CO2 hydrate stability in oceanic sediments under brine conditions

Carbon capture and storage (CCS) is a critical approach to reducing atmospheric carbon emissions. The United Nations [UN] Climate Change Conference COP26 Glasgow [2021] emphasized setting execution plans to reach the goal of a zero-carbon economy by 2050 as per the Paris Agreement [2015]. CO2 sequestration in deep-sea sediments in the form of clathrate hydrates is a promising technique as it provides a significant capacity for CO2 storage. Deep-sea sediments contain high salinity water, which will impair the CO2 storage capacity and hydrate stability. Therefore, it's essential to examine the effect of salinity on CO2 hydrate stability in simulated deep-sea sediments to foster real-time field application. In this first-gen experimental work, the stability of CO2 hydrates across and inside the deep oceanic saline sediments has been evaluated for an extended period [14 days]. An artificial seabed, saturated with saline solution [3.5 wt% NaCl], was created using silica sand inside a high-pressure reactor system and stability tests were conducted at oceanic conditions (10 MPa, 4 °C). In phase 1, CO2 hydrates were formed across the seabed by pressurizing the system multiple times to 3.5 MPa using pure CO2 gas. In phase 2, the hydrates were immersed in a brine solution [3.5 wt% NaCl] and their stability was observed over 2 weeks [>14 days]. The experimental results indicate that CO2 hydrates are adequately stable when submerged inside the brine solution and layers of hydrates were visible at the end of 2 weeks of the stability experiment. In phase 3, a hybrid depressurization heating approach was used at the end of the stability test to confirm the presence of a good quantity of CO2 hydrates inside the sand bed.