In geologic storage, CO₂ is injected under pressure into suitable geologic formations, taking advantage of the natural trapping mechanisms in those formations. In fact, the CO₂ is injected at sufficiently high pressures and temperatures so that it becomes what scientists call a "supercritical fluid." Supercritical fluids are like gases in that they can diffuse readily through the pore spaces of solids but, like liquids, they take up much less space than gases.  Supercritical CO₂ compresses further as the depth increases, increasing the amount that can be stored in the same volume of rock. High pressure at sufficient depths (i.e., greater than 800 meters [2,600 feet]) maintains the supercritical fluid state.

Illustration of Pressure Effects on CO2 The blue numbers show the volume of CO2 at each depth compared to a volume of 100 at the surface (based upon image from CO2CRC).

In order to reach CO₂ storage sites, the CO₂ is transported in pipelines.  Pipelines for transporting nearly 30 million tons per year of CO₂ for enhanced oil recovery (EOR) are available in some regions of the United States, including the Southeast and Southwest regions and the Rocky Mountains. The figure below shows the location of current CO₂ pipelines in the United States.

Location of Current CO2 Pipelines in the United States

However, new pipelines, monitoring systems, piping systems, pumping equipment, and wells will be needed for the establishment of a robust CCS industry. A study prepared for the Interstate Natural Gas Association of America Foundation found that, depending upon the quantity of CO₂ that must be stored and the degree to which EOR will be involved, the length of pipeline needed to transport CO₂ will be in the range of 15,000 miles to 66,000 miles by 2030. These statistics highlight the scaleup challenge that faces the widespread deployment of CCS. An expanded pipeline infrastructure will affect numerous stakeholders (e.g., landowners, nearby residents, pipeline companies, storage site owners, power plants, environmental groups). Therefore, examination of the associated legislative, regulatory, policy, and funding issues that might impact the deployment of pipeline technologies is needed.  The Interstate Oil and Gas compact Commission (IOGCC) released such a study in February 2011.  The report is titled, "A Policy, Legal, and Regulatory Evaluation of the Feasibility of a National Pipeline Infrastructure for the Transport and Storage of Carbon Dioxide."

The design, permitting, construction, and operation of CO₂ pipelines are comparable to natural gas pipelines because they both transport a pressurized gas and utilize carbon steel pipe. Due to these similarities, statistics such as material costs, labor costs, and difficulties in obtaining rights-of-way (ROWs) can be used to anticipate future costs and challenges.  However, there are differences between CO₂ and natural gas pipelines, including: CO₂ is transported at higher pressures, thus requiring thicker and more expensive pipe and welds; CO₂ is piped as a liquid-like supercritical fluid (as discussed above), which utilizes pumps instead of compressors; and CO₂ and natural gas require different materials for joints and seals.