Carbon dioxide can be stored as a liquid in deep underground conditions that over time will solidify into new minerals.

Carbon dioxide can be stored deep underground reservoirs generally greater than 2600 ft (800 m) below the land surface with sufficient pore space and permeability such as saline reservoirs, basalt flows, active and depleted oil and gas reservoirs.

Carbon dioxide is stored at depths generally well below groundwater aquifers. In addition storage is emplaced under impermeable seals that prevent it from migrating upwards into shallower environments.

It shouldn’t. Carbon storage is required to be much deeper (1000s of feet below) any source of drinking water. Carbon can only be stored in places where there is impermeable rock between the carbon storage zone and drinking water sources.

There are numerous examples of naturally occurring underground deposits of CO2 (as well as other gasses like natural gas, helium, and nitrogen). These deposits show that gasses can stay in underground rock layers for millions of years. CO2 has been injected safely into two fields in the Permian Basin for Enhanced Oil Recovery for 50 years with no documented escape to the surface.

While rocks are often thought of as solid, many types of rocks (like sandstones and limestones) are porous. These pores tend to be smaller than the pores in a sponge, but can often add up to 25% or more of the rock being empty space that can be filled with water, oil, natural gas or CO2.

No. In CO2 injection, the goal is to inject it at pressures that are low enough that the storage rock is not fractured apart. CO2 is injected into rocks (storage reservoirs) that are thousands of feet deep. The best reservoirs have lots of pore space (high porosity) that is easy to inject the gas into (high permeability). The reservoirs are contained above and below by rocks that are good seals  — unfractured rock that is strong, impermeable, and hard to break even with very high pressure.

Not necessarily, especially if the project uses anthropogenic Not necessarily, especially if the project uses anthropogenic CO2 from a source like a gas processing plant, power plant, ethanol plant or other industrial source. In a project where CO2 is used for enhanced oil recovery, much of the CO2 that is injected underground actually stays there. Some is dissolved into the other reservoir fluids (oil and brine), some is trapped by capillary forces in very tiny pores, and some is actually trapped by reacting with fluids and rocks in the reservoir to become new minerals. Unless the CO2 is removed on purpose, estimates and modeling predict that between 70 and 90% of the CO2 remains underground after a project is finished. CO2 enhanced recovery is often used in older oil fields where there is infrastructure and equipment in place; this may further reduce the carbon footprint of the operation over what would be associated with manufacture of new equipment for other types of energy production. from a source like a gas processing plant, power plant, ethanol plant or other industrial source. In a project where CO2 is used for enhanced oil recovery, much of the CO2 that is injected underground actually stays there. Some is dissolved into the other reservoir fluids (oil and brine), some is trapped by capillary forces in very tiny pores, and some is actually trapped by reacting with fluids and rocks in the reservoir to become new minerals. Unless the CO2 is removed on purpose, estimates and modeling predict that between 70 and 90% of the CO2 remains underground after a project is finished. CO2 enhanced recovery is often used in older oil fields where there is infrastructure and equipment in place; this may further reduce the carbon footprint of the operation over what would be associated with manufacture of new equipment for other types of energy production.

CO2 has been injected for many years into oilfields without inducing significant seismicity. What has been learned is that geomechanical assessment to understand potential earthquake risk is an important part of site selection for any project that injects fluids into the earth. Engineers and geoscientists choose subsurface locations without active faults or locations where faults might be reactivated.

There are many reasons why carbon capture and storage (CCS) should be a part of the energy system in the future. One important reason is that some forms of renewable energy are intermittent. The sun does not shine 24 hours a day and the wind only blows part of the time. Hence, either energy storage or CCS are needed for very low or zero emissions of CO2. CCS provides a rapid path for reducing emissions of CO2 to the atmosphere and for utilizing a greater amount of intermittent renewable energy without having to build expensive energy storage facilities.