Evaluating liquid CO2 hydrate formation kinetics, morphology, and stability in oceanic sediments on a lab scale using top injection

Abstract

Storing captured CO2 into the deep oceanic sediments as CO2 hydrates offers a potential approach to reducing atmospheric carbon emissions. However, two major challenges are slow CO2 hydrate formation kinetics and lack of an understanding of CO2 hydrate stability dynamics. To counter these challenges, the conversion of high-pressure liquid CO2 (LCO2) to CO2 hydrates has been experimentally explored [with and without a hydrate kinetic promoter L-tryptophan] in a lab-scale reactor embedded with an artificial seabed. The stability of these CO2 hydrates was also evaluated by submerging them in the aqueous phase (mimicking hydrostatic pressure of fluid) at thermodynamic conditions found at an oceanic depth of 1 km [3–4 °C, 10 MPa] for 14 days. In-situ high-pressure Raman spectroscopy was used to estimate the real-time solubility of CO2 in the aqueous medium, and an image processing thresholding technique was used for detecting CO2 hydrate formation/dissociation patterns in sediments during the stability testing.The lab-scale experimental results indicate that in comparison to gaseous CO2, the liquid CO2 forms hydrates much faster [60 times] in the sediments. These CO2 hydrates exhibited decent stability over 14 days when submerged in an aqueous medium [3–4 °C, 10 MPa]. At the end of the stability test, hydrates were dissociated by thermal stimulation to assess the CO2 hydrates inside the sediments qualitatively. A significant decrease in the height of the sand bed [6.0 cm to 5.5 cm] and the evolution of CO2 across the sediments confirmed the presence of a good number of hydrates inside the sediments.