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

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 1 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 2 orders of magnitude.