NMR Studies of the Effect of CO₂ on Oilfield Emulsion Stability

Abstract

Formation of water-in-crude oil emulsions is a pervasive problem for crude oil production and transportation.Here we investigate the effectiveness of a comparatively low pressure CO 2 treatment in terms of breaking these water-in-crude oil emulsions. To this end, we used unique benchtop nuclear magnetic resonance (NMR) technology to measure the droplet size distribution (DSD) of the emulsions. Treatment with 50 bar CO 2 for 2 h resulted in significant emulsion destabilization; this was replicated when CO 2 was replaced by N 2 O, which has a solubility in both the aqueous and oil phases similar to that of CO 2 . Low solubility gases, N 2 and CH 4 , by contrast had no effect on emulsion stability. Treatment with CO 2 was also found to have no effect on a model water-in-paraffin oil emulsion stabilized by a synthetic surfactant (Span 80). Collectively, this supported the hypothesis that emulsion destabilization results from CO 2 precipitation of asphaltenes as opposed to emulsion droplet film disruption during depressurization, which are the two competing theories reported in the literature to explain the observed supercritical CO 2 destabilization of emulsions. Treatment of a water-in-crude oil emulsion featuring partial removal of asphaltenes from the oil phase was consistent with this hypothesis, as the effect of the CO 2 treatment on emulsion destabilization was significantly more pronounced.

Explosive Emulsion Characterisation using Nuclear Magnetic Resonance

“…Over all practical experimental parameter space, the BGP method has been demonstrated to provide improved predictions of droplet radius a [39] compared to the SGP and GPD models. The consistency of this method was demonstrated in several previous studies [30,[45][46][47][48] and will be deployed in this work.…”

“…As demonstrated in the work of Hollingsworth and Johns [50], a generalized cross validation (GCV) method can be used to determine the required regularisation parameters. This regularisation approach to determine P(a) has been extensively used and validated in several previous studies [30,[45][46][47][48].…”

The Effect of Inert Salts on Explosive Emulsion Thermal Degradation

“…The degree of restriction on self‐diffusion experienced by the dispersed phase molecules is related to the droplet size; this phenomenon is exploited to determine the emulsion droplet size. The successful implementation of the pulsed field gradient technique for emulsion droplet sizing has been detailed in our previous explosive emulsion study [26] as well a number of previous publications concerning emulsions (e. g. [23–25, 34, 37–39]).…”

Low‐Field High‐Resolution PFG‐NMR to Predict the Size Distribution of Inner Droplets in Double Emulsions

“…[29,30] This relatively novel technique is finding an interest in literature. [31][32][33][34] Douglass and McCall [17] and Stejskal and Tanner [35] proposed methods to measure free diffusion of molecules by PFG-NMR; Murday and Cotts [10] adapted this method to measure selfdiffusion of confined molecules. The signal attenuation, E, due to diffusion in spherical cavities of radius r is given by [10] ln E ( , g, Δ, r…”