How does carbon dioxide that is injected underground stay there?
Only certain geologic formations are amenable to carbon dioxide storage. In general, carbon dioxide can be stored in a layer of permeable rock that has a thick layer of impermeable rock above it. Permeable rock has pores through which fluids can flow and gather. Fluids cannot pass through impermeable rock, and so the top layer traps carbon dioxide that is injected into the permeable formation. Such cavities are the same type of formation that have trapped crude oil and natural gas over millions of years, and geologic formations are already used for disposal of hazardous wastes, so the idea of injecting a fluid underground for storage is not completely new.
