Study on the hydrate inhibition effect of nano-silica in drilling fluids

Abstract

Preventing hydrate crystallization in drilling fluid is the key to ensure the safety of deep water drilling. In this work, hydrate inhibition effect of nano-silica in deep water drilling fluids was measured and compared with the typical hydrate inhibitors containing KCl-PVP and EG-PVP. The three phase equilibrium and the formation kinetics of CH4 hydrate in the drilling fluids were measured. The micro-morphological features of the formed hydrates were observed by SEM. Results showed that EG-PVP drilling fluid was found to have the best thermodynamic inhibition effect on CH4 hydrate where the deviation of the equilibrium pressure in EG-PVP drilling fluid and pure water was initially 2 MPa as the temperature was below 5 °C and increased up to about 5 MPa when the temperature was 10 °C. Nano-silica had almost no thermodynamic inhibition performance on CH4 hydrate. Kinetic measurements revealed that EG-PVP and KCl-PVP drilling fluids prolonged the hydrate nucleation to more than 48 h, but failed to remain the hydrate inhibition effect after aging tests. Nano-silica was unable to prolong the nucleation time, but was effective in reducing the initial hydrate growth rate and less affected by aging tests. SEM images revealed that nano-silica prevented phase separation in hydrate growth and induced the CH4 hydrate to form a spongy-like structure which was fragile in agitated drilling fluid. Therefore, nano-silica could be viewed as a potential synergist of hydrate inhibitors.