Nuclear Magnetic Resonance Device Research Articles

Development of a NMR Device Adapted to Operando Analysis of Electrochemical Commercial Cells

NMR (Nuclear Magnetic Resonance) spectroscopy is a common analytical technique for analysing electrode materials. Most of these analyses are ex situ NMR measurements, a post mortem analysis of the cell. Yet, development of in situ and operando NMR considerably increased. Since the first in situ measurement reported by Gerald et al [1] in 2000, a large variety of operando NMR approaches have been developed and applied to batteries [2–5].Two levers of improvement remain for operando NMR: the battery-casing design, usually home-made, and the geometry of the NMR resonator used to detect the spectrum.Battery-casing goes from flexible cells in a clear pouch to capsule, Swagelok or coin cells. Home-made casings are usually used to avoid distortion and sensitivity loss in the NMR measurement, attributed to the conductive casings. Another way of improvement is the type of NMR resonator to fit a larger variety of cell geometries. Solenoids, saddle coil, hairpin coil or parallel plates are currently used.Electrochemistry is sensitive to cell fabrication, so home-made cells are intrinsically less reproducible than commercial cells. To increase the repeatability for a higher number of cycles and from one cell to another, we collaborate with a cell maker to get industrial pouch cells and we use commercial protocols. Nevertheless, studying such cells implies new challenges. First, strong and controlled pressure must be applied on the cell. An innovative pressure system was created to be compatible with the NMR requirements, mainly low available space and the absence of magnetic or strongly paramagnetic materials. It also involved adapting the resonator to the commercial cell geometry. The second challenge is the attenuation and distortion of the NMR signal by conductors (skin effect for radio-frequency fields).Recently, Walder [6]. arose our interest with their report on operando NMR measurement for a stainless steel coin cell. We will present measurements that quantify the influence of the components of a commercial battery (casing material, electrodes, current collector and number of stacks).This development and these measurements will lead in close future to performing operando NMR of commercial cells in fast charging conditions (for example on silicon Li-ion batteries).[1] R. E. Gerald et al., J. Power Sources 89, 237 (2000).[2] X. Liu et al., Adv Mater 33, 2005878 (2021).[3] O. Pecher et al., Chem. Mater. 29, 213 (2017).[4] K. Gotoh et al., J. Mater. Chem. A 8, 14472 (2020).[5] K. J. Sanders et al., Carbon 189, 377 (2022).[6] B. J. Walder et al., Sci. Adv. 7, eabg8298 (2021).

Study on Three-dimensional Water-Bearing Response Characteristics of Surface-to-Underground NMR Traversal

Nuclear magnetic resonance (NMR) is the only geophysical method that can directly detect groundwater. However, the response signal collected by nuclear magnetic resonance method is very weak, and it is difficult to detect reliable results by conventional ground nuclear magnetic resonance when the water-bearing anomaly is located deeper underground. In order to increase the detection depth, the surface-to-underground nuclear magnetic resonance device received in the ground launch roadway can be used. In this paper, the basic principle and working method of surface-to-underground NMR are introduced. The three-dimensional numerical simulation of different water-bearing structures and different device forms is carried out, and the response law and advantage range of surface-to-underground NMR to underground water are summarized.

A Study on Mechanical Properties of Modified Soil–Cement Mixed with Ferronickel Slag Powder under Dry–Wet Cycles in Marine Environments

Soft soil foundations in marine environments are under coupling actions of seawater erosion and dry–wet cycles due to tides. Ferronickel slag is a solid waste produced in the smelting of ferronickel alloys. To recycle industrial solid waste and conserve energy, ferronickel slag is partially substituted for cement to solidify the soft soil foundations in marine environments. Unconfined compression tests were conducted for soil–cement mixed with ferronickel slag of various proportions to investigate its apparent erosion characteristics and mechanical characteristics under dry–wet cycles. In the tests, the corresponding numbers of cycles were set to 0, 6, 12, and 18. To further investigate the microscopic action mechanism of ferronickel slag on soil–cement, a nuclear magnetic resonance (NMR) device was utilized to analyze the microstructure of the soil–cement. According to the testing results, the unconfined compressive strength of soil–cement first increased and then decreased when the number of cycles of seawater erosion increased. With other conditions being the same, the addition of ferronickel slag can improve soil–cement strength, and changes in soil–cement strength were more significant than that with no ferronickel slag mixed. Moreover, the optimal amount of admixture was proved to be 45%. As the number of dry–wet cycles increased, the mass of soil–cement first increased and then decreased. With the same number of dry–wet cycles, soil–cement mixed with ferronickel slag had a smaller mass loss rate than that with no ferronickel slag added. After six dry–wet cycles, apparent erosion of soil–cement becomes increasingly serious, including the absence of edges and corners, deformation of surfaces, and even spalling and cracking. The NMR analysis revealed that dry–wet cycles can promote the evolution of small pores into larger ones within the soil–cement, thereby increasing the number of larger pores, leading to an increase in porosity, a decrease in the compactness of the soil–cement, and a reduction in strength.

Research on the influence of liquid nitrogen freeze-thaw cycles on gas emission characteristics of coal

ABSTRACT To research the effect of freeze-thaw cycles of liquid nitrogen (LN2) on gas emission characteristics of different coal types, using low-field nuclear magnetic resonance device (NMR) and the emission of gas (Eg) experimental platform built independently, the pore structure characterization and dispersion characteristics of saturated anthracite and coking coal samples after 3, 6, and 9 exposures were studied. The experimental results show that the LN2 freeze-thaw cycles can significantly increase the Eg of coal under experimental conditions and have different effects on the gas emission characteristics of anthracite and coking coal. After exposure, the T2 spectra area (AT2) of anthracite and coking coal increases by 51.58% and 67.06%, the Eg max increases by 37.26% and 41.44%, and the initial gas emission velocity (Vg0) increases by 91.18% and 80.77%. In the freeze-thaw cycles, the changes of Eg and Vg0 are correlated with the changes of AT2 to a certain extent. The freeze-thaw cycles of LN2 can effectively transform the pore structure of coal, improve the permeability of coal seam, and promote the migration of coal gas. The research results of this paper provide theoretical support for the cryogenic cracking of coal seam by LN2, anti-permeability, and suction promotion in coal mine site.

Corrigendum to “Investigation of gastric disintegration of carrot during digestion in vitro by a low-field nuclear magnetic resonance device” [J. Food Eng. 292 (2021) 110307

Corrigendum to “Investigation of gastric disintegration of carrot during digestion in vitro by a low-field nuclear magnetic resonance device” [J. Food Eng. 292 (2021) 110307

Analytical Validation of GFRNMR: A Blood-Based Multiple Biomarker Assay for Accurate Estimation of Glomerular Filtration Rate

Accurate and precise monitoring of kidney function is critical for a timely and reliable diagnosis of chronic kidney disease (CKD). The determination of kidney function usually involves the estimation of the glomerular filtration rate (eGFR). We recently reported the clinical performance of a new eGFR equation (GFRNMR) based on the nuclear magnetic resonance (NMR) measurement of serum myo-inositol, valine, and creatinine, in addition to the immunoturbidometric quantification of serum cystatin C, age and sex. We now describe the analytical performance evaluation of GFRNMR according to the Clinical and Laboratory Standards Institute guidelines. Within-laboratory coefficients of variation (CV%) of the GFRNMR equation did not exceed 4.3%, with a maximum CV% for repeatability of 3.7%. Between-site reproducibility (three sites) demonstrated a maximum CV% of 5.9%. GFRNMR stability was demonstrated for sera stored for up to 8 days at 2–10°C and for NMR samples stored for up to 10 days in the NMR device at 6 ± 2°C. Substance interference was limited to 4/40 (10.0%) of the investigated substances, resulting in an underestimated GFRNMR (for glucose and metformin) or a loss of results (for naproxen and ribavirin) for concentrations twice as high as usual clinical doses. The analytical performances of GFRNMR, combined with its previously reported clinical performance, support the potential integration of this NMR method into clinical practice.

A passive shimming method for Halbach magnet based on magnetic sheet arrays

Halbach magnet has great potential in nuclear magnetic resonance device, where the field homogeneity requirement puts heavy demands on high efficiencypassive shimming (PS) technique. Conventional PS involves a tedious iteration process of the magnetic block/sheet number and positions optimization. In this paper, we propose a PS method based on magnetic sheet arrays (MSAs) targeting at spherical harmonic basis up to the 3rd order including dedicated composition of Y(4Z2-X2-Y2), Z3 and X(4Z2-X2-Y2) (n = 3, m = −1,0,1) with cross terms to implement structural field compensation. With this approach, the homogeneity of a 0.5 T Halbach magnet was improved from the original 811 ppm to 4.7 ppm in a L15 mm × R2.5 mm water sample. Rough shimming in another 0.93 T Halbach magnet also improved the homogeneity from 1103 ppm to 125 ppm in R2.5 mm sphere. This work provides a flexible, convenient PS method based on MSAs for compact Halbach magnet, which can be applied in NMR spectrometers and other high homogeneity application circumstances.

Porosity of gas shale: Is the NMR-based measurement reliable?

Aiming at obtaining an accurate porosity of gas shale, various approaches are attempted. Therein, nuclear magnetic resonance (NMR), being treated as a kind of new-developed technique, possesses the representative significance. However, as a booming technique, the reliability of NMR-based porosity of shale is not exactly defined. Depending on NMR device, this work measured the porosity of shale experiencing different water soaking time, accordingly, judging the reliability of NMR-based porosity. Results indicate the NMR outcomes vary with the water soaking time, making a doubt about the objectivity of NMR-based porosity in reflecting the real shale porosity. Furthermore, some supplementary means were adopted to verify the water soaking-induced variation in the pore system of shale sample, which intensities the suspicion if the NMR-based porosity is reliable or not. To sum up, this work considers that the NMR-based porosity of shale is not reliable enough when water is used as the probe. Besides, this work also offers some suggestions on how to enhance the reliability of NMR-based porosity of shale sample. Basically, this work selects a fresh perspective to analyze the NMR approach in determining shale porosity, which is hopefully helpful in promoting the development of NMR technique in the shale-related field.

Is the Calibration Transfer of Multivariate Calibration Models between High- and Low-Field NMR Instruments Possible? A Case Study of Lignin Molecular Weight.

Although several successful applications of benchtop nuclear magnetic resonance (NMR) spectroscopy in quantitative mixture analysis exist, the possibility of calibration transfer remains mostly unexplored, especially between high- and low-field NMR. This study investigates for the first time the calibration transfer of partial least squares regressions [weight average molecular weight (Mw) of lignin] between high-field (600 MHz) NMR and benchtop NMR devices (43 and 60 MHz). For the transfer, piecewise direct standardization, calibration transfer based on canonical correlation analysis, and transfer via the extreme learning machine auto-encoder method are employed. Despite the immense resolution difference between high-field and low-field NMR instruments, the results demonstrate that the calibration transfer from high- to low-field is feasible in the case of a physical property, namely, the molecular weight, achieving validation errors close to the original calibration (down to only 1.2 times higher root mean square errors). These results introduce new perspectives for applications of benchtop NMR, in which existing calibrations from expensive high-field instruments can be transferred to cheaper benchtop instruments to economize.

Nuclear magnetic resonance footprint of Wharton Jelly mesenchymal stem cells death mechanisms and distinctive in-cell biophysical properties in vitro.

The importance of the biophysical characterization of mesenchymal stem cells (MSCs) was recently pointed out for supporting the development of MSC‐based therapies. Among others, tracking MSCs in vivo and a quantitative characterization of their regenerative impact by nuclear magnetic resonance (NMR) demands a full description of MSCs’ MR properties. In the work, Wharton Jelly MSCs are characterized in a low magnetic field (LF) in vitro by using different approaches. They encompass various settings: MSCs cultured in a Petri dish and cell suspensions; experiments‐ 1D‐T 1, 1D‐T 2, 1D diffusion, 2D T 1‐T 2 and D‐T 2; devices‐ with a bore aperture and single‐sided one. Complex NMR analysis with the aid of random walk simulations allows the determination of MSCs T 1 and T 2 relaxation times, cells and nuclei sizes, self‐diffusion coefficients of the nucleus and cytoplasm. In addition, the influence of a single layer of cells on the effective diffusion coefficient of water is detected with the application of a single‐sided NMR device. It also enables the identification of apoptotic and necrotic cell death and changed diffusional properties of cells suspension caused by compressing forces induced by the subsequent cell layers. The study delivers MSCs‐specific MR parameters that may help tracking MSCs in vivo.

Sensing mammographic density using single-sided portable Nuclear Magnetic Resonance

This research paper presents a quantitative approach to sensing mammographic density (MD) using single-sided portable Nuclear Magnetic Resonance (NMR). It focuses on three main techniques: spin–lattice relaxation (recovery) time (T1), spin–spin relaxation (decay) time (T2), and Diffusion (D) techniques by testing whether or not the aforementioned techniques are in agreement with the gold standard and with each other when used for scanning breast tissue specimens with a variety of mammographic densities (MDs). The high mammographic density (HMD), intermediate MD, and low mammographic density (LMD) regions of each slice were identified according to the mammogram images. Subsequently, the grayscale values for these regions were quantified. One region was measured from the first sample while the remaining ones were measured from the second sample. The same areas were then exposed to portable NMR, and the sequences used as following: the stimulated echo sequence for diffusion (D), the Carr-Purcell-Meiboom-Gill (CPMG) sequence for T2, and saturation recovery sequence for T1. The correlations between the grayscale values and NMR techniques were strongly correlated. The Pearson correlation coefficient, R, of T1 (%) versus grayscale value, D (%) versus grayscale value, and T2 (%) versus grayscale value, was 0.91, 0.91, and 0.93, respectively. Furthermore, the relative water content of the breast slices based on T1, T2, and diffusion (D) measurements were strongly in agreement with each other. The Pearson correlation coefficient, R, of D (%) versus T1 (%), D (%) versus T2 (%), and T1 (%) versus T2 (%), was 0.984, 0.966, and 0.9868, respectively. The three pulse sequences can be employed in a portable NMR device to deliver continuous quantitative measurements of MD in breast tissue samples. As a result, the method demonstrated to be acceptable for determining the distribution of MDs among breast tissue samples without the need for additional qualitative analysis.

Improving of the Probing Signal’s Spectral Content for Devices Nuclear Magnetic Logging

The method of nuclear magnetic logging (NML) allows to distinguish easily enough the intervals in which there are hydrocarbons and to forecast their extraction. Moreover, the principles of measuring using this method are simple enough, despite the difficulties of processes. There were described method of improving spectral composition of probing voltage NML device in this article. The disadvantage of the method is that the resonance area covers all reservoir fluids. Therefore, search for a way to reduce the frequency spectrum and extend the range of the device of nuclear magnetic resonance is a rather urgent task. In the article is stated that within conducting researches is necessary probing signals of large capacity. In this case, it is more appropriate to use switch mode of the power converters. The system of multilevel inverter is created on the base of these converters that allows to get probing signal simply enough. A three-level inverter that generates high-frequency pulses is considered. A virtual model of the converter is constructed together with smoothing and resonant filters, which generate the probing voltage in nuclear magnetic resonance (NMR) devices, using a modified Carr-Purcell-Meiboom-Gill sequence. The result is a wide range of voltages with side harmonics, which have the significant influence on the output signal relative to the base frequency which the NMR device is tuned. The analysis of the harmonic composition of this voltage is conducted. Calculations of intermodulation distortion coefficients for the first and two side harmonics are given. To reduce the influence of side harmonics in the output signal on the quality of measurement by NMR devices, it is proposed to implement additional generators with the phase difference between the side harmonic and the initial phase will be a half of period. The inductors used are transformers that have a ratio of primary and secondary windings of 1: 1 and the secondary winding has the same value of inductance as the replaced coil that was in the model without modifications. Anti-phase side harmonic generators are connected to the primary windings. In this way additionally implemented a galvanic isolation between the generator and the main signal. As a result of simulation of such a converter is obtained an alternative spectral composition of the output signal. After calculations and comparison of the obtained coefficients, it is shown that the proposed method really improves the spectral composition of the output signal. The disadvantages of using this method of spectrum improvement are considered as well. The relative voltage improvement in the case of a 30 ohms load is calculated. The simulation results of the proposed method show an improvement in the spectral composition of the probing voltage by ~ 2.68 times. With this method, it is possible to dampen unwanted side harmonics by adjusting the appropriate frequencies and initial phases so that the generator is always running in antiphase.

Characterization of Structural Bone Properties through Portable Single-Sided NMR Devices: State of the Art and Future Perspectives.

Nuclear Magnetic Resonance (NMR) is a well-suited methodology to study bone composition and structural properties. This is because the NMR parameters, such as the relaxation time, are sensitive to the chemical and physical environment of the 1H nuclei. Although magnetic resonance imaging (MRI) allows bone structure assessment in vivo, its cost limits the suitability of conventional MRI for routine bone screening. With difficulty accessing clinically suitable exams, the diagnosis of bone diseases, such as osteoporosis, and the associated fracture risk estimation is based on the assessment of bone mineral density (BMD), obtained by the dual-energy X-ray absorptiometry (DXA). However, integrating the information about the structure of the bone with the bone mineral density has been shown to improve fracture risk estimation related to osteoporosis. Portable NMR, based on low-field single-sided NMR devices, is a promising and appealing approach to assess NMR properties of biological tissues with the aim of medical applications. Since these scanners detect the signal from a sensitive volume external to the magnet, they can be used to perform NMR measurement without the need to fit a sample inside a bore of a magnet, allowing, in principle, in vivo application. Techniques based on NMR single-sided devices have the potential to provide a high impact on the clinical routine because of low purchasing and running costs and low maintenance of such scanners. In this review, the development of new methodologies to investigate structural properties of trabecular bone exploiting single-sided NMR devices is reviewed, and current limitations and future perspectives are discussed.

Compact low-field NMR spectroscopy and chemometrics applied to the analysis of edible oils

Compact nuclear magnetic resonance (NMR) spectroscopy combined with chemometric tools opens new perspectives for NMR use. This work compares the potential of 43, 60 and 400 MHz NMR spectroscopy for quality control of edible oils. Partial least squares regression (PLSR) and support vector regression (SVR) models built on the three NMR devices had equivalent performances for fatty acids and iodine value, and the models built with the low field spectra were equivalent to the high field. Moreover, performances for calibration indicated that most of the models built with medium/or high-resolution fields presented reproducibility values lower than the minimum accepted by the American Oil Chemists' Society (AOCS). Compared to classical methods, this new approach allows the application of medium resolution devices as a sample screening tool in analytical laboratories since it allows the spectrum obtention in a few seconds, without the need for sample preparation or the use of deuterated solvents.

Improved Configuration of Halbach Magnets with a Homogeneous Magnetic Field for Portable NMR Device

Halbach array magnets are widely used in portable nuclear magnetic resonance (NMR) devices that the homogeneity of the magnetic field generated by the array affects the imaging quality. In this paper, we propose some improvements to the construction of the Halbach magnets to enhance magnetic field uniformity. Using a Halbach array model comprising 16 magnets, all the calculations are based on 3D finite element method (FEM) analysis and optimized using the particle swarm optimization (PSO) algorithm. Comparisons of the results are shown to support the observations that the optimized and improved constructions can generate a more homogeneous magnetic field.

Investigation of non-isothermal effect of cyclic carbon dioxide on the petrography of coals for coal mine methane recovery

Effective extraction of methane from underground coal seams is vital to eliminate the potential resource waste and ensure mining safety. Enhanced coal mine methane recovery by injecting CO2 has been proved to be a promising method due to its phase-blasting and flooding effects. The occurrence of non-isothermal kinetics of CO2 flowing in the porous coal media might have some impacts on the pore structure and matrix integrity. A high-pressure and low-temperature experimental system was established to simulate the introduction of liquid CO2 (LCO2) to the coals, and low-field nuclear magnetic resonance and velocity testing device were used to characterize the pore structure change and the crack evolution, and the related elastic parameters were also tested by uniaxial compression test. The T2 spectrum curves showed that the pore structure changed greatly under the impact of LCO2, and the affecting cycles was positively correlated to the pore volume change and was negatively correlated to the wave velocity of coals, which manifested that the cyclic LCO2 effect had positive impacts on the crack volume increase and the improvement of the crack connection. The peak strength σmax of coals all decreased as the LCO2 affecting cycles increased, and the larger the cycles, the greater decrease of coal’s strength. The increased pore volume and the decreased coal strength reflected that the non-isothermal effect of cyclic LCO2 could produce some flow channels for methane seepage by destroying the matrix structure and weakening the intensity. Moreover, a conceptual destruction model was established to explain the fracturing mechanism of non-isothermal effect of LCO2 cyclic injection. The results provide some significant guidelines to enhance methane recovery by producing crack networks and decreasing the coal strength.

Calibration Transfer of Partial Least Squares Regression Models between Desktop Nuclear Magnetic Resonance Spectrometers.

Low-field proton nuclear magnetic resonance (LF-1H NMR) devices based on permanent magnets are a promising analytical tool to be extensively applied to the process analytical chemistry scenario. To enhance its analytical applicability in samples where the spectral resolution is compromised, multivariate regression methods are required. However, building a robust calibration model, such as partial least squares (PLS) regression, is a laborious task because (1) the number of measurements required during the calibration process is large and (2) the procedure must be repeated when the instrument is changed or after a certain period due to the long-term stability of the instrument. Thus, the present work describes the application of calibration transfer methodologies (direct standardization (DS), piece-wise direct standardization (PDS), and double-window piece-wise direct standardization (DWPDS)) on LF-1H NMR to exempt the necessity of a recalibration procedure when moving from the original spectrometer to a second one with the same, lower, or higher magnetic field. These calibration transfer methodologies were tested with PLS models built on a 60 MHz (for the proton Larmor frequency) spectrometer to predict the specific gravity (SG), distillation temperature (T50%), and final boiling point (FBP) of commercial gasoline. The results showed that the DWPDS method applying only 2 to 7 transference samples enables the transference of all PLS models built on the primary instrument (60 MHz) to other (43, 60, and 80 MHz) different instruments, reaching the same RMSEP values as the primary instrument: 1.2 kg/m3 for SG, 5.1 °C for FBP, and 1.1 °C for T50%.

Investigation of gastric disintegration of carrot during digestion in vitro by a Low-Field Nuclear Magnetic Resonance device

Abstract Knowledge of the process and kinetics of solid food disintegration in the human stomach is essential for assessing bioaccessibility of nutrients and understanding gastric emptying. It is desirable to develop advanced techniques for non-invasively and non-destructively studying the kinetics of gastric disintegration and nutrient release during digestion. The main objective of this study was to verify the feasibility of monitoring gastric disintegration of carrot sample during digestion in vitro by a Low-Field Nuclear Magnetic Resonance (LF-NMR) device. Static soaking in different liquid medium was also carried out using as comparison with the LF-NMR data to validate the feasibility. The wet and dry weight retention ratio, water content, hardness and effective diffusivity of the carrot were measured during the soaking tests following a course of time. The transverse relaxation time (T2) and magnetic resonance imaging (MRI) from the LF-NMR was employed to illustrate the transient water status throughout each sample. The T23 relaxation time at peak maximum migrated from ~1300 ms to 500 ms after static soaking in the simulated gastric juice with pH of 1.8 for 240 min, with the total peak area decreasing by 9.10% throughout the measurement of T2 quantitatively supporting the similar reduction of 8.89% in the wet mass retention ratio. Moreover, the time evolutions of the carrot sample size as shown from the MRI imaging results were also in line with the decrease of the solid loss during the static soaking. These consistent results indicate that the LF-NMR provides a non-invasive and non-destructive technique for potentially characterizing the disintegration of solid food samples during gastric digestion.

Detection of acidic paper recovery after alkaline nanoparticle treatment by 2D NMR relaxometry.

Cellulose-based artefacts are highly prone to degradation, especially in the presence of acidic compounds, which trigger the depolymerization of cellulose chains and lead to a loss in the original mechanical resistance of the material. Calcium hydroxide nanoparticles dispersed in organic solvent have been recently proposed for the deacidification of cellulose-based artworks. In this work, changes induced on paper by a deacidification treatment, following an acidification bath, were studied by nuclear magnetic resonance (NMR) relaxometry and by the so-called NMR diffraction of water trapped in the cellulose network. The deacidification treatment modifies intrachain and interchain bonds in hydrolyzed and degraded cellulose, leading to a buffered cellulose network configuration, which is similar to that characterizing the untreated reference sample in terms of relaxation parameters. Overall, calcium hydroxide nanoparticles are demonstrated effective in hindering the degradation of cellulose induced by acids and ageing in strong environmental conditions, even from the standpoint of cellulose network arrangement. It is worth noting, too, that the unilateral NMR device used for the relaxation measurements may represent a powerful tool for the preservation of cellulose-based artworks because it allows for the monitoring of the conservation status of cellulose in a completely non-invasive manner.

Experimental investigations of fracturing fluid flowback and retention under forced imbibition in fossil hydrogen energy development of tight oil based on nuclear magnetic resonance

Experimental works have proved that imbibition under forced pressure (FP, the difference between hydraulic fluid pressure and original pore pressure) has a positive effect on fossil hydrogen energy development in tight oil reservoir. However, the knowledge of the influence of imbibition under forced pressure (forced imbibition, FI) on fracturing fluid flowback and water retention is still limited. In this paper, experiments were designed and conducted to reveal the mechanism of fracturing fluid flowback and water retention under imbibition effect in tight sandstones. As a comparison, unconsolidated sandstones were also investigated in this study. Core samples were divided into two categories: the imbibition ones (treated by imbibition) and the filtration ones (treated by displacement), in accordance with the real oil-water distribution after well shut-in. An imbibition core and a filtration core were stitched together to conduct a flowback experiment. During the experiment, fluid distribution in different pore sizes was monitored continuously by using a low-field nuclear magnetic resonance device. Results show that the flowback recovery in tight sandstones is much lower than that in unconsolidated sandstones due to the difference of pore structure. Meanwhile, forced imbibition leads to higher oil recovery than spontaneous imbibition (SI) in tight sandstones since forced pressure enhances water imbibition. The water imbibed into small-macro and macro pores contributes the major flowback recovery, but the imbibed water in micro pores is rather difficult to displace and finally retains in these pores during the flowback process. Overall, forced imbibition not only enhances oil recovery but also increases water retention, explaining the mechanism of well productivity increase by using the shut-in method in the field. This study can help to clarify the influence of forced imbibition on fracturing fluid flowback and enhancement of fossil hydrogen development, and further provide guidance for flowback designs.