(690a) Kinetic Hydrate Inhibitors: Gas Hydrate Induction Time Probability Distributions and Deviations from Classical Nucleation Theory

As subsea oil and gas production moves toward deeper water, high-pressure and low-temperature conditions leads to increased risk of gas hydrate formation. The agglomeration and aggregation of hydrate particles can then lead to costly pipeline plugging events. Various inhibitor chemicals can be injected into flowlines to prevent or delay hydrate formation. Unlike Thermodynamic Hydrate Inhibitors (THIs) such as methanol however, Kinetic Hydrate Inhibitors (KHIs) do not affect the hydrate phase equilibrium curve, rather they delay hydrate formation. Robust KHI performance qualification thus requires formation itself to be measured rather than the dissociation curve (which can be used to qualify THI performance). This poses a challenge since hydrate nucleation is stochastic and thus necessitates a high number of independent measurements of hydrate formation events, a requirement which is challenging to realise with conventional apparatus that are only capable of relatviely slow temperature ramping.

Here we detail the use of a high-pressure-stirred-automated-lag-time-apparatus (HPS-ALTA) to enable efficient quantification of methane hydrate formation probability in the presence of a KHI. Typically 100 independent hydrate formation events are obtained for each experimental condition, enabling the construction of smooth induction time probability distributions. We confirm previous findings in that we demonstrate that increasing KHI concentration leads to increased induction times, albeit with diminishing returns as the concentration is increased in the (1-2) wt% range. We also show that although induction times distributions are exponentially distributed for the KHI-free system (consistent with predictions from Classical Nucleation Theory), this is not the case in the presence of a KHI where our experimental data can be best described by a gamma distribution with lower relative standard deviation. This result has significance not only for understanding hydrate formation risk in the presence of KHIs but also for improving our theoretical understanding of the mechanism by which KHIs delay hydrate formation.