Field Nuclear Magnetic Resonance Relaxometry Research Articles

Prediction of the stability and compatibility of Colombian heavy crude oils by 1D low field nuclear magnetic resonance relaxometry and chemometric methods

Stability and compatibility can be described by the insolubility number (IN), the solubility blending number (SBN) and the ratio (R) between them, which has become a critical index in daily refineries operation. In this work, a new methodology for predicting the stability and compatibility of heavy crude oils by 1D low field nuclear magnetic resonance (LF-NMR) relaxometry has been developed. Various chemometric models were developed to predict the IN,SBN and R properties of Colombian heavy crude oils (°API from 6 to 27), by integrating intervals of either the 1D free induction transverse magnetization decay curves (T2 FID) obtained with a low-field (LF) nuclear magnetic resonance (NMR) spectrometer, or their T2 relaxation distributions obtained via the inverse Laplace transform (ILT). Correlations between the relaxometry curves and said properties were evaluated using the principal component regression (PCR) and the partial least squares regression (PLSR) methodologies. The obtained prediction models yielded coefficients of determination (R2) above 95% with as few as 6 components and values of cross validated root mean squared error of prediction (RMSEP) as low as 0.71 for the IN, 2.37 for the SBN and of 0.03 for the R property, respectively. The best prediction models were attained using PLSR and employing the FIDs as the predictors. The use of chemometric predictive models from LF-NMR measurements represent a low-cost and faster alternative to estimate critical properties of the independent crude oils to be blended, and thus, will help in predicting the stability and compatibility of crude oil blends, which in turn may help accelerate the decision-making process in daily refineries tasks.

Estimates of blood plasma water content using portable NMR relaxometry

Although blood plasma water content (PWC) is a relevant metric for many medical diagnostic procedures, the routine clinical measurement of PWC has remained elusive. Portable nuclear magnetic resonance (NMR) offers one way to nondestructively and quickly measure PWC. Contrived pseudoplasma samples that mimic blood plasma while also allowing rigorous control over water content are used to demonstrate the role of NMR in this work. Calibration curves relating measured NMR relaxation time constants (T2 and T1) to gravimetric PWC values for a set of human lyophilized plasma samples are used to predict the PWC in porcine and model human blood plasma from respective NMR T2 and T1 values. It is shown that the T2 and T1 decay constants measured with low field NMR relaxometry correlate with the PWC values for pseudoplasma and human lyophilized plasma samples. Statistical testing of the NMR-PWC correlation model demonstrated a prediction accuracy exceeding 98%. The PWC obtained in this way was used to correct sodium cation concentrations reported from direct ion-selective electrode tests. The accuracy of PWC determination with NMR is comparable to that of the gravimetric method that requires sample lyophilization. The rapid turnaround time, non-destructive nature, and portable footprint of the NMR-PWC measurement makes rapid, point-of-care clinical electrolyte estimates possible.

Capillary Trapping of CO2 in Sandstone Using Low Field NMR Relaxometry

AbstractInjecting carbon dioxide into geological formations for long‐term storage is considered integral to reducing greenhouse gas emissions. Residual trapping of CO2 is a primary storage mechanism, whereby CO2 ganglia are trapped in the pore space by capillary forces. Experimental knowledge of residual trapping processes in rocks is critical to the development of safe storage strategies. Here we present a quantitative low field 1H nuclear magnetic resonance (NMR) core flooding study of CO2 residual trapping in three different sandstones. It was found that transverse relaxation (T2) measurements were sensitive to the dissolution of paramagnetic ions from rock matrix minerals after exposure to carbonic acid; this response was observed on time scales relevant to core flooding experiments (i.e., minutes to hours). Subsequently, a brine aging protocol was designed and implemented to minimize this chemical effect, and hence, by applying the well‐known T2‐pore size relationship, changes in T2 time distributions during core flooding could be related to displacement of brine from pores of different sizes. Comparison of T2 distributions for partially CO2/brine‐saturated cores to previously published data for N2/H2O systems shows an increased displacement of brine from small pores by CO2. Furthermore, results from cyclical brine/CO2 injections showed an increase in the total volume of residually trapped CO2 and an increase in trapping efficiency; compared to the results observed for N2/H2O, however, the improvement in trapping efficiency with cyclic injection was less pronounced. Potential causes for the observed differences are discussed in the context of effective N2 and CO2 wetting.

Low field NMR relaxation as a probe to study the effect of activators and retarders on the alkali-activated GGBFS setting process

Low field nuclear magnetic resonance relaxometry (LF-NMR) was used to study the setting process of alkali-activated GGBFS (AA-GGBFS) paste during the early curing hours. LF-NMR measurements were carried out from fresh paste casting until hardening (generally no more than 8 h). The transverse relaxation time T2 was used as a probe to assess the setting process. Combined with Vicat penetration and temperature monitoring, an important threshold indicator was defined as the deadline for paste casting (DPC). The physical meaning of the DPC is a threshold point where the developing micro pores make loss of movable water attain a certain level so that the semi-solid paste has slight strength. Moreover, several periods related to AA-GGBFS early-hour paste development are proposed: (1) dissolution; (2) setting; (3) acceleration; and (4) hardening. By analysing each period during the early hours, it was found that the hybrid retarder of zinc nitrate and sodium gluconate works for the AA-GGBFS system.

Probing diffusion dynamics during hydrate formation by high field NMR relaxometry and diffusometry.

High-field nuclear magnetic resonance (NMR) relaxometry and diffusometry along with magnetic resonance imaging were used to monitor phase transition molecular dynamics during hydrate formation occurring in water droplets dispersed in liquid cyclopentane. 1D T2 relaxation measurements indicate the extent of hydrate formation as well as a reduction in water droplet size with progression of hydrate growth. MRI intensity maps and T2 relaxation maps indicate spatially dependent hydrate formation rates due to the heterogeneity of the system. Spectrally resolved diffusion measurements indicate a reduction in the porosity of the hydrate agglomerate as the hydrate shell increases in thickness. A novel signal rise observed in two dimensional T1-T2 relaxation correlation experiments indicates complex diffusion dynamics due to coupling between regions with varying relaxation and diffusion. These results indicate the ability to monitor hydrate growth and phase transition molecular dynamics due to evolution of the porous hydrate agglomerate by means of high-field NMR.

Measuring hydrological connectivity inside a soil by low field nuclear magnetic resonance relaxometry

AbstractHydrological connectivity inside the soil is related to the spatial patterns inside the soil (i.e., the structural connectivity). This, in turn, is directly associated with the physical and the chemical processes at a molecular level (i.e., the functional connectivity). Nuclear magnetic resonance (NMR) relaxometry can be successfully applied to reveal both structural and functional components of soil hydrological connectivity. In the present study, the low field NMR relaxometry was applied on water suspended soils sampled at the upstream‐ and downstream‐end of three different length plots. Also the sediments collected from the storage tanks at the end of each plot were water suspended and monitored by NMR relaxometry. The results from the NMR investigations were elaborated by using a mathematical approach in order to quantify both the functional and structural connectivity components. In particular, following integration of the T1 distribution curve, an S‐shaped curve was obtained. It revealed two plateaus corresponding to the shortest (low component) and the longest (high component) intervals of relaxation times, respectively. According to relaxometry theory, the two T1 intervals, associated to the different plateaus, were attributed to micro and macro soil pores, respectively. The two T1 intervals were used to define a functional connectivity index, while the central part of the S‐shaped distribution was used to define a structural connectivity index. Here we provide the physical meaning of the our mathematical approach, thereby revealing that functional connectivity index increases with plot length, as a result of a selective eroded particle transport. Moreover, the relationship structural connectivity index versus plot length resulted quasi‐independent of grainsize distribution, whereas the values of the structural connectivity index for the sediment samples resulted lower than those obtained for the corresponding soils.

Characteristics of Xanthosoma sagittifolium roots during cooking, using physicochemical analysis, uniaxial compression, multispectral imaging and low field NMR spectroscopy.

To effectively promote the industrial utilization of cocoyam (Xanthosoma sagittifolium) roots for enhanced food sustainability and security, there is a need to study their molecular, mechanical and physicochemical properties in detail. The physicochemical and textural characteristics of the red and white varieties of cocoyam roots were thus analysed by low field nuclear magnetic resonance relaxometry, multispectral imaging, uniaxial compression testing, and relevant physicochemical analysis in the current study. Both varieties had similar dry matter content, as well as physical and mechanical properties. However, up to four fast-interacting water populations were observed in the roots, dependent on the root variety and their degree of gelatinization during cooking. Changes in the relaxation parameters indicated weak gelatinization of starch at approximately 80°C in both varieties. However, shorter relaxation times and a higher proportion of restricted water in the white variety indicated that this variety was slightly more sensitive towards gelatinization. A strong negative correlation existed between dry matter and all multispectral wavelengths>800nm, suggesting the potential use of that spectral region for rapid analysis of dry matter and water content of the roots. The small, but significant differences in the structural and gelatinization characteristics of the two varieties indicated that they may not be equally suited for further processing, e.g. to flours or starches. Processors thus need to choose their raw materials wisely dependent on the aimed product characteristics. However, the spectroscopic methods applied in the study were shown to be effective in assessing important quality attributes during cooking of the roots.

Rotatable Small Permanent Magnet Array for Ultra-Low Field Nuclear Magnetic Resonance Instrumentation: A Concept Study.

ObjectWe studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability.Materials and MethodsThe finite element method (COMSOL®) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field.ResultsA concentric small permanent magnet array can be used to generate strong sample pre-polarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20–50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres.ConclusionsA dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably.

1H low field nuclear magnetic resonance relaxometry for probing biodiesel autoxidation

The oxidation stability of biodiesel composed of fatty acid esters derived from vegetable oils, is one of the major issues challenging its wide-spread use as an alternative fuel. The poor oxidative stability of biodiesel compared to petrodiesel, is due to its high content of unsaturated fatty acid methyl esters that negatively affects fuel properties such as storage lifetime. Moreover, the relationship between new molecules formed by oxidation and their new solution morphologies is a complex subject that affects physico-chemical properties of the fuel. The goal of this work was to understand how the oxidized unsaturated fatty acid methyl esters and the non-oxidized components of the biodiesel interact and affect the final properties of multi component biodiesel mixtures. Towards this objective standard pure fatty acid methyl esters and biodiesel mixtures were heated for different time periods with constant stirring to induce autoxidation, and then analyzed by 1H low field nuclear magnetic resonance (LF-NMR) relaxometry. To further define the molecular consequence of autoxidation and appearance of autoxidation products, a combination of supporting methods, including, gas chromatography, Fourier transform infrared, 1H high field NMR, and thermogravimetric analysis were used.1H LF-NMR relaxometry was proven to be an advantageous tool to study autoxidation of biodiesel. It is a direct, rapid, non-destructive method that can be used to study the underlying structural and compositional mechanisms that contribute to changes in the fuel’s physico-chemical properties. For example we describe in this paper the interactive effect of new oxidative products and stable non-oxidized components upon each other’s molecular movement and morphology during the process of oxidation. One major result was to show that the oxidized products of fatty acid methyl esters have different secondary interactions between themselves and the biodiesel components which were not oxidized but are mutually affected by each other. Characterizing these changes in molecular interactions and how they affect biodiesel properties is one of the major contributions of 1H LF-NMR relaxometry. Also, the possibility of 1H LF-NMR to analyze heterogeneous and at times heterophasic whole samples directly, including their physicochemical state, is of great value when studying the effect of different antioxidants on the oxidation stability of fuels and other food and biological systems.

Methane Storage in Nanoporous Media as Observed via High-Field NMR Relaxometry

The storage properties of methane gas in Vycor porous glass (5.7 nm) are characterized in a wide pressure range from 0.7 MPa-89.7 MPa using Nuclear Magnetic Resonance (NMR). We demonstrate the capability of high field NMR relaxometry for the determination of the methane gas storage capacity and the measurement of the Hydrogen Index, to a high degree of accuracy. This helps determine the excess gas in the pore space which can be identified to exhibit Langmuir properties in the low pressure regime of 0.7 MPa to 39.6 Mpa. The Langmuir model enables us to determine the equilibrium density of the monolayer of adsorbed gas to be 8.5% lower than that of liquid methane. We also identify the signatures of multilayer adsorption at the high pressure regime from 39.6 Mpa to 89.7 Mpa and use the Brunauer-Emmet-Teller (BET) theory to determine the number of adsorbed layers of methane gas. We show how these measurements help us differentiate the gas stored in the Vycor pore space into free and adsorbed fractions for the entire pressure range paving way for similar applications such as studying natural gas storage in gas shale rock or hydrogen storage in carbon nanotubes.

On the synthesis and structure of resorcinol-formaldehyde polymeric networks – Precursors to 3D-carbon macroassemblies

With the new impetus towards the development of hierarchical graphene and CNT macro-assemblies for application in fields such as advanced energy storage, catalysis and electronics; there is much renewed interest in organic carbon-based sol–gel processes as a synthetically convenient and versatile means of forming three dimensional, covalently bonded organic/inorganic networks. Such matrices can act as highly effective precursors, scaffolds or molecular ‘glues’ for the assembly of a wide variety of functional carbon macro-assemblies. However, despite the utility and broad use of organic sol–gel processes – such as the ubiquitous resorcinol-formaldehyde (RF) reaction, there are details of the reaction chemistries of these important sol–gel processes that remain poorly understood at present. It is therefore both timely and necessary to examine these reactions in more detail using modern analytical techniques in order to gain a more rigorous understanding of the mechanisms by which these organic networks form. The goal of such studies is to obtain improved and rational control over the organic network structure, in order to better direct and tailor the architecture of the final inorganic carbon matrix. In this study we have investigated in detail, the mechanism of the organic sol–gel network forming reaction of resorcinol and formaldehyde from a structural and kinetic standpoint, by using a combination of real-time high field solution state nuclear magnetic resonance (NMR), low field NMR relaxometry and differential scanning calorimetry (DSC). These investigations have allowed us to track the network formation processes in real-time, gain both detailed structural information on the mechanisms of the RF sol–gel process and a quantitative assessment of the kinetics of the global network formation process. It has been shown that the mechanism, by which the RF organic network forms, proceeds via an initial exothermic step correlated to the formation of a free aromatic aldehyde. The network growth reaction then proceeds in a statistical manner following a first order Arrhenius type kinetic relationship – characteristic of a typical thermoset network poly-condensation process. And despite the relative complexity and ill-defined nature of the formaldehyde staring material, the final network structure is to a large extent, governed by the substitution pattern of the resorcinol molecule.

Numerical study of ultra‐low field nuclear magnetic resonance relaxometry utilizing a single axis magnetometer for signal detection

This paper investigates optimal placement of a localized single-axis magnetometer for ultralow field (ULF) relaxometry in view of various sample shapes and sizes. The authors used finite element method for the numerical analysis to determine the sample magnetic field environment and evaluate the optimal location of the single-axis magnetometer. Given the different samples, the authors analysed the magnetic field distribution around the sample and determined the optimal orientation and possible positions of the sensor to maximize signal strength, that is, the power of the free induction decay. The authors demonstrate that a glass vial with flat bottom and 10 ml volume is the best structure to achieve the highest signal out of samples studied. This paper demonstrates the importance of taking into account the combined effects of sensor configuration and sample parameters for signal generation prior to designing and constructing ULF systems with a single-axis magnetometer. Through numerical simulations the authors were able to optimize structural parameters, such as sample shape and size, sensor orientation and location, to maximize the measured signal in ultralow field relaxometry.

In-situ characterization of the cure reaction of HTPB and IPDI by simultaneous NMR and IR measurements

The progress of the cure reaction of hydroxyl-terminated (poly)butadiene (HTPB) and isophorone diisocyanate (IPDI) to a polyurethane is of major importance for the adjustment of process parameters as well as final product properties. Simultaneous low field nuclear magnetic resonance relaxometry and near infrared spectroscopy are applied in-situ to study the progress of the cure reaction with respect to time. The sensitive spots of both methods are coincident, allowing quantitative comparison of the results of both methods, as the same region of the sample is examined. The aim is to get a more comprehensive insight into the reaction by the combination of the two analytical methods. Molecular dynamics as provided by NMR relaxation data and chemical concentration information via near infrared spectroscopy allow detailed monitoring and deeper insight into the complex reaction.

Mesophase formation investigation in pitches by NMR relaxometry

Carbonaceous pitches are used as raw materials in advanced carbon products. This work aims at combining solvent extraction methodology with low field nuclear magnetic resonance relaxometry technique in order to characterize heated-treated samples of petroleum pitches. The T1 relaxation times showed two distinct domains: one was referring to the aromatic region and the other one was attributed to mesophase. The results also evidenced that the 1H NMR relaxometry could be used as a new tool for the characterization of this kind of system.

Determination of Oil and Water Compositions of Oil/Water Emulsions Using Low Field NMR Relaxometry

Abstract During production operations in heavy oil and bitumen formations where thermal recovery methods are applied, the fluids produced are often in the form of emulsions. This is also true in non-thermal recovery methods whenever oil and water are coproduced, but to a lower degree of severity. Conventional flow measuring devices are capable of measuring oil and water streams when they are segregated, but they fail when oil-in-water or water-in-oil emulsions form. Conventional methods are also not reliable when there are solids flowing in the stream. Low field NMR relaxometry was successfully tested as a tool for accurately measuring the oil and water content of such streams with and without emulsions present in the samples. The method was proved to be at least as good as conventional extraction methods (i.e., Dean-Stark). The technology was tested with both artificially and naturally occurring emulsified streams with accuracy better than 96﹪. This extremely encouraging result led to the design of an online NMR relaxometer for oil/water stream measurements under the conditions encountered in the production of heavy oil and bitumen. Introduction In the recovery of bitumen, viscosity reduction becomes important, both below and above the ground. The addition of a liquid diluent is thought to break down or weaken the intermolecular forces which create high viscosity in bitumen(1). The effect is so dramatic that the addition of even 5﹪ diluent can cause a viscosity reduction in excess of 80%; thus, facilitating the in situ recovery and pipe line transportation of bitumen. The knowledge of the bitumen-diluent viscosity is highly important, since without it, calculations in upgrading process, in situ recovery, well simulation, heat transfer, fluid flow, and a variety of other engineering problems would be difficult or impossible to solve. This paper presents the development of a simple correlation to predict the viscosity of binary mixtures of bitumen-diluent in any proportion. Experimental The data used for the development of the correlation was TABLE 1: Bitumen data at 30 °CDATA[C. Available In Full Paper. TABLE 2: Diluent data at 30 °CDATA[C. Available In Full Paper. obtained from Wallace et al.(2) and Wallace and Henry(3).The data consisted of a total of 99 points obtained from three bitumens and five diluents, respectively, listed in Tables 1 and 2. Each of these bitumen samples was diluted at 30 °CDATA[C to 5, 10, 25, 50 and 75 weight ﹪ diluent with each of the diluents. After mixing, the samples were reweighed, and any weight loss was attributed to solvent evaporation. The diluent weight fractions were adjusted accordingly, and the viscosities of the mixtures measured. For a detailed account of experimental procedures, refer to Wallace and Henry(3). Correlation Development Many correlations have been developed to predict the viscosity characteristics of bitumen-diluent mixtures(1-6). While several have been successful in making these predictions, most are cumbersome to use. Low Field Nuclear Magnetic Resonance (NMR) relaxometry techniques were developed in the laboratory to enhance and support comparable NMR logging tools that are currently used downhole.