Search Results (102)

Natural gas hydrates, with their vast reserves and high gas storage density, have emerged as a highly promising alternative energy source and technology for gas storage and transportation. Wettability, as a core surface property of porous media, directly influences hydrate nucleation, growth, occurrence morphology, and flow behavior. In this study, quartz sand with varying surface properties was prepared with the octyltrimethoxysilane (OTMS) silane coupling agent via surface chemical reactions. The methane hydrate (MH) equilibrium conditions as well as the formation kinetics in silica sand were measured, and the mechanism and potential of the surface modification for enhancing methane hydrate storage capacity were analyzed. The experimental results indicate that surface modification of quartz sand has no significant effect on the MH equilibrium condition. Hydrophobic modification of quartz sand provides more gas–liquid interfaces, increases the contact area, and thereby significantly enhances mass transfer under high-water-saturation conditions and accelerates the MH formation rate. However, excessively high surface hydrophobicity may reduce the effective gas–liquid interfacial area and limit the overall hydrate formation rate. Due to the influences of the hydrate distribution and aggregation, as well as gas diffusion on hydrate formation, the effect of the initial formation pressure on MH formation is only observed during the early stages of MH formation, while the temperature effect is less pronounced than that of formation pressure. It is suggested to further consider combining stirring with continuous gas injection to enhance gas–liquid flow and improve gas–liquid contact, thereby increasing the formation rate of hydrates. Full article

The growing use of PET strapping in packaging has increased plastic waste, prompting interest in its reuse in cement-based materials. This study evaluates waste PET strapping powder as a partial replacement for natural sand in cement mortar. Mortars were prepared with three water–cement ratios (0.4, 0.5, and 0.6) and four replacement levels (0%, 5%, 10%, and 15%). Slump, flow, compressive strength, flexural strength, ultrasonic pulse velocity (UPV), four-point resistivity, and sulphate resistance were examined at different curing ages. Increasing PET content reduced slump and flow, indicating lower workability. It also decreased compressive and flexural strengths, with flexural strength showing a greater reduction. UPV declined as PET replacement increased, which was attributed to the combined effects of acoustic-property contrast between PET and the cementitious matrix, interfacial wave scattering, and local microstructural defects. However, PET increased electrical resistivity and reduced sulphate-related weight loss, indicating lower continuity of ion-conducting pathways and potentially improved resistance to the transport of aggressive ions under the adopted test conditions. SEM observations showed limited interfacial defects at 5% PET, whereas higher contents produced a more porous interfacial transition zone. Overall, the mix with 5% PET and W/C = 0.5 showed the best balance of properties, supporting the reuse of PET strapping powder as a sustainable sand replacement. Full article

To enhance quantitativeness and interpretability in identifying the mechanisms of complex oil–mineral–surfactant systems, this paper introduces an algorithmic molecular simulation analysis approach, transforming molecular dynamics trajectory data into comparable multidimensional molecular descriptors. Specifically, based on parameters such as radial distribution functions, mean square displacement, interface concentration distribution, adsorption energy attenuation, hydrogen bond statistics, and electrostatic interactions, an algorithm analysis framework was constructed covering “trajectory data acquisition—feature descriptor extraction—interface behavior recognition—separation mechanism classification.” This framework can identify differentiated regulatory patterns of different surfactants on SARA (saturates, aromatics, resins, asphaltenes) component migration, adsorption, and desorption behavior from a large amount of dynamic simulation data, thereby improving the structural expression and mechanism discrimination capabilities of molecular simulation results. In order to clarify the component-selective microscopic mechanisms of surfactants in the separation of heavy oil from oil sands, this work employs molecular dynamics simulations to study the interactions of the non-ionic surfactant TX-100 and the biosurfactants sophorolipid and rhamnolipid with the SARA fractions of heavy oil, both in the absence and presence of calcite mineral surfaces. The results show that all three surfactants act mainly through weak long-range interactions, but with distinct mechanisms: TX-100 preferentially screens small-molecule saturates through long-chain steric hindrance and hinders the diffusion of asphaltenes; sophorolipid promotes the preferential desorption of resins via hydrogen bonding; and rhamnolipid drives the desorption of aromatics at later stages through hydrophobic–electrostatic synergy. The C001 crystal surface exhibits the strongest adsorption affinity across all systems; the mineral surface overall prolongs the diffusion equilibrium time and amplifies the above kinetic differences. This study establishes three molecular-scale mechanisms—steric hindrance sieving, hydrogen-bond-promoted desorption, and electrostatically driven desorption—and reveals the universal adsorption platform effect of the C001 crystal surface, providing a theoretical basis for the molecular design of surfactants aimed at the selective separation of heavy oil components. Full article

In oil-rich countries, petroleum contamination of soils frequently occurs during refining, transportation, and exploitation. Such contamination significantly alters soil behavior and properties from a geotechnical perspective. Given that some fine-grained soils exhibit insufficient bearing capacity or excessive settlement, soil improvement is often necessary. The selective use of nanoparticles offers a promising novel approach in this regard. This study investigates the effects of diesel contamination and nanosilica modification on the physical and mechanical properties of clayey sand and aims to interpret the variations in the mechanical properties and the permeability of the treated soil based on microstructural observations. Diesel (0–10% in 2% increments) and nanosilica (0%, 1%, 2%) were added to the soil, preparing a total of 18 mixtures for testing. The microstructural changes directly alter the physical parameters such as specific gravity, optimum moisture content (OMC), and maximum dry unit weight, consequently affecting the permeability and the mechanical behavior. The microstructural analysis via scanning electron microscopy revealed diesel-induced clay flocculation and increasing macroporosity, while the nanosilica at 1% improved the soil fabric through pore filling and interparticle bonding, whereas 2% nanosilica led to partial dispersion and agglomeration. The findings demonstrate that soil behavior is controlled by the interplay between diesel (lubrication, pore blocking, hydrophobicity) and nanosilica (surface activation, micro-bonding, agglomeration). Increasing the diesel content consistently reduces the specific gravity across all the mixtures, due to the replacement of heavier mineral particles by lighter hydrocarbon, diesel adsorption onto the soil grains, the formation of low-density organic films, and increased micro-voids. Diesel addition reduces the OMC but increases the maximum dry unit weight due to its lubrication effect. Mechanically, the unconfined compressive strength (UCS) peaked at approximately 4% diesel contamination, with the addition of 1% nanosilica yielding the highest strength overall. Conversely, the California Bearing Ratio (CBR) increased continuously with diesel due to improved packing and frictional resistance and was further improved by nanosilica. The results show that permeability decreases with increasing diesel content due to hydrophobic diesel molecules coating soil particles, filling micro-voids, and blocking pore channels, while the consolidation parameters exhibit non-monotonic trends, peaking at moderate contamination levels. An optimal nanosilica content effectively mitigated some of the adverse effects of diesel and enhanced the mechanical performance, providing valuable insights for managing hydrocarbon-contaminated soils. Full article

The anti-corrosion performance of epoxy coatings in saline solution environments is restricted by their surface hydrophilicity and microporous defects. Herein, we developed a modified epoxy (MEP)-based superhydrophobic anticorrosive coating by fluorinated resin matrix and incorporation of polyaniline@expanded graphite (FPANI@MEG) anticorrosive fillers. The FPANI@MEG fillers were fabricated via in situ polymerization of aniline on the surface of dopamine-modified expanded graphite to construct the micro-nano hierarchical structure required for superhydrophobicity, while providing barrier shielding and active passivation functions. The results showed that the final coating exhibited excellent superhydrophobicity with a water contact angle of 156.5 ± 1.8° and sliding angle of 3.0 ± 0.6°, along with excellent adhesion and adaptability to various complex environments. Meanwhile, the coating maintained superhydrophobicity after 400 cycles of Taber abrasion and 450 g of falling-sand impact, demonstrating hydrophobic robustness. Furthermore, the coating exhibited a low-frequency impedance modulus of 2.30 × 10⁷ Ω·cm² after immersion in NaCl solution for 15 days. The synergistic combination of air film shielding, physical barrier, and active passivation endowed the coating with good anticorrosion performance. This work may provide a theoretical reference for improving the corrosion protection of epoxy-based superhydrophobic coatings on carbon steel in aggressive saline solution environments. Full article

Fine migration is widely recognized as a primary cause of production decline in unconsolidated sandstone reservoirs. Migrated fines may accumulate within pore throats and obstruct flow channels, or they may be transported into the wellbore with the produced fluids, leading to operational issues such as wellbore plugging, pump sticking, and equipment abrasion. Despite extensive studies on fine migration, the role of particle wettability has received limited attention. In this study, the mineralogical composition of formation particles was first characterized using X-ray diffraction (XRD) and quantitative clay analysis. Surface modification experiments were then conducted to investigate the effect of hexadecylamine (HDA) on particle wettability and to determine the optimal reaction conditions. Surface characterization techniques were employed to elucidate the modification mechanism. Subsequently, sand-packed tube displacement experiments were performed to evaluate the influence of wettability alteration on fine migration behavior. The underlying mechanisms were further interpreted through interfacial thermodynamic analysis. Two potential field application schemes are proposed to facilitate practical implementation in oilfield operations. The results indicate that the water contact angle of formation particles increased from 0° to 150° when treated with 0.8 wt% HDA for 24 h. Surface characterization confirms that HDA molecules were physically adsorbed onto the particle surfaces. Displacement experiments demonstrate that the permeability reduction rate decreases significantly with increasing particle hydrophobicity. Thermodynamic analysis suggests that the work of adhesion on the modified particle surface was reduced by 93.3%, thereby weakening fluid–particle interfacial coupling and suppressing fine mobilization. This study provides a wettability-based approach for mitigating permeability damage caused by fine migration in unconsolidated sandstone reservoirs. Full article

With the increasing prevalence of microplastics (MPs) and nanoplastics (NPs) in global aquatic environments, their potential ecotoxicological and health impacts have become a major concern in environmental science. Slow sand filtration (SSF) is widely recognized for its low energy demand, ecological compatibility, and operational stability; however, its efficiency in removing small or neutrally buoyant MPs remains limited. In recent years, integrating modified activated carbon (MAC) into SSF systems has emerged as a promising approach to enhance MP removal. This review comprehensively summarizes the design principles, adsorption and bio-synergistic mechanisms, influencing factors, and recent advancements in MAC-SSF systems. The results indicate that surface modification of activated carbon—through controlled pore distribution, functional group regulation, and hydrophilic–hydrophobic balance—significantly enhances the adsorption and interfacial binding of MPs. Furthermore, the coupling between MAC and biofilm facilitates a multi-mechanistic removal process involving electrostatic attraction, hydrophobic interaction, physical entrapment, and biodegradation. In addition, this review discusses the operational stability, regeneration performance, and environmental sustainability of MAC-SSF systems, emphasizing the need for future research on green and low-cost modification strategies, interfacial mechanism elucidation, microbial community regulation, and life-cycle assessment. Overall, MAC-SSF technology provides an efficient, economical, and sustainable pathway for microplastic control, offering valuable implications for a safe water supply and aquatic ecosystem protection in the future. Full article

Coalbed methane development is constrained by reservoir characteristics including high gas adsorption, high salinity, and high closure pressure, which impose significant limitations on conventional polymer fracturing fluids regarding viscosity enhancement, proppant transport, and fracture maintenance. In this study, a novel polymer fracturing fluid system, Z-H-PAM, was designed and synthesized to achieve strong salt tolerance, low adsorption affinity, and high elasticity to withstand closure pressure. This was accomplished through the molecular integration of a zwitterionic monomer ZM-1 and a hydrophobic associative monomer HM-2, forming a unified structure that combines rigid hydrated segments with a hydrophobic elastic network. The results indicate that ZM-1 provides a stable hydration layer and low adsorption tendency under high-salinity conditions, while HM-2 contributes to a high-storage-modulus, three-dimensional physically cross-linked network via reversible hydrophobic association. Their synergistic interaction enables Z-H-PAM to retain viscoelasticity that is significantly superior to conventional HPAM and to achieve rapid structural recovery in high-mineralization environments. Systematic evaluation shows that this system achieves a static sand-suspension rate exceeding 95% in simulated flowback fluid, produces broken gel residues below 90 mg/L, and results in a core damage rate of only 10.5%. Moreover, it maintains 88.8% of its fracture conductivity under 30 MPa closure pressure. Notably, Z-H-PAM can be prepared directly using high-salinity flowback water, maintaining high elasticity and sand-carrying capacity while enabling fluid recycling and reducing reservoir damage. This work clarifies the multi-scale mechanisms of strongly hydrated and highly elastic polymers in coalbed methane reservoirs, offering a theoretical and technical pathway for developing efficient and low-damage fracturing materials. Full article

Naphthenic acid fraction compounds (NAFC) are prevalent in petrochemical wastewater, including from oil sands processing, and induce reactive oxygen species (ROS) emissions in isolated mitochondria. The purpose of this study was to verify if a primary carboxylic acid, the moderately hydrophobic NAFC 3,5-dimethyladamantane-1-acetic acid, would cause the mitochondrial ROS (hydrogen peroxide; H₂O₂) production and affect its consumption by mitochondria in multiple bioenergetic states. Intact mitochondria isolated from rainbow trout (Oncorhynchus mykiss) liver were exposed to commercially available 3,5-dimethyladamantane-1-acetic acid. The emission of ROS during States 3 and 4 respiration was quantified using fluorometry with an Oroboros fluorespirometer. Subsequently, select ROS emission sites in the mitochondrial complexes were isolated using inhibitors, and the ROS emission of each site was measured using the Amplex UltraRed-horseradish peroxidase (AUR-HRP) system. The compound 3,5-dimethyladamantane-1-acetic acid was equally potent in causing ROS emission in State 3 and State 4 ROS sites. The baseline (no NAFC) proportion of ROS emission by site was II_F > I_Q > III_Qo > I_F. The 3,5-dimethyladamantane-1-acetic acid compound increased ROS emission in a dose-dependent manner at II_F with an EC₅₀ of 0.2 mM, which was not significantly different than the State 3 and 4 Oroboros response. In contrast, there was no consistent concentration-effect response at the other three ROS sites (I_Q, III_Qo, and I_F). Malonate, an inhibitor of succinate dehydrogenase, eliminated ROS production in Oroboros experiments. These findings identify site II_F as the predominant source of NAFC-stimulated ROS and provide mechanistic insight into how adamantane-type NAFCs impair mitochondrial redox balance in fishes. Full article

In this study, four types of Fe₃O₄-based magnetic nanospheres were functionalized with distinct surface groups to examine how surface chemistry influences their co-transport with tetracycline (TC) in porous media. The functional groups investigated are carboxyl (−COOH), epoxy (−EPOXY), silanol (−SiOH), and amino (−NH₂). Particles bearing −COOH, −EPOXY, or −SiOH are negatively charged, facilitating their transport through porous media, whereas −NH₂-modified particles acquire a positive charge, leading to strong electrostatic attraction to the negatively charged TC and quartz sand, and consequently substantial retention with reduced mobility. Adsorption of TC onto Fe₃O₄-MNPs is predominantly chemisorptive, driven by ligand exchange and the formation of coordination complexes between the ionizable carboxyl and amino groups of TC and the surface hydroxyls of Fe₃O₄-MNPs. Additional contributions arise from electrostatic interactions, hydrogen bonding, hydrophobic effects, and cation–π interactions. Moreover, the carboxylate moiety of TC can coordinate to surface Fe centers via its oxygen atoms. Molecular dynamics simulations reveal a hierarchy of adsorption energies for TC on the differently modified surfaces: Fe₃O₄-NH₂ > Fe₃O₄-EPOXY > Fe₃O₄-COOH > Fe₃O₄-SiOH, consistent with experimental findings. The results underscore that tailoring the surface properties of engineered nanoparticles substantially modulates their environmental fate and interactions, offering insights into the potential ecological risks associated with these nanomaterials. Full article

Surface pretreatment significantly influences the hygroscopic behavior of wood, which in turn affects surface stability when exposed to variable climatic conditions. This study focuses on how different surface pretreatment methods impact the performance of protective coating applied on spruce wood (Picea abies (L.) Karst.) during one year of natural weathering. Samples were prepared using various surface treatments: milling and sanding with grit sizes P40, P80, and P120, respectively. Two types of coatings were applied: a solventborne coating (ADLER Pullex Plus-Lasur) and a waterborne coating (DColor FK 47 UV Protect). The samples were exposed for 12 months at an outdoor testing site in Suchdol, Czech. Surface properties were assessed through color changes in the CIE Lab* space, gloss measurements (ISO 2813), contact angle analysis, and visual inspection. The results showed that exposure to UV radiation and microbial activities led to the gradual degradation of the optical properties and aesthetic appearance of the wood. Surfaces with greater roughness preserved their aesthetic properties more effectively, indicating a higher absorption of the coating. Untreated wood exhibited low water repellency, while the coated surface demonstrated enhanced hydrophobicity. Notably, the waterborne coating showed a temporary increase in contact angle around the sixth month, indicating surface clogging by dust particles. In contrast, the solventborne coating had a rapid decrease in wettability during the first nine months. These findings suggested the importance of surface pretreatment and coating type in maintaining the long-term performance and aesthetic appearance for wood used in exterior conditions. Full article

To address the challenges of low permeability, high gas adsorption, and a fragile structure in coalbed methane reservoirs, this study developed a high-strength composite proppant with an activated carbon skeleton via nitric acid pretreatment, silica–alumina sol coating, and calcination. Orthogonal experiments optimized the preparation conditions: 30–40 mesh activated carbon, Si/Al molar ratio of 4:1, calcination at 650 °C for 2 h. The resulting proppant exhibited an excellent performance: a single-particle compressive strength of 55.5 N, porosity of 33.2%, crushing rate of only 2.3% under 50 MPa closure pressure, and permeability 48.5% higher than quartz sand. In simulated acidic coalbed environments (pH 3–5), its acid corrosion rate was <2.8%, and it enhanced methane desorption by 16.2% compared to pure coal. Additionally, the proppant showed a superior transport performance in fracturing fluids, with better distribution uniformity in fractures than ceramsite, and its hydrophobic surface (contact angle 115.32°) improved fracturing fluid flowback efficiency. This proppant integrates high strength, good conductivity, gas desorption promotion, and corrosion resistance, offering a novel material solution for efficient coalbed methane extraction. Full article

Water infiltration into soil is a key process in regulating the hydrological cycle and sustaining ecosystem services in high-Andean environments. However, limited information is available regarding its dynamics in these ecosystems. This study evaluated the influence of three types of vegetation cover and soil properties on water infiltration in a high-Andean environment. A double-ring infiltrometer, the Water Drop Penetration Time (WDPT, s) method, and laboratory physicochemical characterization were employed. Soils under forest cover exhibited significantly higher quasi-steady infiltration rates (i_s, 0.248 ± 0.028 cm·min⁻¹) compared to grazing areas (0.051 ± 0.016 cm·min⁻¹) and agricultural lands (0.032 ± 0.013 cm·min⁻¹). Soil organic matter content was positively correlated with i_s. The modified Kostiakov infiltration model provided the best overall fit, while the Horton model better described infiltration rates approaching i_s. Sand and clay fractions, along with K⁺, Ca²⁺, and Mg²⁺, were particularly significant during the soil’s wet stages. In drier stages, increased Na⁺ concentrations and decreased silt content were associated with higher water repellency. Based on WDPT, agricultural soils exhibited persistent hydrophilic behavior even after drying (median [IQR] from 0.61 [0.38] s to 1.24 [0.46] s), whereas forest (from 2.84 [3.73] s to 3.53 [24.17] s) and grazing soils (from 4.37 [1.95] s to 19.83 [109.33] s) transitioned to weakly or moderately hydrophobic patterns. These findings demonstrate that native Andean forest soils exhibit a higher infiltration capacity than soils under anthropogenic management (agriculture and grazing), highlighting the need to conserve and restore native vegetation cover to strengthen water resilience and mitigate the impacts of land-use change. Full article

Lost circulation is a major challenge in oil and gas drilling operations, severely restricting drilling efficiency and compromising operational safety. Conventional bridging and plugging materials rely on precise particle-to-fracture size matching, resulting in low success rates. Self-healing gels penetrate loss zones as discrete particles that progressively swell, accumulate, and self-repair in integrated gel masses to effectively seal fracture networks. Self-healing gels effectively overcome the shortcomings of traditional bridging agents including poor adaptability to fractures, uncontrollable gel formation of conventional downhole crosslinking gels, and the low strength of conventional pre-crosslinked gels. This work employs stearyl methacrylate (SMA) as a hydrophobic monomer, acrylamide (AM) and acrylic acid (AA) as hydrophilic monomers, and graphene oxide (GO) as an inorganic dopant to develop a GO-based self-healing organic–inorganic hybrid plugging material (SG gel). The results demonstrate that the incorporation of GO significantly enhances the material’s mechanical and rheological properties, with the SG-1.5 gel exhibiting a rheological strength of 3750 Pa and a tensile fracture stress of 27.1 kPa. GO enhances the crosslinking density of the gel network through physical crosslinking interactions, thereby improving thermal stability and reducing the swelling ratio of the gel. Under conditions of 120 °C and 6 MPa, SG-1.5 gel demonstrated a fluid loss volume of only 34.6 mL in 60–80-mesh sand bed tests. This gel achieves self-healing within fractures through dynamic hydrophobic associations and GO-enabled physical crosslinking interactions, forming a compact plugging layer. It provides an efficient solution for lost circulation control in drilling fluids. Full article