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

Abstract

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.

NMR Studies of the Effect of CO2 on Oilfield Emulsion Stability

“…Our implementation is detailed in a number of publications, 23,24,42,43 the salient features of which are reported here for clarity. With respect to the pulse sequence Energy Fuels XXXX, XXX, XXX−XXX in Figure 4, the acquired NMR signal, S, can be related to the free self-diffusion of molecules (e.g., water), D, via the Stejskal Tanner equation: 44…”

Rapid, non-invasive characterization of the dispersity of emulsionsviamicrowaves

“…Compared to paraffins, both the crude oil and tar oil have a rather complex composition, containing hundreds of compounds. Due to the opaqueness of emulsified oil, one cannot measure the droplet size distribution accurately using dynamic light scattering technique 10. Thus, it is of considerable value to examine if the microwave analysis could be applied to investigate the droplet size distribution of emulsified heavy oil.…”

Effect of hydrate anti-agglomerants on water-in-crude oil emulsion stability

“…Tikhonov regularisation has been applied to invert Eq. 3 numerically (Hollingsworth and Johns 2003) and has been successfully demonstrated on a wide range of emulsions in previous work (Fridjonsson et al 2014;Haber et al 2015;Ling et al 2014Ling et al , 2016a.…”

“…(Lingwood et al 2012) determined that for the case of restricted diffusion inside spherical droplets, the block gradient pulse (bgp) approximation method is more accurate, where the diffusion is restricted within a spherical geometry and the consequential evolution in magnetisation is modelled using an arbitrary magnetic field based on the general gradient waveform set of methods. The bgp method is detailed elsewhere along with several successful applications to various emulsion systems (Fridjonsson et al 2014;Haber et al 2015;Ling et al 2014Ling et al , 2016a; this data analysis method is employed in this work. Both Eq.…”