Kinetics of Methane Hydrate Inhibition in MgBr2, CaBr2, and ZnBr2 Solutions

Abstract

Hydrate inhibition in the presence of high-density completion fluids such as bromide salts relevant in completion and workover operations and natural gas transportation pipelines is less studied in the literature. In this work, an experimental investigation has been carried out to study the kinetics of methane hydrate formation and dissociation in the presence of MgBr2, CaBr2, and ZnBr2 solutions at 1, 3, 5, 10, and 15 wt % concentrations to understand the effect of these salts on hydrate inhibition compared to pure water. The presence of salts decreases the moles of methane consumed, and the consumption decreases with an increase in the salt concentration. A stronger hydrate inhibition is observed in the presence of MgBr2 solution than in CaBr2 and ZnBr2. The hydrate formation rate decreased with the passage of time, but the rate was higher later if there were two induction points, such as in the case of 3, 5, and 10 wt % solutions of MgBr2 and 5 wt % solutions of CaBr2. The water-to-hydrate conversion (W–H) and the gas-to-hydrate conversion (G–H) decrease with an increase in concentration of the salt. The maximum reduction in W–H and G–H conversions observed is ∼55% when MgBr2 is present in 15 wt % concentrations compared to pure water. The number of moles of methane recovered during hydrate dissociation is maximum in the case of pure water, followed by ZnBr2 solutions, while for CaBr2 and MgBr2 solutions, it is almost the same when these salts are in 15 wt % concentrations. The hydrate dissociation rate is the highest in the case of pure water, but there are intervals of time when the dissociation rate in the MgBr2 and CaBr2 solutions observed is higher than that in pure water.