(413h) Evaluating CO2 Hydrate Stability in Oceanic Sediments for CO2 Sequestration

Increase in atmospheric carbon dioxide (CO₂) emissions is a major global problem, resulting in global climate change and other issues such as increasing sea levels, melting Arctic ice sheets, flooding, land loss, and the development of a variety of diseases that are harmful to human health. Global CO₂ emissions were expected to reach 36.4 GtCO₂ in 2021. The United Nations Climate Conference COP26 Glasgow [2021] strongly emphasized developing action plans to achieve the Paris Agreement's [2015] goal of a zero-carbon economy by 2050. Carbon Capture and Storage (CCS) is widely regarded as a critical technology for achieving this aim and it has the potential to considerably reduce CO₂ emissions in the atmosphere.

Oceanic CO₂ sequestration using gas hydrates is a potential storage approach that is receiving increased interest and research for areas without conventional geologic storage. Gas hydrates are crystalline compounds that are formed when small CO₂ molecules are trapped within water molecules at high pressure and low-temperature conditions. One unit of gas hydrate can store up to 184 units of gas at STP. Converting CO₂ captured from industry emissions into liquid CO₂ and injecting it into the deep ocean sediments to be stored as gas hydrates offers an additional option to existing storage methods. However, the key concern to alleviate is the stability of the CO₂ hydrates underneath the deep oceanic sediments or sea bed.

In this work, stability of the CO₂ hydrates in oceanic sediments has been evaluated on a lab-scale for an extended period [14-30 days] using a high-pressure reactor system mimicking the thermodynamic conditions [10 MPa, 4 ^oC] found at the oceanic depth of 1 Km. The high-pressure reactor was equipped with two cameras mounted at the top and front of it. First, the CO₂ hydrates were formed across the sediments [Silica sand] using CO₂ gas, and then these hydrates were submerged in the water column for the period of 14-30 days. The experimental results indicate that the CO₂ hydrates hold an adequate level of stability and a good amount of hydrates were visible across the sediments throughout the stability test. Intentional heating and depressurization of the system after the stability test also indicated that the hydrates inside the sediments tend to be more stable than the hydrates at the surface of the sand bed.