Search Results (143)

Low gas recovery in the Sebei-2 gas field is linked to residual gas trapping under water encroachment. This study investigates the pore-scale trapping behaviour of residual gas in three types of layer: conventional, low-resistivity, and low-acoustic high-resistivity. High-fidelity pore structures were reconstructed by integrating mercury intrusion porosimetry with thin-section data and microfluidic models were designed using the Quartet Structure Generation Set method and fabricated by wet etching. Visualized displacement experiments were performed under different wettability conditions and water invasion rates, and image analysis was used to quantify the distribution of trapped gas. Results show that the low-resistivity gas layer exhibits the highest residual gas saturation (30.57%), followed by the low-acoustic high-resistivity gas layer (20.20%), while the conventional gas layer has the lowest (15.29%). These values correspond to apparent pore-scale gas recoveries of about 48.95%, 65.01%, and 72.14% for the low-resistivity, low-acoustic high-resistivity and conventional gas layers, respectively. In hydrophilic systems, wetting-film thickening and flow diversion are the main trapping processes, whereas in hydrophobic systems, flow diversion dominates and residual gas decreases markedly. Increasing the water invasion rate reduces trapped gas in the conventional and low-resistivity layers, whereas in the strongly heterogeneous low-acoustic high-resistivity layer, higher invasion intensity strengthens preferential channelling/viscous fingering, leading to a non-monotonic residual gas response. These findings clarify the differentiated pore-scale trapping mechanisms of gas under water encroachment and highlight that mitigating water film-controlled trapping in low-resistivity layers and flow diversion trapping in low-acoustic high-resistivity layers is essential for mobilizing trapped gas, improving dynamic reserves, and ultimately enhancing the economic recovery of water-bearing gas reservoirs similar to the Sebei-2 gas field. Full article

The Chang 7 shale oil reservoirs of the Yanchang Formation in the Heishui Area of the Ordos Basin display typical tight sandstone characteristics, marked by complex microscopic pore structures and limited flow capacity, which severely constrain efficient development. Using a suite of laboratory techniques—including nuclear magnetic resonance, mercury intrusion porosimetry, oil–water relative permeability, spontaneous imbibition experiments, scanning electron microscopy, and thin section analysis—this study systematically characterizes representative tight sandstone samples and examines the microscopic distribution of remaining oil, flow behavior, and their controlling factors. Results indicate that residual oil is mainly stored in nanoscale micropores, whereas movable fluids are predominantly concentrated in medium to large pores. The bimodal or trimodal T₂ spectra reflect the presence of multiscale pore–fracture systems. Spontaneous imbibition and relative permeability experiments reveal low displacement efficiency (average 41.07%), with flow behavior controlled by capillary forces and imbibition rates exhibiting a three-stage pattern. The primary factors influencing movable fluid distribution include mineral composition (quartz, feldspar, lithic fragments), pore–throat structure (pore size, sorting, displacement pressure), physical properties (porosity, permeability), and heterogeneity (fractal dimension). High quartz and illite contents enhance effective flow pathways, whereas lithic fragments and swelling clay minerals significantly impede fluid migration. Overall, this study clarifies the coupled “lithology–pore–flow” control mechanism, providing a theoretical foundation and practical guidance for the fine characterization and efficient development of tight oil reservoirs. The findings can directly guide the optimization of hydraulic fracturing and enhanced oil recovery strategies by identifying high-mobility zones and key mineralogical constraints, enabling targeted stimulation and improved recovery in the Chang 7 and analogous tight reservoirs. Full article

Methylmercury (MeHg) is a well-known environmental neurotoxicant that preferentially affects sensory neurons in the peripheral nervous system. While sensory-dominant neuropathy has long been described in Minamata disease, the temporal dynamics of dorsal root ganglion (DRG) injury and recovery remain incompletely understood. In this study, Wistar rats were exposed to MeHg for five consecutive days, followed by a two-day treatment-free period; this regimen was repeated once. The DRG and peripheral sensory fibers were analyzed up to 70 days after exposure. Histological and immunohistochemical analyses, DNA microarrays, and mercury quantification and distribution mapping were performed. The A-fiber density was significantly reduced at Day 14 but recovered by Day 70, whereas C-fibers showed no significant change. The total number of DRG neurons remained stable. Immunohistochemical analyses demonstrated that subtype marker-selected neurons (NF, TrkA, FAM19A1, TAC1, SST) decreased at Day 14 and gradually recovered thereafter. DNA microarray analysis at Day 14 revealed a broad downregulation of DRG neuronal subtype marker genes. The mercury concentration in the DRG peaked at Day 14 and declined to the control level by Day 70, with in situ imaging confirming preferential accumulation in DRG neurons. These data suggest that the short-term MeHg exposure caused a transient functional suppression of DRG neurons without widespread neuronal loss. The selective and reversible downregulation of neuronal phenotypes, coupled with preferential Hg accumulation in DRG neurons, underlies the sensory-dominant and potentially reversible features of MeHg neurotoxicity. Full article

Mercury’s severe toxicity and persistence demand fast, low-cost, and sustainable detection. In this work, a Juglans regia ethanolic extract is introduced as an efficient biogenic reducing and stabilizing agent for the green synthesis of silver nanoparticles (AgNPs). This plant-mediated route enables environmentally friendly nanoparticle formation with suitable optical properties for sensing applications. To overcome the poor visual selectivity observed in the colloidal AgNPs suspension, the nanoparticles were immobilized onto filter paper to produce a solid-phase colorimetric sensor. The paper-based platform exhibited a highly selective response toward Hg²⁺, showing complete suppression of the yellow coloration exclusively in the presence of Hg²⁺, even when challenged with a 200-fold excess of potentially interfering ions. Quantitative colorimetric analysis revealed a broad linear detection range from 1 × 10⁻⁸ to 1 × 10⁻³ mol dm⁻³ and an excellent limit of detection of 1.065 × 10⁻⁸ mol dm⁻³, with visible color changes consistent with the calculated values. The sensor’s performance was further validated using real tap water samples, with recovery values ranging from 96% to 102%, confirming minimal matrix interference and reliable quantification. Altogether, this study demonstrates that Juglans regia-mediated AgNPs, integrated into a simple paper-based format, provide a fully green, low-cost, and portable platform for sensitive and selective on-site detection of Hg²⁺ in environmental waters. Full article

China possesses abundant tight conglomerate oil resources. However, these reservoirs are typically characterized by low porosity and permeability, high clay mineral content, and complex pore structures, resulting in poor performance of conventional waterflooding development. Challenges including insufficient energy replenishment and high flow resistance ultimately lead to low oil recovery factors. This study systematically investigates surfactant-assisted CO₂ huff-n-puff (SA-CO₂-HnP) for enhanced oil recovery in tight conglomerate reservoirs. For a tight conglomerate reservoir in a Xinjiang block, a fully implicit, multiphase, multicomponent dual-porosity numerical model was established. By integrating pore–throat distributions acquired through high-pressure mercury intrusion with a self-developed MATLAB PVT package, nanoconfinement-induced shifts in the phase envelope were rigorously embedded into the simulation framework. The calibrated model was subsequently employed to conduct a comprehensive sensitivity analysis, quantitatively delineating the influence of petrophysical, completion, and operational variables on production performance. Simulation results demonstrate that compared to conventional CO₂ huff-n-puff, the addition of surfactants increases the cumulative recovery factor by 3.5 percentage points over a 20-year production period. The enhancement mechanisms primarily include reducing CO₂–oil interfacial tension (IFT) and minimum miscibility pressure (MMP), improving reservoir wettability, and promoting CO₂ dissolution and diffusion in crude oil. Sensitivity analysis reveals that injection duration, injection pressure, and injection rate significantly influence recovery efficiency, while soaking time exhibits relatively limited impact. Moreover, an optimal surfactant concentration (0.0003 mole fraction) exists; excessive concentrations lead to diminished enhancement effects due to competitive adsorption and pore blockage. This study demonstrates that SA-CO₂-HnP technology offers favorable economic viability and operational feasibility, providing theoretical foundation and parameter optimization guidance for efficient tight conglomerate oil reservoir development. Full article

Over 292 million tons of municipal solid waste (MSW) are generated annually in the United States, with more than half disposed of in landfills. Municipal solid waste landfills (MSWLFs) are stationary sources of air pollution and potential health risks for nearby communities. The Agency for Toxic Substances and Disease Registry (ATSDR) has completed over 300 public health assessments (PHAs) and related investigations at MSWLFs and open dumps since the 1980s. This paper reviews the ATSDR’s evaluations of air pathway concerns at 125 MSWLF sites assessed between 1988 and early 2025, with many being evaluated during the 1990s. Most sites were located in the Midwest and Northeast, and only 25% remained active. The ATSDR found no air-related public health hazard at 86% of sites. At sites where hazards were identified, common issues included elevated outdoor or indoor toxicants (e.g., hydrogen sulfide, benzene, trichloroethylene, and mercury) and unsafe methane accumulations. Contributing factors included older site designs, inadequate gas-collection, subsurface fires, and distance from nearby residences. Corrective actions effectively reduced exposures at the affected sites. Results suggest that well-located and maintained landfills minimize public health hazards, while aging or poorly managed sites pose risks. Continued monitoring and research are warranted as waste management shifts toward reducing, reusing, recycling, composting, and energy-recovery technologies to improve efficiency, advance technologies, and address systemic public health challenges. Full article

The Cenomanian Bahariya Formation exposed at Gebel El Dist in the Western Desert of Egypt provides valuable surface analogues for evaluating the reservoir quality of subsurface Bahariya sandstones. The formation was analyzed using 27 oriented samples and 91 core plugs from quartz arenite (QA) and quartz wacke (QW) facies. Analyses included XRD, petrography, SEM, helium porosity–permeability, and capillary tests, as well as measurements of pore-throat radii (R) at 35% and 36% mercury saturation. X-ray diffraction analyses reveal a heterogeneous mineral composition dominated by quartz, feldspars, dolomite, pyrite, siderite, goethite, hematite, clay minerals, glauconite, and gypsum. QA displays higher porosity and permeability than QW, along with larger pore radii, and lower specific surface area per unit pore volume (Spv) and per unit grain volume (Sgv). Multivariate regression equations, specific to each facies, were developed to convert standardized XRD mineral percentages directly into pore-system and flow attributes (ϕ, k, r, Spv, Sgv, R35, R36), quantifying capillary-based recovery contrasts between facies. Across both facies, regressions linking mineralogy to ϕ, k, r, Spv, Sgv, R35, and R36 are strong (R² = 0.78–1.00). The established predictive equations provide a low-cost method to estimate reservoir quality from mineralogy alone, enabling rapid screening of Cenomanian Bahariya analogues and similar clastic reservoirs where core data are limited. Full article

Ultra-deep fractured tight sandstone reservoirs are key targets for natural gas development, where gas flow is controlled by pore structure, capillary forces, and water saturation. Using the ultra-deep tight sandstones from the Tarim Basin as study object, this paper investigates the gas flow behavior in matrix and fractured cores under high-temperature, high-pressure, and various water saturation conditions. The controlling factors of gas flow are investigated through scanning electron microscopy, casting thin-section, and high-pressure mercury intrusion measurements. The results show that increasing the water saturation can significantly reduce the permeability. The permeability of matrix and fractured cores decreases by 71.15% and 79.67%, respectively, when water saturation reaches 50%. The gas slippage is negligible, but the effect of gas threshold pressure is significant, which is primarily controlled by the pore structure and water saturation. The threshold pressure gradient of gas flow ranges from 0.0004 to 0.8762 MPa/cm, with the matrix cores exhibiting values approximately 13.21 times higher than the fractured cores. The water phase preferentially occupies the larger pores, forcing gas flow to rely on the finer pores. The pores with a maximum radius of 0.21 μm require 0.66 MPa of driving pressure for gas, whereas pores with a median radius of 0.033 μm require 4.18 MPa. The fracture networks can significantly reduce the lower limit for gas flow, serving as the key flow channels for the efficient development of ultra-deep tight sandstone gas. These findings not only reveal the gas flow mechanisms under water invasion but also provide theoretical and practical guidance for enhancing gas recovery from ultra-deep tight sandstone reservoirs. Full article

Artisanal and Small-Scale Gold Mining (ASGM) is a primary source of global mercury pollution, creating an urgent need for sustainable, low-cost alternatives to amalgamation. This study investigates the use of cassava wastewater (manipueira), a cyanogenic agricultural byproduct, as a lixiviant for a gold concentrate (14.30–15.87 ppm Au) from an artisanal mine. Two approaches were evaluated: direct leaching with manipueira in natura (250 ppm CN⁻) in single and double 8 h and 12 h cycles, and leaching with a cyanide solution concentrated from dilute manipueira (100 ppm CN⁻) via a simplified air-stripping system. Results were benchmarked against the mine’s amalgamation (44.7% recovery) and 30-day heap leach (75.8% recovery) processes. The most effective method observed was a two-cycle, 8 h leach with manipueira in natura, which achieved a mean gold recovery of $76.75\pm 4.71\%$. This result is comparable to the efficiency of the site’s lengthy heap leach process and suggests a promising, faster, route to eliminating mercury use. Longer (12 h) leaching cycles yielded lower recoveries, suggesting process limitations such as preg-robbing. The cyanide concentration method proved inefficient, recovering a maximum of 12.40% of the available cyanide and resulting in a weaker lixiviant. The findings demonstrate that while direct leaching is a viable alternative to mercury, the inherent instability of manipueira necessitates a focus on developing efficient, controlled systems to extract and concentrate its cyanide content, thereby creating a standardized “green” reagent from a large-volume agricultural waste stream. Full article

Mercury is a highly toxic heavy metal that poses serious threats to human health and environmental safety, highlighting the critical importance of accurate Hg²⁺ detection. In this study, a novel fluorescent probe AP was synthesized by conjugating fluorescein, serving as the luminescent group, with pyridine-2-carboxaldehyde to enable selective Hg²⁺ detection. Hg²⁺ binds to AP in a 1:2 stoichiometric ratio, inducing the opening of the spiro-lactam ring and resulting in a significant fluorescence enhancement. The probe exhibited excellent selectivity and sensitivity toward Hg²⁺. A strong linear correlation was observed between its fluorescence intensity and Hg²⁺ concentration (R² = 0.99952), with a detection limit of as low as 9.75 × 10⁻⁸ mol/L. The average recoveries of Hg²⁺ across various water matrices ranged from 95.23% to 103.40%, with relative standard deviations (RSDs) below 3.07%. These results indicate that the probe performs effectively in real water-sample testing. Full article

This study systematically investigates the pore–fracture architecture of deep coal seams in the JiaTan (JT) block of the Ordos Basin using an integrated suite of advanced techniques, including nuclear magnetic resonance (NMR), high-pressure mercury intrusion, low-temperature nitrogen adsorption, low-pressure carbon dioxide adsorption, and micro-computed tomography (micro-CT). These complementary methods enable a quantitative assessment of pore structures spanning nano- to microscale dimensions. The results reveal a pore system overwhelmingly dominated by micropores—accounting for more than 98% of the total pore volume—which play a central role in coalbed methane (CBM) storage. Microfractures, although limited in volumetric proportion, markedly enhance permeability by forming critical flow pathways. Together, these features establish a dual-porosity system that governs methane transport and recovery in deep coal reservoirs. The multiscale characterization employed here proves essential for resolving reservoir heterogeneity and designing effective stimulation strategies. Notably, enhancing methane desorption in micropore-rich matrices and improving fracture connectivity are identified as key levers for optimizing deep CBM extraction. These insights offer a valuable foundation for the development of deep coalbed methane (DCBM) resources in the Ordos Basin and similar geological settings. Full article

This study presents a comprehensive multifractal characterization of full-scale pore structures in middle- to high-rank coal reservoirs from the Western Guizhou–Eastern Yunnan Basin and establishes a permeability prediction model integrating fractal heterogeneity and pore throat parameters. Eight coal samples were analyzed using mercury intrusion porosimetry (MIP), low-pressure gas adsorption (N₂/CO₂), and multifractal theory to quantify multiscale pore heterogeneity and its implications for fluid transport. Results reveal weak correlations (R² < 0.39) between conventional petrophysical parameters (ash yield, volatile matter, porosity) and permeability, underscoring the inadequacy of bulk properties in predicting flow behavior. Full-scale pore characterization identified distinct pore architecture regimes: Laochang block coals exhibit microporous dominance (0.45–0.55 nm) with CO₂ adsorption capacities 78% higher than Tucheng samples, while Tucheng coals display enhanced seepage pore development (100–5000 nm), yielding 2.5× greater stage pore volumes. Multifractal analysis demonstrated significant heterogeneity (Δα = 0.98–1.82), with Laochang samples showing superior pore uniformity (D₁ = 0.86 vs. 0.82) but inferior connectivity (D₂ = 0.69 vs. 0.71). A novel permeability model was developed through multivariate regression, integrating the heterogeneity index (Δα) and effective pore throat diameter (D₁₀), achieving exceptional predictive accuracy. The strong negative correlation between Δα and permeability (R = −0.93) highlights how pore complexity governs flow resistance, while D₁₀’s positive influence (R = 0.72) emphasizes throat size control on fluid migration. This work provides a paradigm shift in coal reservoir evaluation, demonstrating that multiscale fractal heterogeneity, rather than conventional bulk properties, dictates permeability in anisotropic coal systems. The model offers critical insights for optimizing hydraulic fracturing and enhanced coalbed methane recovery in structurally heterogeneous basins. Full article

This study developed a vinyl acetate-ethylene rapid repair mortar (VAE-RRM) by using a binary blended cementitious system (ordinary Portland cement and sulfoaluminate cement) and vinyl acetate-ethylene (VAE) redispersible polymer powder. The effects of the polymer-to-cement ratio (P/C: 0~2.0%) on setting time, mechanical properties, interfacial bonding, and microstructure were systematically investigated. The results reveal that VAE delayed cement hydration via physical encapsulation and chemical chelation, extending the initial setting time to 182 min at P/C = 2.0%. At the optimal P/C = 0.9%, a synergistic organic–inorganic network enhanced flexural strength (14.62 MPa at 28 d, 34.0% increase) and interfacial bonding (2.74 MPa after interface treatment), though compressive strength decreased to 65.7 MPa due to hydration inhibition. Excessive VAE (P/C ≥ 1.5%) suppressed AFt/C-S-H growth, increasing harmful pores (>1 μm) and degrading performance. Microstructural analysis via scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) demonstrates that VAE films bridged hydration products, filled interfacial transition zones (ITZ), and refined pore structures, reducing the most probable pore size from 62.8 nm (reference) to 23.5 nm. VAE-RRM 3 (P/C = 0.9%) exhibited rapid hardening (initial setting time: 75 min), high substrate recovery (83.3%), and low porosity (<10%), offering an efficient solution for urban infrastructure repair. This work elucidates the dual mechanisms of pore refinement and interface reinforcement driven by VAE, providing theoretical guidance for designing high-performance repair materials. Full article

Brazil has made progress in Municipal Solid Waste (MSW) management through national legislation focused on integrated waste handling. However, challenges persist, particularly regarding MSW overproduction. A sustainable alternative is Refuse-Derived Fuel (RDF), generated from MSW with or without biomass addition. To be viable for combustion, RDF must meet established energy and environmental quality standards. In this context, a mathematical model based on fuzzy logic was developed to classify RDF quality and support decision-making. Five RDF samples were tested, evaluating their Lower Heating Value (LHV), chlorine, and mercury contents using calorimetry, atomic absorption, and X-ray fluorescence. Results indicate that RDF produced solely from MSW tends to have inadequate LHV, necessitating drying pretreatment. Even with the addition of peanut shells, the highest classification achieved was “Regular”, suggesting limited suitability for combustion in furnaces or boilers without pretreatment. Since the general composition of MSW in Brazil is consistent with the characteristics analyzed, RDF may remain unviable for energy recovery under similar conditions. Economic feasibility studies on drying are recommended, especially in urban centers with limited landfill space. Full article

This study systematically investigates the heterogeneity of the Chang 6 reservoir in the Wuqi–Dingbian region of the Ordos Basin through integrated petrographic analysis using scanning electron microscopy (SEM), thin-section petrography, and mercury intrusion porosimetry. The results reveal that this feldspathic sandstone reservoir exhibits significant compositional and textural variations controlled by depositional environments. Dingbian samples displayed elevated feldspar (avg. 42.3%), lithic fragments (18.1%), and carbonate cementation (15.7%), accompanied by intense mechanical compaction and cementation processes. Pore systems in Dingbian were dominated by residual intergranular pores (58–62% of total porosity) and secondary dissolution pores. In contrast, Wuqi reservoirs demonstrated superior pore connectivity through well-developed intergranular pores (65–72%), grain boundary pores, and microfracture networks. Pore throat characterization revealed distinct architectural patterns: Wuqi exhibited broad bimodal/multimodal distributions (0.1–50 μm) with 35–40% macro-throat (>10 μm) contribution to flow capacity, while Dingbian showed narrow unimodal distributions (1–10 μm) with <15% macro-throat participation. These microstructural divergences fundamentally governed contrasting production behaviors. Wuqi wells achieved higher initial flow rates (15–20 m³/d) with 60–70% water cut, yet maintained stable production through effective displacement systems enabled by dominant macropores. Conversely, Dingbian wells produced lower yields (5–8 m³/d) with 75–85% water cut, experiencing rapid 30–40% initial declines that transitioned to prolonged low-rate production phases. This petrophysical framework provides critical insights for optimized development strategies in heterogeneous tight sandstone reservoirs, particularly regarding water management and enhanced oil recovery potential. Full article