(4ck) Prospects of CO2 Sequestration in Deep Oceanic Sediments Using Experimental and Modelling Approaches

To limit global temperature rise to within 2°C by 2050, cumulative carbon emissions between 2011 and 2050 must be constrained to approximately 1100 GtCO₂. This requires the annual removal of gigatons of CO₂ from the atmosphere, a challenge that current technologies are not adequately equipped to meet. One potential way to manage a large amount of CO₂ in less time is to inject CO₂ at a depth of 1 km in deep-sea sediments, where, CO₂ will be locked into the high storage capacity hydrate lattice (184 m³ /m³). Hydrate is a crystalline compound that is formed at high-pressure and low-temperature conditions (ideally found in deep seas), where guest molecules are encapsulated into the cage formed by water molecules. Similar to the natural gas hydrates in oceanic sediments that have been stable for millions of years. However, no experimental evidence is available, and lab/pilot scale studies are crucial for the field scale test. So, a high-pressure reactor was set up, outfitted with a variety of sensors and in-situ measurement tools. Afterward, CO₂ hydrate dynamics, morphologies, and various parameters were recorded.

Initially, using liquid CO₂, fundamental studies were conducted to investigate the CO₂ hydrate formation within water, brine, and seawater media in both stirred/unstirred and sediment mediums. Visual results suggested three stages of hydrate formation: nucleation, film formation, and bulk hydrate formation in the stirred/unstirred medium. The kinetic promoter L-tryptophan (300–1000 ppm) enhanced the formation kinetics in stirred experiments, while interfacial hydrate formation hindered kinetics in unstirred media. Sediment presence significantly improved CO₂ hydrate kinetics compared to unstirred conditions.

Subsequently, CO₂ hydrate dynamics were studied in sediments of varying size and porosity. A novel four-parameter CO₂ hydrate kinetics model was developed and using a supervised machine learning algorithm, trained on 32,843 experimental data points. This model predicted water-to-hydrate conversion with an Average Absolute Relative Deviation [%AARD] of 4.23–13.29%. The conversion efficiency followed the order: dual-layered sand [88.26 (±4.62)%] > coarse [77.77 (±5.72)%] > granules [65.36 (±2.3)%].

Lastly, for the first time, the liquid CO₂ potential for CO₂ sequestration as hydrates was examined experimentally on the lab scale. In addition to that, the CO₂ hydrate stability test was done at a thermodynamic condition equivalent to 1 km deep sea to evaluate the long-term feasibility of CO₂ storage. Lab-scale experiments indicated that liquid CO₂ forms hydrates 60 times faster than gaseous CO₂ in sediments. These hydrates demonstrated substantial stability over 14 days under aqueous conditions [3–4 °C, 10 MPa]. Hydrate dissociation by thermal stimulation confirmed significant CO₂ hydrate presence within sediments, proving the feasibility of hydrate-based CO₂ sequestration technology.

Research Interests: Carbon Capture and Sequestration, Clathrate Hydrate, Energy Transition, Climate Change, and Mathematical Modeling,