Exploiting Natural Oil Surfactants to Control Hydrate Aggregation

Abstract

The growth and aggregation potential of gas hydrates in subsea flowlines are critical risk parameters for oil and gas production flow assurance. Hydrate interfaces may be exposed to water and hydrocarbon phases where natural oil surfactants may have a tendency to adsorb. The cohesion and growth between cyclopentane hydrate (structure II hydrate) particles exposed to natural oil surfactants in modified hydrocarbon phases were studied using a micromechanical force (MMF) apparatus. An Australian crude oil (unmodified), isolated asphaltenes and resins obtained via SARA fractionation and, when added to the cyclopentane phase, reduced the hydrate cohesive force by up to 98% (<1 wt % of additive). During cases of flowline shutdown, hydrate particles may have the opportunity to sinter with each other, whereby the force required to separate particles may be representative of the shear requirement to fracture aggregates in a flowline restart. The force required to separate hydrate particles was measured as a function of interparticle contact time to quantify the activity of naturally present surface-active material at resisting sintering-type phenomena. The results indicate that naturally occurring species adsorb to hydrate interfaces and decrease the extent of sintering between particles across the range of contact times studied. In a modified experimental setup, cyclopentane hydrate film growth rate measurements illustrated a comparable suppression in hydrate film growth rate to previous work. These results indicate that naturally derived surfactants from some crude oils may stabilize both water-in-oil emulsions and hydrate-in-oil suspensions. The elimination of otherwise necessary chemical management may be suitable if natural oil surfactants can perform suitable flow assurance functions.