Characterization of porous media using NMR methods

A nuclear magnetic resonance advance. Imaging fluorinated anesthetics in the brain.

Nuclear Magnetic Resonance (NMR) methods offer the determination of pore size distributions of loose sediments, which is the basis of investigations concerning ground water dynamics, i.e. water content and hydraulic conductivity of the subsurface. The NMR resolution range of pore radii depends on many parameters such as the technology of the applied NMR system, the Larmor frequency and the properties of the pore fluid and the pore surface, respectively. Different NMR methods do not necessarily show the same results at the same samples. At core samples from a shallow aquifer we compare Earth’s field NMR measurements with conventional lab NMR measurements and show the influence of the dead time and the Larmor frequency on the resolution limits of the pore size distribution.

Nuclear magnetic resonance (NMR) methods for the noninvasive, chemically specific investigation of living tissue have proliferated in number and advanced greatly in power since the first NMR images of anatomy appeared in the 1970s. By 1994, about 50 different NMR measurements had become available for the study of normal and pathological brain. These include aspects of biochemistry, angiography, perfusion, activation- sensitive metabolic rates for glucose and oxygen, monitoring of function through activation-induced changes in blood flow and water diffusion, and normal and pathological anatomy with submillimeter resolution. At least as many more measurements of biomedical importance are under development. Neuroscience research and management of neurological illness will be profoundly affected by NMR methods as they mature and become routine. The Neuroscientist 1:84-94, 1995

Chemical shift assignment and conformational structure of small molecules are fundamental for their study of interaction with biological targets, like proteins and nucleic acids. Chemical shift assignments are usually obtained with the very efficient nuclear magnetic resonance (NMR) methods COSY, HSQC, HMBC, TOCSY and NOESY. When these NMR methods do not afford all information or need the results confirmation to determine the complete molecular chemical shift assignment, it is necessary to use other procedures, especially for determination of long range 1H-13C coupling constants and 13C multiplicity. In this work, it is demonstrated that Gated decoupling 13C NMR spectrum, which is a simple and easy to use method, is very appropriate to complete the unambiguous chemical shift assignment and the conformational condition of arylidene barbiturates. The NMR conformational results were also confirmed by molecular modeling.

Appropriate drilling fluid additives which can build effective filter cakes are key components to minimize formation damage. Today there exists no effective and quantitative technique which can assess the formation damage minimization potential of any novel drilling fluid. This study provides the methodology for such a technique, by integrating HP/HT fluid loss data, derived from standard API HP/HT filter press, with filter cake quality and filtrate penetration depth, derived by Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) techniques. Novel nano-based drilling fluidwas made of de-ionized water, 7 wt% commercial Na-bentonite, and addition of custom made iron oxide (CM Fe3O4) nanoparticles (NP) at 0.5 wt%. Its excellent filtration characteristics were determined at elevated pressures and temperatures using a HP/HT filter press (500 psi/350°F) with ceramic discs, mimicking the formation, as filter media of k=775 mD. NMR T2 relaxation time measurements provided the pore size distribution of the ceramic discs, and a newly developed MRI technique by our team allowed direct visualization on the core-ceramic disc of the produced filter cake and filtrate penetration depth, providing insights on filtration characteristics. Addition of 0.5 wt% Fe3O4 NP resulted in a decrease of fluid loss by 47% compared to that obtained from the base fluid (BF) without the nanoparticles. The excellent filtration characteristics were attributed to the synergistic interaction of NP with bentonite platelets producing a strong microstructure network leading to rigid and very low permeability filter cakes. Spin-spin relaxation time (T2) NMR measurements revealed different pore size distribution of the nano-enhanced drilling fluid showing its tendency to occupy the smallest pores of the filter medium (ceramic disc). MRI T2 measurements revealed the saturation profiles of the drilling fluids inside the ceramic discs, in 3-D space. This allowed the visual representation of the penetration depth of the filtrate produced in the ceramic discs of the different tested drilling fluids. Our integrated characterization approach, gives us tools to analyze inter-particle interactions in the filter cakes at HP/HT conditions in order to explain the significant improvement in fluid loss performance of novel drilling fluids. The information gained in this study is considered to be extremely significant for deriving an effective methodology for assessing formation damage potential of any newly developed drilling fluid which can lead to more efficient and cost-effective drilling activities.

Measurement of body composition (fat mass) is an important item in pathophysiological and pharmacological studies using small animals (mice) in the fields of obesity and diabetes. The existing methods are, however, difficult, time consuming, and require a shielding facility. Now a novel system using nuclear magnetic resonance (NMR) technique was developed for measurement of body composition in small animals (mice) that provides noninvasive and rapid measurement without anesthetics; we introduced and evaluated this system and tried another application of this system. First, we validated this system using canola oil, soft tissues (adipose and skeletal muscle), and various kinds of rodent chows. Accuracy, precision, and reproducibility of this system were demonstrated to be equal to those in standard chemical methods. A strong positive correlation (y=x) between the results of NMR and chemical methods was found. Secondly, we evaluated accuracy and assay range of the NMR method using live mice that were fasted overnight or fed high fat diet (HFD). In fasted mice, a small but quantitative decrease of fat mass (5.1% from 9.1%) was detected. Total decrease of fat and lean mass (5.0 g) in fasted mice was equivalent to the decrease of body weight (5.0 g). In mice fed the HFD, increase of fat mass with relative decrease of lean mass were qualitatively detected in a time-dependent manner. We would like to emphasize that operation of the system was actually easy and measurements were accomplished in a short time (1 minute). Thirdly, we tried to use the NMR system for determination of hepatic fat contents using mice fasted or treated with a PPARgamma agonist; our results showed a quantitative increase in fat by fasting or in decrease in fat by the drug treatment. The changes of fat contents determined by the NMR method were well correlated with the changes in triglyceride and total cholesterol values obtained by the biochemical assays. In conclusion, body composition data acquired by the new NMR system are equivalent in accuracy and precision to classical chemical methods. The NMR analysis is simple, fast, and does not require anesthesia for acquisition of data, which are remarkable advantages compared to the existing methods. This system is expected to contribute to drug discovery and appropriate evaluation in the fields of obesity and diabetes.

We present a simple, accurate, stability-indicating nuclear magnetic resonance (NMR) method for determining active (S,S) and inactive (R,S) epimers of S-adenosyl-L-methionine (SAM) in tablets. The SCH3 resonances of SAM epimers were well resolved at 300 MHz. Individual assays of 5 SAM tablets gave SAM values of 101.3 +/- 1.7% of declared amounts. Tablet solutions were assayed at a level of 8.0 mg/mL, but the method was linear for SAM concentrations ranging from 64 to 1 mg/mL (correlation coefficient, 0.9996). Reproducibility was indicated by a relative standard deviation of 0.33% for 6 replicate assays for total SAM at a concentration of 8 mg/mL. In contrast to the propietary liquid chromatographic (LC) method, which requires SAM as an external standard, the NMR method uses sodium trimethylsilylpropionate-d4 (TSP) both as an internal standard and as a chemical shift reference. The method was used to test the stability of SAM analytes under various pH levels and temperatures. We found 8% inactivation of SAM due to epimerization over a 24 h period at room temperature and pH 5. SAM solutions showed no detectable inactivation after 14 days when stored below 0 degrees C.

The size of elongated micelles in a system containing 2 wt.% sodium dodecylsulfate (SDS), 3.5 wt.% NaCl and 94.5 wt.% water has been studied by means of two different nuclear magnetic resonance (NMR) methods and time-resolved fluorescence quenching with special emphasis on a comparison between the results from the three methods. The two NMR methods were the determination of self-diffusion coefficients by means of the pulsed-gradient spin–echo method and the determination of relaxation rates for specifically deuterium labelled SDS. In the analysis of the former data, the obstruction effect due to the finite micellar concentration was taken into account. In the analysis of the relaxation data, the combined effect of lateral surfactant diffusion over the micellar surface and micellar rotational tumbling was taken into account in an exact manner for the case of prolates and in an approximate way for the case of hemisphere-capped rods. The results obtained from the three methods were in reasonable agreement. If the micelles are modelled as prolates, the axial ratios obtained was ca. 6 while if they are described as hemisphere-capped rods, the axial ratio is ca. 5.

P034 Z-99 MOBILE INSTRUMENT FOR NMR MEASURE- Introduction 1 MENTS ON SAMPLES IN THE EARTH’S MAGNETIC FIELD TINO RADI� Radic Research Zehntwerderweg 188A 13469 Berlin Germany E-mail: radic@radic-research.de Web: www.radic-research.de The Nuclear Magnetic Resonance (NMR) method (Abragam 1983) allows beside other parameters a non-destructive measurement of the water content and the pore radii distribution of a rock sample. Therefore it is not surprising that the NMR method has developed into an important geophysical instrument. But up to now the main application area is still the laboratory. Unfortunately samples show many unwanted modifications on their way from the field to the

Quantitative characterization of multiphase methane and investigation of the methane dynamic adsorption process of coals were performed by a low-field nuclear magnetic resonance (NMR) method. Meanwhile, methane diffusion behaviors during the step-by-step pressurization adsorption process were evaluated by three diffusion models. The results indicate that the transverse relaxation time (T2) spectra of methane demonstrate two distinct peaks of adsorbed methane (P1, T2 < 2.5 ms) and porous medium-confined methane (P2) at a low-pressure step (∼1.0 MPa), and the third peak of bulk methane (P3) obviously appears when the pressure >2.0 MPa. The integrated T2 amplitude of adsorbed methane increases quickly during the first 2 h (>75% of total) and then gradually reaches a maximum value in the last 4 h during the initial pressure step of ∼1.0 MPa, whereas it reaches >90% of total amplitude in 1 h as the pressure is increased step-by-step. According to the strong linear relationship between the adsorbed methane volume and the integrated T2 amplitude, the real-time methane adsorption volume can be determined, and adsorption isotherms from the NMR method are found to be mostly overlapped with those of the volumetric method. Moreover, the effective diffusion coefficient of the unipore model (10–6 to 10–5 s–1) coincides with the micropore diffusion coefficient of the bidisperse model and the slow diffusion coefficient of the multiporous model, which is generally 1–3 orders of magnitude less than the macropore diffusion coefficient (10–3 to 10–2 s–1) and the fast diffusion coefficient (10–2 s–1) or transitional diffusion coefficient (10–4 to 10–3 s–1). The dynamic changes in diffusion parameters with pressure may be related to the comprehensive effects of methane diffusion mechanisms and coal matrix swelling under different adsorption pressures.

Nuclear magnetic resonance (NMR) relaxation and imaging are shown to give information on the changes of the pore space structure in ceramics during the sintering process. On a set of ceramic samples held at fixed maximum firing temperature of 1280 °C for different lengths of time, called “soaking times” in the ceramics industry, NMR methods were applied to quantify pore space properties such as connected porosity and pore size distributions. The longer the soaking time the lower the connected porosity, but no corresponding general statement can be made with regard to the pore size distribution. The homogeneous distribution of pores where the porosity is 17% for minimal soaking times becomes heterogeneous and with bigger pores but with porosity only about 5% after 10 min of soaking time. The results obtained are combined with those from traditional techniques such as scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The measured connected porosities and SEM analysis are in agreement with the NMR results. The “pore size” distributions obtained by magnetic resonance relaxation and MIP differ substantially and give complementary information, because in relaxation measurements “size” tends to correspond to pore dimensions, while in MIP “size” corresponds to the dimensions of the pore “throats,” the channels connecting the pores. The discrepancy between pore and pore-channel size increases with the soaking time and makes it clear that a higher level of sintering allows the formation of larger pores connected by smaller channels. For the longest soaking time sample, the SEM photos and the lack of a NMR signal make it clear that there is substantial isolated porosity and essentially no connected porosity.

SummaryWettability is a fundamental parameter significantly influencing fluid distributions, saturations, and relative permeability in porous media. Despite the availability of several wettability measurement techniques, obtaining consistent wettability index results, particularly in tight reservoirs, remains a challenge. Nevertheless, obtaining accurate wettability indices is crucial for gaining a more profound understanding of rock properties and precisely identifying and evaluating oil recovery processes. This study adapts T1-T2 nuclear magnetic resonance (NMR) in twin plugs (cores cut in half from the middle) style wettability measurement for different reservoirs. The fluid typing in different lithologies by T1-T2 NMR is proved to be effective by introducing D2O with a modified pressurization saturation process. Therefore, demarcating the regions requires multiple experiments, including sole brine, sole oil phase, and D2O imbibition processes, to define oil and water distribution regions. Such fluid typing ability enables better accuracy in wettability characterization. The weighing method shows good agreement with the T2 spectrum but lacks the ability to differentiate fluids. It is observed that the same fluid in various porous media displays different divisions of T1/T2 ratios. The wettability index of sandstone, tuff, and shale measured by weighing and T1-T2 NMR method are compared and studied to demonstrate the applicability of different methods. The weighing method and the NMR method, as modified-Amott methods, share the same fundamental principle but differ in their measurement techniques. This study’s T1-T2 NMR wettability indices are −0.52, 0.06, and 0.14, whereas the weighing wettability indices are −0.63, 0.07, and 0.34 of sandstone, tuff, and shale, respectively. In addition to the difference in shale wettability index, there are also differences in shale porosity measured by methods with/without the ability to differentiate the fluid types. The T1-T2 NMR method is more accurate in measuring the wettability of shale because it can distinguish among free water in pores, structural water, and clay-bound water in smectitic clay minerals. If the clay-related water is not treated properly, the hydrophilicity of the shale will be overestimated. Ultimately, four types of pores (water-wet, oil-wet, mixed-wet, and unconnected pores) are classified and quantified by the proposed NMR method.

Investigation on water status and distribution in broccoli and the effects of drying on water status using NMR and MRI methods

The self-diffusional motion of fluid molecules in a porous medium is expected to be different from that in the bulk fluid due to the presence of pore boundaries which restrict the molecules diffusing within the pore space. Thus it is conceivable that the study of restricted diffusion may provide information leading to pore structure characterization. We report the use of pulsed field gradient nuclear magnetic resonance (PFG NMR) techniques to study proton restricted self-diffusion in porous media. Measurements were conducted in model porous media consisting of different sized glass bead packs, as well as porous rocks. Computational analyses were carried out to obtain apparent diffusivities and other characteristics from the experimental results.

An understanding of transport, flow, diffusivity and mass transfer processes is of central importance in many fields of environmental biotechnology such as biofilm, bioreactor and membrane engineering, soil and groundwater bioremediation, and wastewater treatment. Owing to its remarkable sensitivity to molecular displacements and to its noninvasive and nondestructive character, pulsed field gradient (PFG) nuclear magnetic resonance (NMR) can be a valuable tool for investigating such processes. In conventional NMR microscopy, spatial encoding is achieved by using static magnetic field gradients (B(0) gradients). However, an interesting alternative is to use radio-frequency magnetic field gradients (RF or B(1) gradients). Although the latter are less versatile than the former, RF field gradient microscopy is particularly suitable for dealing with heterogeneous systems such as porous media because of its quasi-immunity to background static magnetic field gradients arising from magnetic susceptibility inhomogeneities, unlike the B(0) gradients microscopy. Here, we present an overview of basic principles and the main features of this technique, which is still relatively unused. Different examples of diffusion imaging illustrate the potentialities of the method in both micro-imaging and the measurement of global or local diffusion coefficients within membranes and at liquid-solid interfaces. These examples suggest that a number of environmental problems could benefit from this technique. Different future prospects of application of B(1) gradient NMR microscopy in environmental biotechnology are considered.