NMR relaxometry and diffusometry in characterizing structural, interfacial and colloidal properties of heavy oils and oil sands

• We have reviewed the use of NMR primarily for viscous (heavy) oils and bitumens which currently account for the majority of known crude oil reserves.
• New viscosity and NMR measurements have been included in the review for comparison with published data, and to extend some correlations.
• The review is also related to oil sands and the in-situ determination of bitumen viscosity, and new results given.
• Attempts have been made to demonstrate the length scales over which NMR diffusion measurements can be applied within the context of crude oil and crude oil component analysis. For this purpose, the use of asphaltene molecules, nanoaggregates and clusters has been offered as an example, and combined with aspects of NMR analysis of oil properties, interactions and emulsions, this exemplifies the versatility of this approach for crude oil analysis.
• The associated relevance to oil/water logging of crude oil reservoirs using NMR has been highlighted throughout the review.

We present a discussion of the use of NMR in the characterization of heavy oils and oil sands and their interactions with water and solid surfaces. The phenomena probed by the NMR techniques take place over different length scales, ranging from molecular, through colloidal to macroscopic. During the course of the last 15 years, NMR applications have grown from their initial use in studying conventional oils in rocks to the characterization of more viscous oils in unconsolidated porous media. In particular, 1H NMR relaxometry and diffusometry are considered with a view to the identification of oil and water in oilfield fluids and their environment. After some theoretical considerations, various topics of current significance to petroleum recovery and production are discussed, including oil viscosity (with new experimental viscosity correlations added), oil sands characterization, heavy oil emulsions, and the identification of solvent effects on oil components and asphaltene solution behaviour and interactions. We show that, increasingly, NMR is becoming an invaluable and versatile characterization tool in petroleum science, in both laboratory and field.

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