Characterization of kinetics of hydrate formation in the presence of kinetic hydrate inhibitors during deepwater drilling

• A method to characterize the kinetics of gas hydrate formation was introduced.
• Three periods could be identified by means of the combined method.
• Typical lactam KHIs are more efficient in preventing hydrate growth than nucleation.
• Variation in vinyl lactam KHI concentration mainly affects the hydrate growth period.

An analysis method to characterize the kinetics of gas hydrate formation in downhole dynamic conditions was introduced by combining two plots, one is the pressure versus temperature plot, and the other is pressure and temperature versus time plot. By means of the combined method, the induction time, hydrate growth period and catastrophic formation period could be identified. The typical kinetic hydrate inhibitors (KHIs) which were all vinyl lactam polymers, were chosen for testing, including PVCap (Polyvinyl caprolactam), PVPC (vinyl pyrrolidone/vinyl caprolactam) and VVA (vinyl pyrrolidone/vinyl caprolactam/AMPS). The kinetics of hydrate formation in bentonite mud containing the typical KHIs were experimentally investigated under 3000 m deepwater drilling condition. The results show that these KHIs are more efficient in preventing hydrate growth than nucleation, which means the inhibition mechanism of vinyl lactam KHI polymers is growth inhibition. As the concentration increases, the inhibition effect of these KHIs on hydrate growth gets stronger, thus the delay of catastrophic hydrate formation gets longer, while the induction time can only increase slightly.