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We fractionated a series of West African and West Australian crude oils into the four standard solubility classes: saturates, aromatics, resins, and asphaltenes (SARA). The asphaltene fraction was then separated further into classes we have called binding resins (BR) and residual asphaltenes (RA) using a solvent of near-boiling heptane. The ratio R ≡ BR/RA correlates strongly with the tightness of water-in-oil emulsions that these oils formed either in the field or the laboratory. Crucially, only the oil with R > 1 did not form a stable emulsion and, for the oils which did, the smaller the value of R, the tighter the observed emulsion in terms of its longevity and separation characteristics. Two-dimensional GC-MS was used to analyze the resin and binding resin fractions, which lead to the preliminary identification of the main components.

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 oilphase signal is nulled-out based on differences in the NMR T 1 relaxation parameter between water and oil. However, in the case of crude oil, the oil presents a broad T 1 distribution, rendering this approach infeasible. On the basis of this oil T 1 distribution, we present an optimization routine that adjusts various NMR measurement timing parameters [observation time (Δ) and inversion time (T inv )] 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.