Field Nuclear Magnetic Resonance Measurements Research Articles

Predicting the compressive strength of tight sandstone based on the low field NMR and pseudo-triaxial compression measurements

The compressive strength is very important for petroleum and other engineering studies. However, the effect of pore size and fluid distribution on the rock’s strength is not fully understood. We developed comprehensive research to study the controlling factors of the compressive strength based on low field nuclear magnetic resonance (NMR) measurements and pseudo-triaxial compression test for tight sandstones. The relationship between the compressive strength and the NMR obtained parameters are investigated completely, aiming for a better estimation of the compressive strength using the NMR data. The result shows that the rock’s strength is strongly controlled by the pore size distribution and the fluid existing state. Generally, the compressive strength is negatively correlated with the average transversal relaxation time, the movable water saturation, and the porosity, but positively correlated with the irreducible water saturation. The result reveals that the rock with larger pore radius and higher percentage of movable fluid is easier to reach the failure state. Further, the precision of the empirical model by multiple regression of the geometric mean of the relaxation time and the porosity is greatly improved compared with the model established by the brittle minerals, which is potentially to be use for geophysical prospecting when the NMR logging data is available.

Assessing the Efficiency of Saturating Shale Oil Cores and Evaluating Hydrocarbon Gas Huff ‘n’ Puff Using Nuclear Magnetic Resonance

SummaryShale oil formations have a very low primary yield despite advances in multistage hydraulic fracturing and horizontal drilling. In so doing, gas huff ‘n’ puff (HnP), among other improved oil recovery methods, is implemented to recover more liquid hydrocarbons. Gas HnP has proven to be an effective recovery process in shales taking into account the fracture properties, fluid-fluid interactions, and gas diffusion controlled by matrix properties. However, a laboratory-scale understanding of the gas HnP mechanism proves challenging. At this scale, measuring saturation before and after HnP tests in a nonintrusive and nondestructive manner, and understanding rock properties that affect diffusion is essential. In addition to ascertaining how the multiscale pore systems and varying mineral composition of shales affect its evaluation. The nuclear magnetic resonance (NMR) is considered a suitable tool for estimating fluid content in shales and understanding rock/fluid interactions. Generally, synthetic oil samples are used on either outcrop core plugs or crushed reservoir samples for NMR measurements, which may not be representative of rock/fluid interactions in bulk shales.This study is focused on carrying out NMR tests with dead oil on reservoir core plugs at relatively different depths to determine an effective means of saturation and understand oil production due to gas HnP. Gas HnP experiments were performed at reservoir conditions (3,500 psi and 125°C) on representative rock types from the Lower Eagle Ford (LEF) interval. Low field NMR measurements were subsequently carried out on the LEF core plugs at different states: as-received, saturated, and after gas HnP. The results show that oil recovery due to gas HnP occurred mainly in the organic pores (OPs) and inorganic pores (IPs) and ranged from 48 to 56% of the oil-in-place with indications of adsorbed/trapped methane (CH4) and remaining heavier components. This plays a vital role in evaluating the HnP process to know the extent of invasion and remaining oil components.In saturating the core plugs, the optimum saturation period was found to be 2 weeks for the LEF shale at current conditions. This presents an idea of how long to saturate a shale oil core effectively before it is tested for gas HnP. On the basis of the impact of varying mineral composition on the recovery mechanism, we observed the LEF core plug with the highest clay content to have the least recovery. This is in line with a high T1/T2 ratio alluding to reduced mobility of fluids in the presence of clay minerals with relatively small sizes of clay porosity and adsorptive surfaces.

Microscopic evidence for Mn-induced long range magnetic ordering in MAX phase compounds

Zero and low field nuclear magnetic resonance measurements have been performed on MAX phase samples (Cr1−x Mn x )2AC with A = Ge and Ga in order to obtain local microscopic information on the nature of magnetism in this system. Our results unambiguously provide evidence for the existence of long-range magnetic order in (Cr0.96Mn0.04)2GeC and for (Cr0.93Mn0.07)2GaC, but not for (Cr0.97Mn0.03)2GaC. We point to a possible dependence of long range magnetic order in these MAX phase compounds on the A atom.

Assessing the Dispersion Quality of Carbon Nanotubes Suspensions by Low Field Nuclear Magnetic Resonance

In this study, a novel method based on low field nuclear magnetic resonance measurements were used to characterize the dispersion quality of carbon nanotube suspensions. The liquid specific surface area, which calculated with the relaxation time, were used as an indicator of dispersion quality of the carbon nanotubes suspensions. The experimental results were compared with those measured by the conventional method methods, including Zeta potentiometer method and ultraviolet visible spectrophotometer method. The results show that low field nuclear magnetic resonance has the advantages in the characterizing the dispersion quality of high concentration carbon nanotube suspensions and tracking its re-agglomeration process non-destructively.

Pulsed magnetic field generation suited for low-field unilateral nuclear magnetic resonance systems

Pulsed magnetic fields can be used to provide instantaneous localized magnetic field variations. In presence of static fields, pulsed field variations are often used to apply torques and in-effect to measure behavior of magnetic moments in different states. In this work, the design and experimental performance of a pulsed magnetic field generator suited for low static field nuclear magnetic resonance (NMR) applications is presented. One of the challenges of low bias field NMR measurements is low signal to noise ratio due to the comparable nature of the bias field and the pulsed field. Therefore, a circuit is designed to apply pulsed currents through an inductive load, leading to generation of pulsed magnetic fields which can temporarily overpower the effect of the bias field on magnetic moments. The designed circuit will be tuned to operate at the precession frequency of 1H (protons) placed in a bias field produced by permanent magnets. The designed circuit parameters may be tuned to operate under different bias conditions. Therefore, low field NMR measurements can be performed for different bias fields. Circuit simulations were used to determine design parameters, corresponding experimental measurements will be presented in this work.

Evaluation of concentration and dispersion of functionalized carbon nanotubes in aqueous media by means of Low Field Nuclear Magnetic Resonance

Dispersions of functionalized carbon nanotubes (fx-CNTs) have been analyzed by means of Low Field Nuclear Magnetic Resonance measurements (LF-NMR). This technique showed that the presence of the fx-CNTs strongly influences the structuring of the water molecules. Thereupon, the water transversal relaxation rate (r2) can be used to get information about the concentration of the CNTs in aqueous dispersion and their aggregation tendency. Finally, the effect of the addition of an anionic polyelectrolyte, namely alginate, on aqueous dispersion of CNTs was explored by using LF-NMR, which revealed different dependence of r2 from CNT concentration, depending on the type and charge of fx-CNTs.

Spectroscopic studies of the interactions between β-lactoglobulin and bovine submaxillary mucin

The structural changes occurring during the interaction between β-lactoglobulin (BLG), the major whey protein, and bovine submaxillary mucin (BSM), a major salivary protein, were studied using high and low field Nuclear Magnetic Resonance (NMR), Dynamic Light Scattering (DLS), and Circular Dichroism (CD) spectroscopy. The zeta potentials of the proteins were also measured to provide information on the role of electrostatic forces in the interaction. The ratio between BLG and BSM was 1:1, and pH was adjusted to 3.0, 5.0 and 7.4 at room temperature. These spectroscopic results suggested that the interaction between BSM and BLG led to a compact aggregation. DLS results of the mixture showed a size distribution which is intermediate between that of BLG (215 nm) and BSM (200 nm). While no particular changes in the secondary structure were observed in either BSM or BLG, a weak tertiary structure, observed in BLG only, was further weakened upon interaction with BSM. High field NMR results for the BSM-BLG mixture indicated that spectral differences were mostly observed for solvent exposed groups, especially the mucin glycan chains, while hydrophobic core residues were less affected. The interaction between the two proteins can thus be concluded to be mostly of hydrophilic origin. Moreover, low field NMR measurements showed a decrease in transverse relaxation times in the mixture compared to the pure BLG and buffer solutions. This is possibly connected to fewer hydrophilic binding sites available in the BLG–BSM mixtures for water–protein interaction after aggregation of the two proteins.

Using NMR Decay-time Measurements to Monitor and Characterize DNAPL and Moisture in Subsurface Porous Media

Knowing how environmental properties affect dense nonaqueous phase liquid (DNAPL) solvent flow in the subsurface is essential for developing models of flow and transport in the vadose zone necessary for designing remediation and long-term stewardship strategies. For example, one must know if solvents are flowing in water-wetted or solvent-wetted environments, the pore-size distribution of the region containing DNAPLs, and the impact of contaminated plumes and their transport mechanisms in porous media. Our research investigates the capability and limitations of low-field proton nuclear magnetic resonance (NMR) relaxation decay-rate measurements for determining environmental properties affecting DNAPL solvent flow in the subsurface. The measurements that can be performed with the laboratory low-field system can also be performed in situ in the field with the current generation of commercial borehole logging tools. The oil and gas industry uses NMR measurements in deep subsurface, consolidated formations to determine porosity and hydrocarbon content and to estimate formation permeability. These determinations rely on the ability of NMR to distinguish between water and hydrocarbons in the pore space and to obtain the distribution of pore sizes from relaxation decay-rate distributions. In this paper, we will show how NMR measurement techniques can be used to characterize, monitor, and evaluate the dynamics of mixed fluids (water-DNAPL) in unconsolidated near-surface porous environments, and describe the use of proton NMR [Formula: see text] (spin-spin relaxation time) measurements in unconsolidated sandy-soil samples to identify and characterize the presence of DNAPLs in these environments. The potential of NMR decay-rate distributions for characterizing DNAPL fluids in the subsurface and understanding their flow mechanisms has not previously been exploited; however, near-surface unsaturated vadose zone environments do provide unique challenges for using NMR measurements. These challenges are addressed through systematic laboratory experiments and a program of research to extend and adapt current field NMR measurements to near-surface environmental problems.

Liquid state nuclear magnetic resonance at low fields using a nitrogen cooled superconducting quantum interference device

Nuclear magnetic resonance (NMR) spectra of liquids were studied at fields from 470nTto65μT using a nitrogen cooled radio frequency superconducting quantum interference device. The authors demonstrated that low field NMR measurements with this device are feasible and may yield useful information. In particular, they determined the natural linewidth of distilled water to be 0.17±0.06Hz. In addition, they recorded J-coupled spectra of 2,2,2-trifluoroethanol in a measurement field regime that was determined to provide the best signal-to-noise ratio. Four peaks with frequency differences of about 2Hz were well separated.

The effects of Al substitution on the magnetic and electronic properties of Sr 2Fe 1−xAl xMoO 6

We report the results from magnetic, transport and Mo zero field nuclear magnetic resonance measurements on polycrystalline Sr 2Fe 1− x Al x MoO 6. We find that there is a small electron-doping effect induced by Al 3+ substitution for Fe, which suggests that Fe is not in the 3+ state assumed in some theoretical models. We show that the decrease in the Curie temperature, T c, with increasing Al concentration can be interpreted in terms of 3D random site dilution. The saturation moment per formula unit, as determined from magnetization measurements, decreases with increasing x but the Mo moment shows a very small increase. The spin-wave dispersion is complicated in this compound and the temperature-dependent Mo moment does not follow the Bloch T 3/2 law. There is no correlation between the resistivity or the magneto-resistance at 77 K with the Al concentration, which may be due to different grain boundary properties in each sample.

Magnetic, transport and structural properties of Co/Ir multilayers grown by molecular beam epitaxy

We report on the structural properties of a [Co30/Ir10]10× (Å) superlattice, as well as on the magnetic and transport properties of a Co15/Ir5/Co30 (Å) artificial ferrimagnetic system. The samples were grown by molecular beam epitaxy (MBE) on MgO(001) substrates covered with a Ir130 (Å) buffer layer. High resolution cross section and plan view transmission electron microscopy (TEM) images present a high quality epitaxial stack [100]MgO(001) ‖ [100]Ir(001) ‖ [100]Co(001), with a tetragonalization of the Co fcc structure, due to strains induced by the Ir buffer. TEM images also show that the Co/Ir interfaces are flat, while the layers are continuous and free of bridges. These observations are consistent with zero field nuclear magnetic resonance measurements which indicate an fcc structure of the Co layers, and an interface mixing between Co and Ir limited to one atomic layer. As a consequence the antiferromagnetically coupled Co/Ir/Co sandwich presents large saturation and coercive fields which exceed 20 kOe and 220 Oe, respectively. Annealing made on the same sandwich indicate that the magnetic and transport properties are stable up to 300 °C. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Sensitivity of nuclear magnetic resonance relaxation measurements to changing soil redox conditions

Laboratory proton nuclear magnetic resonance (NMR) relaxation measurements were made on fluid‐saturated soil samples under reducing and oxidizing conditions. We used well‐characterized kaolinite and sand samples with known concentrations of Fe(II) and Fe(III) compounds as the representative soils. Changes in dissolved oxygen concentration in the water in the soils caused changes in relaxation time that are too small to be reliably detected by field NMR measurements. In contrast, NMR relaxation measurements were shown to be very sensitive to small changes in the concentration of Fe(III) species in soil, as a consequence of changing redox conditions. Oxidation of as little as 0.030 mg/g of Fe(II) species to Fe(III) oxyhydroxides resulted in a 30–50% decrease in relaxation time. These results have important implications for the potential use of NMR field instruments to monitor changing redox conditions using the Fe(III)‐Fe(II) redox couple as an indicator.

The phosphorus-31 spectra of dielectrophoretically reoriented tubules in the H II phase of DOPE

31P electric field nuclear magnetic resonance measurements are described which assess the effect of electric field on the orientation of tubules comprising the H II phase of dioeleoylphosphatidylethanolamine. A model, based on dielectrophoretic effects, was used to predict that a field of 4 MV/m would change the orientation of the lipid tubules in a H II phase. The excitation pulse was biphasic to help discriminate electric field interactions with free ions or permanent dipoles from interactions with induced dipoles, as well as to control the problems of ohmic heating, electrolysis and polarisation associated with do or unbalanced ac excitation voltages. Spectra consistent with irreversible electrorotation and with reversible and transient electrorotation were observed. No response to the electric field was seen in certain cases. The conditions for irreversible and reversible electrorotation and failure to rotate have been tabulated and are discussed. Finally, some simple models are considered, in order to calculate the energies involved, if the observed NMR spectra are interpreted as arising from lipid H II phase reorientations.