NMR relaxation time measurements of solvent effects in an organocatalysed asymmetric aldol reaction over silica SBA-15 supported proline

Immobilisation of organocatalysts onto solid supports represents a very promising solution to tackle their low productivity by enabling their reuse. Herein, the use of NMR relaxation measurements, coupled with reaction...

Temperature Dependence of Nuclear Magnetic Resonance Relaxation Time in Carbonate Reservoirs

Summary Nuclear magnetic resonance (NMR)-based interpretation models are commonly calibrated using laboratory ambient core NMR measurements. For applying the core calibrated models to downhole NMR logging interpretation, the difference between the NMR responses measured at ambient and reservoir temperature needs to be evaluated. The temperature dependence of NMR relaxation time in high-quality (HQ) carbonate reservoirs has been studied, and NMR temperature dependence models were established using data analytic methods. In this paper, we extend our early studies on temperature dependence of NMR relaxation time to low-quality (LQ) carbonate formations. For more than 95% of the LQ samples investigated, NMR relaxation time shows a positive correlation with temperature. The correlation is similar to that observed in HQ carbonate rocks but slightly less significant. Temperature-dependent correlations for predicting the geometric mean of NMR transverse relaxation time (T2,GM) from a measured temperature to any other temperature were derived from HQ to LQ carbonate rocks independently first, then a unified T2,GM correlation was derived including both the HQ and LQ carbonate reservoirs. Predicting NMR transverse relaxation time T2 distribution from one temperature to other temperatures was achieved using a dimension reduction approach involving the principal component analysis (PCA) technique. It was found that the T2 distributions at any given temperature for both HQ and LQ carbonate reservoirs can be predicted robustly from the T2 distributions at the ambient temperature by representing the T2 distributions with principal components (PCs) at the ambient temperature and then using these PCs to predict the PCs at a different temperature. The optimal number of PC components depends on the multimodality of the T2distribution. This work extends the validity range of the data analytic methods, in particular parameter and dimension reduction methods, that quantify the temperature dependence of carbonate NMR properties. The new NMR temperature model enables the integration of NMR laboratory studies and downhole measurements for advanced petrophysical analyses in a wide range of carbonate reservoirs.

Temperature Dependence of NMR Relaxation Time in Carbonate Reservoirs

NMR-based carbonate interpretation models are commonly calibrated using laboratory ambient core NMR measurements. For applying the core calibrated models to downhole NMR logging interpretation, the difference between the NMR responses measured at ambient and reservoir conditions needs to be evaluated. The temperature dependence of NMR relaxation time in high-quality carbonate reservoirs was investigated, and NMR temperature dependence models were determined using data analytic methods (Hursan et al, 2019). This paper focuses on temperature dependence of NMR relaxation time in low-quality carbonate formations. For more than 95% of the samples investigated, NMR relaxation time shows a positive correlation with temperature. The correlation is similar to that observed in high-quality carbonate rocks but slightly less significant. Temperature dependent correlations for predicting T2GM from a measured temperature to any other temperature are derived from high- and low-quality carbonate rocks independently first, then a unified T2GM correlation is derived including both the high- and low-quality carbonate reservoirs. Predicting T2 distribution from one temperature to other temperatures is achieved using dimension reduction approach involving principal component analysis (PCA) technique. It is found that the T2 distributions at any given temperature for both the high- and low-quality carbonate reservoirs can be predicted robustly from the T2 distributions at the ambient temperature by representing the T2 distributions with principal components (PCs) at the ambient temperature then using these PCs to predict the PCs at a different temperature. The optimal number of PC components depends on the multimodality of the T2 distribution. This work extends the validity range of a data analytic method that quantifies the temperature dependence of carbonate NMR properties. The new NMR temperature model enables the integration of NMR laboratory studies and dowhole measurements for advanced petrophysical analyses in a wide range of carbonate reservoirs.

Understanding the microstructural evolution of hypersaline cemented paste backfill with low-field NMR relaxation

Cemented paste backfill (CPB) comprising mineral tailings, binders and mixing waters is an important potential support material in the mining industry. As the mechanical properties of CPB are significantly influenced by its microstructural characteristics the development of measurement tools to better understand its pore structure evolution is important for its increased utilisation. This study reports the application of low-field nuclear magnetic resonance (NMR) relaxation time measurements to characterise the microstructural evolution of CPB materials over 56 days of hydration, contrasting common tap water and hypersaline water (~22 wt% salt) as mixing waters. Distinct NMR relaxation time populations were evidenced within each CBP sample, revealing the presence of both capillary (T1,2 ≈ 10 ms) and gel pore water (T1,2 ≈ 300 – 500 µs), with time-dependent relaxation measurements facilitating characterisation of capillary pore structure evolution over the hydration period assessed. Hypersaline samples demonstrated a time-lag in this measured capillary pore evolution, relative to those hydrated with tap water, while hydration rates were observed to increase with increased CPB binder content. Further, both T1 and T2 NMR relaxation times were found to correlate with the uniaxial compressive strength of the CPB materials investigated, facilitating the formulation of a predictive correlation function between NMR relaxation characteristics and mechanical properties.

A laboratory study of the effect of clay, silt, and sand content on low-field NMR relaxation time distributions

We have developed a laboratory nuclear magnetic resonance (NMR) study to investigate the effect of clay, silt, and sand content on the NMR relaxation time distribution. Transverse NMR relaxation times ( T2) were determined for water-saturated unconsolidated sediment mixtures of 1%–60% kaolinite clay, 5%–85% silt-size glass beads, and 8%–94% quartz sand by mass. Nearly all of the mixtures were characterized by a unimodal T2 distribution. When clay is present in quantities greater than 10%, the clay content dominates the response. For these samples, the mean-log relaxation times ( T2ML) range from 0.03 to 0.06 s, regardless of silt or sand content. For mixtures with <10% clay, T2ML decreases with increasing clay content. When the clay content is kept the same, T2ML decreases with increasing silt content and increases with the increasing sand content. The strong effect of the clay content on the NMR response is due to the high specific surface area of the clay and the distribution of clay throughout the samples. These results will help improve the interpretation of NMR field data in soils and unconsolidated sediments.

Nuclear spin relaxation as a probe of zeolite acidity: a combined NMR and TPD investigation of pyridine in HZSM-5

The relative surface affinities of pyridine within microporous HZSM-5 zeolites are explored using two-dimensional 1H nuclear magnetic resonance (NMR) relaxation time measurements. The dimensionless ratio of longitudinal-to-transverse nuclear spin relaxation...