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Gas hydrate technologies have steadily gained interest in several industries for their potential use in natural gas transport and carbon dioxide sequestration applications. To further develop these emerging technologies, significant focus has been placed on additives, and particularly nanoparticles, which optimize their efficiencies. The addition of materials such as graphene nanoflakes (GNFs) has previously been proven to enhance the production of methane hydrates and other hydrate systems. In this study, the growth rates of methane hydrates were measured in the presence of both hydrophobic (as-produced) and hydrophilic (plasma-functionalized) GNFs at 2 °C and 4646 kPa. The effect of GNF loading in the aqueous phase for both types was also determined. Small-scale agglomeration limited the growth rate enhancement effect of hydrophobic GNFs at low concentrations of around 0.5 ppm while significantly increasing the formation kinetics by about 101% at concentrations of 5 ppm. At even higher concentrations (10 ppm), the performance decreased due to large-scale agglomeration. Enhancement rose rapidly at low concentrations (0.1−1 ppm) of hydrophilic GNFs, peaking at about 288% before dropping to around 215% at 5 ppm due to mean free path limitations then rising again as surface area increased.

Several industries have steadily gained interest in gas hydrate technologies for their potential use in natural gas transport and storage applications. Additives which optimize the efficiencies of these technologies, particularly nanoparticles, have lately been subject to an increasing investigative focus. Graphene nanoflakes (GNFs) have previously been proven to enhance hydrate systems, particularly methane hydrate systems. In this study, the dissolution rates of methane and molar saturation values were measured in nanofluids containing both hydrophobic (as-produced) and hydrophilic (plasma-functionalized) GNFs at 2 °C and 3146 kPa. For both types of GNFs, the effect of loading in the aqueous phase was equally determined. Dissolution rate enhancement was limited at low concentrations of around 0.5 ppm for hydrophobic GNFs due to small-scale agglomeration while significantly increasing dissolution kinetics by about 18.84% at concentrations of 5 ppm. The performance eventually decreased at higher concentrations (10 ppm) due to large-scale agglomeration. Hydrophilic GNFs, which exhibited no agglomeration, enhanced dissolution rates further with each successive loading until a 44.45% plateau at 10 ppm. This plateau may have been a limit of the system or a result of mean free path limitations. Either type of GNFs nearly triples the dissolution rates of methane investigated in previous studies on multi-walled carbon nanotubes due to their higher specific surface area.

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.