NMR Transverse Research Articles

Permeability modeling of Upper Cretaceous Bahariya Formation rocks, Abu Sennan field, Western Desert, Egypt

The present work aims to describe in detail the petrophysical properties of the Bahariya Formation (Abu Sennan field) through processing the core sample data and finding out the possible relations between permeability and other reservoir parameters such as porosity, specific internal surface, formation factor, and nuclear magnetic resonance to obtain reliable permeability prediction model of the Upper Cretaceous formation. The core samples have a length range of 2–4 cm with a diameter of 2.54 cm. Many petrophysical reservoir parameters were measured, such as permeability, porosity, density, formation factor, and special measurements such as spectral induced polarization, nuclear magnetic resonance, and specific internal surface. The samples cover a wide range of porosity (11.82–23.68 %) and permeability (0.06–133.65 mD). The porosity-permeability relationship indicates the increase of the permeability with porosity increase for the studied samples. The reservoir quality index ranges from 0.02 to 0.78 μm. The flow zone indicator ranges from 0.09 to 3.39 μm where pore throat radius (R35) ranges from 0.10 to 7.40 μm. The reservoir quality index (RQI) and flow zone indicator (FZI) cross-plot show a better understanding of the formation evaluation. The hydraulic flow units are (0.09 μm < FZI ≤ 3.39 μm) and RQI < (1 μm). NMR longitudinal relaxation time T1 range is 1.21–175 ms, NMR transversal relaxation time T2(100) range is 0.70–91.77 ms, and T2(600) range is 0.74–75.86 ms. Models that incorporate porosity and NMR relaxation times will be more accurate and suitable for permeability prediction. Using multiple regression to determine the exponents of the power-law equation and replacing the porosity with the formation factor can improve the permeability prediction for the samples under investigation. The utilizing of NMR in predicting the permeability through a robust model considers an additional value for the Upper Cretaceous rocks in Egypt.

19 F NMR transverse and longitudinal relaxation filter experiments for screening: a theoretical and experimental analysis.

Ligand-based 19 F NMR screening represents an efficient approach for performing binding assays. The high sensitivity of the methodology to receptor binding allows the detection of weak affinity ligands. The observable NMR parameters that are typically used are the 19 F transverse relaxation rate and isotropic chemical shift. However, there are few cases where the 19 F longitudinal relaxation rate should also be used. A theoretical and experimental analysis of the 19 F NMR transverse and longitudinal relaxation rates at different magnetic fields is presented along with proposed methods for improving the sensitivity and dynamic range of these experiments applied to fragment-based screening. Copyright © 2016 John Wiley & Sons, Ltd.

Innovative Nondestructive Measurements of Water Activity and the Content of Salts in Low-Salt Hake Minces

Impedance spectroscopy (IS), low-field proton nuclear magnetic resonance (LF (1)H NMR), chloride titration, ion chromatography, and an ion selective electrode were used to investigate the physicochemical parameters and measure sodium and potassium contents in low-salt brines and fish. Salt solutions (0-3 w/w, %) and model products of minced hake with added NaCl (0.5-3.0 w/w, %), or a mixture of NaCl and KCl (50/50 w/w, %), were analyzed. Good correlation was observed between the sodium content determined by using the ion selective electrode method and ion chromatography (R(2) = 0.97). In both salt solutions and fish minces, the impedance spectroscopy measurements could detect the difference in salt contents in mince with salt contents down to 0.5%. The NMR transversal relaxation time T2 measurements clearly distinguished samples with 0, 0.5, and 1.0-3.0% salt, based on principal component analysis (PCA). Therefore, LF (1)H NMR seems to be a suitable technique for studies of low-salt products.

Proton mobility for the description of dynamic aspects of freeze-dried fruits

The partitioning of water sorption isotherms into different zones, according to the strength of water interactions with solids has very important practical applications. However, the dynamic properties of water play an important role in complementing the information provided by water sorption isotherms. One of the most successful techniques used to prove the dynamic behavior of water in foods systems is pulsed NMR. The aim of this study was to apply the concept of proton mobility in order to better define the water-related dynamic aspects of freeze-dried fruits. Different water mobility populations were defined through 1H NMR transversal relaxation times, obtained after the application of several pulses sequences. The water content limits at which proton populations with different mobility appeared, allowed a more complete and precise description of water behavior at the different sorption stages than the parameters obtained by the application of sorption mathematical models.

The effect of salt and fibre direction on water dynamics, distribution and mobility in pork muscle: A low field NMR study

The effect of salt concentration and fibre orientation on water within the meat matrix was investigated by low-field nuclear magnetic resonance (LF-NMR), water-binding capacity (WBC), diffusion studies and histological analysis. Pork M. longissimus thoracis et lumborum samples were cured with 5.7, 15.3 or 26.3% w/w NaCl at a parallel or perpendicular fibre direction. NMR transverse (T2) relaxation identified three water components (T2b, T21 and T22) which all exhibited characteristics correlated to WBC. Results indicated that T2b increases with increasing NaCl concentration. Increasing intra-myofibrillar water and decreasing extra-myofibrillar water resulted in the highest WBC. Water diffused more quickly into the extra-myofibrillar space in samples cured at a parallel fibre direction. This water remained loosely bound in samples cured with the saturated solution (26.3% w/w NaCl) leading to decreased WBC. This study provides further information on water binding within the meat matrix by applying the results of LF-NMR to traditional water-binding theories.

B1 mapping of liquid NMR transversal RF coils: Analysis of heterogeneity and nonlinearity

AbstractB1 fields generated by transversal RF coils in a high‐resolution NMR probe were studied using a nutation experiment combined with gradient echo 1D‐profiling. Signal amplitude, B1 strength, and relaxation time were mapped as a function of longitudinal axial position. Numerical Bloch simulations in a rotating frame could reproduce the overall features of the experimentally observed nutation profiles. The 3D rotating frame trajectories of magnetization during pulsing are presented in spherical coordinates. Nutating magnetization (i.e., sinusoidal oscillation) was detectable even outside the RF coil, although the signal amplitude was low and the spin relaxation during pulsing was fast. As the axial position got closer to the edges of the RF coil, low frequency components began overlapping on the nutating component. At the edge regions, the low frequency magnetizations dominated and the oscillating component almost disappeared, resulting in a cycloidal 3D trajectory of magnetization. Inside the RF coil, the low frequency component increased the frequency of oscillation as the axial position got closer to the center. Only a narrow central region of the RF coil gave a near linear response against pulse width, wherein the highest B1 field strength and very small relaxation were observed. A significant nonlinearity between pulse duration and flip angle was observed in the edge portion of the RF coil and at the outside. The heterogeneity and nonlinearity led to an inaccurate 90° pulse width when the pulse duration at null points (e.g., 180° or 360°) was simply divided by 2 or 4. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 1–12, 2012

Morphology, Phase Composition, and Molecular Mobility in Polyamide Films in Relation to Oxygen Permeability

The effect of phase composition and molecular mobility on oxygen permeability is studied for stretched films prepared from polyamide 6 (PA6) and a blend of PA6 with semiaromatic amorphous polyamide (aPA)−PA6/aPa, which is a random co-polyamide containing iso- and terephthalic chain units. The effect of stretching degree of films on crystallinity and strain-induced immobilization of the amorphous phase is studied by DSC and solid-state proton NMR transverse (T2) magnetization relaxation, respectively. Changes of these parameters upon strain are determined. Crystallinity and Tg are hardly affected by strain, as shown by DSC. Molecular mobility in the amorphous phase of stretched films is largely restricted upon increasing strain. At temperatures well above Tg, the amorphous phase consists of two fractions of nanometer thickness: one behaves like glassy polyamides, and the other one, a semirigid fraction, reveals largely hindered chain mobility. The amount of the glassy-like fraction increases proportionally to the strain. In addition, molecular mobility in the semirigid fraction decreases with increasing strain. According to high-resolution solid-state 13C NMR experiments, the composition of the semirigid fraction in PA6/aPA films is enhanced by aPA. It is shown that the immobilization of the amorphous phase has a large influence on the permeability of the films. It appears that oxygen permeability correlates well with a parameter describing strain-induced decrease in molecular mobility in the amorphous phase. This parameter is the reciprocal product of the amount of the semirigid fraction at temperatures well above Tg and molecular mobility in this fraction as determined by NMR T2 relaxation time. It is suggested that the semirigid fraction of the amorphous phase could be considered as “channels” for diffusion of oxygen molecules. Despite lower oxygen solubility in PA6 films, as shown by low-temperature proton NMR T1 relaxation data, the permeability of all PA6/aPA films under humid conditions is significantly lower than that of PA6 films. It is suggested that the lower permeability of PA6/aPA films is due to complex formation between oxygen molecules and aromatic rings of aPA, which slows down oxygen diffusion. Results of the present study are of interest for a better understanding of both permeability of polyamide films and other phenomena in polyamides that are affected by transport properties of small molecules, such as the rate of water uptake, dyeability of fibers, thermal oxidation, and blooming.

NMR Transversal relaxivity of aqueous suspensions of particles of Ln3+-based zeolite type materials

A series of zeolite-type silicates containing stoichiometric amounts of Ln(3+) ions in the framework (Ln-AV-9 materials), with composition (Na(4)K(2))(Ln(2)Si(16)O(38)).10H(2)O (Ln = Nd, Sm, Eu, Tb, Gd, Dy) has recently been synthesized and characterized. They form paramagnetic microparticles, which as aqueous suspensions have negligible water (1)H longitudinal relaxivities (r(1)) for all Ln(3+) ions studied and quite large transverse relaxivities (r(2)). In this work we further analysed the size distribution of the Ln-AV-9 particles and their r(2)* and r(2) relaxivities. The r(2)* relaxivity effects are explained by the static dephasing regime (SDR) theory. The r(2) relaxivities appear to be strongly dependent on the interval between two consecutive refocusing pulses (tau(CP)) in the train of 180 degrees pulses applied. For long tau(CP) values, the r(2) of the systems saturates at a value, which is always an order of magnitude smaller than r(2)*. These features are explained by a crude model, which takes into account the residual diffusion effect in the static dephasing regime. The large microparticles, although not efficient in T(1) relaxation, are quite effective in enhancing T(2) relaxation, particularly at high magnetic fields. The r(2)* values and the saturation values for r(2) were found to increase linearly with B(0) and mu(0)(2). The largest transversal relaxation rate enhancements were observed for Dy-AV-9 with a saturation value of r(2) of 60 s(-1) mM(-1) and a r(2)* value of 566 s(-1) mM(-1) at 9.4 T and 298 K.

Use of a void network model to correlate porosity, mercury porosimetry, thin section, absolute permeability, and NMR relaxation time data for sandstone rocks

The Pore-Cor void network model is used to construct stochastic realizations of the void structures of five sandstone samples of varying lithography. A close match was achieved to experimental porosity and mercury intrusion curves. The samples were resin impregnated and the fragments of voids revealed in thin sections photographed by backscatter electron microscopy at two magnifications. The sizes of these pore fragments matched those derived from a simulated microtoming of the network model much more closely than the sizes derived from the traditional capillary bundle approximation. Absolute permeabilities of the network were calculated by finding the flow capacity of the entire flow network, based on parametrized Navier Stokes equations with Klinkenberg correction, applied to each pore-throat-pore arc. A match to the experimental trend was obtained, although the network model considerably underestimated the experimental values. The results were also compared with the semiempirical equations of Thomson et al. and Kozeny and Carmen modified to accept thin section image analysis. Finally, the simulated pore and throat size distributions were compared to proton NMR transverse (T2) spin-echo relaxation times. Although the shapes of the distributions differed markedly, the mean values trended together. The capillary bundle approximation, however, gave a poor match to the NMR data.

Determination of crosslink densities of carbon black filled natural rubber sulfur vulcanizates by 13C NMR MAS spectroscopy and 1H NMR transversal relaxation

AbstractTwo NMR spectroscopic methods were applied to carbon black filled NR vulcanizates to determine the chemical crosslink density. Both methods give corresponding results. Addition of carbon black leads to a decrease of crosslink density with increasing filler content. The influence is more pronounced at higher sulfur content.

MC‐determination in elastomers by 1H‐NMR relaxation and 2H‐NMR spectroscopy

AbstractWe show how 1H–NMR transversal relaxation and 2H–NMR spectroscopy can be used for the determination of the number average molecular mass MC in typical elastomers at temperatures well above the glass transition temperature. MC‐results of the different NMR methods are compared among one another and with MC‐results of other common independent methods. Moreover, the NMR measurements provide a number of additional useful parameters: correlation times, portions of dangling chain ends and of sol molecules, molecular order.

A study of crosslinking in epoxide-amine systems by pulsed NMR spectroscopy

The process of crosslinking in a polymer prepared from diphenylolpropane diglycidyl ether and 1,3-bis-(aminomethyl)-adamantane was studied by the methods of NMR transversal relaxation, differential microcalorimetry and IR spectroscopy. In native samples a group of slowly relaxing protons was observed, with a glass temperature higher by 20 K than T g of the polymer cured to the limit. The temperature of mobility melting in structural elements in native and post-cured polymer samples falls with an increase in the temperature of isothermic curing.

Phosphorus-31 Nuclear Magnetic Relaxation Times in the PBr3–PBr2Cl–PBrCl2–PCl3 System

The NMR transverse and longitudinal relaxation times of 31P in a liquid mixture of PCl3 and PBr3, and in a liquid mixture of PBr3, PBr2Cl, PBrCl2, and PCl3 were measured at 40.5 MHz as a function of temperature from 80 to −100°C. Transverse relaxation times of 35Cl in a liquid mixture of PCl3 and PBr3 and in neat liquid PCl3 were measured over the temperature region 70–29°C. The 35Cl relaxation time in PCl3 is entirely due to a quadrupolar interaction mechanism, thus the reorientational correlation time of the PCl3 molecule is determined from the 1/T2 values and the known quadrupole coupling constant. The 31P transverse relaxation time is controlled by a scalar coupling interaction mechanism while the longitudinal relaxation time is controlled by a spin—rotation interaction mechanism at high temperatures and a combination of dipolar, scalar coupling, and anisotropic chemical shift interaction mechanisms at lower temperatures. The scalar coupling constants calculated for P–35Cl in PCl3 and P–79Br in PBr3 are 127 and 296 Hz, respectively. The value for PCl3 is in excellent agreement with previous work, while that for PBr3 is believed to be more accurate than the value reported from previous studies. The spin—rotation coupling constants for PBr3, PBr2Cl, PBrCl2, and PCl3 are 3.49, 4.41, 5.95, and 9.09 kHz, respectively. The values for PBr3 and PCl3 do not agree with those obtained from previous relaxation measurements, but are in excellent agreement with the theoretical values.