Vol 49, No 7 (2018)

Soil particles generally possess negative ions, and form an electronic field nearby the particles, which results in generating diffuse double layers on the surface of the particles. There is no diffuse double layer at dry state, and it develops diffuse double layers first when wetted by solution. This paper investigates the effect of NaCl solution on swelling characteristics of bentonite with different initial water contents by performing a series of wetting tests. The wetting test results indicate that when the initial water content is less than 10%, the NaCl solution has no effect on the swelling. When the initial water content is larger than 10%, the swelling strain decreases with increase in the NaCl solution concentration. The nuclear magnetic resonance (NMR) tests on compacted bentonite specimens were performed. The test results indicate that the strongly bound water content is 10%, which is similar to that by other method. The NMR tests on full wetting specimens, whose initial water content is less than 10%, show that the NaCl solution has no effect on NMR tests results. When the initial water content is larger than 10%, the proportion of curves from the NMR tests decreases with increase in the NaCl solution concentration. The NMR tests results indicate that the swelling occurred mainly in the intra-aggregate rather than in the inter-aggregate.

Process and reaction monitoring by nuclear magnetic resonance (NMR) spectroscopy has attracted considerable attention in the last years not only because of the new generation of low-field NMR spectrometers, but also because of an industrial need of more effectivity and process optimization via real-time monitoring of process and reaction details by diverse analytical tools. Most often, bypass solutions are realized in liquid state monitoring, which leads to questions of residence time distribution, mixing phenomena and accuracy of concentration determination. Exploring chemical engineering knowledge of fluid dynamics and combining it with NMR knowledge of magnetization buildup allow the calculation of magnetization in NMR measurements on flowing substances. This approach reveals the essential parameters to be considered when constructing flow cells and when processing data in NMR process monitoring. 3D computational fluid dynamics combined with Bloch equations allows detailed time and spatially resolved insights into the significant mechanisms of magnetization distribution and opens up new possibilities for experiment design in flow NMR. An experimental confirmation was provided by MRI experiments.

Thick tight Ordovician carbonate rocks are present at depths exceeding 5300 m in the Tahe oilfield and their matrix is considered to contain no storage space. An integrated petrographical and petrophysical study was conducted on a set of 25 tight carbonate core samples from Ordovician strata, covering a wide range of lithologies and textures. Six carbonate rock types were characterized by integrating both petrographical and petrophysical data, including thin-section observations and porosity, permeability, mercury injection capillary pressure and nuclear magnetic resonance (NMR) measurements. We found that thick grainstone and limestone with half-filled fractures exhibited good reservoir properties. NMR testing is an invaluable tool for characterizing pore structures in tight carbonate rocks. For example, six rock types can be identified from the NMR T₂ distributions and the changes in pore volume under different pressures (up to 20 MPa) can be calculated. NMR technology can be used to perform rapid and accurate rock-type identification and pore network evaluation in tight carbonate rocks. The results provide an experimental foundation for NMR logging interpretations and advance the understanding of geological and geophysical characteristics of ultra-deep carbonate reservoirs.

Time-domain nuclear magnetic resonance (NMR) has been widely used in food science. In this work, we demonstrate that the NMR decay obtained with the Carr–Purcell–Meiboom–Gill (CPMG) sequence can be used to estimate the peroxidase activity (PA) in cassava roots. This enzyme has been involved in post-harvest physiological deterioration (PPD), which limits the storage of fresh cassava to a few days. Cassava is a staple food for almost one billion people in tropical areas in Americas, Africa and Asia. A multivariate method using CPMG data and reference values of PA from a standard biochemical assay was built with 216 measurements for non-refrigerated and refrigerated samples of cassava roots. The figures of merit of the global partial least squares model using both types of roots showed a 0.06 μmol min⁻¹ limit of detection (LOD) and a 0.2 μmol min⁻¹ limit of quantification (LOQ) for PA, with 0.4 [intensity (a.u.)/(μmol min⁻¹)] sensitivity and a standard error of cross-validation (SECV) of 0.7 μmol min⁻¹. All of the results demonstrated that TD-NMR has the potential to predict PA in cassava roots that is indicative of the PPD problem.