When CO2 is injected into geological formations 800m or below, what state is it in?

When CO2 is injected into geological formations at depths of 800m or more, it is in a supercritical state.

Here's a step-by-step explanation:

1. Carbon dioxide (CO2) can exist in three states: solid, liquid, and gas. The state depends on the temperature and pressure conditions.

2. At standard atmospheric conditions, CO2 is a gas.

3. However, when CO2 is subjected to high pressure and temperature conditions, it can become a supercritical fluid. This state has properties of both a gas and a liquid.

4. The critical point of CO2 is at a pressure of 7.38 MPa (about 73 atmospheres) and a temperature of 31.1 °C. Above these conditions, CO2 will be in a supercritical state.

5. When CO2 is injected into geological formations at depths of 800m or more, the pressure and temperature conditions exceed the critical point of CO2. The pressure at such depths is much higher than 73 atmospheres, and the temperature is also typically higher than 31.1 °C.

6. Therefore, at these depths, CO2 is in a supercritical state. In this state, CO2 has the ability to dissolve in water, making it a suitable medium for geological sequestration of carbon dioxide.