Investigating hydrate formation rate and the viscosity of hydrate slurries in water-dominant flow: Flowloop experiments and modelling

Water dominated flow is typically encountered in mature oil and gas fields after water breakthrough has occurred; gas hydrate formation in these systems is generally associated with a high risk of flowline blockage. With the move towards production of natural hydrate deposits as an abundant source of gas, understanding water dominated flow will become increasingly important, particularly as these systems inherently operate near or within the hydrate equilibrium region. In this work, we present an improved mass-transfer limited hydrate growth rate model, which includes the effect of hydrate slurry viscosification on formation. This is validated through several methane hydrate formation experiments employing a 10 mm ID flowloop operating at high water cut (100 vol% water). The model is based on understanding mass transfer limitations for hydrate slurry systems; the mass transfer coefficient itself was estimated by the small eddy cell model and considers changes in the viscosity and diffusion coefficient due to an increase in hydrate volume fraction. Further, differential effective medium theory was employed to predict the viscosity of the hydrate slurry. The gas-water interfacial area was directly estimated (without any correlations) by employing high quality images captured through an in-line camera instrumented on the flowloop. Experimental results obtained from the flowloop were used to validate the overall growth rate predictions of our model. Overall, this work offers a pathway to improve predictive capabilities for the coming generation of natural gas hydrate production, and to increase confidence in our ability to actively manage hydrate formation for water dominant systems.