of geologically deposited sediments that are the hosts for fossil fuel deposits. They may become even more important in the future if their large storage capacity is utilized for disposing of carbon dioxide. Sedimentary basins are dynamic, in the sense that they have an intricate plumbing system defined by the location of high and low permeability strata that control the flow of fluids throughout the basins and define "hydrogeological" traps. The most secure type of hydrogeological trapping is found in oil and gas reservoirs in the form of "structural" or "stratigraphic" traps, termed "closed" hydrogeological traps which have held oil and gas for millions of years. Obviously, these would be very attractive for CO₂ storage due to their long history of containment. A second type of hydrogeological trapping has been recognized in aquifers of sedimentary basins that have slow flow rates. The pore space in such "open" hydrogeological traps is usually filled with saline ground or formation water. A volume of CO₂ injected into a deep open hydrogeological trap can take over a million years to travel updip to reach the surface and be released to the atmosphere. Although the capacity of structural/stratigraphic traps for CO₂ storage is small relative to open hydrogeological traps in deep sedimentary basins, they are likely to be used first as they are known to be secure, having held oil and gas for geological time. As the capacity of closed traps is exhausted and more is learned about geochemical trapping, the large storage capacity available in open hydrogeological traps will be utilized where security of the geological storage of CO₂ can be enhanced by geochemical reactions of the CO₂ with basic silicate minerals to form carbonates. Potential short circuits to the surface through faults or abandoned wells must be located and their stability evaluated before injection of CO₂. In any event, a monitoring scheme must be put in place. This CO₂ storage technology could be the basis for transition from a fossil fuel based energy economy to one based on renewables over the next 100 years.