  The viscosity of methane and carbon dioxide hydrate systems were measured
using a high-pressure rheometer up to 30 MPag. Where hydrate formation was not
detected, the effect of temperature on the viscosity was one order of magnitude
higher than the pressure effect on viscosity in most of the experimental
pressure range (-0.048 mPa s/C at 1 MPag and 0.009 mPa s/MPag at 2C). The
pressure effect on the viscosity of carbon dioxide systems where no hydrate
formation was observed was up to one order of magnitude higher than that of the
methane systems, due to carbon dioxide's higher solubility in water. Novel
rheological phases diagrams were developed to further characterize the gas
hydrate systems. Several systems with high driving forces for hydrate formation
(2.07 MPag to 4.1 MPag) did not form gas hydrates. System limitations to the
formation of hydrates were categorized as kinetic, mass diffusion, and/or heat
of crystallization effects.
