The kinetic effects of hydrate anti-agglomerants/surfactants

Abstract

The addition of anti-agglomerants (AAs) is a promising solution for decreasing the risk of gas hydrate plugging in deepwater hydrocarbon flowlines or during drilling operations. AAs (usually surfactants) can adsorb on small hydrate particles and make them dispersing, thus leading to the prevention of agglomeration. However, it is not fully clear whether AAs promote or inhibit hydrate nucleation and growth during this process. Here, a series of AAs/surfactants (dodecyl benzene sulfonic acid, 1-naphthylacetic acid, tetramethyl ammonium bromide, Span80, rhamnolipid, and cocamidopropyl dimethylamine) with different types and concentrations were studied so as to clarify the effects of AAs/surfactants on formation kinetics of CH4 hydrate using a dynamic experimental system. In the experiments, 20%, 60%, 95%, 100% water-cut systems with or without 0.5 wt% and 1.0 wt% concentrations of AAs/surfactants were pressurized with CH4 at 3.0 °C and 6.0 MPa. The induction time, the amount of hydrate formation, and the average rate of hydrate growth in these systems were measured. The results show that AAs/surfactants can promote hydrate formation in pure water (100%) and high water cut (95%) systems. Only in these high water cut systems will the pressure decrease in a multi-step manner. The occurrence of this interesting phenomenon is related to the water cut and the type of AAs, which may be due to the rapid hydrate formation and large expansion of the hydrate volume. While in relatively low water cut (20% and 60%) systems, AAs/surfactants slow down or even completely prevent the hydrate nucleation and growth under our experimental conditions, which may mainly result from the mass transfer barrier of AAs/surfactants. This study will be conducive to revealing the kinetic inhibition mechanism of AAs on hydrate agglomeration, and can be of importance to the safe implementation of multiphase flow transportation and deepwater oil and gas exploration.