Complex trimalleolar ankle fractures are a major orthopaedic challenge,with an incidence of 4.22 per 10000 person-years in the United States and an annual cost of 3.4 billion dollars.This review synthesizes current ev...Complex trimalleolar ankle fractures are a major orthopaedic challenge,with an incidence of 4.22 per 10000 person-years in the United States and an annual cost of 3.4 billion dollars.This review synthesizes current evidence on diagnostic protocols and management strategies,highlighting optimal approaches and emerging trends.Initial care emphasizes soft tissue assessment,often guided by the Tscherne classification,and fracture classification systems.External fixation may be required in open injuries,while early open reduction and internal fixation within six days is linked to improved outcomes.Minimally invasive techniques for the lateral malleolus,including intramedullary nailing and locking plates,are effective,while medial malleolus fractures are commonly managed with screw fixation or tension-band wiring.Posterior malleolus fragments involving more than 25%of the articular surface usually warrant fixation.Alternatives to syndesmotic screws,such as cortical buttons or high-strength sutures,reduce the need for secondary procedures.Arthroscopic-assisted open reduction and internal fixation benefits younger,active patients by enabling concurrent management of intra-articular and ligamentous injuries.Postoperative care prioritizes early weight-bearing and validated functional scores.Despite advances,complications remain common,and further research is needed to refine surgical strategies and improve outcomes.展开更多
To investigate the fracture initiation and propagation behavior of fractures in tight sandstone under the supercritical CO_(2)(SCCO_(2))shock fracturing,laboratory fracturing experiments were conducted using a true-tr...To investigate the fracture initiation and propagation behavior of fractures in tight sandstone under the supercritical CO_(2)(SCCO_(2))shock fracturing,laboratory fracturing experiments were conducted using a true-triaxial-like SCCO_(2)shock fracturing system.Computed tomography(CT)scanning and three-dimensional fracture reconstruction were employed to elucidate the effects of shock pressure,pore pressure,and in-situ stress on fracture characteristics.In addition,nuclear magnetic resonance(NMR)transverse relaxation time spectra were used to assess the internal damage induced by SCCO_(2)shock fracturing.The results indicate that,compared with conventional hydraulic fracturing and SCCO_(2)quasi-static fracturing,SCCO_(2)shock fracturing facilitates multidirectional fracture initiation and the formation of complex fracture networks.Increasing shock pressure more readily activates bedding-plane weaknesses,with main and subsidiary fractures interweaving into a dense fracture network.Under the same impulse intensity,elevated pore pressure reduces the effective normal stress and alters stress-wave scattering paths,thereby inducing more branch fractures and enhancing fracture complexity.An increase in differential in-situ stress promotes fracture propagation along the direction of the maximum principal stress,reduces branching,and simplifies fracture morphology.With increasing SCCO_(2)shock pressure,pore volume and connectivity generally increase:small-to-medium pores primarily respond through increased number and enhanced connectivity;when the shock pressure rises to 40-45 MPa,crack coalescence generates larger pores and fissures,which play a dominant role in improving flow pathways and effective storage space,ultimately forming a multiscale pore-fracture network.展开更多
The migration,accumulation,and high yield of hydrocarbons in tight sandstone reservoirs are closely tied to the natural fracture systems within the reservoirs.Large-scale fracture networks not only enhance reservoir s...The migration,accumulation,and high yield of hydrocarbons in tight sandstone reservoirs are closely tied to the natural fracture systems within the reservoirs.Large-scale fracture networks not only enhance reservoir seepage capacity but also influence effective productivity and subsequent fracturing reconstruction.Given the diverse mechanical behaviors,such as migration,penetration,or fracture arrest,traditional assumptions about fracture interaction criteria fail to address this complexity.To resolve these issues,a global cohesive element method is proposed to model random natural fractures.This approach verifies intersection models based on real-time stress conditions rather than pre-set criteria,enabling better characterization of interactions between hydraulic and natural fractures.Research has shown that the elastic modulus,horizontal stress difference,and fracturing fluid pumping rate significantly promote the expansion of hydraulic fractures.The use of low viscosity fracturing fluid can observe a decrease in the width of fractures near the wellbore,which may cause fractures to deflect when interacting with natural fractures.However,simulations under these conditions did not form a“complex network of fractures”.It is worth noting that when the local stress difference is zero,the result is close to the formation of this network.Excessive spacing will reduce the interaction between fractures,resulting in a decrease in the total length of fractures.By comprehensively analyzing these factors,an optimal combination can be identified,increasing the likelihood of achieving a“complex fracture network”.This paper thoroughly investigates hydraulic fracture propagation in naturally fractured reservoirs under various conditions,offering insights for developing efficient fracturing methods.展开更多
The research presented in this paper aimed to analyze the evolution of fractures in strata in relation to the progress of longwall mining.To achieve this objective,an introscopic probe equipped with a highresolution c...The research presented in this paper aimed to analyze the evolution of fractures in strata in relation to the progress of longwall mining.To achieve this objective,an introscopic probe equipped with a highresolution camera was developed,along with additional equipment that enables continuous recording of the internal surfaces of drainage boreholes exceeding 100 m in depth.The probe was utilized to test two methane drainage boreholes in the Z-3b longwall,which operates within the 501/3 coal seam of the Jankowice mine in Poland.Automatic image analysis methods were applied to evaluate the recorded images,based on a newly developed classificationsystem for fractures categorized by size and number.The results were compared with an analysis of changes in the methane capture rate from the drainage boreholes,which correlated with longwall mining progress.A strong correlation was observed between the number of fractures and the lithology of the strata layers.The largest number of fractures and their evolution were recorded in the coal layers,followed by the shale layers,while the sandstone layers exhibited the least number of fractures.Based on parallel measurements of the methane capture rate from the drainage boreholes during the progress of longwall mining,the extent of the strata's fracture zone was determined to range from 6 m to 36 m.Within the fracture zone,the strata are highly fractured,which leads to an increase in methane emissions through seepage and diffusion processes.展开更多
Taking the underground shale of the Silurian Longmaxi Formation in southern Sichuan Basin as the research object,stress-sensitive experiments on self-supporting fractures and micro-visualization experiments on gas-wat...Taking the underground shale of the Silurian Longmaxi Formation in southern Sichuan Basin as the research object,stress-sensitive experiments on self-supporting fractures and micro-visualization experiments on gas-water flow were conducted under simulated reservoir conditions to study the mechanism of microscopic gas-water flow during the fracture closure process and discuss its engineering applications.The results show that as the effective stress gradually increased from 5 MPa to 60 MPa with an increment of 5 MPa per step,the self-supporting fracture closure exhibited a two-stage characteristic of being fast in the early stage and slow in the later stage,with the inflection point stress ranging from 32 MPa to 35 MPa,and the closure degree of 47%-76%.The effective stress increase gradually rose from 5 MPa per step to 20 MPa per step,and the early fracture closure accelerated,with the maximum closure degree increasing by 8.6%.As the fracture width decreased from 500μm to 50μm,the gas-phase shifted from continuous to discontinuous flow,and the proportion of the critical gas-phase flow to maintain the continuous gas-phase flow increased.In the early stage of fracture closure(fracture width greater than 300μm),the continuous gas-phase flow is controlled by the fracture width-the larger the fracture width,the smaller the proportion of the critical gas-phase flow to maintain the continuous gas-phase flow.In the late stage of fracture closure(fracture width less than 300μm),as the fractures continue to close,the dominant role of the surface roughness of the fractures becomes stronger,and the proportion of the critical gas-phase flow to maintain the continuous gas-phase flow exceeds 70%.A reasonable pressure control during stable production and pressure reduction in the early stage(the peak pressure drop at the wellhead is less than 32 MPa)to delay the self-supporting fracture closure is conducive to the stable and increased production of gas wells.展开更多
The effective channeling of fluid flow by fractures is a liability for enhanced oil recovery(EOR)methods like CO_(2) flooding or CO_(2) storage.Developing a distributed fracture model to understand the heterogeneity o...The effective channeling of fluid flow by fractures is a liability for enhanced oil recovery(EOR)methods like CO_(2) flooding or CO_(2) storage.Developing a distributed fracture model to understand the heterogeneity of the fracture network is essential in characterizing tight and low-permeability reservoirs.In the Ordos Basin,the Chang 8-1-2 layer of the Yanchang Formation is a typical tight and low permeability reservoir in the JH17 wellblock.The strong heterogeneity of distributed fractures,differing fracture scales and fracture types make it difficult to effectively characterize the fracture distribution within the Chang 8-1-2 layer.In this paper,multi-source and multi-attribute methods are used to integrate data into a neural network at different scales,and fuzzy logic control is used to judge the correlation of various attributes.The results suggest that attribute correlation between coherence and fracture indication is the best,followed by correlations with fault distance,north–south slope,and north–south curvature.Advantageous attributes from the target area are used to train the neural network,and the fracture density model and discrete fracture network(DFN)model are built at different scales.This method can be used to effectively predict the distribution characteristics of fractures in the study area.And any learning done by the neural network from this case study can be applied to fracture network modeling for reservoirs of the same type.展开更多
This study examined non-uniform loading in goaf cantilever rock masses via testing,modeling,and mechanical analysis to solve instantaneous fracture and section buckling from mining abutment pressure.The study investig...This study examined non-uniform loading in goaf cantilever rock masses via testing,modeling,and mechanical analysis to solve instantaneous fracture and section buckling from mining abutment pressure.The study investigates the non-uniform load gradient effect on fracture characteristics,including load characteristics,fracture location,fracture distribution,and section roughness.A digital model for fracture interface buckling analysis was developed,elucidating the influence of non-uniform load gradients on Fracture Interface Curvature(FIC),Buckling Rate of Change(BRC),and Buckling Domain Field(BDF).The findings reveal that nonlinear tensile stress concentration and abrupt tensile-compressive-shear strain mutations under non-uniform loading are fundamental mechanisms driving fracture path buckling in cantilever rock mass structures.The buckling process of rock mass under non-uniform load can be divided into two stages:low load gradient and high gradient load.In the stage of low gradient load,the buckling behavior is mainly reflected in the compression-shear fracture of the edge.In the stage of high gradient load,a buckling band along the loading direction is gradually formed in the rock mass.These buckling principles establish a theoretical basis for accurately characterizing bearing fractures,fracture interface instability,and vibration sources within overlying cantilever rock masses in goaf.展开更多
Hydraulic fracturing serves as a critical technology for reservoir stimulation in deep coalbed methane(CBM)development,where the mechanical properties of gangue layers exert a significant control on fracture propagati...Hydraulic fracturing serves as a critical technology for reservoir stimulation in deep coalbed methane(CBM)development,where the mechanical properties of gangue layers exert a significant control on fracture propagation behavior.To address the unclear mechanisms governing fracture penetration across coal-gangue interfaces,this study employs the Continuum-Discontinuum Element Method(CDEM)to simulate and analyze the vertical propagation of hydraulic fractures initiating within coal seams,based on geomechanical parameters derived from the deep Benxi Formation coal seams in the southeastern Ordos Basin.The investigation systematically examines the influence of geological and operational parameters on cross-interfacial fracture growth.Results demonstrate that vertical stress difference,elastic modulus contrast between coal and gangue layers,interfacial stress differential,and interfacial cohesion at coal-gangue interfaces are critical factors governing hydraulic fracture penetration through these interfaces.High vertical stress differences(>3 MPa)inhibit interfacial dilation,promoting predominant crosslayer fracture propagation.Reduced interfacial stress contrasts and enhanced interfacial cohesion facilitate fracture penetration across interfaces.Furthermore,smaller elastic modulus contrasts between coal and gangue correlate with increased interfacial aperture.Finally,lower injection rates effectively suppress vertical fracture propagation in deep coal reservoirs.This study elucidates the characteristics and mechanisms governing cross-layer fracture propagation in coal–rock composites with interbedded partings,and delineates the dynamic evolution laws and dominant controlling factors involved.Thefindings provide critical theoretical insights for the optimization of fracture design and the efficient development of deep coalbed methane reservoirs.展开更多
Self-suspended proppants,which enable clear-water fracturing,represent a promising new class of materials for reservoir stimulation.Given the economic limitations associated with their exclusive use,this study investi...Self-suspended proppants,which enable clear-water fracturing,represent a promising new class of materials for reservoir stimulation.Given the economic limitations associated with their exclusive use,this study investigates proppant transport behavior in hybrid systems combining self-suspended proppants with conventional 40/70 mesh quartz sand at various mixing ratios.A dedicated experimental apparatus was developed to replicate field-relevant complex fracture networks,consisting of a main fracture and two branching fractures with different deflection angles.Using this system,sand bank formation and proppant distribution were examined for both conventional quartz sand fracturing and fracturing augmented with self-suspended proppants.The effects of slurry discharge volume,proppant mixing ratio,sand ratio,and injection location of the self-suspended proppant on transport and placement behavior were systematically analyzed.According to the results,the incorporation of self-suspended proppants markedly enhances the proppant-carrying capacity of the slurry and substantially modifies sand bank morphology.Increasing the discharge volume raises the inlet slope angle and promotes greater proppant penetration into branch fractures.The proportion of self-suspended proppant governs slurry viscoelasticity and,consequently,proppant settling behavior.As the fraction of self-suspended proppant decreases,the equilibrium height of the sand bank increases,while the proppant mass fraction within branch fractures exhibits a non-monotonic response,initially decreasing and then increasing.Variations in sand ratio alter both overall proppant concentration and the self-suspended proppant-to-water ratio,thereby modulating slurry rheology and influencing proppant placement.In addition,changes in injection location affect near-wellbore vortex structures,leading to distinct sand bank morphologies.展开更多
The characterization of track irregularities is crucial in railway dynamics,as track irregularities are the primary source of internal excitation in railway systems.In this paper,three mathematical models are proposed...The characterization of track irregularities is crucial in railway dynamics,as track irregularities are the primary source of internal excitation in railway systems.In this paper,three mathematical models are proposed to characterize the track irregularities under different circumstances.The first model is a novel explicit track spectrum function,which performs better in reflecting the inherent periodic components of track irregularities than the existing track spectra.On this foundation,the second model,a parameterized track spectrum random model,is proposed to represent the vast measured track irregularities from the probabilistic perspective.Finally,the third model,an imprecise track spectrum interval model based on a neighborhood uniform sampling Bootstrap method,is presented to identify the confidential interval of the track spectra when the track irregularity data are limited.Three examples are illustrated to demonstrate the feasibility of the three track irregularity models in characterizing the track irregularities in different conditions.This research can help capture the railway deformation status and optimize track maintenance strategies.展开更多
A three-dimensional multiphase particle-in-cell(MP-PIC)method was adopted to establish a liquid-solid two-phase flow model accounting for complex fracture networks.The model was validated using physical experimental d...A three-dimensional multiphase particle-in-cell(MP-PIC)method was adopted to establish a liquid-solid two-phase flow model accounting for complex fracture networks.The model was validated using physical experimental data.On this basis,the main factors influencing proppant transport in fracture network were analyzed.The study shows that proppant transport in fracture network can be divided into three stages:initial filling,dominant channel formation and fracture network extension.These correspond to three transport patterns:patch-like accumulation near the wellbore,preferential placement along main fractures,and improved the coverage of planar placement as fluid flows into branch fractures.Higher proppant density,lower fracturing fluid viscosity,lower injection rate,and larger proppant grain size result in shorter proppant transport distance and smaller planar placement coefficient.The use of low-density,small-diameter proppant combined with high-viscosity fracturing fluid and appropriately increased injection rate can effectively enlarge the stimulated volume.A smaller angle between the main fracture and branch fractures leads to longer proppant banks,broader coverage,more uniform distribution,and better stimulation performance in branch fractures.In contrast,a larger angle increases the likelihood of proppant accumulation near the branch fracture entrance and reduces the planar placement coefficient.展开更多
The forward model of optical fiber strain induced by fractures,together with the associated model resolution matrix,is used to demonstrate the interpretability of fracture parameters once the fracture intersects the f...The forward model of optical fiber strain induced by fractures,together with the associated model resolution matrix,is used to demonstrate the interpretability of fracture parameters once the fracture intersects the fiber.A regularized inversion framework for fracture parameters is established to evaluate the influence of measured data quality on the accuracy of iterative regularized inversion.An interpretation approach for both fracture width and height is proposed,and the synthetic forward data with measurement error and field examples are employed to validate the accuracy of the simultaneous inversion of fracture width and height.The results indicate that,after the fracture contacts the fiber,the strain response is strongly sensitive only to the fracture parameters at the intersection location,whereas the interpretability of parameters at other locations remains limited.The iterative regularized inversion method effectively suppresses the impact of measurement error and exhibits high computational efficiency,showing clear advantages for inversion applications.When incorporating the first-order regularization with a Neumann boundary constraint on the tip width,the inverted fracture-width distribution becomes highly sensitive to fracture height;thus,combined with a bisection strategy,simultaneous inversion of fracture width and height can be achieved.Examination using the model resolution matrix,noisy synthetic data,and field data confirms that the iterative regularized inversion model for fracture width and height provides high interpretive accuracy and can be applied to the calculation and analysis of fracture width,fracture height,net pressure and other parameters.展开更多
Background:Biological osteosynthesis preserves blood supply and promotes rapid healing by aligning fracture fragments without direct surgical exposure.Pedicle screws are primarily designed for internal fixation in spi...Background:Biological osteosynthesis preserves blood supply and promotes rapid healing by aligning fracture fragments without direct surgical exposure.Pedicle screws are primarily designed for internal fixation in spinal procedures.A key objec-tive of many orthopedic studies is to assess the biocompatibility of implants with bone and adjacent soft tissue.This study aims to evaluate the biocompatibility and effects of the Pedicle screw-Rod configuration as a novel external fixation method in canine tibial osteotomy.Methods:With ethics approval,eight healthy,intact male dogs,aged 10-12 months and weighing between 20 and 22 kg,underwent a minimally invasive medial tibial approach for surgical fixation of tibial osteotomy using a Pedicle screw-Rod configu-ration.Postoperative evaluations included ultrasound assessments at the osteotomy site and histological evaluations at the bone-screw interface.Results:B-mode ultrasound evaluation indicated healing progress at all osteotomy sites.The color Doppler examination revealed an initial increase in signals in the sur-rounding soft tissue during the first 4 weeks post-operation,followed by a decrease in signals within the adjacent soft tissue between the 5th and 8th weeks.During this latter period,the signals were primarily concentrated on the bone surface and the callus.The bone-screw interface at various screw sites exhibited similar histological changes,indicating effective integration of the newly formed woven bone into the screw threads.Conclusions:Fixation of non-articular tibial osteotomy with Pedicle screw-Rod con-figuration resulted in secondary bone healing,characterized by abundant callus for-mation and neovascularization.This implant demonstrated favorable biocompatibility with bone and surrounding soft tissue,without significant complications.展开更多
Deep shale gas reservoirs in the southern Sichuan Basin are typically characterized by significant horizontal stress anisotropy(expressed as stress difference),variable brittleness-ductility in rock mechanics,and stro...Deep shale gas reservoirs in the southern Sichuan Basin are typically characterized by significant horizontal stress anisotropy(expressed as stress difference),variable brittleness-ductility in rock mechanics,and strong heterogeneity.These complex geomechanical conditions lead to pronounced differences in hydraulic fracturing outcomes among wells and sections.To investigate hydraulic fracture propagation and fracturing fluid injection behavior under varying geomechanical settings,true triaxial physical simulation tests were performed on 400×400×400 mm artificial rock samples.The samples were designed with different media properties based on similarity criteria.A sensitivity analysis was conducted to assess the effects of brittleness-ductility characteristics,natural fractures,and in-situ stress conditions.The results reveal that:(i)brittle samples with lower stress difference are favorable for forming complex,perforable fracture networks;(ii)brittle samples with higher stress difference tend to develop simple,planar hydraulic fractures,with natural fractures only slightly activated during very short injection periods;(iii)ductile behavior enhances the activation of natural fractures but reduces fracture complexity compared with brittle samples,even under lower stress difference;and(iv)for typical deep shale formations,larger fluid injection volumes combined with high-density,multi-cluster fracturing techniques are recommended.展开更多
Fractures are typically characterized by roughness that significantlyaffects the mechanical and hydraulic characteristics of reservoirs.However,hydraulic fracturing mechanisms under the influenceof fracture morphology...Fractures are typically characterized by roughness that significantlyaffects the mechanical and hydraulic characteristics of reservoirs.However,hydraulic fracturing mechanisms under the influenceof fracture morphology remain largely unexplored.Leveraging the advantages of the finite-discrete element method(FDEM)for explicitly simulating fracture propagation and the strengths of the unifiedpipe model(UPM)for efficientlymodeling dual-permeability seepage,we propose a new hydromechanical(HM)coupling approach for modeling hydraulic fracturing.Validated against benchmark examples,the proposed FDEM-UPM model is further augmented by incorporating a Fourier-based methodology for reconstructing non-planar fractures,enabling quantitative analysis of hydraulic fracturing behavior within rough discrete fracture networks(DFNs).The FDEM-UPM model demonstrates computational advantages in accurately capturing transient hydraulic seepage phenomena,while the asynchronous time-stepping schemes between hydraulic and mechanical analyses substantially enhanced computational efficiencywithout compromising computational accuracy.Our results show that fracture morphology can affect both macroscopic fracture networks and microscopic interaction types between hydraulic fractures(HFs)and natural fractures(NFs).In an isotropic stress field,the initiation azimuth,propagation direction and microcracking mechanism are significantly influencedby fracture roughness.In an anisotropic stress field,HFs invariably propagate parallel to the direction of the maximum principal stress,reducing the overall complexity of the stimulated fracture networks.Additionally,stress concentration and perturbation attributed to fracture morphology tend to be compromised as the leak-off increases,while the breakdown and propagation pressures remain insensitive to fracture morphology.These findingsprovide new insights into the hydraulic fracturing mechanisms of fractured reservoirs containing complex rough DFNs.展开更多
Because of the developed surface of the Triply PeriodicMinimumSurface(TPMS)structures,polylactide(PLA)products with a TPMS structure are thought to be promising bio soluble implants with the potential for targeted dru...Because of the developed surface of the Triply PeriodicMinimumSurface(TPMS)structures,polylactide(PLA)products with a TPMS structure are thought to be promising bio soluble implants with the potential for targeted drug delivery.For implants,mechanical properties are key performance characteristics,so understanding the deformation and failure mechanisms is essential for selecting the appropriate implant structure.The deformation and fracture processes in PLA samples with different interior architectures have been studied through computer simulation and experimental research.Two TPMS topologies,the Schwarz Diamond and Gyroid architectures,were used for the sample construction by 3D printing.ANSYS software was utilized to simulate compressive deformation.It was found that under the same load,the vonMises stresses in the Gyroid structure are higher than those in the Schwartz Diamond structure,which was associated with the different orientations of the cells in the studied structures in relation to the direction of the loading axis.The deformation process occurs in the local regions of the studied TPMS structures.Maximum von Mises stresses were observed in the vertical parts of the structures oriented along the load direction.It was found that,unlike the Gyroid,the Schwartz Diamond structure contains a frame that forms unique stiffening ribs,which ensures the redistribution of the load under the vertical loading direction.An analysis of the mechanical characteristics of PLA samples with the Schwartz Diamond and Gyroid structures produced by the Fused Deposition Modeling(FDM)method was correlated with computer simulation.The Schwarz Diamond-type structure was shown to have a higher absorption energy than the Gyroid one.A study of the fracture in PLA samples with various cell sizes revealed a particular feature related to the samples’periodic surface topology and the 3D printing process.Scanning electron microscopic(SEM)studies of the samples deformed by compression showed thatwith an increase in the density of the samples,the failure mechanism changes from ductile to quasi-brittle due to the complex participation of both cell deformation and fiber deformation.展开更多
The Gabes aquifer system,located in southeastern Tunisia,is a crucial resource for supporting local socio-economic activities.Due to its dual porosity structure,is particularly vulnerable to pollution.This study aims ...The Gabes aquifer system,located in southeastern Tunisia,is a crucial resource for supporting local socio-economic activities.Due to its dual porosity structure,is particularly vulnerable to pollution.This study aims to develop a hybrid model that combines the Fracture Aquifer Index(FAI)with the conventional GOD(Groundwater occurrence,Overall lithology,Depth to water table)method,to assess groundwater vulnerability in fractured aquifer.To develop the hybrid model,the classical GOD method was integrated with FAI to produce a single composite index.Each parameter within both GOD and FAI was scored,and a final index was calculated to delineate vulnerable areas.The results show that the study area can be classified into four vulnerability levels:Very low,low,moderate,and high,indicating that approximately 8%of the area exhibits very low vulnerability,29%has low vulnerability,25%falls into the moderate category,and 38%is considered highly vulnerable.The FAI-GOD model further incorporates fracture network characteristics.This refinement reduces the classification to three vulnerability classes:Low,medium,and high.The outcomes demonstrate that 46%of the area is highly vulnerable due to a dense concentration of fractures,while 17%represents an intermediate zone characterized by either shallow or deeper fractures.In contrast,37%corresponds to areas with lightly fractured rock,where the impact on vulnerability is minimal.Multivariate statistical analysis was employed using Principal Components Analysis(PCA)and Hierarchical Cluster Analysis(HCA)on 24 samples across six variables.The first three components account for over 76%of the total variance,reinforcing the significance of fracture dynamics in classifying vulnerability levels.The FAI-GOD model removes the very-low-vulnerability class and expands the spatial extent of low-and high-vulnerability zones,reflecting the dominant influence of fracture networks on aquifer sensitivity.While both indices use a five-class system,FAI-GOD redistributes vulnerability by eliminating very-low-vulnerability areas and amplifying low/high categories,highlighting the critical role of fractures.A strong correlation(R2=0.94)between the GOD and FAI-GOD indices,demonstrated through second-order polynomial regression,confirms the robustness of the FAI-GOD model in accurately predicting vulnerability to pollution.This model provides a useful framework for assessing the vulnerability of complex aquifers and serves as a decision-making tool for groundwater managers in similar areas.展开更多
Conglomerate rock's complex and heterogeneous microstructure significantly affects its mechanical properties,especially under dynamic loading.However,research on their dynamic behavior and fracture mechanisms is l...Conglomerate rock's complex and heterogeneous microstructure significantly affects its mechanical properties,especially under dynamic loading.However,research on their dynamic behavior and fracture mechanisms is limited.Through uniaxial compression tests and split Hopkinson pressure bar(SHPB)impact tests,the dynamic compressive mechanical properties and fracture mechanisms of conglomerate rock were studied.Nanoindentation and high-resolution X-ray computed tomography were employed to analyze the micro-mechanical behavior and internal structure of the conglomerate rock.Results indicate significant differences in mechanical properties between different gravel particles and cementing materials,with initial fractures primarily distributed at the gravel-cement interfaces.The dynamic mechanical properties of conglomerate rocks exhibit a clear strain rate dependency.Based on the stress−strain curves and failure characteristics,the dynamic compressive mechanical behavior can be categorized into two types using a critical strain rate.The dynamic compressive strength,peak strain,and toughness of conglomerate rock increased with the strain rate,with the strength at 54 s−1 being 2.6 times that at 6 s−1.The dynamic compressive fracture mechanism of conglomerate rock is related to the strain rate and microstructure;at low strain rates,gravel distribution is the key factor,whereas at high strain rates,gravel content becomes critical.展开更多
The deep coal reservoir in Linxing-Shenfu block of Ordos Basin is an important part of China’s coalbed methane resources.In the process of reservoir reconstruction,the artificial fracture morphology of coal seam with...The deep coal reservoir in Linxing-Shenfu block of Ordos Basin is an important part of China’s coalbed methane resources.In the process of reservoir reconstruction,the artificial fracture morphology of coal seam with gangue interaction is significantly different,which affects the efficient development of coalbed methane resources in this area.In this paper,the surface outcrop of Linxing-Shenfu block is selected,and three kinds of interaction modes between gangue and coal seam are set up,including single-component coal rock sample,coal rock sample with different thicknesses of gangue layer and coal rock sample with different numbers of gangue.Through true triaxial physical simulation and three-dimensional discrete element numerical simulation,the lawof artificial fracture initiation and propagation in multi-gangue interaction coal seam is analyzed in depth,and the hydraulic fracture initiation and propagation mode under different interaction modes of gangue layer in Linxing-Shenfu deep coal reservoir was clarified.The research shows that the initiation of artificial fractures in a single coal seam is affected by geologicalengineering factors.The maximum principal stress dominates the direction of fracture propagation,and the stress difference controls the fracture morphology.When the stress difference is 2 MPa,the fracture morphology is complex,which is easy to connect to the weak surface of coal and rock cleat,and the fracturemorphology of the stress difference is mainly a single main fracture.After the thickness of the gangue layer is increased from 2 to 5 cm,it is difficult for the artificial fracture to penetrate the layer vertically after the fracture initiation,and the effective transformation area of the reservoir is limited.The more the number of gangue layers,the greater the hydraulic energy consumption in the process of fracture propagation,and the more difficult the fracture propagation.展开更多
文摘Complex trimalleolar ankle fractures are a major orthopaedic challenge,with an incidence of 4.22 per 10000 person-years in the United States and an annual cost of 3.4 billion dollars.This review synthesizes current evidence on diagnostic protocols and management strategies,highlighting optimal approaches and emerging trends.Initial care emphasizes soft tissue assessment,often guided by the Tscherne classification,and fracture classification systems.External fixation may be required in open injuries,while early open reduction and internal fixation within six days is linked to improved outcomes.Minimally invasive techniques for the lateral malleolus,including intramedullary nailing and locking plates,are effective,while medial malleolus fractures are commonly managed with screw fixation or tension-band wiring.Posterior malleolus fragments involving more than 25%of the articular surface usually warrant fixation.Alternatives to syndesmotic screws,such as cortical buttons or high-strength sutures,reduce the need for secondary procedures.Arthroscopic-assisted open reduction and internal fixation benefits younger,active patients by enabling concurrent management of intra-articular and ligamentous injuries.Postoperative care prioritizes early weight-bearing and validated functional scores.Despite advances,complications remain common,and further research is needed to refine surgical strategies and improve outcomes.
基金Supported by the National Natural Science Foundation for Outstanding Young Scholars(52425402)National Natural Science Foundation of China(52341401)International(Regional)Cooperation and Exchange Program of the National Natural Science Foundation of China(W2412078)。
文摘To investigate the fracture initiation and propagation behavior of fractures in tight sandstone under the supercritical CO_(2)(SCCO_(2))shock fracturing,laboratory fracturing experiments were conducted using a true-triaxial-like SCCO_(2)shock fracturing system.Computed tomography(CT)scanning and three-dimensional fracture reconstruction were employed to elucidate the effects of shock pressure,pore pressure,and in-situ stress on fracture characteristics.In addition,nuclear magnetic resonance(NMR)transverse relaxation time spectra were used to assess the internal damage induced by SCCO_(2)shock fracturing.The results indicate that,compared with conventional hydraulic fracturing and SCCO_(2)quasi-static fracturing,SCCO_(2)shock fracturing facilitates multidirectional fracture initiation and the formation of complex fracture networks.Increasing shock pressure more readily activates bedding-plane weaknesses,with main and subsidiary fractures interweaving into a dense fracture network.Under the same impulse intensity,elevated pore pressure reduces the effective normal stress and alters stress-wave scattering paths,thereby inducing more branch fractures and enhancing fracture complexity.An increase in differential in-situ stress promotes fracture propagation along the direction of the maximum principal stress,reduces branching,and simplifies fracture morphology.With increasing SCCO_(2)shock pressure,pore volume and connectivity generally increase:small-to-medium pores primarily respond through increased number and enhanced connectivity;when the shock pressure rises to 40-45 MPa,crack coalescence generates larger pores and fissures,which play a dominant role in improving flow pathways and effective storage space,ultimately forming a multiscale pore-fracture network.
基金supported by the National Natural Science Foundation of China(52074313).
文摘The migration,accumulation,and high yield of hydrocarbons in tight sandstone reservoirs are closely tied to the natural fracture systems within the reservoirs.Large-scale fracture networks not only enhance reservoir seepage capacity but also influence effective productivity and subsequent fracturing reconstruction.Given the diverse mechanical behaviors,such as migration,penetration,or fracture arrest,traditional assumptions about fracture interaction criteria fail to address this complexity.To resolve these issues,a global cohesive element method is proposed to model random natural fractures.This approach verifies intersection models based on real-time stress conditions rather than pre-set criteria,enabling better characterization of interactions between hydraulic and natural fractures.Research has shown that the elastic modulus,horizontal stress difference,and fracturing fluid pumping rate significantly promote the expansion of hydraulic fractures.The use of low viscosity fracturing fluid can observe a decrease in the width of fractures near the wellbore,which may cause fractures to deflect when interacting with natural fractures.However,simulations under these conditions did not form a“complex network of fractures”.It is worth noting that when the local stress difference is zero,the result is close to the formation of this network.Excessive spacing will reduce the interaction between fractures,resulting in a decrease in the total length of fractures.By comprehensively analyzing these factors,an optimal combination can be identified,increasing the likelihood of achieving a“complex fracture network”.This paper thoroughly investigates hydraulic fracture propagation in naturally fractured reservoirs under various conditions,offering insights for developing efficient fracturing methods.
基金the PICTO project(RFCR-CT-2018-800711)funded by the European Research Fund for Coal and Steel(RFCS)and the Polish Ministry of Science and Higher Education(W93/FBWiS/2018).
文摘The research presented in this paper aimed to analyze the evolution of fractures in strata in relation to the progress of longwall mining.To achieve this objective,an introscopic probe equipped with a highresolution camera was developed,along with additional equipment that enables continuous recording of the internal surfaces of drainage boreholes exceeding 100 m in depth.The probe was utilized to test two methane drainage boreholes in the Z-3b longwall,which operates within the 501/3 coal seam of the Jankowice mine in Poland.Automatic image analysis methods were applied to evaluate the recorded images,based on a newly developed classificationsystem for fractures categorized by size and number.The results were compared with an analysis of changes in the methane capture rate from the drainage boreholes,which correlated with longwall mining progress.A strong correlation was observed between the number of fractures and the lithology of the strata layers.The largest number of fractures and their evolution were recorded in the coal layers,followed by the shale layers,while the sandstone layers exhibited the least number of fractures.Based on parallel measurements of the methane capture rate from the drainage boreholes during the progress of longwall mining,the extent of the strata's fracture zone was determined to range from 6 m to 36 m.Within the fracture zone,the strata are highly fractured,which leads to an increase in methane emissions through seepage and diffusion processes.
基金Supported by the National Science and Technology Major Project of New-Type Oil and Gas Exploration and Development(2025ZD14041)National Science and Technology Major Project of China(2025ZD14053)+2 种基金Science and Technology Project of CNPC(2023ZZ21)Youth Science and Technology Project of CNPC(2024DQ03241)Postdoctoral Research Project of PetroChina Southwest Oil and Gas Field Company(20230304-13)。
文摘Taking the underground shale of the Silurian Longmaxi Formation in southern Sichuan Basin as the research object,stress-sensitive experiments on self-supporting fractures and micro-visualization experiments on gas-water flow were conducted under simulated reservoir conditions to study the mechanism of microscopic gas-water flow during the fracture closure process and discuss its engineering applications.The results show that as the effective stress gradually increased from 5 MPa to 60 MPa with an increment of 5 MPa per step,the self-supporting fracture closure exhibited a two-stage characteristic of being fast in the early stage and slow in the later stage,with the inflection point stress ranging from 32 MPa to 35 MPa,and the closure degree of 47%-76%.The effective stress increase gradually rose from 5 MPa per step to 20 MPa per step,and the early fracture closure accelerated,with the maximum closure degree increasing by 8.6%.As the fracture width decreased from 500μm to 50μm,the gas-phase shifted from continuous to discontinuous flow,and the proportion of the critical gas-phase flow to maintain the continuous gas-phase flow increased.In the early stage of fracture closure(fracture width greater than 300μm),the continuous gas-phase flow is controlled by the fracture width-the larger the fracture width,the smaller the proportion of the critical gas-phase flow to maintain the continuous gas-phase flow.In the late stage of fracture closure(fracture width less than 300μm),as the fractures continue to close,the dominant role of the surface roughness of the fractures becomes stronger,and the proportion of the critical gas-phase flow to maintain the continuous gas-phase flow exceeds 70%.A reasonable pressure control during stable production and pressure reduction in the early stage(the peak pressure drop at the wellhead is less than 32 MPa)to delay the self-supporting fracture closure is conducive to the stable and increased production of gas wells.
基金supported by the National Science and Technology Project of China(No.2024ZD1004300)。
文摘The effective channeling of fluid flow by fractures is a liability for enhanced oil recovery(EOR)methods like CO_(2) flooding or CO_(2) storage.Developing a distributed fracture model to understand the heterogeneity of the fracture network is essential in characterizing tight and low-permeability reservoirs.In the Ordos Basin,the Chang 8-1-2 layer of the Yanchang Formation is a typical tight and low permeability reservoir in the JH17 wellblock.The strong heterogeneity of distributed fractures,differing fracture scales and fracture types make it difficult to effectively characterize the fracture distribution within the Chang 8-1-2 layer.In this paper,multi-source and multi-attribute methods are used to integrate data into a neural network at different scales,and fuzzy logic control is used to judge the correlation of various attributes.The results suggest that attribute correlation between coherence and fracture indication is the best,followed by correlations with fault distance,north–south slope,and north–south curvature.Advantageous attributes from the target area are used to train the neural network,and the fracture density model and discrete fracture network(DFN)model are built at different scales.This method can be used to effectively predict the distribution characteristics of fractures in the study area.And any learning done by the neural network from this case study can be applied to fracture network modeling for reservoirs of the same type.
基金support provided by the National Natural Science Foundation of China(No.52274077)the Natural Science Foundation of Henan(No.242300421072)+2 种基金the Youth Elite Teachers Cultivation Program for Higher Education Institutions in Henan Province(No.2024GGJS036)the Funds for Distinguished Young Scholars of Henan Polytechnic University(No.J2023-3)the Young Core Teacher Funding Scheme of Henan Polytechnic University(No.2023XQG-09).
文摘This study examined non-uniform loading in goaf cantilever rock masses via testing,modeling,and mechanical analysis to solve instantaneous fracture and section buckling from mining abutment pressure.The study investigates the non-uniform load gradient effect on fracture characteristics,including load characteristics,fracture location,fracture distribution,and section roughness.A digital model for fracture interface buckling analysis was developed,elucidating the influence of non-uniform load gradients on Fracture Interface Curvature(FIC),Buckling Rate of Change(BRC),and Buckling Domain Field(BDF).The findings reveal that nonlinear tensile stress concentration and abrupt tensile-compressive-shear strain mutations under non-uniform loading are fundamental mechanisms driving fracture path buckling in cantilever rock mass structures.The buckling process of rock mass under non-uniform load can be divided into two stages:low load gradient and high gradient load.In the stage of low gradient load,the buckling behavior is mainly reflected in the compression-shear fracture of the edge.In the stage of high gradient load,a buckling band along the loading direction is gradually formed in the rock mass.These buckling principles establish a theoretical basis for accurately characterizing bearing fractures,fracture interface instability,and vibration sources within overlying cantilever rock masses in goaf.
文摘Hydraulic fracturing serves as a critical technology for reservoir stimulation in deep coalbed methane(CBM)development,where the mechanical properties of gangue layers exert a significant control on fracture propagation behavior.To address the unclear mechanisms governing fracture penetration across coal-gangue interfaces,this study employs the Continuum-Discontinuum Element Method(CDEM)to simulate and analyze the vertical propagation of hydraulic fractures initiating within coal seams,based on geomechanical parameters derived from the deep Benxi Formation coal seams in the southeastern Ordos Basin.The investigation systematically examines the influence of geological and operational parameters on cross-interfacial fracture growth.Results demonstrate that vertical stress difference,elastic modulus contrast between coal and gangue layers,interfacial stress differential,and interfacial cohesion at coal-gangue interfaces are critical factors governing hydraulic fracture penetration through these interfaces.High vertical stress differences(>3 MPa)inhibit interfacial dilation,promoting predominant crosslayer fracture propagation.Reduced interfacial stress contrasts and enhanced interfacial cohesion facilitate fracture penetration across interfaces.Furthermore,smaller elastic modulus contrasts between coal and gangue correlate with increased interfacial aperture.Finally,lower injection rates effectively suppress vertical fracture propagation in deep coal reservoirs.This study elucidates the characteristics and mechanisms governing cross-layer fracture propagation in coal–rock composites with interbedded partings,and delineates the dynamic evolution laws and dominant controlling factors involved.Thefindings provide critical theoretical insights for the optimization of fracture design and the efficient development of deep coalbed methane reservoirs.
基金the China National Petroleum Corporation’s Forward-Looking Fundamental Technology Breakthrough Project(2021DJ2305).
文摘Self-suspended proppants,which enable clear-water fracturing,represent a promising new class of materials for reservoir stimulation.Given the economic limitations associated with their exclusive use,this study investigates proppant transport behavior in hybrid systems combining self-suspended proppants with conventional 40/70 mesh quartz sand at various mixing ratios.A dedicated experimental apparatus was developed to replicate field-relevant complex fracture networks,consisting of a main fracture and two branching fractures with different deflection angles.Using this system,sand bank formation and proppant distribution were examined for both conventional quartz sand fracturing and fracturing augmented with self-suspended proppants.The effects of slurry discharge volume,proppant mixing ratio,sand ratio,and injection location of the self-suspended proppant on transport and placement behavior were systematically analyzed.According to the results,the incorporation of self-suspended proppants markedly enhances the proppant-carrying capacity of the slurry and substantially modifies sand bank morphology.Increasing the discharge volume raises the inlet slope angle and promotes greater proppant penetration into branch fractures.The proportion of self-suspended proppant governs slurry viscoelasticity and,consequently,proppant settling behavior.As the fraction of self-suspended proppant decreases,the equilibrium height of the sand bank increases,while the proppant mass fraction within branch fractures exhibits a non-monotonic response,initially decreasing and then increasing.Variations in sand ratio alter both overall proppant concentration and the self-suspended proppant-to-water ratio,thereby modulating slurry rheology and influencing proppant placement.In addition,changes in injection location affect near-wellbore vortex structures,leading to distinct sand bank morphologies.
基金supported by the National Natural Science Foundation of China(Grant No.52208445,52478321,52378468)the Fundamental Research Funds for the Central Universities(Grant No.G2021KY05105)+7 种基金the Basic Research Program of Natural Science in Shaanxi Province(Grant No.2022JQ-369)the Open Foundation of National Engineering Laboratory for High Speed Railway Construction(No.HSR202001)the Youth Talent Support Program Project of Xi’an Association for Science and Technology(Grant No.959202413090)Science and Technology Research and Development Program Project of China railway group limited(Major Special Project,No.:2020-Special-022021-Special-082023-Special-07)Innovation-driven project of Central South University(2023CXQD072)the National Natural Science Foundation of Hunan Province(Grant No.:2022-JJ-20071).
文摘The characterization of track irregularities is crucial in railway dynamics,as track irregularities are the primary source of internal excitation in railway systems.In this paper,three mathematical models are proposed to characterize the track irregularities under different circumstances.The first model is a novel explicit track spectrum function,which performs better in reflecting the inherent periodic components of track irregularities than the existing track spectra.On this foundation,the second model,a parameterized track spectrum random model,is proposed to represent the vast measured track irregularities from the probabilistic perspective.Finally,the third model,an imprecise track spectrum interval model based on a neighborhood uniform sampling Bootstrap method,is presented to identify the confidential interval of the track spectra when the track irregularity data are limited.Three examples are illustrated to demonstrate the feasibility of the three track irregularity models in characterizing the track irregularities in different conditions.This research can help capture the railway deformation status and optimize track maintenance strategies.
基金Supported by the National Natural Science Foundation of China(U21B2071,U23B20156)。
文摘A three-dimensional multiphase particle-in-cell(MP-PIC)method was adopted to establish a liquid-solid two-phase flow model accounting for complex fracture networks.The model was validated using physical experimental data.On this basis,the main factors influencing proppant transport in fracture network were analyzed.The study shows that proppant transport in fracture network can be divided into three stages:initial filling,dominant channel formation and fracture network extension.These correspond to three transport patterns:patch-like accumulation near the wellbore,preferential placement along main fractures,and improved the coverage of planar placement as fluid flows into branch fractures.Higher proppant density,lower fracturing fluid viscosity,lower injection rate,and larger proppant grain size result in shorter proppant transport distance and smaller planar placement coefficient.The use of low-density,small-diameter proppant combined with high-viscosity fracturing fluid and appropriately increased injection rate can effectively enlarge the stimulated volume.A smaller angle between the main fracture and branch fractures leads to longer proppant banks,broader coverage,more uniform distribution,and better stimulation performance in branch fractures.In contrast,a larger angle increases the likelihood of proppant accumulation near the branch fracture entrance and reduces the planar placement coefficient.
基金Supported by the Ministry of Education U40 Program(ZYGXONJSKYCXNLZCXM-E19)National Natural Science Foundation of China(52574078)。
文摘The forward model of optical fiber strain induced by fractures,together with the associated model resolution matrix,is used to demonstrate the interpretability of fracture parameters once the fracture intersects the fiber.A regularized inversion framework for fracture parameters is established to evaluate the influence of measured data quality on the accuracy of iterative regularized inversion.An interpretation approach for both fracture width and height is proposed,and the synthetic forward data with measurement error and field examples are employed to validate the accuracy of the simultaneous inversion of fracture width and height.The results indicate that,after the fracture contacts the fiber,the strain response is strongly sensitive only to the fracture parameters at the intersection location,whereas the interpretability of parameters at other locations remains limited.The iterative regularized inversion method effectively suppresses the impact of measurement error and exhibits high computational efficiency,showing clear advantages for inversion applications.When incorporating the first-order regularization with a Neumann boundary constraint on the tip width,the inverted fracture-width distribution becomes highly sensitive to fracture height;thus,combined with a bisection strategy,simultaneous inversion of fracture width and height can be achieved.Examination using the model resolution matrix,noisy synthetic data,and field data confirms that the iterative regularized inversion model for fracture width and height provides high interpretive accuracy and can be applied to the calculation and analysis of fracture width,fracture height,net pressure and other parameters.
基金The Vice Chancellor of Research and Technology at Urmia University。
文摘Background:Biological osteosynthesis preserves blood supply and promotes rapid healing by aligning fracture fragments without direct surgical exposure.Pedicle screws are primarily designed for internal fixation in spinal procedures.A key objec-tive of many orthopedic studies is to assess the biocompatibility of implants with bone and adjacent soft tissue.This study aims to evaluate the biocompatibility and effects of the Pedicle screw-Rod configuration as a novel external fixation method in canine tibial osteotomy.Methods:With ethics approval,eight healthy,intact male dogs,aged 10-12 months and weighing between 20 and 22 kg,underwent a minimally invasive medial tibial approach for surgical fixation of tibial osteotomy using a Pedicle screw-Rod configu-ration.Postoperative evaluations included ultrasound assessments at the osteotomy site and histological evaluations at the bone-screw interface.Results:B-mode ultrasound evaluation indicated healing progress at all osteotomy sites.The color Doppler examination revealed an initial increase in signals in the sur-rounding soft tissue during the first 4 weeks post-operation,followed by a decrease in signals within the adjacent soft tissue between the 5th and 8th weeks.During this latter period,the signals were primarily concentrated on the bone surface and the callus.The bone-screw interface at various screw sites exhibited similar histological changes,indicating effective integration of the newly formed woven bone into the screw threads.Conclusions:Fixation of non-articular tibial osteotomy with Pedicle screw-Rod con-figuration resulted in secondary bone healing,characterized by abundant callus for-mation and neovascularization.This implant demonstrated favorable biocompatibility with bone and surrounding soft tissue,without significant complications.
基金the National Natural Science Foundation of China(Nos.52204005,52192622,U20A20265)the Sichuan Science Fund for Young Scholars(23NSFSC4652).
文摘Deep shale gas reservoirs in the southern Sichuan Basin are typically characterized by significant horizontal stress anisotropy(expressed as stress difference),variable brittleness-ductility in rock mechanics,and strong heterogeneity.These complex geomechanical conditions lead to pronounced differences in hydraulic fracturing outcomes among wells and sections.To investigate hydraulic fracture propagation and fracturing fluid injection behavior under varying geomechanical settings,true triaxial physical simulation tests were performed on 400×400×400 mm artificial rock samples.The samples were designed with different media properties based on similarity criteria.A sensitivity analysis was conducted to assess the effects of brittleness-ductility characteristics,natural fractures,and in-situ stress conditions.The results reveal that:(i)brittle samples with lower stress difference are favorable for forming complex,perforable fracture networks;(ii)brittle samples with higher stress difference tend to develop simple,planar hydraulic fractures,with natural fractures only slightly activated during very short injection periods;(iii)ductile behavior enhances the activation of natural fractures but reduces fracture complexity compared with brittle samples,even under lower stress difference;and(iv)for typical deep shale formations,larger fluid injection volumes combined with high-density,multi-cluster fracturing techniques are recommended.
基金supported by the National Natural Science Foundation of China(Grant Nos.52574103 and 42277150).
文摘Fractures are typically characterized by roughness that significantlyaffects the mechanical and hydraulic characteristics of reservoirs.However,hydraulic fracturing mechanisms under the influenceof fracture morphology remain largely unexplored.Leveraging the advantages of the finite-discrete element method(FDEM)for explicitly simulating fracture propagation and the strengths of the unifiedpipe model(UPM)for efficientlymodeling dual-permeability seepage,we propose a new hydromechanical(HM)coupling approach for modeling hydraulic fracturing.Validated against benchmark examples,the proposed FDEM-UPM model is further augmented by incorporating a Fourier-based methodology for reconstructing non-planar fractures,enabling quantitative analysis of hydraulic fracturing behavior within rough discrete fracture networks(DFNs).The FDEM-UPM model demonstrates computational advantages in accurately capturing transient hydraulic seepage phenomena,while the asynchronous time-stepping schemes between hydraulic and mechanical analyses substantially enhanced computational efficiencywithout compromising computational accuracy.Our results show that fracture morphology can affect both macroscopic fracture networks and microscopic interaction types between hydraulic fractures(HFs)and natural fractures(NFs).In an isotropic stress field,the initiation azimuth,propagation direction and microcracking mechanism are significantly influencedby fracture roughness.In an anisotropic stress field,HFs invariably propagate parallel to the direction of the maximum principal stress,reducing the overall complexity of the stimulated fracture networks.Additionally,stress concentration and perturbation attributed to fracture morphology tend to be compromised as the leak-off increases,while the breakdown and propagation pressures remain insensitive to fracture morphology.These findingsprovide new insights into the hydraulic fracturing mechanisms of fractured reservoirs containing complex rough DFNs.
文摘Because of the developed surface of the Triply PeriodicMinimumSurface(TPMS)structures,polylactide(PLA)products with a TPMS structure are thought to be promising bio soluble implants with the potential for targeted drug delivery.For implants,mechanical properties are key performance characteristics,so understanding the deformation and failure mechanisms is essential for selecting the appropriate implant structure.The deformation and fracture processes in PLA samples with different interior architectures have been studied through computer simulation and experimental research.Two TPMS topologies,the Schwarz Diamond and Gyroid architectures,were used for the sample construction by 3D printing.ANSYS software was utilized to simulate compressive deformation.It was found that under the same load,the vonMises stresses in the Gyroid structure are higher than those in the Schwartz Diamond structure,which was associated with the different orientations of the cells in the studied structures in relation to the direction of the loading axis.The deformation process occurs in the local regions of the studied TPMS structures.Maximum von Mises stresses were observed in the vertical parts of the structures oriented along the load direction.It was found that,unlike the Gyroid,the Schwartz Diamond structure contains a frame that forms unique stiffening ribs,which ensures the redistribution of the load under the vertical loading direction.An analysis of the mechanical characteristics of PLA samples with the Schwartz Diamond and Gyroid structures produced by the Fused Deposition Modeling(FDM)method was correlated with computer simulation.The Schwarz Diamond-type structure was shown to have a higher absorption energy than the Gyroid one.A study of the fracture in PLA samples with various cell sizes revealed a particular feature related to the samples’periodic surface topology and the 3D printing process.Scanning electron microscopic(SEM)studies of the samples deformed by compression showed thatwith an increase in the density of the samples,the failure mechanism changes from ductile to quasi-brittle due to the complex participation of both cell deformation and fiber deformation.
文摘The Gabes aquifer system,located in southeastern Tunisia,is a crucial resource for supporting local socio-economic activities.Due to its dual porosity structure,is particularly vulnerable to pollution.This study aims to develop a hybrid model that combines the Fracture Aquifer Index(FAI)with the conventional GOD(Groundwater occurrence,Overall lithology,Depth to water table)method,to assess groundwater vulnerability in fractured aquifer.To develop the hybrid model,the classical GOD method was integrated with FAI to produce a single composite index.Each parameter within both GOD and FAI was scored,and a final index was calculated to delineate vulnerable areas.The results show that the study area can be classified into four vulnerability levels:Very low,low,moderate,and high,indicating that approximately 8%of the area exhibits very low vulnerability,29%has low vulnerability,25%falls into the moderate category,and 38%is considered highly vulnerable.The FAI-GOD model further incorporates fracture network characteristics.This refinement reduces the classification to three vulnerability classes:Low,medium,and high.The outcomes demonstrate that 46%of the area is highly vulnerable due to a dense concentration of fractures,while 17%represents an intermediate zone characterized by either shallow or deeper fractures.In contrast,37%corresponds to areas with lightly fractured rock,where the impact on vulnerability is minimal.Multivariate statistical analysis was employed using Principal Components Analysis(PCA)and Hierarchical Cluster Analysis(HCA)on 24 samples across six variables.The first three components account for over 76%of the total variance,reinforcing the significance of fracture dynamics in classifying vulnerability levels.The FAI-GOD model removes the very-low-vulnerability class and expands the spatial extent of low-and high-vulnerability zones,reflecting the dominant influence of fracture networks on aquifer sensitivity.While both indices use a five-class system,FAI-GOD redistributes vulnerability by eliminating very-low-vulnerability areas and amplifying low/high categories,highlighting the critical role of fractures.A strong correlation(R2=0.94)between the GOD and FAI-GOD indices,demonstrated through second-order polynomial regression,confirms the robustness of the FAI-GOD model in accurately predicting vulnerability to pollution.This model provides a useful framework for assessing the vulnerability of complex aquifers and serves as a decision-making tool for groundwater managers in similar areas.
基金Project(51978674)supported by the National Natural Science Foundation of China。
文摘Conglomerate rock's complex and heterogeneous microstructure significantly affects its mechanical properties,especially under dynamic loading.However,research on their dynamic behavior and fracture mechanisms is limited.Through uniaxial compression tests and split Hopkinson pressure bar(SHPB)impact tests,the dynamic compressive mechanical properties and fracture mechanisms of conglomerate rock were studied.Nanoindentation and high-resolution X-ray computed tomography were employed to analyze the micro-mechanical behavior and internal structure of the conglomerate rock.Results indicate significant differences in mechanical properties between different gravel particles and cementing materials,with initial fractures primarily distributed at the gravel-cement interfaces.The dynamic mechanical properties of conglomerate rocks exhibit a clear strain rate dependency.Based on the stress−strain curves and failure characteristics,the dynamic compressive mechanical behavior can be categorized into two types using a critical strain rate.The dynamic compressive strength,peak strain,and toughness of conglomerate rock increased with the strain rate,with the strength at 54 s−1 being 2.6 times that at 6 s−1.The dynamic compressive fracture mechanism of conglomerate rock is related to the strain rate and microstructure;at low strain rates,gravel distribution is the key factor,whereas at high strain rates,gravel content becomes critical.
基金supported by National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum,Beijing(No.PRE/open-2307).
文摘The deep coal reservoir in Linxing-Shenfu block of Ordos Basin is an important part of China’s coalbed methane resources.In the process of reservoir reconstruction,the artificial fracture morphology of coal seam with gangue interaction is significantly different,which affects the efficient development of coalbed methane resources in this area.In this paper,the surface outcrop of Linxing-Shenfu block is selected,and three kinds of interaction modes between gangue and coal seam are set up,including single-component coal rock sample,coal rock sample with different thicknesses of gangue layer and coal rock sample with different numbers of gangue.Through true triaxial physical simulation and three-dimensional discrete element numerical simulation,the lawof artificial fracture initiation and propagation in multi-gangue interaction coal seam is analyzed in depth,and the hydraulic fracture initiation and propagation mode under different interaction modes of gangue layer in Linxing-Shenfu deep coal reservoir was clarified.The research shows that the initiation of artificial fractures in a single coal seam is affected by geologicalengineering factors.The maximum principal stress dominates the direction of fracture propagation,and the stress difference controls the fracture morphology.When the stress difference is 2 MPa,the fracture morphology is complex,which is easy to connect to the weak surface of coal and rock cleat,and the fracturemorphology of the stress difference is mainly a single main fracture.After the thickness of the gangue layer is increased from 2 to 5 cm,it is difficult for the artificial fracture to penetrate the layer vertically after the fracture initiation,and the effective transformation area of the reservoir is limited.The more the number of gangue layers,the greater the hydraulic energy consumption in the process of fracture propagation,and the more difficult the fracture propagation.
