Two-dimensional (2D) relaxation exchange nuclear magnetic resonance (NMR) is in many ways similar to 2D frequency exchange NMR, except that the encoding times are comparable to the exchange time. This fact prevents the straightforward analysis of the cross-peak intensities in terms of joint probability densities, and quantitative information and understanding can only be obtained by comparison with simulated spectra. Based on simulations, an explanation is proposed as to why interference between relaxation and exchange may lead to asymmetric 2D exchange maps when exchange occurs between more than two sites. Practically, retro-fitting a simulated data set to an experimental one is shown to allow for the determination of the experimental relaxation and exchange parameters. This point is illustrated by studying a two-site model system consisting of interstitial water exchanging within a pack of spherical silica particles.

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.

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The effect of salinity on water-in-oil emulsions was systematically studied using a combination of nuclear magnetic resonance (NMR) pulsed field gradient (PFG) measurements of emulsion droplet size distribution complemented by interfacial tension measurements using the pendant drop method. Long-term emulsion stability over periods of up to 5 days was found to increase with salinity; this was shown to be independent of whether a monovalent (NaCl) or divalent (CaCl2) salt was used. The methodology was applied to water-in-oil emulsions formulated with crude oil, paraffin oil, xylene, crude oil with reduced asphaltene content, and crude oil with reduced organic acid content as the continuous phase, respectively. In all cases, emulsion stability increased consistently with aqueous phase salinity, with no discernible difference between the continuous oil phases with respect to the extent of this stabilization. The enhanced stability could thus not be attributed to differences in density, interfacial tension, or dielectric permittivity. This leaves a potential increased surface accumulation of stabilizing surface-active species driven by increasing salinity as the most plausible explanation for the observations reported here.

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.

The stratigraphies of decorated walls in ancient Herculaneum, Italy, were analyzed by single-sided (1)H NMR. A large version of the NMR-MOUSE® with a maximum penetration depth of 25 mm was used to map proton density profiles at different positions of the Mosaic of Neptune and Amphitrite showing considerable differences between different tesserae and the mortar bed at different times of the year. In the House of the Black Room, different mortar layers were observed on painted walls as well as different proton content in different areas due to different moisture levels and different conservation treatments. The proton density profiles of the differently treated areas indicated that one method leads to higher moisture content than the other. Untreated wall paintings from different times were profiled in a recently excavated room at the Villa of the Papyri showing two different types of mortar layer structures which identify two different techniques of preparing the walls for painting. Reflectance Fourier mid-infrared spectroscopy and in situ X-ray fluorescence measurements complemented the NMR measurements and provided additional insight into the identification of organic coatings as well as the nature of the pigments used, respectively. The information acquired nondestructively by NMR is valued for elaborating conservation strategies and for identifying different schools of craftsmen who prepared the mortar supports of the wall paintings.

The stability of hydrate-in-oil dispersions is a critical parameter in assessing the risk of flowline blockage due to particle aggregation or wall deposition. Many studies of hydrate particle transportability have used deionized water to form the dispersion; however, the resulting lack of ions means that the crude oil's natural surfactants will be less active, which does not represent production conditions. This study presents a new investigation of both hydrate-in-oil dispersion stability and water-in-oil emulsion stability, measured with a differential scanning calorimeter (DSC) and low-field nuclear magnetic resonance (NMR) apparatus, respectively. The results show that hydrate-in-oil dispersion stability increases directly with sodium chloride (NaCl) mass fraction in the aqueous phase; above 5 wt% NaCl, the dispersion was observed to be stable over ten hydrate formation-dissociation trials. This was comparable with the dispersion stability observed previously when an ionic surfactant was dosed at 2 wt% into the same crude oil. In contrast, only 0.1 wt% NaCl was required to stabilize water-in-oil emulsions over a four day observation period. This comparison suggests that, for crude oils containing natural surfactants, the risk of hydrate blockage may decrease as brine salinity increases from 1 to 10 wt%, without affecting the stability of the water-in-oil emulsion. The results demonstrate that experimental studies on hydrate-or water-in-crude oil systems should be performed with realistic values of brine salinity, to accurately capture dispersion stability.

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