Bimodal model for predicting the emulsion-hydrate mixture viscosity in high water cut systems

For many production operations, particularly deepwater fields, those requiring long tiebacks, water flooded and mature reservoirs (where water cuts can be very high), the traditional techniques to prevent hydrate problem may not be economical and/or logistically practical. Thus the industry needs improved techniques to tackle flow assurance problems for such challenging conditions. Preventing hydrate agglomeration and transportation of hydrate slurry could be a new solution. The rheological behaviour of hydrate slurry has mainly been investigated in low water cut systems where water is the limiting factor. In high water cut systems, hydrate former components are the limiting factor and therefore the rheological behaviour of hydrate slurry has to be study in water–oil emulsion and this has a significant role on the viscosity of the system. In this communication, a model to predict the viscosity of water–oil emulsion in the presence of hydrate particles in high water cut systems using the concept for a bimodal mixture is proposed. In the model, water–oil emulsion and hydrate particles in the liquid continuous phase are treated separately as unimodal models. In addition, a modification has been applied to the Mills (1985) model to calculate the viscosity of unimodal hydrate suspensions. The model has been validated using experimental data for high water cut systems (above 50%) in the presence of different anti-agglomerant (AA) concentrations. The predictions of the proposed model are in good agreement with experimental data for both oil-in-water and water-in-oil hydrate mixtures.