Factors controlling hydrate film growth at water/oil interfaces

Spontaneous Lifting and Self-Cleaning of Gas Hydrate Crystals

Crystal fouling, which refers to the accumulation of precipitates on surfaces and the associated damage, is a common problem in many industrial processes. In deepwater oil and gas transportation, hydrate blockage poses as a considerable barrier. Consequently, modifying hydrophobicity of surfaces has become an increasingly focused strategy to mitigate hydrate. However, the design of surfaces that effectively control the hydrate remains challenging. Herein, we report a superior smooth anti-hydrate material based on silanized modification. The low-adhesion silanized silicon wafer (SSW) realizes a win-win strategy of hard formation and easy removal. Through a comprehensive study combining experimental validation with theoretical analysis, the unique characteristics of SSW in the field of anti-hydrate surfaces were deeply discussed. Various hydrate crystals exhibited a completely different hydrate growth mode at the SSW surface, in which hydrate crystals spontaneously elevated and lifted themselves off from the surface. The presence of the fluorine element on the SSW surface allowed self-lifting growth of hydrate crystals after they covered the water droplet. And the loose and porous crystal structure in this self-lifting growth could reduce the contact area between the hydrate crystals and the substrate, allowing the crystals with minimal adhesion force and removal disturbance. Furthermore, the gas enrichment on the SSW surface also reduced the contact with the substrate, thereby decreasing the adhesion and allowing self-cleaning behavior. These results indicate that the silanized surface is a promising candidate for developing anti-hydrate materials for hydrocarbon production and transportation industry.

Study on the Growth Kinetics and Morphology of Methane Hydrate Film in a Porous Glass Microfluidic Device

Natural gas hydrates are widely considered one of the most promising green resources with large reserves. Most natural gas hydrates exist in deep-sea porous sediments. In order to achieve highly efficient exploration of natural gas hydrates, a fundamental understanding of hydrate growth becomes highly significant. Most hydrate film growth studies have been carried out on the surface of fluid droplets in in an open space, but some experimental visual works have been performed in a confined porous space. In this work, the growth behavior of methane hydrate film on pore interior surfaces was directly visualized and studied by using a transparent high-pressure glass microfluidic chip with a porous structure. The lateral growth kinetics of methane hydrate film was directly measured on the glass pore interior surface. The dimensionless parameter (−∆G/(RT)) presented by the Gibbs free energy change was used for the expression of driving force to explain the dependence of methane hydrate film growth kinetics and morphology on the driving force in confined pores. The thickening growth phenomenon of the methane hydrate film in micropores was also visualized. The results confirm that the film thickening growth process is mainly determined by water molecule diffusion in the methane hydrate film in glass-confined pores. The findings obtained in this work could help to develop a solid understanding on the formation and growth mechanisms of methane hydrate film in a confined porous space.

Gas hydrates in sustainable chemistry

This review includes the current state of the art understanding and advances in technical developments about various fields of gas hydrates, which are combined with expert perspectives and analyses.

Simulating Gas-Liquid-Water Partitioning and Fluid Properties of Petroleum under Pressure: Implications for Deep-Sea Blowouts

With the expansion of offshore petroleum extraction, validated models are needed to simulate the behaviors of petroleum compounds released in deep (>100 m) waters. We present a thermodynamic model of the densities, viscosities, and gas-liquid-water partitioning of petroleum mixtures with varying pressure, temperature, and composition based on the Peng-Robinson equation-of-state and the modified Henry's law (Krychevsky-Kasarnovsky equation). The model is applied to Macondo reservoir fluid released during the Deepwater Horizon disaster, represented with 279-280 pseudocomponents, including 131-132 individual compounds. We define >n-C8 pseudocomponents based on comprehensive two-dimensional gas chromatography (GC × GC) measurements, which enable the modeling of aqueous partitioning for n-C8 to n-C26 fractions not quantified individually. Thermodynamic model predictions are tested against available laboratory data on petroleum liquid densities, gas/liquid volume fractions, and liquid viscosities. We find that the emitted petroleum mixture was ∼29-44% gas and ∼56-71% liquid, after cooling to local conditions near the broken Macondo riser stub (∼153 atm and 4.3 °C). High pressure conditions dramatically favor the aqueous dissolution of C1-C4 hydrocarbons and also influence the buoyancies of bubbles and droplets. Additionally, the simulated densities of emitted petroleum fluids affect previous estimates of the volumetric flow rate of dead oil from the emission source.