Reduction of Clathrate Hydrate Film Growth Rate by Naturally Occurring Surface Active Components

Abstract

During the production of offshore oil and gas, the cooling of hydrocarbons toward seafloor temperatures enables the formation of gas hydrates, which may restrict fluid flow and ultimately block the flowline. During the formation of a hydrate blockage, a hydrate film may grow between individual particles or between hydrate particles and the pipeline wall, respectively resulting in a higher slurry viscosity or a reduced hydraulic diameter. This hydrate film growth rate has been previously studied as a function of pressure, temperature, and hydrate guest species, but limited data are available to guide whether naturally-occurring surface active components in the oil may affect the hydrate film growth rate. In this study, we have used a micromechanical force (MMF) apparatus to quantify the film growth rate of cyclopentane hydrate at moderate subcooling. Naturally-occurring surface active species were obtained from an Australian crude oil by solvent extraction to separate out asphaltenes, binding resins, and free resins. Each crude oil fraction was then added to a chemically inert hydrocarbon phase, and the impact of the hydrate film growth rate was measured. The results illustrate that, at mass fractions below 300 ppm, the hydrate film growth rate was reduced by at least one order of magnitude with asphaltenes and free resins being the most and least effective fractions, respectively, at suppressing hydrate film growth rate. The presence of each fraction also caused an increase in the wetting angle of the water droplet on the hydrate particle surface, which suggested that these naturally-occurring components may adsorb to the hydrate particle surface. Measurements with the MMF revealed that each of the three fractions was able to reduce the hydrate particle cohesive force by two orders of magnitude.

Synergistic and Antagonistic Effects of Aromatics on the Agglomeration of Gas Hydrates

“…This could be because polycyclic aromatics yield better packing than monocyclic ones at the interface. The lower concentration of methane at the interface in the presence of aromatic compounds could reduce the hydrate growth rate 9 , which is consistent with the experimental data obtained in the presence of asphaltenes and resins 48 . When AAs are present at low surface density, fewer methane molecules are present at the interfaces compared to results obtained when no AAs are present.…”

“…On the contrary, our results show that pyrene induces an effective repulsion between two approaching hydrate substrates even when no AA is present (red solid line). The results are consistent with the suppressed cohesive force between water droplet/hydrate particle and hydrate particle in the presence of asphaltene or resin extracted from crude oils (at least by 2 orders of magnitude compared to the system without asphaltene or resin), which has been suggested to be due to the adsorption of asphaltene and resins on the hydrate-oil interface 48 . A shallow free energy well was observed for this system at ~5 nm.…”

Cyclopentane hydrates – A candidate for desalination?

“…In the next subsections, some details are provided to explain these phenomena. Presence of activated carbon particles ↓ ↓ [51] Presence of free resins, biding resins, and residual Asphaltenes NA ↓ [141] where ↑: increase; ↓: decrease; NA: Not Acknowledge.…”

“…Li et al [139] Finally, Morrissy et al [141] indicated that free resins (FR), binding resins (BR), and residual asphaltenes (RA) in the crude oil reduce CPH film growth rate with a trend in following order:…”

“…Above a given concentration threshold, these additive species are suspected to settle at the water/CP interface. Consequently, this prevents the growth of CPH crystals [141].…”