Abstract CO2 huff and puff (HnP) is widely recognized as an effective strategy for enhancing shale oil recovery. However, a comprehensive understanding of its multi-scale performance in fractured shale reservoirs remains limited. To bridge this gap, this study investigates the enhanced oil recovery (EOR) potential of CO2 HnP, with a particular focus on the influence of fractures. A series of large-diameter core HnP experiments, combined with online nuclear magnetic resonance (NMR) analysis, were conducted to evaluate both the macroscopic production characteristics and microscopic pore-scale mobilization characteristics under with and without fractures conditions. The results demonstrated that the presence of fractures significantly enhances shale oil recovery by increasing the CO2 injection capacity, facilitating expansion, and interconnection of isolated fractures, and promoting deeper CO2 diffusion into shale matrix, thereby improving seepage capacity. Additionally, fractures increase the total recovery rates in micropores and mesopores by 8.59% and 10.26%, respectively, while their effect on macropores is negligible (only a 0.14% increase). These findings suggest that fractures play a crucial role in mobilizing oil within smaller pores. This study provides valuable insights into the mechanisms of CO2 HnP in a matrix-fracture system and highlights the importance of fracture networks in optimizing shale oil recovery.
To investigate the deterioration of impact toughness in Q690 high-strength steel welded joints, a systematic study was conducted using Gleeble thermal simulated tests combined with Charpy impact tests, microhardness measurements, and microstructural analysis. The research focused on the microstructural evolution in different zones of the welded joint and its influence on mechanical properties. The results indicate that the weld metal (WM) and coarse-grained heat-affected zone (CGHAZ) are the weakest regions of the joint. The CGHAZ exhibits significantly reduced impact toughness (72 J) due to grain coarsening and the formation of lath martensite/bainite, with fracture surfaces showing cleavage characteristics. The weld metal demonstrates inhomogeneous microstructures, leading to an average impact energy of only 79.2 J, much lower than that of the base metal (BM) and other sub-zones. In contrast, the fine-grained HAZ (FGHAZ) and intercritical HAZ (ICHAZ) exhibit improved impact toughness (up to 303 J), attributed to grain refinement and the dominance of granular bainite. Microhardness analysis further confirms that the increased hardness in the CGHAZ and WM is directly related to the formation of brittle and hard microstructures.
The manufacturing of single-crystal superalloy blades consistently aims to avoid grain boundary defects that compromise crystal integrity. Although slivers represent a significant type of grain boundary defect, their formation mechanisms remain inadequately defined. This study investigates sliver formation mechanisms, revealing that slivers in single-crystal blades extracted at a variable rate originate from dendritic fractures. Conversely, slivers in blades extracted at a constant rate stem from dendritic deformation. Temperature field simulations indicate that the cooling rate for blades withdrawn at variable rates varies significantly, generating higher thermal contraction stresses compared to those withdrawn at a constant rate. This increased stress precipitates dendrite fractures, leading to sliver formation. Following dendrite fractures or deformation, shrinkage cavities emerge, resulting from the obstruction of liquid flow by dendrite arms. Moreover, the impact of alumina protrusions in the mold on sliver formation is explored. This research advances our comprehension of dendritic evolution in sliver formation and offers theoretical insights for mitigating sliver defects in single-crystal blade production.
This study explores the friction stir welding (FSW) of thin aluminum sheets, focusing on alloys 1050 and 5754. FSW, a solid-state joining technique, offers advantages like minimal deformation and high joint strength, but optimizing welding parameters is crucial for sound welds. In order to investigate the optimum welding parameters, the Taguchi method was employed, in which key parameters such as rotational and welding speed were optimized to enhance tensile strength and weld quality. The tensile testing of the welded specimens revealed that the optimal combination—1000 RPM rotational speed and 250 mm/min welding speed—produced the highest tensile strength and weld quality. The results highlight the importance of parameter optimization in ensuring strong, stable welds, with rotational speed having the most significant influence. Additionally, excessive rotational speeds were found to weaken welds due to excessive heat input, while a slower welding speed contributed to greater weld stability.
In this paper, the differences in the wetting mechanisms of lignite dust and silica dust were investigated using molecular dynamics simulations and quantum chemical methods. A water-surfactant-lignite coal dust/silica dust model was constructed and the interaction energy, radial distribution function (RDF), mean square displacement (MSD), self-diffusion coefficient (D) and relative number density among the components within 100 ps after equilibrium were investigated by molecular dynamics simulations. The results show that the interaction energy and self-diffusion coefficient between cetyl trimethyl ammonium bromide(CTAB) solution and lignite molecules are larger and the peak value of relative number density is higher compared to silica dust; by comparing the electrostatic potential of lignite dust with that of silica dust, the magnitude of the potential difference of SiO2 varies widely, which shows that the size of the potential difference between the dust surface and water molecules due to active agent adsorption is one of the factors affecting the difference in surface wettability, but the functional groups in lignite increase the intermolecular interactions and play a significant role in the wetting process.
Longbiao Feng, Hongxian Shen, Lunyong Zhang
et al.
The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn (EV32) alloy. The findings indicate a significant increase in the ignition point of the alloy upon Y addition, notably reaching 813.9 °C for the EV32–3Y (wt.%) alloy. Additionally, the calculated residual stresses of the Y2O3 and Gd2O3 films were 2.732 GPa and 2.569 GPa respectively, showcasing a distinct correlation between Y concentration and improved fire resistance. This enhancement can be attributed to the formation of denser oxide films, especially Y2O3 and Gd2O3, effectively reducing the susceptibility of the oxide film to thermal stress-induced tearing. The study elucidates the vital role of Y addition in enhancing fire resistance, thoroughly investigating the mechanisms that impact both the formation of oxide films and ignition within the alloy structure. These findings not only contribute to a deeper comprehension of magnesium alloy performance under high-temperature conditions but also offer valuable theoretical guidance for enhancing its fire resistance through alloy design and application.
Serik D. Fazylov, Oralgazy A. Nurkenov, Zhangeldy S. Nurmaganbetov
et al.
In this study, the synthesis and properties of β-cyclodextrin-functionalized silver nanoparticles and their loading with a drug component are considered. β-Cyclodextrin was used as a reducing agent and stabilizer in the preparation of silver nanoparticles. The use of β-CD-AgNPs in loading molecules of the alkaloid cytisine (Cz) and its O,O-dimethyl-N-cytisinilphosphate (CzP) derivative, which have pronounced antiviral properties, was studied. The formation of β-CD-Cz-AgNPs and β-CD-CzP-AgNPs was confirmed by UV spectroscopy and X-ray diffraction spectroscopy. Scanning electron microscopy and transmission electron microscopy showed that the obtained β-CD-Cz-AgNP and β-CD-CzP-AgNP nanocomposites were well dispersed with particle sizes in the range of 3–20 nm. <sup>1</sup>H-, <sup>13</sup>C-NMR and COSY, HMQC, HMBC and Fourier transform infrared spectroscopy revealed the reduction and encapsulation of AgNPs by β-Cz, and the TEM imaging results showed an increase in the size of nanoparticles after the introduction of cytisine and its phosphorus derivative. The kinetic parameters of the thermal degradation process of β-CD, Cz, CzP and their inclusion complexes Cz(CzP)-β-CD-AgNPs under isothermal conditions, which ensure the preservation of the kinetic triplet, were determined. The differences in the mechanism of thermal decomposition of the studied materials are described by the parameters of the Šesták–Berggren model (m and n), which demonstrated differences for different compounds: for β-CD, the values of the parameters m and n are 0.47 and 0.53, respectively, while for CzP-β-CD-AgNPs they reach values of 0.66 and 1.34. These results indicate differences in the mechanism of thermal decomposition of the studied materials.
AbstractDigitalization and automation technology offer new possibilities to increase productivity and obtain higher levels of autonomy in mining operations. Introducing autonomous systems into mining is not only a technical problem in terms of effectiveness and efficiency, nor a problem of safety in human-automation interactions. The systems also need to be designed and developed so that they foster healthy and attractive working environments. The design and development phase of new mining technology has not been extensively studied previously. To fill this knowledge gap, we investigated technology developers’ basic assumptions about humans and their interactions with the technology they develop. We conducted five semi-structured workshops within an EU funded project concerned with developing digitalization and automation solutions for the mining industry. The data suggests that many critical functions will still be under human control in future mining systems. The results also indicate increased complexity in the interaction between autonomous systems and humans as the technology becomes more advanced. As a result, we suggest that a human perspective, based on sociotechnical principles, should not only be considered in implementing the technology at mines but also in the early conceptual phases of developing and designing the technology. This will ensure healthy and attractive work environments in the future mining industry.
High entropy alloys (HEAs) were prepared using a vacuum arc melting method. The effect of Mo partially substituting Ni on the crystal structure and corrosion behaviors was studied. The results show that the HEAs exhibited a multiphase complex crystal structure which was composed of a BCC matrix and several intermetallic phases. The HEAs showed good corrosion resistance despite multiphase heterogeneity. But cyclic polarization showed that the HEAs were susceptible to pitting corrosion. Selective corrosion of Cr-depleted phases after polarization tests was attributed to the galvanic corrosion between Cr-depleted and Cr-rich phases. The spontaneous passive films on the HEAs surface were characterized by p-type semiconductor. Existence of Mo element of the HEAs accelerated passivation reaction kinetics, improved the stability of passive film, accordingly, acquired better general and pitting corrosion resistance.
The thread rolling process is an advanced bulk forming process to produce thread parts. The superior performance of the formed thread parts as compared to those manufactured by the cutting process closely relates to the microstructure of the formed thread parts. In this study, a finite element model (FEM) was established to analyze the deformation characteristics in the thread rolling process. The viscoplastic self-consistent (VPSC) simulation was coupled with FEM to investigate the texture evolution and distribution. Besides, the thread rolling experiments were carried out, and the microstructure on different positions of formed thread parts was observed to analyze the characteristics of the microstructure and verify the simulation. Simulation and experimental results showed that the materials were mainly stretched on the bottom and top of formed thread parts, while on the flank they were obviously rotated. On the bottom and the flank of the formed thread parts, the grains were severely refined, and an obvious γ fiber texture was formed. On the top of the formed thread part, {001} <110> texture was observed.
Vladimir Promakhov, Alexey Matveev, Olga Klimova-Korsmik
et al.
This research work studies the structural phase parameters and physicomechanical properties of metal-matrix composite materials based on a Ni–TiB<sub>2</sub> system obtained by additive manufacturing (specifically, direct laser deposition). The properties of the composites obtained were investigated at high temperatures (up to 1000 °C). The feasibility of the fabrication of a composite nanostructure of alloy with advanced physicomechanical properties was shown. The introduction of reinforcing TiB<sub>2</sub> particles into an Inconel 625 matrix was confirmed to increase the microhardness and tensile strength of the material obtained. Apparently, the composite structure of the samples facilitates the realisation of several strengthening mechanisms: (1) a grain boundary mechanism that causes strengthening and dislocation movement; (2) a mechanism based on the grain structure breakdown and Hall–Petch relationship realisation.
The effect of cold pre-deformation combined with ageing treatment on age hardening behavior and associated intergranular corrosion (IGC) resistance of an Zn-bearing 5xxx aluminum alloy is investigated in this study. Results reveal that the strength of the alloy is improved greatly by the prior cold deformation basing on the synergistic effect of work hardening and ageing strengthening. With the combination of cold pre-deformation and ageing treatment, the peak yield strength of the alloy is 314.7 MPa, which increases by 110% than that of the T6 treated alloy. Moreover, the intergranular microstructure such as grain boundary precipitates can be optimized by coordinating the pre-deformation and ageing treatment. Hence, Al–Mg–Zn alloy with high strength and excellent IGC resistance can be obtained by combining the prior cold deformation and ageing treatment.
In the present paper, the excavation of the energetic approach that estimates the fatigue crack initiation life of metal is conducted for H62 brass. The benefit of the energetic approach is the division of the actual applied strain range Δε into two parts, that is, a damage strain range Δεd that induces fatigue damage within the metal, and an undamaged strain range Δεc, which does not produce fatigue damage of the metal and corresponds to theoretical strain fatigue limit. The brightness of this approach is that the undamaged strain range Δεc can be estimated by the fundamental conventional parameters of metal in tensile test. The result indicated that the fatigue crack initiation life of H62 brass can be estimated by this approach successfully.
Mining engineering. Metallurgy, Materials of engineering and construction. Mechanics of materials