Investigation on Methane Hydrate Formation in Water-based Drilling Fluid

To guarantee the flow assurance of drilling fluid in deep-water drilling, the inhibitory effect of PVP-K90 on methane hydrate formation was measured at 275.15 and 277.15 K with an initial pressure of 6, 8, and 10 MPa. The effect of PVP-K90 on the rheological properties of drilling fluid was also measured. Results showed that the apparent viscosity enhanced from 27 and 114 mPa·s as the concentration of PVP-K90 increased up to 2.0 wt %, which greatly weakened the fluidity of the drilling fluid. However, the addition of PVP-K90 showed a positive effect on prolonging the hydrate nucleation time and reducing the methane consumption in hydrate growth. The mean induction time of gas hydrate formation at 277.15K with the addition of 1.0 wt % PVP-K90 into the drilling fluid was at least 3 times higher than that without the addition of 1.0 wt % PVP-K90. The initial methane consumption rate and total methane consumption were reduced evidently with the increasing concentration of PVP-K90. In addition, increasing the temperature was also suggested to enhance the inhibitory effect on hydrate formation. Therefore, considering the influence of PVP-K90 on the fluidity of drilling fluid and the inhibitor effect of hydrate formation, 1.0 wt % PVP-K90 was thought to be a suitable concentration for the prevention of methane hydrate formation in drilling fluid at subcooling of less than 4.5 K. These observations have special significance for water-based drilling fluid with hydrate inhibition performance design in deep-water drilling.