Flow of heavy crude oil-in-water emulsions in long capillaries simulating pipelines

Abstract

We studied the rheological properties of heavy oil-in-water emulsions with the final goal of decreasing the high viscosity of oil in pipeline transportation. The emulsions containing 3% silica or 5% montmorillonite were stabilized by Triton X-100. All emulsions were viscoplastic media and also demonstrated viscoelasticity. At low shear stresses, emulsions are in gel-like state that was reflected by the independence of the elastic modulus from frequency. The yield stress of basic emulsion is rather low (∼1 Pa), while the introduction of solid particles leads to a remarkable increase of the yield stress. It was shown that direct transition of the rheological data for oil emulsions measured in a rotational device to capillary rheometer appeared impossible. The apparent viscosity of the samples estimated in tubes (as a model of a capillary viscometer) was not correlated with the shear viscosity measured on a rotational rheometer and overall was dependent on the tube/capillary diameter. The reason for these effects may be related to the stratified flow through a tube consisting of near-wall slippage or the existence at the stream periphery of a low-viscosity layer. This phenomenon should be taken into account in designing pipe transportation lines when viscometric data are obtained in the other conditions of flow.