How is the CO₂ sequestered underground?

CO₂ is stored underground by injecting it through wells into rock formations specially selected and carefully evaluated to ensure the CO₂ can be sequestered permanently and safely. Following injection, the CO₂ will remain within the injection zone and be confined by the caprock, or the sealing rock above the injection zone. Appropriate rock formations for injection are located thousands of feet below the surface and consist of rocks that can hold the CO₂. One example of an appropriate rock is sandstone, which is like beach sand that has been formed into rock over time and accommodates CO₂ in its tiny pore spaces. Above the storage formation are “sealing” formations that prevent the CO₂ from escaping. One example of a sealing rock (or caprock) is shale, which is like mud that has been formed into solid rock over time.