Hydrate Shell Growth Measured Using NMR

Abstract

Benchtop nuclear magnetic resonance (NMR) pulsed field gradient (PFG) and relaxation measurements were used to monitor the clathrate hydrate shell growth occurring in water droplets dispersed in a continuous cyclopentane phase. These techniques allowed the growth of hydrate inside the opaque exterior shell to be monitored and, hence, information about the evolution of the shell's morphology to be deduced. NMR relaxation measurements were primarily used to monitor the hydrate shell growth kinetics, while PFG NMR diffusion experiments were used to determine the nominal droplet size distribution (DSD) of the unconverted water inside the shell core. A comparison of mean droplet sizes obtained directly via PFG NMR and independently deduced from relaxation measurements showed that the assumption of the shell model-a perfect spherical core of unconverted water-for these hydrate droplet systems is correct, but only after approximately 24 h of shell growth. Initially, hydrate growth is faster and heat-transfer-limited, leading to porous shells with surface areas larger than that of spheres with equivalent volumes. Subsequently, the hydrate growth rate becomes mass-transfer-limited, and the shells become thicker, spherical, and less porous.

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.…”

“…All droplet sizing was performed using the stimulated echo pulsed field gradient (STE PFG); the relevant pulse sequence is shown in Figure 2. The successful implementation of this pulsed field gradient technique for emulsion droplet sizing has been detailed in a number of our previous publications [30][31][32][33].…”

“…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].…”

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…”

“…This regularization technique has been extensively validated and used in previous studies. 23,24,42,43 3. RESULTS AND DISCUSSION 3.1.…”