二氧化碳所处的相态有气态、液态、固态和超临界状态，一般情况下其处在气体

二氧化碳所处的相态有气态、液态、固态和超临界状态，一般情况下其处在气体状态，但是由于地层压力大，当从二氧化碳井中开采上来时，二氧化碳通常处在超临界状 态，所以为了充分利用地层能量，节省外加能量，一般管道输送二氧化碳时会让其保持超临界状态。又由于管道输送气态二氧化碳时其相对占用空间大，运输效率低下，所以在实际操作过程中会提高二氧化碳的压力，使其达到液态或者超临界状态，而超临界状态的二氧化碳和液态的相比，其密度略小于液态的，但是粘度远远小于液态的，和气态的相当，因此，管道输送时的沿程摩阻会很大程度上的减小，所以超临界状态输送二氧化碳具有其自身的优势

The phase states of carbon dioxide include gas state, liquid state, solid state, and supercritical state. Generally, it is in a gas state. However, due to the high formation pressure, when extracted from carbon dioxide wells, carbon dioxide is usually in a supercritical state. Therefore, in order to fully utilize surface energy and save external energy, carbon dioxide is generally kept in a supercritical state when transported through pipelines. Due to the relatively large space occupied and low transportation efficiency when transporting gaseous carbon dioxide through pipelines, the pressure of carbon dioxide will be increased during actual operation, causing it to reach a liquid or supercritical state. Compared to liquid carbon dioxide, supercritical carbon dioxide has a slightly lower density but a much lower viscosity than liquid carbon dioxide, which is equivalent to gaseous carbon dioxide. Therefore, The frictional resistance along the pipeline during transportation will be greatly reduced, so supercritical carbon dioxide transportation has its own advantages

The phase states of carbon dioxide are gaseous, liquid, solid and supercritical. Generally, it is in gaseous state. However, due to the high formation pressure, carbon dioxide is usually in supercritical state when it is produced from a carbon dioxide well. Therefore, in order to make full use of formation energy and save additional energy, carbon dioxide is generally kept in supercritical state when transported by pipeline. In addition, due to the relatively large occupied space and low transportation efficiency when transporting gaseous carbon dioxide by pipeline, the pressure of carbon dioxide will be increased in the actual operation process to make it reach liquid or supercritical state, while the density of carbon dioxide in supercritical state is slightly lower than that in liquid state, but its viscosity is much lower than that in liquid state, which is equivalent to that in gaseous state. Therefore, the friction along the pipeline will be greatly reduced, so transporting carbon dioxide in supercritical state has its own advantages.