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Optimized Droplet Sizing of Water-in-Crude Oil Emulsions Using Nuclear Magnetic Resonance

Fridjonsson, Einar O., Graham, Brendan F., Akhfash, Masoumeh, May, Eric F., Johns, Michael L.
Energy & Fuels 2014 v.28 no.3 pp. 1756-1764
droplet size, emulsions, nuclear magnetic resonance spectroscopy, oils, petroleum, spectrometers
Water-in-crude oil emulsions are an increasing problem during production. Essential to any emulsion breaking method is an ability to accurately measure droplet size distributions; this is rendered extremely difficult given that the samples are both concentrated and opaque. Here, we systematically consider the use of a standard, low-field benchtop nuclear magnetic resonance (NMR) apparatus to accurately measure the droplet size distributions. Such measurements are challenging because the NMR signal from the oil phase erroneously contributes to the measured water droplet size distribution. Conventionally, the oil-phase signal is nulled-out based on differences in the NMR T₁ relaxation parameter between water and oil. However, in the case of crude oil, the oil presents a broad T₁ distribution, rendering this approach infeasible. On the basis of this oil T₁ distribution, we present an optimization routine that adjusts various NMR measurement timing parameters [observation time (Δ) and inversion time (Tᵢₙᵥ)] to effectively eliminate this erroneous crude oil contribution. An implementation of this optimization routine was validated against measurements performed using unambiguous chemical-shift selection of the water (droplet) signal, as would conventionally be provided by high-field superconducting NMR spectrometers. We finally demonstrate successful droplet sizing of a range of water-in-crude oil emulsions.