Gas Hydrate Slurry Flow in a Black Oil. Prediction of Gas Hydrate Particles Agglomeration and Linear Pressure Drop

We present a study of the rheological properties of hydrate slurries flowing in a black crude oil, as a function of the water-cut and the flow rate, and its application to a pressure drop model. The experiments were performed in the Lyre pilot loop located at IFP-Lyon and dedicated to flow assurance studies. This paper deals with the methodology applied to the results to separate the role played by various physical phenomenon on the behaviour of the slurry. These include the effects of temperature and gas saturation on density and viscosity of the oil phase, as well as the conversion rate of water into gas hydrate. Moreover, hydrate particles agglomeration is taken into account to interpret particularly high viscosity. Thanks to a fractal approach, an effective size of hydrate aggregates can be deduced from the apparent viscosity, once all the other physical phenomena are handled properly. On the other hand, considering that hydrate aggregates are shear sensitive, their maximum size can be calculated thanks to a force balance equation. As agglomeration is effective when free water is still present in the pipe, a capillary force is considered and an order of magnitude of such particles interaction is given. Finally, it is shown that this approach can be used for pressure drop prediction. In a practical way, two extreme cases can be considered to range the linear pressure drop: they correspond to the saturated and the under-saturated cases. Predictions prove to fit with the experimental data.