Micro-nano Pores Research Articles

Effect of Al2O3 nano/micro powder ratio on microstructures and properties of microporous MgO-MgAl2O4 refractory aggregates

In this work, the microporous MgO-MgAl2O4 refractory aggregates were prepared by in-situ decomposition synthesis method. The effect of Al2O3 nano/micro powder ratio on the microstructures and properties was studied under the premise that the fixed total content of Al2O3 was 15wt%. The results demonstrated that the aggregates were composed of microporous MgO microparticles with nano pores as well as MgAl2O4 grains located among them. The ratio not only influenced the volume expansion through changing the lattice constant of in-situ MgAl2O4, but also affected the formation of two different positions of MgAl2O4 bonds, thereby influencing the microstructures and properties. When the ratio was 4:6, the combined effect of the shrinkage of MgO microparticles and the expansion of in-situ MgAl2O4 grains promoted the formation of the bonds between MgAl2O4 grains and MgO microparticles, as well as among the MgAl2O4 grains, which resulted in the best comprehensive properties of the microporous MgO-MgAl2O4 refractory aggregates, characterized by micro-nano pores, an apparent porosity of 26%, a flexural strength of 23.2 MPa, a flexure strength after thermal shock of 20.4 MPa and a low thermal conductivity of 2.99 W/(m·K) at 800°C.

Investigation of the impact of micro-nano pore geometry on CH4 adsorption

CH4 is a clean fossil fuel that is widely used in the gas supply of homes and industry, and its energy value is increasingly important. Coal pores provide certain conditions for the storage of CH4. In order to reveal the microscopic adsorption mechanism of CH4 in different pores under high pressure, based on the experimental results, a cross-shaped pore model was proposed, and then molecular simulation was used to construct three kinds of cross-shaped, round and slit pore models for simulation experiment verification. The changes of adsorption parameters, such as adsorption amount, adsorption heat, adsorption energy, adsorption potential and adsorption entropy, were analyzed during the adsorption process. Combined with adsorption and condensation theory, the influence of different geometric pores on the adsorption of CH4 was further verified. The results show that round pore have more adsorption sites, larger adsorption quantity and stronger adsorption capacity, followed by cross pore, while slit pore have the weakest adsorption capacity and least adsorption sites. Under high pressure susaturated adsorption, the interaction force between molecules is stronger, the affinity is higher, the molecules are arranged in order, and the adsorption system is more stable, and the adsorption capacity of slit pore > cross pore > round pore is displayed. This study further verifies the mechanism of the effect of pore geometry on CH4 adsorption, which provides a strong support and theoretical basis for CBM mining engineering.

Construction of Carbon Dioxide Responsive Graphene Point Imbibition and Drainage Fluid and Simulation of Imbibition Experiments

The global oil and gas exploration targets are gradually moving towards a new field of oil and gas accumulation with nanopore throats, ranging from millimeter scale to micro-nano pore throats. The development method of tight oil reservoirs is different from that of conventional oil reservoirs, and the development efficiency is constrained. Therefore, it is necessary to construct a nanoscale fluid with strong diffusion and dispersion and improve its permeability, suction, and displacement capabilities. Under the background of CCUS, carbon dioxide flooding is a better way to develop tight reservoirs. However, in order to solve the problem of gas channeling, this paper developed a carbon dioxide-responsive graphene point type surfactant, which has a good gas–liquid synergistic effect. At the same time, graphene nanomaterials are carbon-based and create no environmental damage in oil reservoirs. In this study, graphene quantum dots (GQDs) were prepared using the hydrothermal method, and functional graphene quantum dots (F-GQDs) responsive to carbon dioxide stimulation were synthesized by covalent grafting of amidine functional groups. By characterizing its structure and physical and chemical properties, and by conducting imbibition simulation experiments, its imbibition and drainage ability in nanopore throats is elucidated. Infrared spectrum measurement shows that after functional modification, the quantum dots exhibited new characteristic peaks at 1600 cm−1 to 1300 cm−1, considering the N-H plane-stretching characteristic peak. The fluorescence spectra showed that the fluorescence intensity of F-GQDs was increased after functional modification, which indicated that F-GQDs were successfully synthesized. Through measurements of interfacial activity and adhesion work calculations, the oil–water interfacial tension can achieve ultra-low values within the range of 10−2 to 10−3 mN/m. Oil sand cleaning experiments and indoor simulations of spontaneous imbibition in tight cores demonstrate that F-GQDs exhibit effective oil-washing capabilities and a strong response to carbon dioxide. When combined with carbon dioxide, the system enhances both the rate and efficiency of oil washing. Imbibition recovery can reach more than 50%. The research results provide a certain theoretical basis and data reference for the efficient development of tight reservoirs.

An analytical solution model of oil–water dynamic imbibition considering dynamic contact angle effect and osmotic pressure at micro-nano scale

Spontaneous imbibition is one of the important mechanisms to enhance oil recovery during hydraulic fracturing process of shale reservoirs. The dynamic contact angle effect in imbibition kinetics of liquid–liquid system is complicated due to the large number of micro-nano pores in shale reservoir. Moreover, the content of clay minerals is high, the chemical osmosis effect is significant, and the impact of osmotic pressure on imbibition is not clear. In order to clarify the dynamic contact angle effect in imbibition kinetics and correctly understand the role of osmotic pressure in imbibition process. In this paper, based on the molecular kinetic theory (MKT), the dynamic contact angle effect is successfully coupled with imbibition kinetic equation, and a capillary pressure equation is developed. On the basis, considering the effects of osmotic pressure, external displacement pressure and boundary layer effect on imbibition, An analytical solution model of oil–water dynamic imbibition model is developed. The results shows that under the respective effects of capillary pressure and osmotic pressure, the imbibition velocity initially stabilizes before increasing over time; under the action of displacement pressure, the imbibition velocity increases with time. Imbibition velocity is directly proportional to interfacial tension and capillary radius, but inversely proportional to contact angle and oil viscosity. With the salt concentration difference increasing from 80 mol/m3 to 4710 mol/m3, the imbibition velocity increased by about 54 times. Compared with the membrane efficiency of 30 % and 5 %, the imbibition velocity is increased by 4.95 times. In this work, the dynamic contact angle effect in the imbibition kinetics of liquid–liquid system was accurately characterized, clarified the action mechanism of osmotic pressure, and provided theoretical support for enhancing oil recovery of shale reservoirs.

Study on the regulation of droplet motion behavior on superhydrophobic surfaces

Wettability properties of the surface is essential for controlling the dynamic sliding of droplets, thereby facilitating surface self-cleaning and drag reduction. This study makes use of chemical etching and surface modification techniques to prepare superhydrophobic surfaces with micro-nano pore structures on copper. This research examines and evaluates the chemical composition, surface morphology, and hydrophobic characteristics of superhydrophobic surfaces, also investigates the exhibited excellent superhydrophobic properties, a positive correlation observed between the concentration of the modifier solution and the surface’s hydrophobic strength. Droplets move in an accelerated fashion on superhydrophobic surfaces, and the total resistance to droplet sliding decreases as the surface hydrophobicity increases and the wall tilt angle decreases. During the motion of droplets, the fluctuation range of the receding angle is considerably greater than that of the advancing angle, thereby rendering the receding angle as the primary determinant factor for droplet movement, and as the hydrophobicity of the surface improves, the fluctuation extent of the droplet’s receding angle experiences a significant diminution. Droplet motion on superhydrophobic surfaces comprises both slipping and rolling behaviors, the increased hydrophobicity of the surface and the larger tilt angle facilitate droplet movement in a slipping mode on the surface, within the experimental parameters, the proportion of rolling distance to slipping distance varies from 35 % to 15 %. This study has revealed innovative regulatory approaches for modulating the moving behavior of liquids on microstructured surfaces, potentially enabling the development of superior functional surfaces for fluid drag reduction or droplet manipulation in the future.

Superhydrophobic cement with hierarchically tunable pore structure by additive manufacturing towards super sound absorption

Noise pollution as a form of environmental problem can have significant negative impacts on human health and the economy. To address this issue, a variety of noise-reduction construction materials have been developed. However, most present noise reduction materials suffer from a narrow absorbing band due to the simple pore structure which restricts their ability to absorb sound energy across a wide frequency range. Here, we demonstrate a hydrogel templating method and create hierarchically structured cement-based materials with tunable pore sizes by means of additive manufacturing. The introduction of this hierarchically tunable structure with micro-nano pores generated by cement hydration contributes to the formation of multi-scale pores (micro-, meso- and macropores), which achieves a sound absorption coefficient of 0.89 at 1000 Hz and ensures broadband acoustic absorption performance (noise reduction coefficient of 0.54, around 50 % improvement compared to traditional construction sound absorption materials). Meantime, this lightweight material has good compressive strength (1.31 MPa) and superhydrophobicity (water contact angle of 152.5°), together with thermal conductivity (0.088 W m−1 K−1) and excellent fire resistance. This study provides a new approach for designing cement-based materials with super sound absorption.

Pulsed Airstream-Driven Hierarchical Micro-Nano Pore Structured Triboelectric Nanogenerator for Wireless Self-Powered Formaldehyde Sensing.

Formaldehyde (HCHO), as a common volatile organic compound, has a serious impact on human health in the daily lives and industrial production scenarios. Given the security issue of HCHO detection and danger warning, a ZIF-8/copper foam based pulsed airstream-driven triboelectric nanogenerator (ZCP-TENG) is designed to develop the self-powered HCHO sensors. By combining contact electrification and electrostatic induction, the ZCP-TENG can be utilized for airflow energy harvesting and HCHO concentration detection. The short-circuit current and output power of the ZCP-TENG can reach 2.0 µA and 81 µW (20 ppm). With the high surface area, abundant micro-nano pores, and excellent permeation flux, the ZCP-TENGs exhibit excellent HCHO sensing response (61.3% at 100 ppm), low detection limit (≈2 ppm), and rapid response/recovery time (14/15 s), which can be served as a highly sensitive and selective HCHO sensor. By connecting an intelligent wireless alarm, the ZCP-TENGs are designed to construct a self-powered warning system to monitor and remind the HCHO of exceedance situations. Moreover, by combining a support vector machine model, the difference concentrations can be quickly identified with an average prediction accuracy of 100%. This study illustrates that ZCP-TENGs have broad application prospects and provide guidance for HCHO monitoring and danger warnings.

Enhanced performance in doped micro-nano porous organic thin-film transistors

Molecular doping, as an effective technique for controlling the electrical property of organic semiconductors (OSCs) by introducing additional charges, has been proven to adjust important device parameters in organic thin-film transistors (OTFTs). Doping highly crystalline OSCs without disrupting structural order is a crucial challenge, as it significantly affects the charge carrier mobility. Here, we demonstrate a molecular doping method without disrupting the molecular ordering to improve the charge carrier mobility of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) based OTFTs via a simple thermal spin-coating method. The key is to introduce micro-nano pores into C8-BTBT thin-film for channel doping, which is achieved by mixing with the unsubstituted BTBT as it can be easily removed from the thin-film through an ordinary annealing process. Micro-nano pores allow the dopant molecules (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, F4-TCNQ) to access the conductive channel of OTFT, which is beneficial for charge injection. Indeed, we further discover that F4-TCNQ doped porous C8-BTBT thin-films exhibit better charge mobility than those of neat and F4-TCNQ doped C8-BTBT films in OTFTs. This work proposes an effective way to expose OSC conjugated core to the dopant, which not only improves the charge transfer reaction between organic/dopant semiconductor through cofacial stacking, but also reduces the trap density and contact resistance.

Highly thermal conductive Graphene/Paraffin composite for efficient thermal management of electronics

Enhancing thermal management in modern electronic devices has become more important and challenging than ever before. One promising solution in this field is to take advantage of phase change materials (PCMs) based on paraffin wax (PW). However, the development and application of these PCMs face two major obstacles: poor shape stability and low thermal conductivity. In this study, we have successfully prepared pure graphene micro-nano pores films (GMNFs) through common foaming and heat treatment techniques. These GMNFs can simultaneously offer high thermal conductivity and a stable supporting framework for pure PW, resulting in the creation of graphene-based PCMs (GPCMs). The prepared GPCM demonstrates an impressive thermal conductivity of 208.08 W·m−1·K−1 and a latent heat of 156.97 J·g−1 when the ratio of the pure-graphene framework is 20.6 wt%. Additionally, the GPCM exhibits exceptional stability with minimal mass loss, even at temperatures as high as 147.4 ℃, surpassing the normal operating conditions of electronic devices. The performance of GPCMs can be easily adjusted by modifying the GMNFs to meet different thermal management requirements. These findings highlight the tremendous potential of GPCMs for industrial production and practical implementation in electronic devices.

Characterization of the Macroscopic Impact of Diverse Microscale Transport Mechanisms of Gas in Micro-Nano Pores and Fractures

The objective of this study is to construct a refined microscopic transport model that elucidates the transport mechanisms of gas flow within micro-nano pores and fractures. The collective impact of various microscopic transport mechanisms was explained through the apparent permeability model, specifically related to gases such as methane and carbon dioxide, within the shale matrix. The apparent permeability models, taking into account microscopic transport mechanisms such as slippage flow, Knudsen diffusion, transition flow, and surface diffusion, were established individually. Subsequently, the influencing factors on apparent permeability were analyzed. The results demonstrate that the apparent permeability of the shale reservoir matrix is significantly influenced by pore pressure, temperature, pore size, and total organic carbon (TOC). As pressure decreases, the apparent permeability of Knudsen diffusion and surface diffusion increases, while the apparent permeability of slippage flow decreases. In addition, the apparent permeability of the reservoir matrix initially decreases and then increases. With increasing temperature, the apparent permeability of slippage flow, Knudsen diffusion, and surface diffusion all increase, as does the apparent permeability of the reservoir matrix. As pore size increases, the apparent permeability of surface diffusion and Knudsen diffusion decreases, while the apparent permeability of slippage flow and the reservoir matrix increases. Furthermore, an increase in TOC leads to no change in the apparent permeability of slippage flow and Knudsen diffusion, but an increase in the apparent permeability of surface diffusion and the reservoir matrix. The model presented in this paper enhances the multi-scale characterization of gas microflow mechanisms in shale and establishes the macroscopic application of these micro-mechanisms. Moreover, this study provides a theoretical foundation for the implementation of carbon capture, utilization, and storage (CCUS) in shale gas production.

Research on the Shale Porosity–TOC Maturity Relationship Based on an Improved Pore Space Characterization Method

Shale pore structure characterization is key to shale reservoir evaluation, sweet spot selection, and economic exploitation. It remains a challenge to accurately characterize shale micro-nano pores. Common experimental characterization methods for shale pore systems are listed, and advantages and weaknesses of each method are analyzed. An improved pore structure characterization method for shale is proposed by combining Helium and NMR. The new method does not affect shale samples and has a higher accuracy. The affecting factors for shale pore evolution for shale are also discussed, showing that organic matter content and maturity are key factors in total porosity development. Furthermore, a shale porosity–TOC maturity relationship chart is developed based on the experimental data of shale samples selected from six shale reservoirs. The application of this chart in Well X in the Gulong field of Songliao Basin proves its utility in evaluating shale reservoirs.

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal.

An acid solution improves the pore-plugging problem in hydraulic fracturing, which in turn improves the permeability of the coal seam. The study aimed to investigate the effect of mixed acid on the micronano mechanical properties and permeability of the coal seam. The surface morphology of acidified coal was analyzed from the micronano scale using atomic force microscopy (AFM) and scanning electron microscopy. Additionally, the micronano scale mechanical characteristics of acidified coal were examined using the mechanical mode in an atomic force microscope. Furthermore, the complexity and connectivity of the micronano pores of samples were investigated using the low-temperature nitrogen adsorption and mercury intrusion porosimetry methods and the fractal theory. The results indicated that the surface minerals of acidified coal were dissolved, loosening the coal and increasing the complexity of the pore structure. Mineral deformation and pore deformation weakened the mechanical properties of coal at the micronano scale, and the mean elastic modulus of acidified coal (B# and E#) decreased by 28.78 and 25.66% compared to that of raw coal. The acid solution effectively enlarged the pore diameter, transitioning from micropores to mesopores and macropores, and the total pore volume of acidified coal increased by 1.88 times and 1.25 times, Kn increased from 0.064 to 0.581 and 0.37, respectively. The type of methane diffusion in the diffusion pores changed from Knudsen diffusion to transition-type diffusion. The tortuosity of the pore structure of acidified coal decreased, the fractal dimension of the tortuosity of the pore structure decreased, and the permeability increased by nearly three times. The research results indicate that the mechanical properties of coal decrease after acidification and that the microstructural changes can promote methane migration (diffusion-seepage), which can provide theoretical guidance for coalbed methane extraction in low-permeability coal reservoirs.

Regulating synergistic micro-nano pore structure of CNT sponge to control EMI shielding performance

The aggregation in high-content carbon nanotube reinforced silica carbide composites (CNT/SiC) imposed constraints for further large-scale industrial applications. This study established a synergistic micro-nano pore structure by assembling CNT bundles to fabricate the CNT sponge preform, and then the SiC matrix was in-situ deposited by chemical vapor infiltration method, which facilitates composites with high density and exceptional properties. The pore size distribution and pore area can be regulated by simply adjusting the compression ratios (CRs) of the as-assembled CNT sponge. Samples with CR of 50 % exhibited noteworthy densification, significantly reduced porosity, and a remarkable 163.54 % extra increase in compression strength compared to uncompressed ones. Additionally, the CNT/SiC composites displayed excellent oxidation resistance and demonstrated improved electromagnetic interference (EMI) shielding performance, which exhibited a substantial increase with higher CRs. These findings underscore the significance of employing appropriate multi-level porosity in CNT preforms to fabricate advanced ceramic matrix composites with superior EMI shielding capabilities.

The flooding mechanism and oil recovery of nanoemulsion on the fractured/non-fractured tight sandstone based on online LF-NMR experiments

Hydraulic fracturing and water/nanoemulsion flooding technology are effective stimulation measures for tight oil production. The complex pore structure of ultra-low permeability sandstone greatly affects oil recovery. At present, scholars have done a lot of research on the characteristics of oil-water flow in micro-nano pores of ultra-low permeability sandstone reservoirs. However, few scholars have comprehensively studied the whole process of ultra-low permeability sandstone reservoirs from hydraulic fracturing to enhanced oil recovery. In this paper, the whole process from fracturing to production of ultra-low permeability sandstone reservoirs is comprehensively studied at the laboratory scale by combining triaxial fracturing, CT scanning, online LF-NMR and other technologies, aiming to promote the understanding of tight oil development. The results show that the high confining pressure (45 MPa) inhibits the propagation of fractures in the rock samples more than the low confining pressure (15 MPa) during the triaxial fracturing process. The oil recovery of the rock sample with high fracture volume (1213.42 mm3) is 16.32 % higher than that of the rock sample with low fracture volume (674.22 mm3). Whether it is fractured rock or non-fractured rock, nanoemulsion can further improve the oil recovery of micropores on the basis of water flooding, with a maximum increase of 28.21 %. The oil recovery of the nanoemulsion with a concentration of 0.3 wt% was 25.34 % higher than that of the nanoemulsion with a concentration of 0.05 wt%. Confining pressure conditions have an important impact on oil recovery. The oil recovery of non-fractured rock samples with initial confining pressure of 5 MPa is 8.15 % lower than that of non-fractured rock samples with initial confining pressure of 30 MPa. At the same time, we propose a new T1-T2 map region division scheme based on sandstone to better characterize oil displacement behavior at the pore scale. The research results can guide the exploitation of ultra-low permeability sandstone reservoirs.

Multi-scale dynamic mathematical model of CO2 and fly ash mineralization

The multi-scale structural characteristics of micro-nano pores of fly ash are the core factors affecting the mechanisms of physical transport and chemical reaction of CO2. The existing theoretical models of mineralization do not take such characteristics into account. it is difficult to describe the mechanisms of physical transport and chemical reaction of CO2. In order to address this scientific problem, a theoretical model of multi-scale structures of pore series is established. A mathematical dynamic model of multi-scale internal diffusion-mineralization is also established for accurately describing the concentration variation law in physical transport and chemical reaction processes of CO2 in micro-nano pores of fly ash under natural static conditions. The model is simulated to analyze the key parameters affecting the transport-mineralization reaction rate in the evolutionary mechanism of CO2. The simulated results showed that if the initial apparent diffusion-mineralization coefficient is reduced by 100 times, the concentration of CO2 at the center of the particles is reduced by 25 order in magnitude. The attenuation coefficient is reduced by 2 order in magnitude and the concentration of CO2 at the center of the particles is changed by 9 order in magnitude. These findings indicate that the initial apparent diffusion-mineralization coefficient and attenuation coefficient are the factors affecting the diffusion-mineralization reaction in the evolution of CO2. The reason for the phenomenon of multi-scale evolution and mechanism of diffusion mineralization reaction of CO2 in the micro-nano pores of fly ash is revealed.

Sugarcane-based superhydrophilic and underwater superoleophobic membrane for efficient oil-in-water emulsions separation

The development of ecological, low cost, easy preparation, especially high performance materials for emulsions separation is of great importance due to the rise in pollution of oil-water emulsions from industrial production and domestic waste. Straws as agricultural wastes, including plenty of hydrophilic groups and multi-level pore structures, can be prepared as biomass membranes for oil-water emulsion separation. Herein, a novel super-hydrophilic sugarcane-based (SHS) membrane was prepared using a facile and eco-friendly method including chemical treatment and freeze-drying. The as-prepared SHS membrane has unique wettabilities due to the hydrophilic property of the internal cellulose and the micro-nano pores, including superhydrophilicity (water contact angle of 0°) and underwater superoleophobicity (underwater oil contact angles of over 150°). The SHS membrane has good durability and stability against ultraviolet (UV) irradiation, corrosion by acids and alkalis, mechanical abrasion and especially mould adhesion. Importantly, the SHS membrane can be used for separation of various oil-in-water emulsions, and exhibits excellent separation performances such as high separation efficiency (> 99 %) and good separation flux (above 891 L m−2 h−1 bar−1). The SHS membrane also exhibits excellent recyclability over 10 continuous separation cycles. Furthermore, the SHS membrane can be utilized to selectively absorb water from oils as a water absorbent material. Hence, SHS membrane is a promising and practical material for applications in treatment of wastewater containing oil-water emulsions.

Enhanced thermoelectric performance of Bi2-xCuxS3 by hydrothermal synthesis and spark plasma sintering

Bi2S3 has been considered as a promising medium temperature thermoelectric material due to its low thermal conductivity and cost-effective features. However, the intrinsically poor electrical conductivity of Bi2S3 still limits its further thermoelectric applications. In this work, we optimize the thermoelectric performance of Bi2S3 using Cu doping via a facile hydrothermal method combined with spark plasma sintering. A well-tuned carrier concentration of 1.2 × 1019 cm−3 and electrical conductivity of 47 S cm−1 at 523 K was attained, which is attributed to the increased electrons by Cu doping. In addition, the appeared micro-nano pores in both Bi2S3 and Cu doped Bi2S3 samples after spark plasma sintering benefits the reduction of lattice thermal conductivity (κl). The Bi1.985Cu0.015S3 sample exhibited the lowest κl of 0.405 W m−1 K−1 at 573 K, which is the lowest value as far as we know in the reported Cu doped Bi2S3 materials at the same temperature. Finally, A maximum ZT value of 0.3 at 573 K was achieved in Bi1.985Cu0.015S3 sample. This study provides a new strategy to achieve low κl and high ZT value in Bi2S3-based thermoelectric materials.

Carbon dots nanofluid: Reducing injection pressure in unconventional reservoir by regulating oil/water/rock interfacial properties

Effective development of unconventional resources is impeded by water flooding-related challenges, such as high pressure and under-injection, which hinder the replenishment of formation energy. Nanofluids have shown promise in reducing injection pressure, but traditional nanoparticles (NPs) face limitations in unconventional reservoirs due to their unsuitable size for micro-nano pores and aggregation tendencies. In this paper, novel carbon dots (CDs) with a simple, environmentally benign, and controllable synthetic approach have been developed, and their pressure-reduction performance and mechanism have been systematically explored. The particle size of the CDs could be tailored by a well-timely quenching reaction. CDs nanofluid demonstrated superior stability, dispersibility, and temperature/salinity resistance. In addition, CDs can regulate interfacial properties, including oil/rock and oil/water interfaces. It was found that CDs could be partially absorbed onto pore walls, reducing oil adhesion sites by 39%, altering wettability from oil-wet to neutral, and reducing rock surface roughness by 29.25%. Furthermore, CDs were rapidly adsorbed onto the remaining oil film in the pore space, reducing interfacial tension while solidifying the oil surfaces, increasing shear force around the oil surface by 1.7 times during subsequent water scouring, which makes the oil film break up more readily and remain smaller in size to migrate in the channeling. The modulation of the interface properties by CDs improved the stripping efficiency of the attached oil film and ameliorated the homogeneity and smoothness of flow channel, resulting in a significant reduction in injection pressure. Core displacement tests showed that a 0.1 wt% CDs nanofluid could achieve a pressure reduction rate of 35%. The developed CDs nanofluid represents a promising solution for reducing injection pressure and improving oil recovery in unconventional reservoirs.

Adsorption layer of complex oil components in organic-rich shale: A molecular dynamics simulation study

Shale oil is enriched in organic-rich shale, and its reservoir is mainly composed of micro-nano pore throats. The fluid adsorption layer in nano-confined channels complicates the fluid properties and transport patterns. In this study, equilibrium molecular dynamics was used to study the distribution states and diffusion patterns of complex oil components in organic matter represented by kerogen and four inorganic minerals represented by illite, quartz, calcite, and albite. The thickness and proportion of adsorption layers with different pores are quantitatively calculated. The adsorption capacity is in the following order: kerogen > illite > albite > calcite > quartz. According to the interaction energy, the adsorption stability of oil on surfaces with different pores is in the following order: illite > albite > calcite > kerogen > quartz, and the main forces of adsorption with different pores are obtained. With the increase in pore size, the proportion of light components in the adsorption layer increases, and the proportion of heavy components decreases. The oil components in quartz, calcite, and albite gradually desorb with the increase of pore size, while the oil components in illite are the opposite. The adsorption proportion of other components except for toluene in the kerogen pore increased. The diffusion rate of components in kerogen, quartz, and calcite is related to their relative atomic mass. The diffusion coefficient of components in illite is related to the polarity of components. The diffusion rate of components in small pore sizes of albite minerals is related to the polarity of components, and the diffusion rate of components in large pore sizes is related to the relative atomic mass of components. The effect of temperature and initial moisture content on pores is related to the type of pores.

A novel oil-in-water nanoemulsion as a high-temperature plugging agent for wellbore wettability alteration and strengthening

Wellbore instability associated with shale hydration and micro-nano pores is one of the most crucial concerns in deep oil and gas drilling operations. In this study, we present a nanoemulsion containing silicates and organosilanes to plug microfractures and mitigate shale hydration by forming a superhydrophobic film in situ on the shale surface via emulsion polymerization and sol–gel process, thereby improving the wellbore stability. At the temperature above 150 °C, the nanoemulsion forms a dense, superhydrophobic film in the pores and on the surface of ceramic sheets, reducing filtration loss by 84.3%. The core showed an increase in strength of 2.86% over the original shale after soaking in the nanoemulsion at 180 °C for 48 h. The shale cuttings covered with film reduced water uptake by 91.56%, thus improving water resistance. The film facilitates to maintain or even improve the rock strength by preventing water absorption and hydration. It also exhibits excellent thermal stability and dynamic water repellency properties at high temperature. We determined that the film consisted of tightly stacked nanofilaments of 5–20 nm in diameter and well-distributed nanospheres of 25–50 nm in diameter, which were identified as crystalline and amorphous symbiotic silica modified by long alkyl chains, respectively. Therefore, in order to overcome the wellbore instability encountered in deep well drilling, we propose a strategy in which the downhole temperature triggers the nanoemulsion to polymerize and seal the pores while simultaneously forming a hydrophobic film on the shale surface. Moreover, it is expected to have practical applications in drilling engineering due to its convenient fabrication, eco-friendly and cost-effective characteristics.