Methane Hydrate Growth Kinetics in the Presence of Alkaline Solutions of Sodium Hydroxide and Calcium Hydroxide: Experiments and Modeling

Abstract

Methane hydrate formation frequently causes flow assurance-related issues in the oil and gas sector. Alkalis such as caustic soda (NaOH) and slaked lime [Ca(OH) 2 ] find various applications in oil/gas exploration and production. The effects of these alkalis on the growth kinetics of methane hydrate have not been thoroughly investigated. In this work, methane hydrate growth kinetics with 0.1, 0.5, 1, 2, and 4 wt % aqueous solutions of NaOH and Ca(OH) 2 have been studied separately at 8 MPa and 274.15 K in a high-pressure stirred tank reactor. Essential metrics like gas uptake, water-to-hydrate, and gas-to-hydrate conversions, hydrate yield, and t 90 (the interval between the beginning of the hydrate growth and 90% of the final gas uptake) are reported. Fascinating influence of these alkalis on methane hydrate growth was observed, as the final methane uptake was reduced by 23% compared to pure water with 4 wt % NaOH, while 30% enhancement was observed with 0.1 wt % NaOH. Besides, a 30% rise in the final methane uptake was achieved with 0.1 wt % of Ca(OH) 2 . Furthermore, t 90 values showed that using alkalis delayed the methane hydrate growth. A kinetic model based on the Englezos−Bishnoi model was used with suitable modifications to estimate the combined rate parameter for methane hydrate growth and predict the gas uptake profiles with pure water and aqueous solutions of the alkalis. The absolute average relative deviations (AARD %) in predicted gas uptake from the experimental data were measured. Despite the highly stochastic nature of hydrate growth kinetics, the average AARD % of the predicted values from the experiment was 7.72%, which suggests a fair accuracy of the model. This work will help develop a potent and cost-effective alkali-based kinetic inhibitor for methane hydrate to combat flow assurance-related issues.