Search Results (325)

Deep coalbed methane (CBM) reservoirs exhibit ultralow permeability, high in situ stress, and pronounced stress sensitivity. The resulting feedback between reservoir deliverability, wellbore liquid transport, and surface choking cannot be represented reliably by isolated reservoir or wellbore calculations. This study develops an integrated reservoir–wellbore–choke coupling model for deep CBM wells. The reservoir submodel adopts a dual-porosity, single-permeability formulation for matrix-to-natural-fracture mass transfer, incorporates hydraulic fractures through non-neighboring connections, and accounts for Langmuir adsorption/desorption and effective-stress-dependent permeability. Gas–liquid flow in the tubing or annulus is calculated with the Beggs–Brill correlation, whereas critical and subcritical flow through the wellhead choke is evaluated with the Sachdeva mechanistic model. Bottom-hole flowing pressure (BHP) serves as the coupling variable in a partitioned sequential-iterative scheme. For each time step, the reservoir model predicts gas and water rates at a prescribed BHP; these rates are passed to the choke and wellbore models, whose returned BHP updates the reservoir boundary until convergence. Newton iterations solve the reservoir equations, and the critical liquid-carrying rate identifies the end of stable natural flow and the onset of liquid-loading risk. Application to Well H1 yielded agreement scores of 80.99%, 79.93%, 94.17%, and 90.48% for the gas rate, water rate, BHP, and wellhead tubing pressure, respectively, with an overall mean of 86.39%. Gas content governed the mid- to late-time deliverability, while tubing and choke sizes controlled the trade-off between friction loss, drawdown, and liquid unloading. A 2–3/8 in tubing string combined with a 12 mm choke provided the most balanced performance. The model supports life-cycle production forecasting and integrated completion and production optimization for deep CBM wells. Full article

To address the key problems of the dual-phase magnesium–lithium alloy LAZ931, such as easy corrosion, flammability and low strength, an AA6061 protective coating was fabricated on LAZ931 alloy via cold spraying to form an Al6061/LAZ931/Al6061 sandwich structure. The strengthening mechanism of the coating on interfacial microstructure, mechanical properties, creep behavior and corrosion resistance was systematically investigated. The results show that the cold-sprayed AA6061 coating is compact and uniform with a low porosity of 0.3% and surface roughness of 37.02 μm, which significantly improves the combustion resistance and corrosion resistance of the alloy. The coating/substrate interface exhibits jagged and tight bonding without obvious cracks or delamination. Abundant dislocations and Al–Mg–Li composite precipitates form at the interface, which effectively strengthen the interfacial bonding and enhance the tensile and yield strengths. Room-temperature creep tests reveal that the creep behavior of the composite is dominated by the LAZ931 matrix, and the coating remains intact and well-bonded throughout creep deformation without compromising the creep resistance. Electrochemical impedance spectroscopy shows that the coating increases the low-frequency impedance by more than two orders of magnitude, greatly elevating corrosion resistance. This study confirms that a cold-sprayed AA6061 protective layer can comprehensively enhance LAZ931 alloy through interfacial bonding, microstructural strengthening and protective barrier effects, providing a new strategy for protection and toughening of ultra-light Mg-Li alloys. Full article

Fractured shale oil reservoirs possess ultra-tight matrix pores and suffer unsatisfactory oil recovery under conventional exploitation, while systematic comparisons among CO₂ flooding, CO₂/CH₄ mixed gas flooding, and multi-component thermal fluid (MTF) flooding remain insufficient for guiding field-parameter design. This work establishes a matrix–fracture coupled dual-porosity compositional model and adopts a single-variable method to quantitatively clarify how injection composition, reservoir permeability, injection pressure, and temperature govern sweep efficiency and the oil recovery factor, as well as the synergistic EOR mechanisms of different displacement fluids. The results show that CH₄ acts as a weak active component with limited crude-oil-swelling and displacement capacities; MTF yields the maximum recovery via thermal viscosity reduction, molecular diffusion, and crude oil swelling, whereas pure CO₂ is reported to have comprehensive cost advantages according to field-scale practical experience (no quantitative techno-economic calculation is carried out in this work). An injection miscibility threshold of 20–30 MPa is identified, with declining incremental oil yield beyond this range. According to published engineering observations, excessively high injection temperatures may trigger liquid-phase permeability impairment, which is not captured in the present model. The oil recovery factor positively correlates with permeability within 0.02–0.1 mD, and volumetric fracturing is indispensable for ultra-low-permeability matrices to expand seepage pathways. This study delivers quantitative theoretical references for displacing-agent screening and injection–production parameter optimization in fractured shale oil reservoirs. Full article

Shale gas is a major unconventional energy resource in China. Its low porosity and permeability require large-scale volumetric fracturing to create conductive fracture networks. However, most induced fractures are propped discontinuously because shale reservoirs are geometrically complex. Fracture conductivity and proppant placement efficiency therefore directly control stimulation performance. Following SY/T 6302-2009, this study used linear flow-through experiments and a large-scale visual fracture simulation system to investigate the effects of proppant particle-size distribution, injection sequence, flow rate, and closure pressure on fracture conductivity and placement. The results show that the 20/40:40/70 mesh dual-particle-size combination at a 3:2 ratio provides the best overall performance. A fine-particle content of no more than 16.7% limits conductivity loss and improves the match between particle size and fracture aperture. Multilayer placement at fracture corners distributes high-stress loading and maintains conductivity. Injecting 70–140 mesh fine proppant before 40–70 mesh coarse proppant at 3.6 m³/h improves transport distance, coverage, and placement uniformity. The optimized scheme maintains stable conductivity at closure stresses of 10–80 MPa and achieves at least 95% propped-area coverage. These findings provide experimentally supported parameters for discontinuous propping and can inform shale gas fracturing design. Full article

Biomass-derived nanoengineered carbon materials have emerged as key platforms in environmental technologies due to their high surface area, electrical conductivity, chemical stability, and sustainable synthetic route starting from renewable feedstock. This broad family comprises dimensionally nanoscale materials, such as carbon dots, carbon nanofibers, and graphene-based structures, as well as biochars, hydrochars, activated carbons, and related porous carbonaceous materials whose pore architecture, surface chemistry, or defects are deliberately engineered at the nanometer scale. Beyond their traditional role as passive supports, these materials can actively regulate adsorption phenomena, charge transport, and catalytic microenvironments through precise control of heteroatom doping, graphitic domains, and hierarchical porosity. Among current environmental priorities, carbon dioxide (CO₂) management represents one of the most pressing challenges. Biomass-derived nanocarbons offer tunable adsorption sites for selective CO₂ capture while simultaneously serving as active matrices for catalytic conversion. Tailored doped-carbon frameworks can stabilize key reaction intermediates, suppress competing pathways such as hydrogen evolution, and promote selective transformation into fuels and high-value chemicals. In addition, these materials are excellent hosts for atomically dispersed metals, dual-site catalysts, and semiconductor hybrids used in electrochemical and photocatalytic CO₂ reduction. By combining renewable sourcing with nanoscale control of reactivity, carbon materials create a bridge between environmental remediation and carbon valorization. This review critically examines recent progress in biomass-derived nanoengineered carbon materials for integrated CO₂ capture and conversion, with emphasis on structure-property-performance relationships, mechanistic roles, scalability, and sustainability. Particular attention is also devoted to catalytic conversion and electrochemical CO₂ sensing, where carbon-based and hybrid interfaces enable the transduction of CO₂ recognition into measurable electrical responses. These materials represent a promising yet underexplored pathway toward circular carbon management and the development of next-generation low-carbon chemical technologies. Full article

This study employs COMSOL Multiphysics to build a hydromechanical (HM) coupling model for shale gas production based on classic poroelasticity and Darcy’s law. Considering effective stress variation during depletion, a stress-dependent permeability model is incorporated into the dual-porosity framework. Numerical simulations evaluate three extraction methods—single-well, dual-well, and single-well with hydraulic fracturing—on pressure in the fracture system, permeability evolution, and gas production. The results show consistent fracture permeability decline with extraction, more pronounced in early stages. Single-well hydraulic fracturing accelerates pressure reduction to 6.7 × 10⁵ Pa after one year, equivalent to five years of conventional production. The dual-well model exhibits negligible boundary effects but notable inter-well interference on permeability. These findings provide a preliminary reference for well spacing analysis and fracturing design in shale gas development. Full article

Shale gas reservoirs are characterized by low permeability, nanoscale pore structures, and complex fracture networks. Multistage fractured horizontal wells are an important technology for commercial shale gas development. However, many shale gas productivity models primarily emphasize gas transport within the reservoir and fracture system, while pressure variations caused by frictional losses along the horizontal wellbore are often simplified or treated separately. To address this issue, this study develops a fully coupled multiscale dual-porosity numerical model that integrates the shale matrix, hydraulic fractures, and horizontal wellbore within a unified simulation framework. The model incorporates key physical mechanisms governing shale gas transport, including Knudsen diffusion, Langmuir adsorption–desorption, stress sensitivity, and non-Darcy flow in fractures. Meanwhile, the Darcy–Weisbach equation is introduced to describe wellbore frictional pressure losses. The reliability of the proposed model is validated through history matching with field production data from the Changning shale gas reservoir. The results demonstrate that neglecting wellbore friction losses leads to a 30–50% overestimation of horizontal well productivity, indicating that wellbore friction has a significant impact on fracture flow distribution and productivity prediction. Furthermore, an exponent factor r is introduced to characterize and evaluate non-uniform fracture placement patterns. The results show that toe-dense fracture placement can increase cumulative gas production by approximately 37.8% compared with uniform fracture placement when r = 1.10, which yields the highest cumulative gas production among the tested cases. However, the additional production benefit becomes substantially smaller after the initial increase and remains relatively stable as r further increases. This study improves the understanding of friction-induced heel-to-toe effects and provides an effective numerical approach for productivity prediction and fracture placement design in shale gas horizontal wells. Full article

Coal-bearing tight gas and deep coalbed methane (CBM) widely co-occur in China, and integrated commingled production outperforms separate development. Conventional separated simulation fails to capture coupled reservoir–wellbore gas–water flow. This study develops an integrated geomechanical coupled numerical model with multi-scale fractures and multi-phase wellbore flow: tight gas reservoirs use a stress-sensitive single-porosity model, deep CBM adopts a dual-porosity model for matrix desorption, and EDFM characterizes non-Darcy flow in hydraulic fractures. The Gray gas column and liquid column methods calculate layered bottomhole pressure according to reservoir vertical distribution, and matrix bordering solves the whole coupled system. Validated by field data of Well C-1 in Shanxi, the model yields average relative errors of 8.76% for daily gas output and 2.92% for daily water output. Sensitivity analysis on Well C-2 indicates vertical reservoir stacking controls interlayer pressure difference, and commingled gas curves show dual peaks with shifting dominant gas sources over production stages. A 3.9% rise in deep coalbed methane gas content significantly boosts mid-term peak production and cumulative gas output, making reservoir gas content the dominant geological factor governing commingled production performance. A 120.0% increase in tight gas saturation only delivers a slight uplift in cumulative production under low-porosity conditions. Elevated reservoir stress sensitivity triggers a cumulative gas production reduction of over 50%. Cumulative gas output varies proportionally with hydraulic fracture length, while fracture network width brings mismatched production improvement due to pressure drawdown funnel effects. Therefore, hydraulic fracturing operations should prioritize extending artificial fractures to expand the drainage area of commingled wells. Schemes with constant bottomhole flowing pressure and constant gas rate exert marginal influences on ultimate cumulative production and can be flexibly switched on site. To stabilize daily gas deliverability throughout the early, middle and late production stages, a bottomhole pressure drawdown rate of 0.05 MPa/d or a fixed daily gas rate of 4000 m³/d is recommended. This work provides theoretical support for optimizing commingled development of superimposed tight gas and deep CBM reservoirs. Full article

Chemical glycolysis can convert waste poly(ethylene terephthalate) (PET) into bis(2-hydroxyethyl) terephthalate (BHET), but recyclable heterogeneous catalysts derived from circular carbon sources and showing low metal release remain limited. Here, post-consumer expanded polystyrene (EPS) was transformed into a hypercrosslinked polymer (HCP) and carbonized with Fe to produce Fe@graphitic-carbon (Fe@C) catalysts for PET glycolysis. The catalysts are denoted mFe@EPS-HCP₈₀₀, where m represents the nominal Fe loading (wt.%), and 800 is the carbonization temperature (°C). The optimized 5Fe@EPS-HCP₈₀₀ contained graphitic carbon layers, bamboo-like carbon nanotube (CNT) domains, hierarchical porosity, and Fe-rich domains associated with graphitic carbon coverage. Under atmospheric-pressure conditions (PET, 2.00 g; ethylene glycol, 20.00 g; catalyst, 0.20 g; 200 °C; 2 h), it achieved complete PET conversion and 94.6% BHET yield. The catalyst also maintained BHET yields of ca. 90–94% over ten reuse runs, and post-reaction microscopy confirmed the retention of graphitic carbon layers and Fe-containing domains. Fe was below the detection limit in the product solutions for the 1, 3, and 5 wt.% Fe catalysts, whereas 7Fe@EPS-HCP₈₀₀ released 9.1 mg kg⁻¹ Fe, consistent with incomplete carbon coverage at excessive Fe loading. Conversion profiles followed an Avrami–Erofeev/Weibull model, giving an apparent activation energy of 205.6 kJ mol⁻¹. The data support a two-stage pathway in which external graphitic carbon/CNT domains promote primary PET chain scission to soluble oligomers, followed by Fe@C interfacial secondary glycolysis to BHET. This work demonstrates dual waste-polymer valorization by using EPS waste as catalytic infrastructure for PET chemical recycling. Full article

This study aims to reveal the formation mechanisms of typical defects in copper alloy castings and propose targeted process optimization strategies for production quality control. Taking the ZCuSn10P1 tin bronze outer layer of copper-clad iron core as the core research object, typical fracture and burr defects in actual mass production were systematically analyzed via multi-scale characterizations including SEM and EDS. Results show that fracture arises from abnormal Sn segregation and coarse hard-brittle δ phase, while burrs stem from insufficient matrix hardness during machining. Shrinkage cavity and porosity defects of aluminum bronze are further comparatively analyzed. A dual strategy of composition regulation and process optimization is put forward, which can effectively suppress defects and improve product qualification rate. This study provides a reliable reference for quality control and technical upgrading of copper alloy castings. Full article

The escalating demands of pulsed power technology and high-energy-density capacitors necessitate dielectric ceramics with simultaneously enhanced breakdown reliability and microstructural homogeneity. Herein, Al₂O₃-MgAl₂O₄ composites were fabricated via a solid-state reaction using 80 wt% α-Al₂O₃ with kaolin/MgO mass ratios of 7:1, 4:1, and 1:1. XRD presents a dual-pathway spinel formation mechanism. SEM reveals 2–5 μm columnar spinel grains uniformly dispersed at grain boundaries. Porosity decreased from 4.29% to 2.69% while grain size increased from 3.35 to 5.64 μm as MgO content rose. Weibull analysis (n ≥ 10) showed that the 4:1 group achieved optimal dielectric reliability with a characteristic breakdown strength of 17.74 kV/mm and a Weibull modulus of 16.07, representing 8.76% and 20.93% improvements over the 7:1 (16.31 kV/mm, m = 24.58) and 1:1 (14.67 kV/mm, m = 15.37) groups, respectively. The 4:1 composition balanced grain boundary pinning (4.61 μm) and residual porosity (3.59%), maximizing interfacial charge scattering. Excess MgO (1:1) introduced residual Mg²⁺ into the glassy phase, inducing ionic conduction and premature breakdown. This study establishes a quantitative “microstructural composition–defect size distribution–dielectric breakdown” correlation, providing a theoretical foundation for microstructural optimization of low-cost alumina-based energy storage ceramics. Full article

With the gradual decline in conventional oil and gas production growth, unconventional natural gas has become a strategic alternative for hydrocarbon supply. Coal-rock gas (CRG) represents a deep unconventional gas resource with huge potential. Major exploration breakthroughs of CRG have been achieved in China, while systematic research targeting CRG as an independent gas reservoir is still lacking internationally. After effective commercial development, CRG serves as an important supplementary energy source for the domestic natural gas supply. Existing logging evaluation methods exhibit notable deficiencies, as porosity is typically estimated by fitting well logging data or proximate analysis data, resulting in limited accuracy. To address the lack of a dedicated logging volumetric model, ambiguous coal-matrix framework parameters, and substantial porosity calculation errors in deep CRG reservoirs, this study investigates the medium–high rank No. 8 coal seam of the Benxi Formation in the central-eastern Ordos Basin. From an oil and gas reservoir logging evaluation perspective, multi-scale experiments were conducted to systematically characterize the material composition and microscopic characteristics of the coal rock. From the perspective of oil and gas reservoir logging evaluation, a three-component logging volumetric model, consisting of a coal matrix, inorganic minerals, and pore fluids, was constructed, and the corresponding coal-matrix framework parameters were calibrated. The results demonstrate that coal rock is an organic–inorganic composite system, with organic macerals dominated by vitrinite (averaging 59.1%) and inertinite (27.1%). The sum of fixed carbon and volatiles exhibits strong correlations with total organic carbon (TOC) and micro-CT-derived coal-matrix content, yielding determination coefficients of 0.99 and 0.95, respectively, which validates the reliability of the multi-scale quantitative composition characterization. The coal-matrix framework parameters are non-constant: density ranges from 1.08 to 1.56 g·cm⁻³, acoustic slowness from 281 to 425 μs·m⁻¹, and compensated neutron from 39% to 79%. Borehole enlargement severely affects compensated density and neutron logs but has negligible interference with acoustic slowness. Notably, inertinite content shows a significant negative correlation with the acoustic-slowness framework response (R² = 0.80), indicating that structurally dense inertinite is a key intrinsic factor controlling the elastic response of the coal matrix. For porosity evaluation, a dual-variable framework model is proposed. The core novelty of this method is that it simultaneously incorporates variations in inorganic mineral content and differences in inertinite proportion within organic components as dynamic framework constraints, breaking through the limitation of the conventional constant-matrix assumption. The acoustic-slowness-based model achieves an average relative error of merely 7.1%, effectively resolving the large errors inherent in conventional fitting methods. The dedicated coal-rock logging evaluation system established in this study overcomes the limitations of fixed framework models, offers a scientific basis for fine-scale interpretation and resource assessment of deep CRG reservoirs, and provides a valuable reference for evaluating analogous reservoirs. Full article

High-entropy alloys (HEAs) offer attractive combinations of mechanical performance, thermal stability, and compositional flexibility, making them promising candidates for advanced structural applications. Laser-based additive manufacturing, particularly laser powder bed fusion (LPBF) and laser-directed energy deposition (LDED), enables the fabrication of geometrically complex HEA components with non-equilibrium microstructures. However, the distinct thermal histories of LPBF and LDED, with typical cooling rates of approximately 10⁵–10⁷ K s⁻¹ and 10²–10⁴ K s⁻¹, respectively, strongly govern solidification behavior, elemental segregation, residual stress development, defect formation, and mechanical properties. Although previous reviews have discussed additively manufactured HEAs, an integrated framework linking composition design, printability, LPBF/LDED processing, microstructural evolution, post-processing, and industrial qualification remains limited. Therefore, this review establishes a unified composition–process–structure–property framework for laser additively manufactured HEAs. Fundamental HEA concepts, LPBF/LDED process characteristics, solidification behavior, phase formation, defect evolution, and mechanical performance from ambient to elevated temperatures are systematically discussed across representative FCC, refractory, and dual-phase HEA systems. This review emphasizes that printability should be considered during alloy design by correlating composition-dependent solidification characteristics, cracking susceptibility, phase stability, and defect formation with mechanical performance. Post-processing treatments are shown to modify residual stress, microsegregation, precipitation behavior, porosity, and deformation mechanisms, although their benefits must be balanced against thermal softening or brittle phase formation. Finally, CALPHAD, integrated computational materials engineering (ICME), machine learning (ML), and in situ monitoring are identified as promising tools for accelerating alloy and process optimization, while reproducible process windows, defect-control criteria, databases, and qualification protocols remain essential for industrial implementation. Full article

To tackle the low nitrogen-use efficiency, water scarcity, and insufficient forage supply in improved grasslands in arid Northwest China, a two-factor field trial involving three biochar dosages (0, 10, 20 t ha⁻¹) and two nitrogen (N) application rates (0, 225 kg ha⁻¹) was conducted on mountain grassland in Xinjiang, with Onobrychis viciifolia and Bromus inermis as test forages. Soil physicochemical traits, soil–forage and water–nitrogen dynamics, forage productivity, and economic returns were determined, and partial least squares path modeling (PLS-PM, GoF = 0.373) was conducted to quantify the regulatory pathways. Co-treatments with biochar and N markedly lowered soil bulk density and elevated porosity, soil organic carbon, and the available N pool; application of biochar deferred the peak of soil available N and prolonged fertilizer efficacy by more than seven days. Forage total nitrogen- and water-use efficiency peaked at the first cutting, with the B1N1 treatment (10 t ha⁻¹ biochar + 225 kg ha⁻¹ N) boosting water-use efficiency by 45.2%. O. viciifolia exhibited optimal performance under B1N15, while B2N15 (20 t ha⁻¹ biochar + 225 kg ha⁻¹ N) was more favorable for B. inermis. The B1N15 regime achieved the highest net profit of CNY 12,747.99 ha⁻¹, but high biochar input cut economic gains by 14.1%. The PLS-PM model uncovered a dual regulatory mechanism: combined amendments directly optimized soil microhabitats, and soil water–nitrogen conditions served as a central mediator to facilitate biomass accumulation and economic gains through cascading soil–vegetation transmission, without direct impacts on vegetation productivity or economic outputs. This research provides a scientific reference for the use of fertilization in the sustainable management of arid improved grasslands. Full article

The exploitation of deep coalbed methane is of great significance for easing China’s energy supply pressure and realizing the “Dual Carbon” goals. However, local grid refinement simulation methods for coalbed methane cannot well capture the characteristics of deep coalbed methane reservoirs, including strong stress sensitivity and high brittleness. To tackle this issue, this paper develops a novel numerical simulation approach dedicated to deep coalbed methane development. Integrated with the fluid–solid coupling effect in rock mechanics, this approach considers the interporosity flow between matrix pores and cleat fractures as well as that between cleat fractures and hydraulic fractures, and establishes a multi-dimensional coupled simulation framework on the basis of the dual-porosity single-permeability model and embedded discrete fracture model. Simulation results show that compared with the local grid refinement model, the daily gas production curve simulated by the proposed method is more consistent with the actual field curve. The local grid refinement method fails to accurately characterize the specific morphology of hydraulic fractures. The average relative error of the local grid refinement model reaches 25.61%, while that of the model in this paper is only 7.54%, representing an accuracy improvement of 18.07%. Sensitivity analysis draws the following conclusions: reservoir gas content is the dominant geological factor governing deep coalbed methane output, and raising reservoir gas content can boost cumulative gas production by 45.77%; hydraulic fracture length mainly affects gas production performance in the middle and late production stages, while fracture conductivity dominates early-stage productivity. This method can fully characterize the coupled flow behaviors of three types of media (matrix pores, cleat fractures and hydraulic fractures), and offers solid technical support for productivity forecasting and development scheme optimization of deep coalbed methane reservoirs. Full article