Search Results (236)

Carbonate reservoirs in the Shunbei area develop pronounced fracture networks after acidized hydraulic fracturing and thus have the potential to be repurposed as underground gas storage (UGS) after hydrocarbon depletion. Characterizing their mechanical behavior is essential for safe UGS operation; however, deep to ultra-deep natural cores are difficult to obtain, and conventional macroscopic tests often cannot provide parameters that meet engineering requirements. To address this issue, nanoindentation combined with QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) was employed to quantify microscale mineral distributions and the mechanical properties of the major constituents. The investigated rock is calcite-dominated (89.62%), with minor quartz (9.89%) and trace feldspar-group minerals (1.89%). Minerals are randomly embedded, and soft–hard phase boundaries are widely distributed. A finite–discrete element method (FDEM) model was then constructed and calibrated in ABAQUS. The discrepancies in uniaxial compressive strength and elastic modulus relative to laboratory results were 6.51% and 9.91%, respectively, indicating good agreement in both mechanical response and failure mode. Parametric analyses using three additional models with different mineral proportions show that damage preferentially initiates at mineral phase boundaries and stress concentration zones induced by end constraints. Microcracks then propagate and coalesce into a dominant compressive–shear band, and final failure is mainly governed by slip along the shear band with localized tensile cracking. With increasing quartz and feldspar contents, enhanced heterogeneity and a higher density of phase boundaries lead to a higher density of crack nucleation sites and increased crack branching, and the failure pattern transitions from a single shear-band–controlled mode to a more network-like fracture system. Moreover, macroscopic strength is not determined solely by the intrinsic strength of individual minerals; heterogeneity and phase-boundary characteristics strongly govern microcrack behavior, such that higher hard-phase contents may result in a lower peak strength. Full article

The development and utilization of unconventional shale oil and gas have enhanced the resilience of global energy security. Hydraulic fracturing is the primary method for enhancing unconventional shale oil and gas extraction. Previous studies have predominantly employed homogenized geomechanical models to simulate fracture propagation in rock masses. However, bedding planes and inhomogeneous mineral distributions introduce mechanical anisotropy in shale, rendering conventional homogenized models insufficient for accurately representing hydraulic fracturing in real reservoirs. For this, millimeter-scale indentation testing was employed to systematically quantify the depth-dependent distribution of mechanical parameters across varying bedding orientations, using fragmented shale samples obtained from the Qingshankou Formation of the Songliao Basin, northern China. Then, hydraulic fracturing simulations were performed using the mechanical properties derived from the indentation tests. The key findings include: (1) The elastic modulus of the Qingshankou Formation shale reservoir exhibits significant anisotropic properties in both the depth and bedding orientations. The elastic modulus measured parallel to bedding (10.23–65.08 GPa) is 28% higher than that measured perpendicular to bedding (9.60–47.24 GPa) due to shale bedding anisotropy. The mineralogical composition predominantly governs the depth-dependent anisotropy, with an elevated brittle mineral content increasing the elastic modulus and a higher clay content reducing it. (2) The simulation results reveal that the depth-dependent anisotropy of elastic modulus induces asymmetric hydraulic fracture propagation, with the fractures preferentially extending along the orientations exhibiting a higher elastic modulus. This behavior arises due to the enhanced brittleness and reduced deformation resistance of high-modulus rocks, facilitating fracture advancement. The study offers critical insights for hydraulic fracturing design and operational implementation in bedded shale reservoirs. Full article

To address the problems of strong roof integrity, severe energy accumulation, and difficult caving in thick and hard roofs, a three-dimensional numerical study on fracture propagation and pressure-relief control durisng segmented hydraulic fracturing was carried out based on the engineering geological conditions of the 6125-1 working face at the Haishiwan Coal Mine, Shaanxi Province, China. using the ABAQUS finite element platform coupled with Ins-coh cohesive elements. A systematic analysis was conducted to elucidate the effects of elastic modulus, Poisson’s ratio, injection rate, and fluid viscosity on fracture initiation, stress evolution, and fractured volume. The results show that for every 10 GPa increase in elastic modulus, the average fractured volume decreases by 8%, and the fracture width exhibits a marked reduction; increasing Poisson’s ratio enhances the lateral deformation compatibility of the rock mass, raising the fracture width and volumetric growth rate by approximately 3% and 5%, respectively, although an excessively high Poisson’s ratio induces stress diffusion and reduces fracture stability. When the injection rate increases from 0.01 m³/s to 0.025 m³/s, the fractured volume increases by about 160%, and the maximum fracture width increases by 43%, whereas increasing fluid viscosity exerts a limited influence on volumetric growth but is conducive to stabilizing fracture morphology. Field observations via borehole imaging and seepage confirm full fracture connectivity within the roof and the formation of a continuous rupture zone, promoting timely roof breakage and caving along the dip direction and thereby creating favorable conditions for reducing rockburst hazards at the working face. This study clarifies the mechanical mechanisms and multi-parameter coupling laws governing hydraulic fracture propagation in thick and hard roofs, providing a theoretical basis and engineering reference for roof pressure-relief control and rockburst-resistant design under similar geological conditions. Full article

The construction sector faces increasing pressure to reduce the embodied energy of building materials while valorizing industrial waste streams. This study evaluates the direct incorporation of post-industrial textile waste (100% cotton and cotton–polyester blends) in its native form to develop high-performance cementitious ceiling sheets. Composites were fabricated under a controlled hydraulic compaction pressure of 2.0 MPa, optimized to achieve matrix densification while preserving the integrity of the fibrous network. Viscoelastic recovery of the compressed fibers induced a hierarchical double-porosity architecture characterized by macro-voids and hollow fiber lumens. This microstructural evolution reduced thermal conductivity to 0.091 W/m·K, approximately 50% lower than commercial cement–fiber benchmarks—without compromising mechanical compliance. Scanning Electron Microscopy (SEM) revealed a mechanistic decoupling between water absorption and dimensional stability. Although the CP15 formulation (15 wt.% cotton–polyester) exhibited high moisture uptake (~21%), thickness swelling remained limited to 1.35%. This dimensional stability is attributed to the hydrophobic polyester framework, which bridges microcracks and constrains hygroscopic expansion within the cellulosic phase. The optimized CP15 composite achieved a Modulus of Rupture (MOR) of 8.75 MPa, exceeding ISO 8336 Category C, Class 2 requirements. Despite increased thickness, the areal density (10.84 kg/m²) remains compatible with standard gypsum-grade suspension systems, eliminating the need for structural modification. These findings establish a scalable, direct-valorization strategy for circular construction materials delivering enhanced thermal insulation and robust performance under tropical climatic conditions. Full article

This paper focuses on determining the propagation velocity of pressure waves in closed hydraulic pipes. It is shown that under transient conditions, the propagation velocity of pressure waves depends, among other things, on temperature, pressure and the substitute bulk modulus. Accurate knowledge of the pressure wave propagation velocity is crucial for predicting pressure amplitudes during transient flows, including the phenomenon of water hammer. Excessive pressure amplitudes in the pipe can lead to critical pipeline damage and increased vibrations. Experimental studies were conducted to determine the pressure wave propagation velocity in flexible steel-braided pipes and in a rigid pipe over a wide range of internal pressures. The results of the analyses presented in the papers may be helpful to scientists and engineers when designing pipelines and selecting the strength parameters of pipes, taking into account the possible maximum values of internal pressure amplitudes. Full article

Rock mechanical parameters can provide fundamental data for the numerical simulation of hydraulic fracturing, aiding in the construction of hydraulic fracturing models. Due to the laminated nature of shale, constructing a hydraulic fracturing model requires obtaining the rock mechanical parameters of each lamina and the bedding planes. However, acquiring the mechanical parameters of individual shale laminas through physical experiments demands that, after rock mechanics testing, cracks propagate along the centre of the laminae without connecting additional bedding planes, which imposes extremely high requirements on shale samples. Current research on the rock mechanics of the Minfeng subsag shale is relatively limited. Therefore, to obtain the rock mechanical parameters of each lamina and the bedding planes in the Minfeng subsag shale, a numerical simulation approach can be employed. The model, built using PFC2D, is based on prior X-ray diffraction (XRD) analysis, conventional thin-section observation, scanning electron microscopy (SEM), Brazilian splitting tests, and triaxial compression tests. It replicates the processes of the Brazilian splitting and triaxial compression experiments, assigning initial parameters to different bedding planes based on lithology. A trial-and-error method is then used to adjust the parameters until the simulated curves match the physical experimental curves, with errors within 10%. The model parameters for each lamina at this stage are then applied to single-lithology Brazilian splitting, biaxial compression, and three-point bending models for simulation, ultimately obtaining the tensile strength, uniaxial compressive strength, Poisson’s ratio, Young’s modulus, brittleness index, and Mode I fracture toughness for each lamina. Simulation results show that the Minfeng subsag shale exhibits strong heterogeneity, with all obtained rock mechanical parameters spanning a wide range. Calculated brittleness indices for each lamina mostly fall within the “good” and “medium” ranges, with carbonate laminae generally demonstrating better brittleness than felsic laminae. Fracture toughness also clearly divides into two ranges: mixed carbonate shale laminae have overall higher fracture toughness than mixed felsic laminae. Full article

During the energy storage fracturing process of tight sandstone reservoirs, the pre-injection of fracturing fluid is used to supplement the formation energy, and the physical properties of rocks change under hydration. To reveal the damage mechanism of hydration on tight sandstone, the tight sandstone surrounding the Daqing Changyuan in the northern part of the Songliao Basin was taken as the research object. Through indoor static hydration experiments, combined with scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), Nano-indentation experiments, and other methods, the evolution laws of rock micro-pore morphology, microfracture parameters, Young’s modulus, hardness, and other mechanical indicators under different hydration durations and soaking pressures were systematically explored. The research results show that the water–rock interaction of acidic slick water fracturing fluid significantly changes the mineral composition and microstructure of mudstone and sandstone, controls the development of induced fractures, and degrades the micro-mechanical properties of rocks, with significant lithological differences. In terms of mineral evolution, the soaking time causes the clay minerals in mudstone to increase by up to 12.0%, while pressure causes the carbonate minerals in sandstone to decrease by up to 23.3%. In terms of induced fracture development, the induced fracture widths of sandstone and mudstone under 30 MPa of pressure increase by 122.4% and 85.7%, respectively. The fracture width of mudstone shows a trend of “increasing first and then decreasing” with time, while that of sandstone decreases monotonically. In terms of micro-mechanical properties, after soaking for 168 h, the Young’s modulus of mudstone decreases by up to 66.9%, much higher than that of sandstone (29.5%), while the decrease in hardness of both is similar (58.3% and 59.8%); the mechanical parameters at the induced fractures are only 53.0% to 73.6% of those in the matrix area, confirming the influence of microstructural heterogeneity. This research provides a theoretical basis and data support for optimizing hydraulic fracturing parameters, evaluating wellbore stability, and predicting the long-term development performance in tight sandstone reservoirs. Full article

Clarifying the mechanical properties and failure patterns of layered coal–rock combinations in coal-measure strata is critical to guiding hydraulic fracturing design in petroleum and mining engineering. This paper investigates the mechanical properties, failure patterns, and stress distributions of sandstone–coal–sandstone (SCS) and mudstone–coal–mudstone (MCM) combinations under different confining pressures and thickness ratios based on the 3D combined finite–discrete element method (3D FDEM). The results show that the mechanical strength of the SCS combination is higher than that of the MCM combination under the same conditions. As the thickness ratio increases, the overall peak stress and elastic modulus of the combination decrease gradually and eventually approach those of the pure coal. As confining pressure increases, the peak stress of layered coal–rock combinations rises gradually, plastic behaviors become increasingly prominent, and the failure mode of the mudstone layer transitions from tensile-dominated to shear-dominated. Under different thickness ratios and confining pressures, the coal layer in the combinations primarily develops shear-dominated cracks, whereas the sandstone layer mainly generates tensile-dominated cracks. An increase in confining pressure elevates the critical thickness ratio for sandstone layer failure in the SCS combination. Essentially, the changes in stress state caused by rock types, thickness ratios, and confining pressures are important reasons for the variations in the failure patterns of each layer in layered coal–rock combinations. The key findings of this paper are expected to provide theoretical guidance for the field design of petroleum and coal mine engineering. Full article

The mechanical response of geomembranes in hydraulic structures is strongly influenced by temperature variations, which alter both material stiffness and interface shear strength behavior. This study develops a non-linear, temperature-dependent tensile behavior constitutive model for a polyvinyl chloride (PVC) geomembrane and evaluates its implications for the stability of geomembrane-lined reservoir slopes. The empirical relationship was calibrated using tensile tests reported in literature for temperatures between 10 °C and 60 °C, reproducing the observed non-linear softening and modulus reduction with increasing temperature. A classical thermal dilation formulation was incorporated to simulate cyclic thermal expansion and contraction. The constitutive and thermal formulations were implemented in FLAC2D and applied to a 2H:1V covered geomembrane slope representative of dam lining systems. The results show that temperature-induced softening significantly increases tensile strain within the geomembrane. The model also shows that the lower surface interface friction angle of the geomembrane plays a significant role in the slope stability. Thermal cycle analysis demonstrates the accumulation of efforts resulting from the fatigue of the geomembrane. The proposed model provides a practical framework for incorporating thermo-mechanical coupling in design analyses and highlights the necessity of accounting for realistic thermal conditions in assessing the long-term stability of geomembrane-lined reservoirs. Full article

Pumped-storage power stations (PSPSs) are vital for grid stability, yet pump-turbines (PTs) operating in the S-shaped region often induce severe hydraulic instability. To reveal the mechanism of these self-excited oscillations, this study establishes a nonlinear mathematical model based on rigid water column theory and a cubic polynomial approximation of the PT’s nonlinear characteristics. Both analytical derivations and numerical simulations were conducted. Analytical results indicate that, in the absence of surge tanks, self-excited oscillations occur when the PT’s negative hydraulic impedance modulus exceeds the pipeline impedance. With a single surge tank, the system behaves analogously to the Van der Pol oscillator, exhibiting oscillations that converge to a stable limit cycle governed by system parameters. Numerical simulations for a dual-surge-tank system further reveal that, due to initial negative damping, the PT transitions to alternative stable equilibria. Crucially, the transition direction is governed by the polarity of the initial disturbance: negative perturbations lead to the regular turbine region, while positive ones lead to the reverse pump region. Additionally, pipe friction causes the steady-state discharge to deviate slightly from the theoretical static value, with deviations remaining below 2.96%. This work provides a theoretical basis for stability prediction in PSPSs. Full article

The deterioration of concrete hydraulic structures caused by chemical factors, seepage, and environmental stress necessitates advanced protective coatings that enhance durability, flexibility, and environmental sustainability. Conventional protective systems often exhibit limited durability under combined hydraulic, thermal, and chemical stress. In this study, a novel polyfluorosilicone-based coating system is presented, which integrates a deep-penetrating nano-primer for substrate reinforcement, a crack-bridging polymer intermediate layer for impermeability, and a polyfluorosilicone topcoat providing UV and weather resistance. The multilayer architecture addresses the inherent trade-offs between adhesion, flexibility, and durability observed in conventional waterproofing systems. Informed by a mechanistic study of interfacial adhesion and failure modes, the coating exhibits outstanding high mechanical and performance characteristics, including a mean pull-off bond strength of 4.56 ± 0.14 MPa for the fully cured triple-layer coating system, with cohesive failure occurring within the concrete substrate, signifying a bond stronger than the material it protects. The system withstood 2.2 MPa water pressure and 200 freeze–thaw cycles with 87.2% modulus retention, demonstrating stable mechanical and environmental durability. The coating demonstrated excellent resilience, showing no evidence of degradation after 1000 h of UV aging, 200 freeze–thaw cycles, and exposure to alkaline solutions. This water-based formulation meets green-material standards, with low volatile organic compound (VOC) levels and minimal harmful chemicals. The results validate that a multi-scale, layered design strategy effectively decouples and addresses the distinct failure mechanisms in hydraulic environments, providing a robust and sustainable solution. Full article

The durability of concrete in immersed tunnels is critically influenced by the coupled effects of stress, seepage, and chemical erosion, particularly in inland water environments. However, the spatio-temporal evolution of mechanical property degradation under such multi-field coupling remains insufficiently quantified. Unlike previous studies focused on “load-ion” or “hydraulic pressure-ion” dual coupling, this work introduces a complete stress–seepage–chemical tri-coupling that incorporates the critical seepage effect, representing a fundamental expansion of the experimental scope to better simulate real-world conditions. This study investigates the degradation mechanisms of concrete in the Shunde Lungui Road inland immersed tunnel subjected to such coupled erosion. A novel aspect of our approach is the application of the micro-indentation technique to quantitatively characterize the spatio-temporal evolution of the local elastic modulus at an unprecedented spatial resolution (0.5 mm intervals), a dimension of analysis not achievable by conventional macro-scale testing. Key findings reveal that the mechanical properties of concrete exhibit an initial enhancement followed by deterioration. This behavior is attributed to the filling of pores by reaction products (gypsum, ettringite, and Friedel’s salt) in the short term, which subsequently induces microcracking as the volume of products exceeds the pore capacity. Furthermore, increasing hydro-mechanical loading significantly accelerates the erosion process. When the load increases from 1.596 kN to 3.718 kN, the influence range of elastic modulus variation expands by 9.2% (from 5.186 mm to 5.661 mm). To quantitatively describe this acceleration effect, a novel load-acceleration erosion coefficient is proposed. The erosion rate increases from 0.0688 mm/d to 0.0778 mm/d, yielding acceleration coefficients between 1.100 and 1.165, quantifying a 10–16.5% acceleration effect beyond what is typically captured in dual-coupling models. These quantitative results provide critical parameters for employing laboratory accelerated tests to evaluate the ionic erosion durability of concrete structures under various loading conditions, thereby contributing to more accurate service life predictions for engineering structures. Full article

The development of deep coalbed methane is hindered by the strong heterogeneity of coal mechanical properties and complex hydraulic fracturing behavior. To identify the key factors controlling fracture geometry and permeability enhancement, this study developed a thermo-hydro-mechanical-damage coupled model within a COMSOL Multiphysics 6.3-MATLAB R2022b co-simulation framework, incorporating a Weibull random field to characterize mechanical heterogeneity. Sensitivity analysis demonstrates that tensile strength is the predominant factor governing both the fracturing damage zone and permeability-enhanced area, with its damage area extreme difference (10.094) and coefficient of variation (0.85) significantly surpassing those of other parameters. Poisson’s ratio and elastic modulus emerge as key secondary parameters, while compressive strength shows the lowest sensitivity. The parametric influences exhibit distinct patterns: tensile strength shows a strong negative correlation with damage and permeability-enhanced areas (up to 85% reduction), whereas the maximum permeability enhancement rate follows a non-monotonic trend, peaking at 215 when tensile strength reaches 3.33 MPa. Compressive strength minimally affects the damage area (~15%) but steadily improves the maximum permeability enhancement rate (7.5% increase). Elastic modulus exhibits an optimal value (8.93 GPa) for maximizing damage area, while negatively correlating with maximum permeability enhancement rate (9.1% decrease). Fracture morphology is differentially controlled by multiple parameters: low compressive strength promotes fracture deflection and branching, elastic modulus regulates fracture network complexity, and low Poisson’s ratio enhances coal brittleness to effectively activate natural fractures, thereby facilitating complex fracture network formation. Full article

Shale reservoirs contain abundant organic matter, pyrite, and clay minerals, making them highly susceptible to fluid-sensitivity damage; consequently, conventional hydraulic fracturing often yields poor stimulation performance, with low fracturing fluid flowback and rapid post-treatment production decline. Oxidative dissolution, however, can significantly alter the physical properties of shale reservoirs and improve stimulation effectiveness. In this study, nuclear magnetic resonance (NMR), contact-angle measurements, and triaxial compression tests are combined to systematically evaluate the effects of oxidative dissolution on the pore structure, wettability, and mechanical properties of Wufeng Formation shale from the Sichuan Basin. Core-flooding experiments with NaClO solutions show that, as the oxidant dosage (pore volume) increases, shale permeability rises by 66.67–266.67% and porosity by 1.79–9.58%, while the hydrophilic surface fraction increases from 5.45% to 61.73%. These changes are accompanied by a steady reduction in rock strength: the compressive strength decreases by up to 57.8%, and the elastic modulus exhibits a non-monotonic response to oxidation. Oxidative dissolution preferentially enlarges micropores, improves pore connectivity, and strengthens water wetness by consuming oil-wet organic matter and pyrite, which also enhances gel-breaking efficiency. Based on the experimental results, a series of characterization models are developed for oxidized shale reservoirs, including quantitative relationships linking porosity to compressive strength, elastic modulus, and contact angle, as well as a model relating oxidant dosage to microscopic pore structure evolution and imbibition enhancement. Overall, the coupled modifications of pore structure, wettability, and mechanical behavior produced by oxidative dissolution synergistically broaden the effective action range of fracturing fluids, promote shale gas desorption, and improve hydrocarbon seepage, providing a theoretical basis and practical guidance for oxidation-assisted stimulation in shale reservoirs. Full article

Wastes, biomasses, and nanoparticles have motivated reformulations of adhesives in the wood-based-panel industry. This study investigated the incorporation of glass wool (GW) waste as a filler material in urea–formaldehyde (UF) adhesive, evaluating its effects on the adhesive properties as well as on the physical, mechanical, fire-retardant, and acoustic properties of particleboards. Panels with a target density of 700 kg m⁻³ were produced with different proportions of glass wool in the adhesive (T1: 0%; T2: 3.34%; T3: 4.93%; T4: 6.52%; T5: 9.49%; T6: 12.35%). The adhesive-coated particle mat was pressed in a hydraulic press at 160 °C under a compression force of 72 tons for 10 min. The panels were subjected to analyses of their physical, mechanical, fire-retardant, and acoustic properties, as well as scanning electron microscopy (SEM) analyses. Statistical analysis involved regression, analysis of variance, and a Scott–Knott test (p < 0.05). The results indicated that adding 3.34% GW to the adhesive improved the modulus of rupture, internal bond strength, screw withdrawal resistance, and acoustic efficiency of the panels. A glass wool content of 12.35% enhanced the hardness and the damping factor. These findings highlight the potential of glass wool as a functional filler material in UF adhesive, promoting the development of stronger and more sustainable particleboards. Full article