Resonance Technology Research Articles

Research on the stimulation mechanism of well shut-in imbibition and parameter optimization during fracturing-flooding

ABSTRACT In the development of low-permeability tight oil reservoirs, fracturing-flooding technology, with its dual advantages of “fracture creation and energy replenishment, and displacement by imbibition,” effectively addresses challenges such as poor water injection and low oil recovery. However, the mechanism of oil-water migration within the reservoir and the enhanced oil recovery during the shut-in imbibition process remain unclear, and the construction parameters are primarily based on empirical data. In this study, focusing on the Y block in the Bohai Bay Basin, eastern China, we conducted dynamic imbibition experiments and utilized nuclear magnetic resonance (NMR) technology to analyze the key factors influencing imbibition-driven oil displacement and the microscopic oil-water migration mechanisms within the pore space. Numerical simulation was then employed to optimize the construction parameters for fracturing-flooding operations. The results indicate that displacement and imbibition primarily occur in medium-sized pores, while the poor connectivity of micro- and small-sized pores leads to suboptimal effects. The shut-in process provides favorable conditions for imbibition displacement, allowing oil in small and medium pores to be further displaced into fractures. The main factors affecting imbibition efficiency include core permeability (optimal range: 1.5 mD to 4 mD), fracture length (approximately 2/3 of the core length), fracturing-flooding fluid concentration (optimal around 0.2%), and shut-in time (optimal range: 24 to 48 hours). Based on production capacity simulations, the optimal construction parameters for the Y block include an injection rate of 1152 to 1440 m3/min, a total injection volume of 20,000 to 25,000 m3, and a shut-in time of 30 to 45 days. The application of these optimized parameters resulted in an increase in the average daily oil production in the Y block from 4.4 tons to 7.7 tons, demonstrating a significant enhancement in reservoir productivity and oil recovery.

Fast non-destructive measurement of intramuscular fat in Australian beef and lamb using nuclear magnetic resonance (NMR) technologies

Nuclear magnetic resonance (NMR) is an excellent technique for non-destructive analysis of meat because it has high accuracy, a linear response, and insignificant drift over time, which removes the need for recalibration. Furthermore, single-side NMR devices have open geometries that enable measurements of subsections of larger samples without taking sub-samples. Here we demonstrated long-term reproducibility in a benchtop device and the utility of a single-sided NMR device. We validated long-term reproducibility of NMR measurements of lamb intramuscular fat (IMF) in a commercial processor boning room years after the original model was created. It was hypothesised that the NMR IMF% model would retain precision and accuracy on independent validation. The root mean squared (RMS) error of prediction of lamb IMF was 0.79 %. The R2 between reference measurements, predicted IMF% was 0.74, the slope of the chemical IMF% vs NMR predictions was 0.989, and the bias was 0.53 % IMF. In the second example, we showed that IMF% measurements of high value beef striploins could be measured off a commercial processing belt and returned without damaging the product. It was hypothesised that a commercial prototype single-sided NMR system would predict IMF% in beef M. longissimus thoracis et lumborum. Here the RMS error of the correlation was 1.58 % IMF and R2 was 0.97. We believe the long-term stability, high accuracy, and nondestructive nature make unilateral NMR devices ideal for applications in the red meat industry where intramuscular fat contributes to product value.

Experimental evaluation of temporary plugging performance and mechanism analysis of degradable preformed particle gel based on NMR technology

Utilizing chemical temporary plugging systems to further increase the stimulated reservoir volume (SRV) and improve oil recovery (IOR) has become a hot topic in the current petroleum industry. Pre-formed gel particles (PPG) possess excellent swelling properties and can form high-strength plugging in high-permeability channels. In addition, degradable pre-formed gel particles (DPPG) also exhibit self-degradation characteristics and excellent temporary plugging and fluid diverting performance. In our previous studies, we examined the temporary plugging mechanisms of DPPG prepared with different molecular weight (MW) of crosslinking agents (PEGDA) through bottle tests and core displacement experiments. However, the micro-swelling mechanism and the micro-scale temporary plugging mechanism in pore throats of reservoir cores are still unclear. In this paper, comprehensive research was conducted on the micro-temporary plugging mechanism of DPPG prepared with different MW crosslinking agents using a static temporary plugging performance evaluation method based on nuclear magnetic resonance (NMR) technology and a dynamic temporary plugging performance evaluation method in cores. The research results showed that DPPG with different compositions have different micro-swelling mechanisms. NMR-T2 analysis showed that DPPG-M1 (with the smallest MW of crosslinking agent) gradually decreased in nuclear size during the water absorption and swelling process, and had the largest swelling volume and swelling rate. On the other hand, DPPG-M5 (with the largest MW of crosslinking agent) exhibited a slow diffusion process of surface water towards the nucleus, resulting in the smallest swelling volume and swelling rate. However, its complete degradation time was longer. The T2 (i.e., spin-spin relaxation time) variation results of the cores in the dynamic temporary plugging experiment showed that the decrease of the MW of the crosslinking agent enhanced the plugging performance, and with less damage to the formation. The MRI images confirmed that DPPG-M5 had strong injection capability in the core and caused greater damage to the core. The research results of this study showed that NMR technology can reveal the temporary plugging mechanism of DPPG from a micro-level perspective.

Dependence of the hydrate-based CO2 storage characteristics on sand particle size and clay content in unconsolidated sediments

Storing carbon dioxide (CO2) in the form of hydrate in marine sediments is considered an effective way of carbon reduction. Understanding the influence of sediment properties on CO2 hydrate formation is important for the site selection of CO2 hydrate storage in marine sediments. In this study, the effects of sand particle size and bentonite content on the kinetics of CO2 hydrate formation are analyzed using low-field nuclear magnetic resonance technology, and the hydrate-based liquid CO2 storage capacity is evaluated. Results show that CO2 hydrate forms preferentially in large pores of sand samples, the water content in small pores begins to decrease before the hydrate saturation reaches 20%, and the unhydrated water mainly concentrates in small pores. With the increase of sand particle size, the CO2 storage rate of the early rapid growth stage increases first and then decreases, the CO2 storage rate of the whole hydrate formation process decreases continuously, but the final CO2 storage density is weakly affected by sand particle size. With the increase of hydrate saturation, the CO2 storage rate undergoes a trend of rapid decrease, stability, rapid decrease, and low-speed decrease in sequence. The larger the sand particle size or the higher the bentonite content, the shorter the stability stage of CO2 storage rate. The effect of bentonite on CO2 storage rate is the promotion at low content, the inhibition at medium content, and the weakening of inhibition at high content. The sediments with more than 25% bentonite are beneficial to the storage of more CO2.

Characterization of Stages of CO2-Enhanced Oil Recovery Process in Low-Permeability Oil Reservoirs Based on Core Flooding Experiments

Understanding the CO2 displacement mechanism in ultra-low-permeability reservoirs is essential for improving oil recovery. In this research, a series of displacement experiments were conducted on sandstone core samples from the Chang 6 reservoir in the Huaziping area using a multifunctional core displacement apparatus and Nuclear Magnetic Resonance (NMR) technology. The experiments were designed under conditions of constant pressure, variable pressure, and constant effective confining stress to simulate various reservoir scenarios. The results indicated that the distribution characteristics of the pore structure in the rock samples significantly influenced the CO2 displacement efficiency. Specifically, under identical conditions, rock cores with a higher macropore ratio exhibited a significantly enhanced recovery rate, reaching 68.21%, which represents a maximum increase of 31.97% compared to cores with a lower macropore ratio. Though fractures can facilitate CO2 flowing through pores, the confining pressure applied during displacement caused a partial closure of fractures, resulting in reduced rock permeability. Based on the oil-to-gas ratio and oil recovery in the outlet section of the fractured rock samples, the CO2 displacement process exhibited five stages of no gas, a small amount of gas, gas breakthrough, large gas channeling, and gas fluctuation. Although the displacement stage of different cores varies, the breakthrough stage consistently occurs within the range of 2 PV. These insights not only enhance our understanding of CO2 displacement mechanisms in low-permeability reservoirs but also provide actionable data to inform the development of more effective CO2-EOR strategies, significantly impacting industrial practices.

Investigation on the impact of CO2-Induced precipitation on microscopic pore structure of low-permeable reservoirs

CO2 injection into reservoirs might induce organic or inorganic precipitation in microscopic pores, and some of the pores are blocked by the precipitates, resulting in a decrease in the connectivity of pores and affecting oil recovery. In this paper, a set of experiments on CO2 displacement and CO2-water-oil-rock interaction are conducted to study the microscopic mechanisms of reservoir damage. In-situ Nuclear Magnetic Resonance (NMR) technology is applied to conduct the microscopic analysis of CO2-EOR and reservoir damage at real reservoir conditions. The results reveal that the particle size and the amount of inorganic precipitates formed in the formation water will increase with the rise of CO2 injection pressure, and the inorganic precipitates primarily consist of siderite and kaolinite. The change of NMR T2 spectra of the core samples reveals that the inorganic precipitates primarily block the small pores less than 0.89 μm. However, as a result of stronger mineral dissolution and solute transport, the pore volume of the large pores (greater than 0.89 μm) increases after the CO2-water-rock reaction. Ultimately, this interaction results in a 5.4% increment in pore volume. In addition, the displacement efficiency of water-saturated cores is improved after the first CO2 displacement, which indicates that CO2-water-rock interaction can effectively improve the seepage properties of reservoirs. Nevertheless, the reservoir damage caused by asphaltene precipitation during CO2 flooding is more significant. The asphaltene precipitation percentage in formation oil increases with the rise of CO2 injection pressure, reservoir temperature, and asphaltene content in virgin oil. CO2-induced asphaltene precipitation causes more severe blockage on small pores in comparison with large pores. After 2 h of CO2 injection to the oil-saturated core, permeability and oil recovery caused by CO2-induced precipitation decreased by 17.6% and 11.4%, respectively.

Insights into the wetting mechanisms in low-permeability sandstone reservoirs and its evolution processes: The shahejie formation in the Dongying Depression, Bohai Bay basin

During the accumulation and development processes of low-permeability oil, wettability plays a crucial role in the percolation capacity of fluids. In particular, the evolution of low-permeability sandstones involves complex changes in formation fluid properties and mineral types, leading to a deficient understanding of wetting mechanisms in low-permeability sandstones. This gap significantly impedes research on the accumulation mechanisms of low-permeability oil. Focusing on the low-permeability sandstones in Shahejie formation of Dongying Depression, Bohai Bay Basin, tests like Casting thin section, scanning electron microscope, contact angle measurement, molecular dynamics simulation and the Amott method based on nuclear magnetic resonance technology were performed to comprehensively investigate sandstone wettability and its evolutionary process. The results indicate that the adsorption capacity of hydroxyl groups or monovalent cations (K+and Na+) for water molecules causes residual intergranular pores, feldspar dissolution pores, quartz dissolution pores, clay mineral intercrystalline pores and micro-cracks to exhibit hydrophilicity; while the adsorption capacity of divalent cations (Ca2+and Mg2+) for oil molecules causes the surface of dissolution pores of carbonate minerals to exhibit neutrality or lipophilicity. Additionally, changes in formation conditions (temperature, pressure, ion types, and ion concentration) significantly control the wettability of pore surfaces, further determining the overall wettability of low-permeability sandstone reservoirs. Throughout the evolutionary process of low-permeability sandstones, the Amott-Harvey index of low permeability sandstone is greater than zero, and the wettability exhibited hydrophilic or neutral. From A-stage eodiagenesis to B-stage mesodiagenesis, the Amott-Harvey index is 0.82, 0.12, 0.37, 0.03, and 0.49, and the wettability of reservoirs transitions through phases of strong hydrophilicity, weak hydrophilicity, hydrophilicity, neutrality, and hydrophilicity, respectively. Finally, an evolutionary model of the wettability of low-permeability sandstone reservoirs was established, which is of great significance for predicting the quality of low-permeability sandstone reservoirs.

Debonding Detection of Thin-Walled Adhesive Structure by Electromagnetic Acoustic Resonance Technology.

The detection of debonding defects in thin-walled adhesive structures, such as clad-iron/rubber layers on the leading edges of helicopter blades, presents significant challenges. This paper proposes the application of electromagnetic acoustic resonance technology (EMAR) to identify these defects in thin-walled adhesive structures. Through theoretical and simulation studies, the frequency spectrum of ultrasonic vibrations in thin-walled adhesive structures with various defects was analyzed. These studies verified the feasibility of applying EMAR to identify debonding defects. The identification of debonding defects was further examined, revealing that cling-type debonding defects could be effectively detected using EMAR by exciting shear waves with the minimum defect diameter at 5 mm. Additionally, the method allows for the quantitative analysis of these defects in the test sample. Due to the limited size of the energy exchange region in the transducer, the quantitative error becomes significant when identifying debonding defects smaller than this region. The EMAR identified debonding defects in clad-iron structures of rotor blades with a maximum error of approximately 15%, confirming its effectiveness for inspecting thin-walled adhesive structures.

Detection of Ginkgo biloba seed defects based on feature adaptive learning and nuclear magnetic resonance technology

Detection of Ginkgo biloba seed defects based on feature adaptive learning and nuclear magnetic resonance technology

A Study on Acid Dissolution Characteristics and the Permeability Enhancement of Deep Coal Rock

In order to reveal the acidification and dissolution characteristics of deep coal rock, core acidification and dissolution experiments are carried out based on low-field nuclear magnetic resonance technology to study the dissolution characteristics of different acid types when applied to coal rock, and to quantitatively evaluate the dissolution characteristics of acid solutions when applied to different-scale pore throats and the karst corrosion characteristics of primary fractures. This will help to further understand the dissolution rate and pore volume growth rate of coal powder under the action of different acid types. Improving the seepage effect of coal seams is of great significance. The results show that 15% acetic acid has the best effect with regard to karst erosion and permeability. The pore volume growth rate is 442.49%, and the permeability increases by up to 31 times. With large pores, the rapid dissolution stage of mud acid, hydrochloric acid, and mixed acid mainly occurred in the first 36 h, and the rapid dissolution stage of acetic acid and hydrofluoric acid applied to the core mainly occurred at 36–72 h. The dissolution rate of acid solution is strongly correlated with porosity and permeability, and the higher the acetic acid concentration, the larger the permeability increase.

Acoustic resonance technology and quality by design approach facilitate the development of the robust tetrandrine nano-delivery system

The aim of this study was to develop a sufficiently robust tetrandrine (Tet) nano-delivery system using acoustic resonance (AR) technology and freeze-drying technology. This system can effectively improve the solubility and dissolution properties of Tet, along with high stability and scale-up adaptability. Firstly, 54 stabilizers were screened simultaneously in a high-throughput manner with the help of AR technology to fully explore the optimal prescription space of tetrandrine nanosuspension (Tet-NS). The Plackett-Burman design was used to screen for critical variables severely affecting the quality of Tet-NS. The Box-Behnken design was used to investigate and optimize critical variables to obtain optimal nanosuspensions. The optimal prescription was successfully scaled up by 100 times, which was the initial exploration of its commercial scale production. Solidification studies have shown that formulations with 2.44% fructose as the cryoprotectant have excellent redispersibility. Compared with pure Tet, Tet in Tet-NS showed a significant increase in solubility and dissolution rate in water. Fourier transform infrared (FT-IR) demonstrated that no significant interactions occurred between the drug and excipients in Tet-NS. Powder x-ray diffraction analysis (PXRD) indicated that some of the Tet transformed into amorphous state during the preparation process. In short-term stability study, Tet-NS successfully maintained its physical stability. In summary, under the guidance of the QbD concept, this study rapidly developed Tet-NS using acoustic resonance technology, which can effectively improve the solubility and dissolution properties of Tet. During the development of Tet-NS, AR technology has demonstrated high particle size reduction capability, the ability to process multiple sets of formulations in parallel, and excellent scale-up capability. Meanwhile, the method and concept of this study are not limited to Tet, but also applicable to other poorly water-soluble drugs.

Boosting charge separation and active sites exposure by hollow S-scheme MoSe2/Fe2O3 heterojunction for enhanced photocatalytic peroxymonosulfate activation towards ciprofloxacin removal

Regulating the properties of heterogeneous catalyst for efficient peroxymonosulfate (PMS) activation to pollutants degradation remains a challenge in photo-assisted Fenton-like reaction (PF) system. In this study, the novel S-scheme MoSe2/Fe2O3 (H-FMS) heterojunction with hollow nanostructure was successfully developed as visible-light-driven PMS activator for removal of ciprofloxacin (CIP). The prepared H-FMS catalyst in PMS/H-FMS/light system exhibits outstanding photocatalytic performance for CIP degradation, achieving 95.92 % removal of 5 mg/L CIP in 30 min with 0.5 mM PMS. The construction of S-scheme heterojunction provides photoinduced carriers with longer lifetime and higher redox abilities, thus sufficient photogenerated carriers are supplied to directly activate PMS. Simultaneously, the hollow nanostructure possessing multiple light reflection and scattering behaviors further facilitates the utilization of visible light. More importantly, high concentration of photoinduced electrons with high reduction ability in MoSe2 is conducive to continuous exposure of Mo4+ active sites for PMS activation through cycling between transition metal valence states. Overall, effectively separated electron-hole pairs and continuously exposed transition metal active sites both contribute to efficient activation of PMS as well as multi-path generation of ROS, leading to significant improvement in CIP degradation. The results of quenching experiment, electron spin resonance (ESR) technology, liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculation confirm that both free radicals (SO4∙-, •OH and O2∙-) and non radicals (1O2 and h+) attack the active sites of CIP possessing high Fukui index, thus contributing to CIP degradation. This work would provide a novel insight for future development and application of photocatalytic PMS activation catalysts in water remediation.

Unconventional reservoir stimulation method based on electrohydraulic discharge shock and frequency resonance technology

To increase the production of unconventional oil and gas, it is necessary to improve reservoir porosity through reservoir reconstruction. High voltage electro-hydraulic discharge can generate strong shock waves, which not only meets the requirements of reservoir reconstruction, but also has the advantages of high efficiency and environmental protection, and has become a research hotspot. In order to further improve the effectiveness of reservoir transformation, a reservoir stimulation method based on electrohydraulic discharge shock and frequency resonance is proposed. Firstly, an electrohydraulic discharge equipment was designed, and according to the material and structure of the designed rod plate electrode, a theoretical electrohydraulic discharge model was built based on the bubble theory. The high voltage breakdown process under the condition of applied voltage of 12 kV and electrode gap of 2 mm is simulated in detail. The simulation results show that the discharge time is within 0.3 μs, and the extremely short discharge time not only produces strong shock waves, but also forms an arc channel to cause circuit damping oscillation. Then, an electrohydraulic discharge experimental platform was built according to the developed equipment. The discharge process was recorded by a high-precision oscilloscope, and the arc formation was photographed by a high-speed camera. The experimental results not only verify the correctness of the theoretical analysis, but also confirm that the developed electro-hydraulic discharge device can generate 0-60 Hz adjustable electrical pulses and has the ability to cause reservoir resonance. Finally, a comparative experiment was carried out with shale core samples to test the influence of resonance factors on the development of internal fractures in unconventional reservoir rocks. The CT scan images show that the shale fracture porosity in the resonance group increased by 46.4 %, which is much higher than that in the non-resonance group (11.8%). To further test the frequency resonance effect on reservoir reconstruction, a field test was carried out on the coalbed methane wells in Shanxi using the developed equipment. The experimental results show that the average gas production rate after on-site construction is increased from 11.46 m3/h to 12.49 m3/h, an increase of 8.99 %, indicating that the proposed technology can significantly promote the development of rock fractures and enhance the production recovery.

Simultaneous Regulation of Organic and Inorganic Components in Interphase by Fiber Separator for High-Stable Sodium Metal Batteries.

Uncontrollable side reactions at the metal interface have been identified as the root cause of the formation of a fragile solid electrolyte interphase, leading to irreversible sodium loss in sodium metal batteries. Here, we proposed an interface engineering strategy that employed a carboxyl functionalized cellulose separator to provide strong dipole moments and induce the cleavage of P-F bond to construct a solid electrolyte interphase (SEI) rich in NaF. In addition, we employed nuclear magnetic resonance technology confirmed that the separator with strong dipole moments prevented the reduction of organic solvents by attracting electrons, thereby inhibiting the formation of organic oligomers. SEI with high NaF content and few oligomers is smooth and robust, obviously decreasing the interface impedance of the Na anode. The symmetric Na||Na cells, equipped with the functionalized separator, efficiently operated for 1400 hours with a stable 72 mV overpotential at 0.25 mA cm-2, exhibiting low energy barrier and fast ion transport kinetics. The Na||Na3V2(PO4)3 cell also showed stable cycling performance, with the capacity remaining at 94.83 % of the initial capacity after 1000 cycles at 1C. The proposed separator could control the formation and composition of SEI, paving the way for the development of long-life sodium metal batteries.

Competitive SPR chaser assay to study biomolecular interactions with very slow binding dissociation rate constant

Binding kinetics of drug and its target protein is crucial for the efficacy and safety of the drug. Using surface plasmon resonance (SPR) technology, we performed a competitive SPR chaser assay, a method to study biomolecular interactions with very slow dissociation rate constants (kd < 1E-4 s−1). This report described the principle and the experimental setup of the chaser assay, which involves using a competitive probe (chaser) to detect changes in target occupancy by a test molecule over time. We demonstrated the applicability of the chaser assay for both small and large molecules and compared the results with conventional SPR kinetic analysis and other methods. We suggest that the chaser assay is a useful and robust technique to characterize very tight biomolecular interactions, and that it can also be used to study cooperativity in ternary complex formation.

Optimized strategies for efficient CO2 trapping using hydrate technology by pressure adjustment

The hydrate-based method enhances oceanic CO2 storage capacity and is deemed beneficial for controlling greenhouse gas emissions. However, the non-uniform CO2 hydrate crystal interface in the sub-seabed storage layer acts as a barrier, slowing down mass transfer kinetics. This work employed in-situ nuclear magnetic resonance (NMR) technology to compare three different pressure adjustment strategies and observe CO2 bubble dispersion after hydrate dissociation, secondary nucleation, and crystal growth mechanism, along with pore water changes. The presence of micro/nano CO2 bubbles with high internal pressure and high specific surface area in the dissociation liquid significantly accelerated secondary micro-structural phase transition rates. The optimal hydrate-based CO2 storage efficiency reached up to 81.7 %. Moreover, the secondary formation of CO2 hydrates distributed more uniformly within the large, medium, and small pores and led to a significantly increased residual water conversion rate (reaching up to 88 %) in medium pores. The post-secondary formation of high-density hydrates resulted in low fluid mobility (T1/T2 mostly distributed in the range of 0 ∼ 10) and exhibited a mixed wettability state between pore fluids. Utilizing the “memory effects” of CO2 hydrate effectively overcame late-stage mass transfer barriers of solid hydrates films. Our findings extend the understanding of CO2 hydrate formation kinetics under pressure adjustment strategies.

Evaluation of T2 Magnetic Resonance (T2MR®) Technology for the Early Detection of ESKAPEc Pathogens in Septic Patients.

Bloodstream infections (BSIs) and sepsis are a major cause of morbidity and mortality. Appropriate early antibiotic therapy is crucial for improving the survival of patients with sepsis and septic shock. T2 magnetic resonance (T2MR®) technology may enable fast and sensitive detection of ESKAPEc pathogens directly from whole-blood samples. We aimed to evaluate concordance between the T2Bacteria® Panel and standard blood culture and its impact on antibiotic therapy decisions. We conducted a single-centre retrospective study on patients with sepsis-induced hypotension or septic shock admitted to general, post-operative/neurosurgical, and cardiothoracic Intensive Care Units who were tested with the T2Bacteria® Panel from January 2021 to December 2022. Eighty-five consecutively admitted patients were included, for a total of 85 paired tests. A total of 48 ESKAPEc pathogens were identified by the T2Bacteria® Panel. The concordance rate between the T2Bacteria® Panel and blood cultures was 81% (69/85), with 20 concordant-positive and 49 concordant-negative cases. For the 25 microorganisms grown from accompanying blood cultures, blood pathogen coverage by the T2Bacteria® Panel was 88%. In this cohort of severely ill septic patients, the T2Bacteria® Panel was highly concordant and was able to detect more ESKAPEc pathogens, with a significantly shorter turn-around time compared to conventional blood cultures. The T2Bacteria® Panel also significantly impacted decisions on antibiotic therapy.

Study on the Contribution of Different Pore Throat Sizes to Oil Displacement Efficiency in Fracture-Pore Tight Sandstone Reservoir

The pore throat and fracture system of tight sandstone reservoir are complex, the reservoir is highly heterogeneous, and the production often decreases rapidly, the development degree is low, and the development effect of water injection is poor. CO2 injection is an important means to supplement formation energy and achieve efficient reservoir development in tight reservoirs. Based on nuclear magnetic resonance technology (NMR) and high temperature and high pressure physical flow simulation experiment system, the contribution of different scales of pore throat and fracture to the improvement of oil recovery in different phases of CO2 -crude oil system is studied. The results show that the contribution of mesopores, macropores and fractures to oil displacement efficiency in the supercritical CO2 displacement stage reaches 74.58%. In immiscible CO2 displacement stage, the contribution of micropores, small pores and medium pores to oil displacement efficiency reached 73.27%. In the miscible CO2 displacement stage, the contribution of micropores and small pores to oil displacement efficiency reached 52.32%. In the supercritical CO2 displacement stage, the contribution of oil displacement efficiency is mainly provided by macropore throats and fractures. The contribution of immiscible and miscible CO2 displacement stage to oil displacement efficiency mainly comes from small pore throat with smaller scale.

Research on the Potential of Persistent Free Radicals Triggering Open-Pit Coal Oxidation and Spontaneous Combustion

ABSTRACT This study attempts to reveal the triggering pathways of open-pit coal oxidation and spontaneous combustion from the perspective of persistent free radicals (PFRs). To this end, electron spin resonance technology, spin trap technology, and quantum chemical calculations were combined to study the occurrence characteristics of PFRs in coal and their photoreaction characteristics. Based on typical coal molecular fragments, the mechanism of PFRs triggering open-pit coal oxidation was further revealed. The results indicate that coal contains abundant PFRs, which produce reactive oxygen species (ROS) after exposure to sunlight, mainly including hydroxyl radicals (•OH) and superoxide anion radicals (O2 •−). Among them, the higher the initial content of PFRs or the longer the time of sunlight exposure, the more favorable it is for the production of •OH, the concentration of photoinduced •OH remains at the level of 1011 spin/mm3. Compared to O2 in the air, these photoinduced •OH have stronger oxidizing properties and can trigger free radical chain reactions of coal oxidation at room temperature (activation energies ＜ 40 kJ/mol), releasing reaction heat (average enthalpy change is −65.53 kJ/mol). As a common oxidant in coal spontaneous combustion (CSC) process, O2 does not possess these abilities (activation energies greater than 190 KJ/mol and enthalpy change greater than 160 KJ/mol). From the perspectives of thermodynamics and kinetics, PFRs in coal have the potential to indirectly trigger open-pit coal oxidation and spontaneous combustion. Therefore, the efficient quenching of PFRs or inhibiting the production of •OH will be beneficial for preventing the oxidation and spontaneous combustion of open-pit coal. This study provides a new perspective on revealing the mechanism of CSC and developing new inhibitors.

Piezoelectrically and Capacitively Transduced Hybrid MEMS Resonator with Superior RF Performance and Enhanced Parasitic Mitigation by Low-Temperature Batch Fabrication

This study investigates a hybrid microelectromechanical system (MEMS) acoustic resonator through a hybrid approach to combine capacitive and piezoelectric transduction mechanisms, thus harnessing the advantages of both transducer technologies within a single device. By seamlessly integrating both piezoelectric and capacitive transducers, the newly designed hybrid resonators mitigate the limitations of capacitive and piezoelectric resonators. The unique hybrid configuration holds promise to significantly enhance overall device performance, particularly in terms of quality factor (Q-factor), insertion loss, and motional impedance. Moreover, the dual-transduction approach improves the signal-to-noise ratio and reduces feedthrough noise levels at higher frequencies. In this paper, the detailed design, complex fabrication processes, and thorough experimental validation are presented, demonstrating substantial performance enhancement potentials. A hybrid disk resonator with a single side-supporting anchor achieved an outstanding loaded Q-factor higher than 28,000 when operating under a capacitive drive and piezoelectric sense configuration. This is comparably higher than the measured Q-factor of 7600 for another disk resonator with two side-supporting anchors. The hybrid resonator exhibits a high Q-factor at its resonance frequency at 20 MHz, representing 2-fold improvement over the highest reported Q-factor for similar MEMS resonators in the literature. Also, the dual-transduction approach resulted in a more than 30 dB improvement in feedthrough suppression for devices with a 500 nm-thick ZnO layer, while hybrid resonators with a thicker piezoelectric layer of 1300 nm realized an even greater feedthrough suppression of more than 50 dB. The hybrid resonator integration strategy discussed offers an innovative solution for current and future advanced RF front-end applications, providing a versatile platform for future innovations in on-chip resonator technology. This work has the potential to lead to advancements in MEMS resonator technology, facilitating some significant improvements in multi-frequency and frequency agile RF applications through the original designs equipped with integrated capacitive and piezoelectric transduction mechanisms. The hybrid design also results in remarkable performance metrics, making it an ideal candidate for integrating next-generation wireless communication devices where size, cost, and energy efficiency are critical.