Class VI

In 2010, the EPA finalized regulatory standards for a new class of UIC wells. This new class is for the geologic sequestration of carbon dioxide (CO₂), also known as carbon capture and storage (CCS). Operators of industrial or power facilities divert CO₂ gas that would be released to the atmosphere and store it in subsurface rock formations. This injection is different from Class II enhanced oil recovery gas injection because the quantity of gas is usually greater, and the destination of the gas injected is to non-producing formations. So far, there are very few Class VI wells in the United States.

CO₂ is relatively buoyant and therefore apt to migrate toward the surface. Also, it is corrosive in the presence of water. High injection pressures and large injection volumes at CCS sites add more dimensions to the regulatory conversation. As such, these wells require sites with geology able to contain CO₂ at high volume and pressure and construction that can withstand contact with CO₂ for long periods of time.

As interest grows in carbon storage projects, more states plan to apply for primacy over these wells. North Dakota and Wyoming have already been awarded primacy. Technology for carbon capture utilization and storage projects is discussed further in our lesson on Carbon Capture Utilization and Storage Technology.