Effects of Poly(vinylpyrrolidone) on the Dynamic Viscosity of Methane Hydrate Systems at High-Pressure Driving Forces: Investigation of Concentration, Molecular Weight, and Shear Rate

Abstract

The viscosity of methane hydrate slurries with poly(vinylpyrrolidone) (PVP) at 700 and 7000 ppm by weight, molecular weights of 40 000 (PVP40) and 360 000 (PVP360) Da, and shear rates of 400 and 80 s–1 were measured in a high-pressure rheometer with pressures up to 30 MPag and compared to pure water systems. The additives successfully reduced the formation of high-viscosity slurries but at low concentrations were incapable of delaying hydrate agglomeration at the late growth stage. The average relative time required for PVP40 solutions at 700 ppm to grow to 50 mPa·s was 1.9 times the water reference value but only 1.2 times to reach 200 mPa·s. Improved inhibition was observed for the higher concentration and higher molecular weight sets, where the relative times to reach 50 mPa·s were 8.2 and 2.6 times the water reference value, respectively. While the additives demonstrated antinucleation properties and suppressed crystal growth initially, they accelerated the hydrate clusters agglomeration rate and potentially weakened the hydrate mechanical properties.

Effects of Poly(styrene/Pentafluorostyrene-block-vinylpyrrolidone) Amphiphilic Kinetic Hydrate Inhibitors on the Dynamic Viscosity of Methane Hydrate Systems at High-Pressure Driving Forces

“…A direct comparison was made between the viscosity of hydrate slurries with and without polymer additives. The increase in viscosity of aqueous solutions due to dissolved KHIs was considered to be negligible for the concentrations selected for this study, since a previous study has shown that the viscosity difference between pure water and aqueous solutions with 7000 ppm of PVP was in the order of 10 –1 mPa·s for temperatures between 0 and 10 °C and for pressures between 0 and 5 MPag …”

“…Median time required for methane hydrate slurries to reach 200 mPa·s for Left: PVP40 700 ppm (data from Du et al, 2022) and Right: PS4- b -PVP40 700 ppm.…”

“…Geometric mean of relative time for methane hydrate slurries to reach to 200 mPa·s for PVP40 (data from Du et al 2022), PS4- b -PVP40, and PPFS4- b -PVP40 at 700 ppm, with 95% confidence interval error bars.…”

“…The profiles shown in Figure 5 were all selected as the median run within the 3 repeated runs to reach agglomeration. In comparison to previous reports using water 15 and PVP40, 21 an overall longer growth period was observed with these amphiphilic block copolymers. A direct comparison was made between the viscosity of hydrate slurries with and without polymer additives.…”

“…The increase in viscosity of aqueous solutions due to dissolved KHIs was considered to be negligible for the concentrations selected for this study, since a previous study has shown that the viscosity difference between pure water and aqueous solutions with 7000 ppm of PVP was in the order 10 −1 mPa•s for temperatures between 0 and 10 °C and for pressures between 0 and 5 MPag. 21 Previous studies have defined the dynamic viscosity profiles as typically comprising of a slurry phase followed by an agglomeration phase. Although particle size was not directly measured, it was assumed that the sharp viscosity rise at the end of the curve was due to sudden particle clustering, since the methane consumption rate is expected to be linear.…”