Enhancing the CO₂ Sequestration Potential in Subsea Terrain by Hydrate Formation from Liquid CO₂

Abstract

The oceanic sequestration has immense potential to sequestrate giga tonnes of CO 2 in a subsea environment primarily in the hydrate form. The seafloor and upper zone of subsea sediments are primarily clay-dominated loosely bound sediments. Under these subsea conditions, CO 2 will be in the liquid state during sequestration. Rheology of CO 2 hydrate formation and dissociation in loosely bound clay sediments is important to infer hydrate stability and impact on possible subsidence during hydrate dissociation, especially in slopy and muddy subsea terrain. In this work, experimental investigations on CO 2 hydrate formation in seawater using liquid CO 2 in the presence of bentonite clay (1–5 wt % in seawater) have been performed at 277.15 K and 5 MPa. Experimental pressure and temperature conditions are considered such that they closely indicate the subsea conditions. A sample hydrate promoter, tetrahydrofuran, in varying concentrations has also been used to enhance the CO 2 hydrate formation and to investigate its impact on the rheology. Hydrate slurry shows a shear thinning (pseudoplastic) rheological behavior. A peculiar trend in terms of increase in viscosity profiles during hydrate formation has been observed when THF is used, whereas minimal changes in the viscosity of the CO 2 hydrate slurry are observed in the absence of THF. The magnitude of shear stress and viscosity increases with THF concentration in the solution. However, the synergism between bentonite and THF at different concentrations also plays a crucial role in hydrate growth and stability. This work is crucial for understanding CO 2 hydrate formation from liquid CO 2, typically at higher CO 2 injection depths in clay-bound oceanic sequestration conditions, and will be useful to examine hydrate formation, flow tendency, and rheology in slopy and muddy subsea terrains.

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