CO₂-rich gas injection into natural gas hydrate reservoirs is proposed as a carbon-neutral, novel technique to store CO₂ while simultaneously producing CH₄ gas from methane hydrate deposits without disturbing geological settings. This method is limited by the mass transport barrier created by hydrate film formation at the liquid–gas interface. The very low gas diffusivity through hydrate film formed at this interface causes low CO₂ availability at the gas–hydrate interface, thus lowering the recovery and replacement efficiency during CH₄-CO₂ exchange. In a first-of-its-kind study, we have demonstrate the successful application of low dosage methanol to enhance gas storage and recovery and compare it with water and other surface-active kinetic promoters including SDS and L-methionine. Our study shows 40–80% CH₄ recovery, 83–93% CO₂ storage and 3–10% CH₄-CO₂ replacement efficiency in the presence of 5 wt% methanol, and further improvement in the swapping process due to a change in temperature from 1–4 °C is observed. We also discuss the influence of initial water saturation (30–66%), hydrate morphology (grain-coating and pore-filling) and hydrate surface area on the CH₄-CO₂ hydrate swapping. Very distinctive behavior in methane recovery caused by initial water saturation (above and below S_wi = 0.35) and hydrate morphology is also discussed. Improved CO₂ storage and methane recovery in the presence of methanol is attributed to its dual role as anti-agglomerate and thermodynamic driving force enhancer between CH₄-CO₂ hydrate phase boundaries when methanol is used at a low concentration (5 wt%). The findings of this study can be useful in exploring the usage of low dosage, bio-friendly, anti-agglomerate and hydrate inhibition compounds in improving CH₄ recovery and storing CO₂ in hydrate reservoirs without disturbing geological formation. To the best of the authors’ knowledge, this is the first experimental study to explore the novel application of an anti-agglomerate and hydrate inhibitor in low dosage to address the CO₂ hydrate mass transfer barrier created at the gas–liquid interface to enhance CH₄-CO₂ hydrate exchange. Our study also highlights the importance of prior information about methane hydrate reservoirs, such as residual water saturation, degree of hydrate saturation and hydrate morphology, before applying the CH₄-CO₂ hydrate swapping technique.

The concentration of surfactant in solution for which micelles start to form, also known as critical micelle concentration is a key property in formulation design. The critical micelle concentration can be determined experimentally with a tensiometer by measuring the surface tension of a concentration series. In analogy with experiments, in-silico predictions can be achieved through interfacial tension calculations. We present a newly developed method, which employs first principles-based interfacial tension calculations rooted in COSMO-RS theory, for the prediction of the critical micelle concentration of a set of nonionic, cationic, anionic, and zwitterionic surfactants in water. Our approach consists of a combination of two prediction strategies for modelling two different phenomena involving the removal of the surfactant hydrophobic tail from contact with water. The two strategies are based on regular micelle formation and thermodynamic phase separation of the surfactant from water and both are required to take into account a wide range of polarity in the hydrophilic headgroup. Our method yields accurate predictions for the critical micellar concentration, within one log unit from experiments, for a wide range of surfactant types and introduces possibilities for first-principles based prediction of formulation properties for more complex compositions.

Geological sequestration of CO₂-rich gas as a CO₂ capture and storage technique has a lower technical and cost barrier compared to industrial scale-up. In this study, we have proposed CO₂ capture and storage via hydrate in geological formation within the hydrate stability zone as a novel technique to contribute to global warming mitigation strategies, including carbon capture, utilization, and storage (CCUS) and to prevent vast methane release into the atmosphere caused by hydrate melting. We have attempted to enhance total gas uptake and CO₂ capture efficiency in hydrate in the presence of kinetic promoters while using diluted CO₂ gas (CO₂-N₂ mixture). Experiments are performed using unfrozen sands within hydrate stability zone condition and in the presence of low dosage surfactant and amino acids. Hydrate formation parameters, including sub-cooling temperature, induction time, total gas uptake, and split fraction, are calculated during the single-step formation and dissociation process. The effect of sands with varying particle sizes (160–630 µm, 1400–5000 µm), low dosage promoter (500–3000 ppm) and CO₂ concentration in feed gas (20–30 mol%) on formation kinetic parameters was investigated. Enhanced formation kinetics are observed in the presence of surfactant (1000–3000 ppm) and hydrophobic amino acids (3000 ppm) at 120 bar and 1 ℃ experimental conditions. We report induction time in the range of 7–170 min and CO₂ split fraction (0.60–0.90) in hydrate for 120 bar initial injection pressure. CO₂ split fraction can be enhanced by reducing sand particle size or increasing the CO₂ mol% in incoming feed gas at given injection pressure. This study also reports that formation kinetics in a porous medium are influenced by hydrate morphology. Hydrate morphology influences gas and water migration within sediments and controls pore space or particle surface correlation with the formation kinetics within coarse sediments. This investigation demonstrates the potential application of bio-friendly amino acids as promoters to enhance CO₂ capture and storage within hydrate. Sufficient contact time at gas-liquid interface and higher CO₂ separation efficiency is recorded in the presence of amino acids. The findings of this study could be useful in exploring the promoter-driven pore habitat of CO₂-rich hydrates in sediments to address climate change.

Industrial-scale capture, storage, and transport of gases and gas mixtures, such as natural gas, CH₄, and CO₂ in the form of gas hydrate, is an attractive and feasible solution. However, low formation rate and low water-to-hydrate conversion make it challenging to adopt at commercial scale. Selection of an appropriate chemical as hydrate promoter is crucial to the success of such technologies. Amino acids are seen as potential chemicals to use in such applications due to their environmentally benign nature. However, there are uncertainties around their behavior and classification, since their thermodynamic and kinetic effects on gas hydrates are not well established. In this study, we have identified the kinetics of select amino acids (L-valine, L-methionine, L-histidine, and L-arginine) in methane hydrate formation. Results indicate that hydrophobicity of amino acids plays an important role in methane hydrate kinetics. L-methionine and L-valine show maximum normalized gas uptake and lowest induction time compared to L-histidine and L-arginine.