Characterizing oils in oil-water mixtures inside porous media by Overhauser dynamic nuclear polarization

We present a method to identify and sort the oils in oil-water mixtures based on the Overhauser dynamic nuclear polarization (ODNP) enhancement at low field. Through combining two types of radicals, e.g. ODNP enhancer TEMPO and relaxation reagent Mn2+, we can selectively enhance the 1H NMR signal of oil in oil-water mixture infiltrated in porous media. More importantly, we have found that the enhancements of light oils in porous materials are inversely dependent of their viscosities but independent of pore size approximately above 10 μm. This allows us to roughly sort oils according to their ODNP enhancement values. The verification experiments in sandstones saturated with several oil and water mixtures show that the method is useful for oils identification and classification in porous media, especially for reservoir assessment or development.