Achieving Long‐Range Arbitrary Uniform Alignment of Nanostructures in Magnetic Fields

In order to explore the change characteristics of the adsorption and desorption performance of coal under high gas pressure, low-field nuclear magnetic resonance (LFNMR) technology was used to conduct experimental research on coal adsorption and desorption. The results show that (1) the T 2 spectrum distribution diagram shows adsorption peaks ( T 2 = 0.01 ms ~ 1 ms ) and free peaks ( T 2 = 5 ms ~ 1000 ms ); (2) with the increase of equilibrium pressure, the peak area of adsorbed methane gradually increased at first and then tended to equilibrium. The initial increase rate of free methane was slower than that of adsorbed methane, and the increase rate of free methane was faster in the later stage; (3) the relationship between the amount of adsorbed gas in the adsorption state of coal and the gas pressure conforms to the Langmuir equation. Taking the equilibrium pressure P = 8.7 MPa as the critical hysteresis pressure, it can be divided into two stages which are higher gas pressure (0.5~8.7 MPa) and high gas pressure (8.7~10.33 MPa); the amount of adsorbed gas in the free state has a linear relationship with the gas pressure, and there is no obvious hysteresis; (4) comparative analysis under the same experimental conditions, the mass of the adsorbed gas in the desorption process is greater than the mass of the adsorbed gas in the adsorption process, and there is basically no difference in the mass of the free gas.

Characterization of mechanical properties and microstructure of silica mortar and coral mortar based on nuclear magnetic resonance technology

With the increasing shortage of timber resources and the advancement of environmental protection projects, many artificial fast-growing forests are planted and used as raw materials in China. There are significant differences in the properties of natural forest wood and artificial fast-growing forest wood, and the properties of wood mainly depend on the change in the status of bound water in the cell wall. In this study, the fiber saturation point (FSP) and pore size distributions within the cell wall of six species of fast-growing forest wood were studied by low-temperature nuclear magnetic resonance (NMR) technology. The effects of species, growth rings, and extractives on the FSP and pore structure were analyzed. The water vapor sorption experiments were performed, and the adsorption isotherms of the samples were fitted through the Guggenheim-Anderson-de Boer (GAB) equation. According to the least-square regression of the adsorption isotherms and combined with the low-temperature NMR experiments, the content and proportion of the different types of bound water were analyzed. The results showed that the average FSP of each Chinese fir was about 40% and that of each poplar was about 35%. There is about a 10% difference between the FSP measured by NMR technology and the adsorption bound water content obtained by adsorption isothermal. The pore size distribution results show that in all samples, the proportion of pores larger than 10.5 nm is very low, about 10%; the proportion of 1.92-10.5 nm pores is about 30%; and the proportion of pores smaller than 1.92nm is more than 50%. This work will be helpful to the study of the wood moisture status and provide reference data for wood modification.

Natural gas hydrate, as an unconventional resource, has been attracting increasing attention. Understanding the characteristics of methane hydrate formation and dissociation in porous media is important for developing gas hydrate-bearing reservoirs. This work discusses the use of low-field nuclear magnetic resonance (LF-NMR) technology to investigate the formation and dissociation of methane hydrate in the sandstone. In this work, an experimental assembly wherein methane hydrate can form and dissociate, is used to conduct LF-NMR measurements. LF-NMR, as a noninvasive measurement technology, combines the transverse relaxation time (T2) measurement with the magnetic resonance imaging (MRI). T2 measurements can explore the characteristics of methane hydrate formation and dissociation in core samples from a pore-scale perspective. MRI can display the spatial distribution of water from a core-scale perspective. The excess-gas method and the excess-water method are successively applied to form methane hydrate, and depressurization is applied to dissociate methane hydrate in the laboratory. The characteristics of methane hydrate formation and dissociation is studied in the sandstone. Experimental results show that the signal intensity of short T2 and long T2 decreases simultaneously in the process of the methane hydrate formation using the excess-gas method, indicating that methane hydrate is formed in both small and large pores. When using the excess-water method, the signal intensity of long T2 decreases, and the signal intensity of short T2 increases in the process of the methane hydrate formation, indicating that methane hydrate is mainly formed in large pores. Methane hydrate is dissociated simultaneously in both small and large pores when using the depressurization method. Water content in small pores gradually increases. Capillary pressure causes some water to remain in the core samples following dissociation. Water content in large pores decreases initially and then increases during depressurization. In the early stages of depressurization, more water leaves large pores than is generated by hydrate dissociation. In the later stages of depressurization, less water leaves the large pores than is generated by hydrate dissociation. This study may inspire the new understanding on distribution of fluid in sediments during the process of accumulation and exploitation of natural gas hydrates.

In this study, changes in the transverse relaxation time (T2), signal intensity (A2), and images of ‘Jinxiu’ yellow peach fruits were investigated using low-field nuclear magnetic resonance (LF-NMR) and proton magnetic resonance imaging (1H-MRI). The water content, (determined using centrifuging technology), fruit firmness, and ethylene production were evaluated at 4±1°C and 25±2°C. The results showed a signal peak (A2) and T2 at 500–1000 ms. On days 4–6, T2 changed from 796 ms to 861 ms, and decreased with longer time at 25°C. Water content also decreased and high adjusted determination coefficient (adj-R2) values with water content were found for T2 (R2 = 0.95) and A2 (R2 = 0.99), indicating a high degree of fit for the prediction equations. A2 decreased and T2 shortened after prolonged storage at 4°C and high adj-R2 values were found between the water content and T2 (R2 = 0.93) and A2 (R2 = 0.97).Ethylene production and firmness were the same as for T2, A2, and internal breakdown at 25°C for 4–6 days, and 4°C for 16–21 days. Compared with storage at 25°C, low temperature storage inhibited water loss and also prohibited internal breakdown. T2 and A2 can be used to evaluate the storage characteristics of yellow peach fruits, and the internal breakdown of pulp tissue could be clearly observed by 1H-MRI, which is a function of LF-NMR. 1H-MRI can provide high-resolution images showing the internal structure of intact peaches. Thus, LF-NMR is a new technology that could be an effective and simpler method for monitoring and predicting water content, as well as detecting quality issues during peaches storage.

Shale oil is mainly stored in the nano–micro-pores of shale in the form of adsorption or in a free state. Among them, only free-state oil is the main contributor to shale oil production under natural elastic energy. Therefore, it is crucial to evaluate the movability of crude oil effectively. In this paper, focusing on the Jurassic shale oil reservoir core in the middle-eastern Sichuan region of China, low-field nuclear magnetic resonance (NMR) technology is used to analyze the basic characteristics of shale oil core samples. Experiments on the low-field NMR one-dimensional and two-dimensional spectrum characteristics of the original core, heat-treated core, and thermogravimetric-treated shale core are carried out. The effects of the TG-MS method, T2 method, and the volatilization of light oil components on the movability of shale oil reservoirs are analyzed, and the movability characteristics of shale oil reservoirs in the middle-eastern Sichuan region are preliminarily clarified. The results show that under thermal treatment, the distribution range of the two-dimensional spectrum of the core oil occurrence area is significantly reduced, and the T1 and T2 distribution ranges are reduced by 10.9% and 60.7%, respectively. According to the TG-MS method, the mobile oil, bound oil, and adsorbed oil account for 74.7%, 8.1%, and 17.2%, respectively. The quantitative calculation of movable oil saturation by NMR combined with heat treatment is 65.6%, which is lower than that calculated using the thermogravimetric method. In order to calculate the movability more accurately, the scale effect between different samples should be considered. This study could provide a theoretical basis for the subsequent shale oil development program.

A comparative evaluation of low-field and high-field NMR untargeted analysis: Authentication of virgin coconut oil adulterated with refined coconut oil as a case study

A review of nuclear magnetic resonance (NMR) technology applied in the characterization of polymer gels for petroleum reservoir conformance control

Mechanism of expanding swept volume by nano-sized oil-displacement agent

At present, the drug substitutes represented by new psychoactive substances are gradually becoming popular, leading to an increasing demand for identifying novel drugs with unknown structures in drug investigation. Nuclear magnetic resonance (NMR) spectroscopy is an important tool for analyzing molecular structures. In the absence of standard substances, quantitative NMR (qNMR) can undertake the quantitative analysis of target substances in complex mixtures and has unique advantages in the research of new drugs and their precursor drugs. Due to the limitations of the site and maintenance costs, as well as relatively complex operation, high-field superconducting NMR is less commonly applied in drug research. The desktop low‑field NMR developed in recent years provides a new alternative solution. Due to the use of permanent magnets, its size is reduced, and the operation and maintenance costs are lowered. It has been widely used in various research fields. This article reviews the development of low-field NMR technology, summarizes the application of desktop low-field NMR in screening and identification of suspicious substances, rapid content determination, analysis of drug manufacturing processes and synthetic routes, and correlation traceability. It also looks forward to the prospects and development directions of this technology in drug research, aiming to provide a reference for researchers who work in analytical chemistry and drug research.

Summary In the context of developing unconventional liquid-rich reservoirs, the application of supercritical carbon dioxide (sc-CO2) has shown many advantages, including enhanced oil recovery (EOR), reducing formation damage, reducing water usage, and promoting the formation of complex fracture networks. However, sc-CO2 faces certain limitations in shale oil reservoirs that hinder its widespread application, such as ultralow viscosity, asphaltene deposition, and high miscible pressure. The addition of chemical agents is expected to overcome some limitations of sc-CO2 and further improve the CO2-EOR performance. Diluted microemulsion (DME) shows great potential as a chemical additive in water-based fracturing fluids to improve oil recovery by wettability alteration during the shut-in period after hydraulic fracturing. It is essential to explore the synergistic mechanism of DME and sc-CO2 through laboratory experiments to understand the microscopic mechanism of oil mobilization in shale reservoirs and to guide field applications. In this study, three soaking sequences were designed and compared to explore the EOR mechanisms combining sc-CO2 with DME using crude oil and core samples from the Lucaogou shale formation. To distinguish the DME at different stages, the DME injection in the subsequent stage is referred to as post-DME (pDME). The soaking sequences consist of only sc-CO2 soaking, water–sc-CO2–pDME (W-C-D) soaking, and DME–sc-CO2–pDME (D-C-D) soaking. They correspond, respectively, to the CO2 fracturing process and the process of CO2-EOR technology after hydraulic fracturing with different water-based fracturing fluids. Low-field nuclear magnetic resonance (NMR) technology was used to quantify the oil distribution among different pores and to monitor changes in the fluid state during each soaking stage. Additionally, the component changes of the produced oil were characterized using gas chromatography (GC). The T2 spectra results indicate that sc-CO2 soaking yields the highest oil recovery in the first soaking stage compared with water soaking and DME soaking. DME soaking effectively mobilizes more oil in small pores than water soaking. Subsequent sc-CO2 soaking and pDME soaking exhibit better EOR performance in the W-C-D soaking sequence than in the D-C-D soaking sequence, primarily mobilizing the remaining oil in larger pores. The sequence of total oil recovery is D-C-D soaking > only sc-CO2 soaking > W-C-D soaking. While the total oil recovery from large pores is similar across different soaking sequences, the D-C-D sequence achieves the highest oil recovery in small pores. The GC results suggest that DME can enhance the recovery of heavy components (C17+) by reducing interfacial tension (IFT) and altering wettability, thereby providing a conducive environment for heavy component mobilization in the subsequent soaking period. DME enables balanced mobilization of both heavy and light components, while sc-CO2 enhances oil mobilization from the unswept area by the aqueous phase. Therefore, combining sc-CO2 and DME can result in a higher ultimate oil recovery factor in shale oil reservoirs. The findings of this study provide an in-depth understanding of the oil mobilization mechanism during the soaking period and inform the design of soaking sequences for field applications in shale oil reservoirs.

Freeze-thaw damage evolution of fractured rock mass using nuclear magnetic resonance technology

“Fracturing network+imbibition oil production” is a new attempt to effectively develop low-permeability tight reservoirs. Fracturing fluid is not only a carrier for sand carrying but also a tool in the process of imbibition. On the basis of imbibition experiments, combined with nuclear magnetic resonance and pseudo-color processing technology, this paper clarified the dominant forces of different types of pore-throat and quantitatively characterized the contribution of different levels of pore-throat to imbibition oil recovery. The results show that gravity is the main controlling force of imbibition for reservoirs with higher permeability. Fluid replacement mainly occurs in the early period of imbibition. Macropores contribute most of the imbibition recovery, mesopores have a weak contribution, and the contribution of micropores and pinholes can be ignored. For the reservoirs with low permeability, capillary force is the main controlling force of imbibition. Fluid replacement mainly occurs in the later period of imbibition. Macropores contribute most of the imbibition recovery rate, mesopores contribute a small part of the imbibition recovery factor, and the contribution of micropores and pinholes can be ignored. This paper clarified that macropores and mesopores are the main sources of the contribution of imbibition recovery efficiency, and oil content and connectivity are key factors for the imbibition recovery efficiency.

Biofilm and dairy fouling formation is difficult to study non-invasively in closed systems such as flexible tubing. Nuclear magnetic resonance (NMR) is considered as a promising non-invasive detection method for different deposits. This study aimed to investigate three deposit models: (1) Paenibacillus polymyxa biofilm, (2) dairy biofouling, and (3) dairy fouling, in different experimental set-ups by low-field 1H NMR. The transverse relaxation time T2 of each component in samples of experimental set-ups was studied. The results show that low-field NMR offers the possibility of qualitatively measuring the selected deposit models and differentiating non-destructively between the tubing and each deposit. The samples in each experimental set-up showed characteristic relaxation behavior of flexible tubing, deposit, and liquid. For the P. polymyxa biofilm, longer relaxation times T2 of about 100 ms were detected, while relaxation times T2 for dairy biofouling and dairy fouling were in range of 50–60 ms. It was thus concluded that low-field NMR has a great potential for non-invasive detection of deposit formation at practical industrial scales.

Cocaine is the second most popular traditional illicit drug in the European Union, after cannabis, and its high potential for addiction makes it a significant public health concern. Therefore, monitoring trends in the content and purity of street samples can provide valuable information to support harm reduction strategies. This study analysed a selection of 160 street cocaine samples collected at a large British summer festival between 2014 and 2024. A comparison between a low-cost, transportable 60 MHz benchtop nuclear magnetic resonance (NMR) instrument and a more expensive, larger laboratory-based 400 MHz NMR device was used to assess variations in composition and purity levels. Despite a lower signal-to-noise ratio and signal overlap causing some differences in values, the benchtop NMR produced almost identical results to those of the 400 MHz system. Until 2014, cocaine samples were highly adulterated; their purity increased sharply from 2015 onwards, with levels ranging from 80% to 98%, before showing a downward trend in 2024. The most commonly detected cutting agents were benzocaine, levamisole, caffeine, phenacetin, and lactose. Overall, this work demonstrates that low-field NMR can be effectively used to quantify cocaine in street samples. This could be especially beneficial on-site for guiding and enhancing harm reduction services and law enforcement.