Using Low Field NMR to Predict Viscosities of Crude Oils and Crude Oil Emulsions

ABSTRACT

Knowledge of oil viscosity is vital to most areas of the petroleum industry, and is especially important in the production of heavy oil and bitumen. Stable crude oil emulsions are also prevalent in many stages of the production and transport of heavy oil and bitumen. These emulsions contain water as a dispersed phase, which makes them even more viscous than their constituent oil. Knowledge of emulsion viscosity is necessary for determining energy requirements for transport and upgrading of the produced crude. As viscosity increases, conventional measurements become less accurate and more difficult to obtain. An alternate method of predicting viscosities would be extremely beneficial to the industry.

Low field nuclear magnetic resonance is examined in this work for its potential to predict viscosity of crude oil and crude oil emulsions. NMR is an attractive alternative to conventional measurements because it provides fast, unbiased and non-destructive data even for high viscosity oils. A correlation was developed which predicts the viscosity of heavy oils and bitumens over a wider range of viscosities than any other published NMR viscosity correlation. Viscosity is increased further by the emulsified water fraction, which can also be measured with NMR. Emulsion NMR models were also developed that provide order of magnitude viscosity predictions over a wide range of emulsion viscosities by incorporating the effect of the suspended water and the size of the water droplets. Data for these correlations have been obtained at different temperatures, proving that NMR can be used to predict viscosity changes with temperature as well.

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