To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compress...To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compression and uniaxial loading–unloading tests were conducted under five saturation levels.The effect of saturation on the mechanical properties and elastic energy density was analyzed,and a method for obtaining peak energy density was proposed.The effect of saturation on the energy evolution was examined,and the energy mechanism of water in preventing rockburst was revealed.The results indicate that an increase in saturation of red sandstone decreases the input energy density,elastic energy density,dissipated energy density,peak strength and peak strain;the compaction phase of the stress–strain curve becomes shorter;the failure mode transitions from X-conjugate oblique shear to single oblique shear;the variation in the debris ejection trajectory is as follows:radiation→X-ray→oblique upward parabola→horizontal parabola→oblique downward parabola;the degree of failure intensity and fragmentation is decreased gradually.Elastic energy density is interconnected with both saturation and stress but independent of the loading path.Saturation exhibits a dual effect on the energy storage property,i.e.,increasing saturation increases the energy storage efficiency and reduces the energy storage capacity.The ratio of peak elastic energy density to peak input energy density remains constant irrespective of saturation levels.Water prevents rockburst by decreasing the energy storage capacity of surrounding rock,alleviating the stress of surrounding rock to reduce energy storage,and elevating the energy release threshold of high-energy surrounding rock.The findings of this study contribute to understanding the effect of water on rock failure from an energy perspective,as well as provide theoretical guidance for rockburst prevention by water in deep tunnels.展开更多
The tight sandstone reservoirs in the first sub-member of Chang 7 member(Chang 71)of Triassic Yanchang Formation in the Jiyuan area,Ordos Basin,show significant variations in microscopic pore-throat structure(PTS)and ...The tight sandstone reservoirs in the first sub-member of Chang 7 member(Chang 71)of Triassic Yanchang Formation in the Jiyuan area,Ordos Basin,show significant variations in microscopic pore-throat structure(PTS)and fluid mobility due to the influences of the northeast and northwest dual provenance systems.This study performed multiple experimental analyses on nine samples from the area to determine the petrological and petrophysical properties,as well as the PTS characteristics of reservoirs in different provenance-controlled regions.On this basis,the pore-throat size distribution(PSD)obtained from high-pressure mercury injection(HPMI)was utilized to convert the NMR movable fluid T2spectrum,allowing for quantitative characterization of the full PSD and the occurrence characteristics of movable fluids.A systematic analysis was conducted on the primary controlling factors affecting fluid mobility in the reservoir.The results indicated that the lithology in the eastern and western regions is lithic arkose.The eastern sandstones,being farther from the provenance,exhibit higher contents of feldspar and lithic fragments,along with the development of more dissolution pores.The reservoir possesses good petrophysical properties,low displacement pressure,and high pore-throat connectivity and homogeneity,indicating strong fluid mobility.In contrast,the western sandstones,being nearer to the provenance,exhibit poor grain sorting,high contents of lithic fragments,strong compaction and cementation effects,resulting in poor petrophysical properties,and strong pore-throat heterogeneity,revealing weak fluid mobility.The range of full PSD in the eastern reservoir is wider than that in the western reservoir,with relatively well-developed macropores.The macropores are the primary space for occurrence of movable fluids,and controls the fluid mobility of the reservoir.The effective porosity of movable fluids(EPMF)quantitatively represents the pore space occupied by movable fluids within the reservoir and correlates well with porosity,permeability,and PTS parameters,making it a valuable parameter for evaluating fluid mobility.Under the multi-provenance system,the eastern and western reservoirs underwent different sedimentation and diagenesis processes,resulting in differential distribution of reservoir mineral components and pore types,which in turn affects the PTS heterogeneity and reservoir quality.The composition and content of reservoir minerals are intrinsic factors influencing fluid mobility,while the microscopic PTS is the primary factor controlling it.Low clay mineral content,welldeveloped macropores,and weak pore-throat heterogeneity all contribute to the storage and seepage of reservoir fluids.展开更多
In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical...In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.展开更多
Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of ...Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of SC-CO_(2),the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations.In this study,cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO_(2)fractu ring experiments under true-triaxial stre ss conditions.The spatial morphology and quantitative attributes of fracture induced by water and SC-CO_(2)fracturing were compared,while the impact of in-situ stress on fracture propagation was also investigated.The results indicate that the SCCO_(2)fracturing takes approximately ten times longer than water fracturing.Furthermore,under identical stress condition,the breakdown pressure(BP)for SC-CO_(2)fracturing is nearly 25%lower than that for water fracturing.A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern,with the primary fracture distribution predominantly controlled by bedding planes.In contrast,SC-CO_(2)fracturing results in a more complex fracture morphology.As the differential of horizontal principal stress increases,the BP for SC-CO_(2)fractured rock exhibits a downward trend,and the induced fracture morphology becomes more simplified.Moreover,the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO_(2)fracturing,simultaneously enhancing the development of a more conductive fracture network.These findings provide critical insights into the efficiency and behavior of SC-CO_(2)fracturing in comparison to traditional water-based fracturing,offering valuable implication for its potential applications in unconventional reservoirs.展开更多
Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timesca...Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.展开更多
Understanding the mesoscopic tensile fracture damage of rock is the basis of evaluating the deterioration process of mechanical properties of heat-damaged rock. For this, tensile tests of rocks under high-temperature ...Understanding the mesoscopic tensile fracture damage of rock is the basis of evaluating the deterioration process of mechanical properties of heat-damaged rock. For this, tensile tests of rocks under high-temperature treatment were conducted with a ϕ75 mm split Hopkinson tension bar (SHTB) to investigate the mesoscopic fracture and damage properties of rock. An improved scanning electron microscopy (SEM) experimental method was used to analyze the tensile fracture surfaces of rock samples. Qualitative and quantitative analyses were performed to assess evolution of mesoscopic damage of heat-damaged rock under tensile loading. A constitutive model describing the mesoscopic fractal damage under thermo-mechanical coupling was established. The results showed that the high temperatures significantly reduced the tensile strength and fracture surface roughness of the red sandstone. The three-dimensional (3D) reconstruction of the fracture surface of the samples that experienced tensile failure at 900 °C showed a flat surface. The standard deviation of elevation and slope angle of specimen fracture surface first increased and then decreased with increasing temperature. The threshold for brittle fracture of the heat-damaged red sandstone specimens was 600 °C. Beyond this threshold temperature, local ductile fracture occurred, resulting in plastic deformation of the fracture surface during tensile fracturing. With increase of temperature, the internal meso-structure of samples was strengthened slightly at first and then deteriorated gradually, which was consistent with the change of macroscopic mechanical properties of red sandstone. The mesoscopic characteristics, such as the number, mean side length, maximum area, porosity, and fractal dimension of crack, exhibited an initial decline, followed by a gradual increase. The development of microcracks in samples had significant influence on mesoscopic fractal dimension. The mesoscopic fractal characteristics were used to establish a mesoscopic fractal damage constitutive model for red sandstone, and the agreement between the theoretical and experimental results validated the proposed model.展开更多
This research employs micro-CT scanning technology to analyze the porosity,pore fractal dimension,and spatial variability of sandstone preheated to 600℃ and subsequently cooled in water at varying temperatures(20℃,6...This research employs micro-CT scanning technology to analyze the porosity,pore fractal dimension,and spatial variability of sandstone preheated to 600℃ and subsequently cooled in water at varying temperatures(20℃,60℃,100℃).The study investigates the mechanisms by which various factors influence thermal shock damage,focusing on the effects of cooling water temperature and the boiling phase transition.The objective is to develop a method for characterizing thermal shock damage that considers spatial variability.The findings indicate that thermal shock damage is limited to a shallow depth beneath the surface,with increased severity near the surface.The boiling phase transition significantly enhances the convective heat transfer coefficient,resulting in substantially higher thermal shock damage when cooled with 100℃ boiling water compared to 20℃ and 60℃ water.Furthermore,for the entire specimen,heating damage exceeds thermal shock damage,and the influence of thermal shock diminishes as specimen size increases.This study addresses the limitations of traditional methods for assessing thermal shock damage that disregard spatial variability and provides practical guidance for engineering projects to manage thermal shock damage more effectively.展开更多
The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study em...The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.展开更多
Existing sandstone rock structure evaluation methods rely on visual inspection,with low efficiency,semi-quantitative analysis of roundness,and inability to perform classified statistics in particle size analysis.This ...Existing sandstone rock structure evaluation methods rely on visual inspection,with low efficiency,semi-quantitative analysis of roundness,and inability to perform classified statistics in particle size analysis.This study presents an intelligent evaluation method for sandstone rock structure based on the Segment Anything Model(SAM).By developing a lightweight SAM fine-tuning method with rank-decomposition matrix adapters,a multispectral rock particle segmentation model named CoreSAM is constructed,which achieves rock particle edge extraction and type identification.Building upon this,we propose a comprehensive quantitative evaluation system for rock structure,assessing parameters including particle size,sorting,roundness,particle contact and cementation types.The experimental results demonstrate that CoreSAM outperforms existing methods in rock particle segmentation accuracy while showing excellent generalization across different image types such as CT scans and core photographs.The proposed method enables full-sample,classified particle size analysis and quantitative characterization of parameters like roundness,advancing reservoir evaluation towards more precise,quantitative,intuitive,and comprehensive development.展开更多
Evaluation of water richness in sandstone is an important research topic in the prevention and control of mine water disasters,and the water richness in sandstone is closely related to its porosity.The refl ection sei...Evaluation of water richness in sandstone is an important research topic in the prevention and control of mine water disasters,and the water richness in sandstone is closely related to its porosity.The refl ection seismic exploration data have high-density spatial sampling information,which provides an important data basis for the prediction of sandstone porosity in coal seam roofs by using refl ection seismic data.First,the basic principles of the variational mode decomposition(VMD)method and the random forest method are introduced.Then,the geological model of coal seam roof sandstone is constructed,seismic forward modeling is conducted,and random noise is added.The decomposition eff ects of the empirical mode decomposition(EMD)method and VMD method on noisy signals are compared and analyzed.The test results show that the firstorder intrinsic mode functions(IMF1)and IMF2 decomposed by the VMD method contain the main eff ective components of seismic signals.A prediction process of sandstone porosity in coal seam roofs based on the combination of VMD and random forest method is proposed.The feasibility and eff ectiveness of the method are verified by trial calculation in the porosity prediction of model data.Taking the actual coalfield refl ection seismic data as an example,the sandstone porosity of the 8 coal seam roof is predicted.The application results show the potential application value of the new porosity prediction method proposed in this study.This method has important theoretical guiding significance for evaluating water richness in coal seam roof sandstone and the prevention and control of mine water disasters.展开更多
Numerous slope failures have been reported during periods of water level fluctuations.Understanding the influence of water on the creep behavior of joints is essential for evaluating the long-term stability of slopes....Numerous slope failures have been reported during periods of water level fluctuations.Understanding the influence of water on the creep behavior of joints is essential for evaluating the long-term stability of slopes.This study focuses on the effects of drying-wetting cycles and soaking conditions on the long-term behavior of sandstone joints.A total of 12 multi-stage shear creep tests are carried out on sandstone joints subjected to varying drying-wetting cycles under both soaking and un-soaking conditions.Based on the experimental results,the influences of drying-wetting cycles as well as soaking conditions on the microstructure,shear creep displacement,strength,and failure morphologies of sandstone joints are investigated comprehensively.Results indicate that increasing drying-wetting cycles not only yields larger shear creep displacements but also leads to a negative exponential decrease in the strength of sandstone joints.Besides,soaking conditions strongly influence the creep behavior of sandstone joints.The failure strength and long-term strength of sandstone joints for soaked samples decrease by 13.6%–29.0%and 19.4%–37.5%,respectively,as compared to unsoaked samples.Furthermore,four distinct stages in the shear creep process were identified according to the results obtained from multi-stage shear creep tests and computerized tomography scans,and three creep failure modes of sandstone joints are thus determined.Finally,the influence mechanism of drying-wetting cycles and soaking conditions on the creep failure modes of sandstone joints is revealed.Drying-wetting cycles and soaking conditions diminish the influence of asperities on the shear creep behavior of joints,thereby reducing the resistance of joints to long-term deformation.展开更多
As an efficient monitoring and prediction tool,chemical tracers have been widely applied in reservoir characterization,production monitoring,water resources monitoring,and various other fields.Chemical tracer technolo...As an efficient monitoring and prediction tool,chemical tracers have been widely applied in reservoir characterization,production monitoring,water resources monitoring,and various other fields.Chemical tracer technology is characterized by high efficiency,high precision,relatively simple operational procedures,and low cost.Owing to the limitations of existing tracers,such as minimal options,limited transport efficiency,and complex detection methods,this study used fluorescein isothiocyanate and a ruthenium complex(Ru(phen_(3))^(2+))to synthesize 50 nm multi-color fluorescent silica nanoparticle tracers using an improved St ober method based on fluorescence resonance energy transfer(FRET).Due to the FRET between the two compounds,the synthesized tracer exhibited the characteristics of multi-color fluorescence,and its fluorescent color varied with the mixing ratio of the two precursor solutions.The fluorescence intensity of the synthesized tracer was significantly higher than that of the monochromatic fluorescent nano-tracer.Fourier-transform infrared spectroscopy,ultraviolet spectrophotometry,and fluorescence spectrometry were used to characterize the structure,maximum absorption wavelength,and fluorescence characteristics of the synthesized tracer,respectively.The experimental results show that the synthesized tracer has a maximum absorption wavelength of 450 nm and an emission wavelength of 576 nm.Under field emission scanning electron microscopy,the tracer appears as uniformly spherical particles with a size of 50±5 nm.It exhibited good dispersibility and fluorescence characteristics in reservoir environments that varied in temperature(25-85°C)and salinity(1000-10000 mg/L).The effects of environmentally sensitive clay minerals,tracer particle size,injection concentration,fluid salinity,and flow rate on the transport characteristics(retention)of tracers in sandstone cores were studied using 12 sets of tracer breakthrough experiments.The experimental results showed that increased sensitivity to clay minerals,salinity,and tracer particle size were not conducive to tracer migration in the core.In contrast,increased tracer injection concentration and flow rate were beneficial to tracer migration in the core.展开更多
To study the energy evolution and failure characteristics of saturated sandstone under unloading conditions,rock unloading tests under different stress paths were conducted.The energy evolution mechanism of the unload...To study the energy evolution and failure characteristics of saturated sandstone under unloading conditions,rock unloading tests under different stress paths were conducted.The energy evolution mechanism of the unloading failure of saturated sandstone was systematically explored from the perspectives of the stress path,the initial confining pressure,and the energy conversion rate.The results show that(1)before the peak stress,the elastic energy increases with an increase in deviatoric stress,while the dissipated energy slowly increases first.After the peak stress,the elastic energy decreases with the decrease of deviatoric stress,and the dissipated energy suddenly increases.The energy release intensity during rock failure is positively correlated with the axial stress.(2)When the initial confining pressure is below a certain threshold,the stress path is the main factor influencing the total energy difference.When the axial stress remains constant and the confining pressure is unloading,the total energy is more sensitive to changes in the confining pressure.When the axial stress remains constant,the compressive deformation ability of the rock cannot be significantly improved by the increase in the initial confining pressure.The initial confining pressure is positively correlated with the rock's energy storage limit.(3)The initial confining pressure increases the energy conversion rate of the rock;the initial confining pressure is positively correlated with the energy conversion rate;and the energy conversion rate has a high confining pressure effect.The increase in the axial stress has a much greater impact on the elastic energy than the confining pressure.(4)When the deviatoric stress is small,the confining pressure mainly plays a protective role.Compared with the case of triaxial compression paths,the rock damage is more severe under unloading paths,and compared with the case of constant axial stress,the rock damage is more severe under increasing axial stress.展开更多
In this study,a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepa...In this study,a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepage of different chemical solutions.It is observed that with the increase of confining pressure,the peak stress,dilatancy stress,dilatancy stress ratio,peak strain,and elastic modulus of the sandstone increase while the Poisson ratio decreases and less secondary cracks are produced when the samples are broken.The pore pressure and confining pressure have opposite influences on the mechanical properties.With the increase of the applied axial stress,three stages are clearly identified in the permeability evolution curves:initial compaction stage,linear elasticity stage and plastic deformation stage.The permeability reaches the maximum value when the highest volumetric dilatancy is obtained.In addition,the hydrochemical action of salt solution with pH=7 and 4 has an obvious deteriorating effect on the mechanical properties and induces the increase of permeability.The obtained results will be useful in engineering to understand the mechanical and seepage properties of sandstone under the coupled chemical-seepage-stress multiple fields.展开更多
Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the ...Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system.Through the combination of dynamic and static stresses,the deformation and damage of rocks under deep rock excavation and blasting were simulated.As the results show,the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases:weakening,stabilizing,and surging periods.In addition,the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases.The degree of fragmentation of specimens increases with the applied stress level;therefore,the stress level is one of the important factors influencing the damage pattern of specimens.The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting.Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz,a loading rate of 0.1 mm/min,a cyclic amplitude of 5 MPa,and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments.Among them,the fine-grained sandstones are the most sensitive to the sinusoidal cyclic perturbation,followed by the muddy siltstone and the medium-grained sandstones.On this basis,the acoustic emission energy release characteristics were analyzed,and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.展开更多
The mechanical behavior of fractured rock mass is significantly different from that of intact rock mass,and it is of great significance to study the mechanical response and damage law of crack rock to clarify the occu...The mechanical behavior of fractured rock mass is significantly different from that of intact rock mass,and it is of great significance to study the mechanical response and damage law of crack rock to clarify the occurrence mechanism of deep geological disasters.Based on this,this paper prepared samples with cracks of different angles,simulated deep stress environment,and conducted triaxial compression test on the samples.Combined with crack strain theory and energy dissipation theory,the mechanical failure characteristics of the sample were analyzed.The results indicate that fractures significantly weaken the mechanical properties of the samples,with the strength of fractured rock decreasing by 53.85-64.67%compared to intact rock,and the strength of frac-tured sandstone samples slightly increases as the crack angle increases.The evolution of crack volume strain reflects the damage and failure processes of the rock,while the slope of the crack volume strain curve indicates the rate of crack growth.The crack initiation stress and damage stress divide the crack volume strain process into the crack closing compaction stage,linear elastic deformation stage and stable expansion stage.With the crack angle increases,both crack initiation stress and damage stress initially decrease and then increase.The sample with an angle of 45◦is the smallest,and the sample with an angle of 90◦is the largest,indicating that the sample with a prefabricated angle of 45◦is the most prone to failure.A mechanical crack propagation model was established to analyze the propagation behavior of the cracks,and the deflection propagation characteristics of the fractured sandstone are explained.Using damage mechanics and statistical theory,a multi-parameter damage evolution expression is developed.It is found that the slow damage growth stage of the sample with the crack angle of 45◦lasted the longest and exhibited the fastest damage growth rate,explaining why it is most prone to failure.The evolution trends of total absorbed energy,elastic strain energy,and dissipated strain energy closely align with the stages of microcrack evolution in the sandstone samples.The evolution of energy dissipation reflects the overall damage and failure trends of the sample,and the theoretical model developed can charac-terize the damage and failure characteristics at a certain stage.Finally,based on the law of crack volume strain,a constitutive model for specimen damage and failure is developed,which is consistent with the test results,thereby verifying its accuracy.展开更多
A novel fractional elastoplastic constitutive model is proposed to accurately characterize the deformation of sandstone under true-triaxial stress states.This model is founded on the yield function and the fractional ...A novel fractional elastoplastic constitutive model is proposed to accurately characterize the deformation of sandstone under true-triaxial stress states.This model is founded on the yield function and the fractional flow rule.The yield function includes parameters that govern the evolution of yield surface,enabling an accurate description of three-dimensional stress states.The direction of plastic flow is governed by the two different fractional orders,which are functions of the plastic internal variable.Additionally,a detailed process is proposed for identifying the yield function parameters and fractional orders.Subsequently,the relationship between the fractional order and the direction of plastic flow in the meridian and deviatoric planes is examined,characterized by the dilation angle and the plastic deflection angle,respectively.The non-orthogonal flow rule,also referred to as the fractional flow rule,allows for a border range of plastic deflection and dilation angles compared to the orthogonal flow rule,thereby significantly enhancing its applicability.The validity and accuracy of proposed model are verified by comparing the analytical solution of the constitutive model with the experimental data.A comparison between the non-orthogonal flow rule and orthogonal flow rule is conducted in both the deviatoric and meridian planes.The further comparison of the stress-strain curves for the non-orthogonal and orthogonal flow rules demonstrates the superiority of the fractional constitutive model.展开更多
During underground excavation,the surrounding rock mass is subjected to complex cyclic stress,significantly impacting its long-term stability,especially under varying water content conditions where this effect is ampl...During underground excavation,the surrounding rock mass is subjected to complex cyclic stress,significantly impacting its long-term stability,especially under varying water content conditions where this effect is amplified.However,research on the mechanical response mechanisms of surrounding rock mass under such conditions remains inadequate.This study utilized acoustic emission(AE)and resistivity testing to monitor rock fracture changes,revealing the rock’s damage state and characterizing the damage evolution process during uniaxial cyclic loading and unloading.First,a damage variable equation was established based on AE and resistivity parameters,leading to the derivation of a corresponding damage constitutive equation.Uniaxial cyclic loading and unloading tests were then conducted on sandstone samples with varying water contents,continuously monitoring AE signals and resistivity,along with computed tomography scans before and after failure.The predictions from the damage constitutive equation were compared with experimental results.This comparison shows that the proposed damage variable equation effectively characterizes the damage evolution of sandstone during loading and unloading,and that the constitutive equation closely fits the experimental data.This study provides a theoretical basis for monitoring and assessing the responses of surrounding rock mass during underground excavation.展开更多
The deterioration of rock mass in the Three Gorges reservoir area results from the coupled damage effects of macro-micro cracks and dry-wet cycles,and the coupled damage progression can be characterized by energy rele...The deterioration of rock mass in the Three Gorges reservoir area results from the coupled damage effects of macro-micro cracks and dry-wet cycles,and the coupled damage progression can be characterized by energy release rate.In this study,a series of dry-wet cycle uniaxial compression tests was conducted on fractured sandstone,and a method was developed for calculating macro-micro damage(D_(R))and energy release rates(Y_(R))of fractured sandstone subjected to dry-wet cycles by considering energy release rate,dry-wet damage and macro-micro damage.Therewith,the damage mechanisms and complex microcrack propagation patterns of rocks were investigated.Research indicates that sandstone degradation after a limited cycle count primarily exhibits exsolution of internal fillers,progressing to grain skeleton alteration and erosion with increased cycles.Compared with conventional methods,the D_(R) and Y_(R) methodologies exhibit heightened sensitivity to microcrack closure during compaction and abrupt energy release at the point of failure.Based on D_(R) and Y_(R),the failure process of fractured sandstone can be classified into six stages:stress adjustment(I),microcracks equal closure(II),nonlinear slow closure(III),low-speed extension(IV),rapid extension(V),and macroscopic main fracture emergence(VI).The abrupt change in damage energy release rate during stage V may serve as a reliable precursor for inducing failure.The stage-based classification may enhance traditional methods by tracking damage progression and accurately identifying rock failure precursors.The findings are expected to provide a scientific basis for understanding damage mechanisms and enabling early warning of reservoir-bank slope failure.展开更多
The influence of FT(freeze-thaw)cycles and average strain rate on the dynamic impact performance,energy evolution characteristics,and failure behavior of sandstone was studied through dynamic impact tests.Results disp...The influence of FT(freeze-thaw)cycles and average strain rate on the dynamic impact performance,energy evolution characteristics,and failure behavior of sandstone was studied through dynamic impact tests.Results displayed that the FT damage process of samples can be divided into three stages based on the changes in weight,porosity,and P-wave velocity.The dynamic peak strength,dynamic elastic modulus,and strength ratio decreased with increasing FT cycles,and increased with increasing average strain rate.Moreover,the average strain rate reduced the influence of FT cycles on dynamic peak strength.In general,the incident energy,reflected energy and dissipated energy increased with increasing average strain rate,the transmitted energy was negligibly affected by the average strain rate,and the energy dissipation ratio decreased with increasing average strain rate.In addition,the influence of FT cycles on each type of energy and energy dissipation ratio during sample failure was smaller than that of average strain rate.The average size of fragments can accurately demonstrate the impact of FT damage and average strain rate on dynamic peak strength and failure mode,and quantitatively evaluate the sample’s fragmentation degree.Fractal dimension varies with FT cycles and average strain rate,and the threshold is between 148.30 and 242.57 s^(-1).If the average strain rate is in the threshold range,the relationship between the fractal dimension and dynamic peak strength is more regular,otherwise,it will become complicated.The results reveal the dynamic failure mechanism of white sandstone samples,providing assistance for dynamic rock-breaking and disaster prevention in cold regions.展开更多
基金supported by the National Natural Science Foundation of China(52104133,52304227)the Natural Science Foundation of Hunan Province(2021JJ40465,2023JJ40548)the Opening Foundation of the State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines(SKLMRDPC20KF03).
文摘To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compression and uniaxial loading–unloading tests were conducted under five saturation levels.The effect of saturation on the mechanical properties and elastic energy density was analyzed,and a method for obtaining peak energy density was proposed.The effect of saturation on the energy evolution was examined,and the energy mechanism of water in preventing rockburst was revealed.The results indicate that an increase in saturation of red sandstone decreases the input energy density,elastic energy density,dissipated energy density,peak strength and peak strain;the compaction phase of the stress–strain curve becomes shorter;the failure mode transitions from X-conjugate oblique shear to single oblique shear;the variation in the debris ejection trajectory is as follows:radiation→X-ray→oblique upward parabola→horizontal parabola→oblique downward parabola;the degree of failure intensity and fragmentation is decreased gradually.Elastic energy density is interconnected with both saturation and stress but independent of the loading path.Saturation exhibits a dual effect on the energy storage property,i.e.,increasing saturation increases the energy storage efficiency and reduces the energy storage capacity.The ratio of peak elastic energy density to peak input energy density remains constant irrespective of saturation levels.Water prevents rockburst by decreasing the energy storage capacity of surrounding rock,alleviating the stress of surrounding rock to reduce energy storage,and elevating the energy release threshold of high-energy surrounding rock.The findings of this study contribute to understanding the effect of water on rock failure from an energy perspective,as well as provide theoretical guidance for rockburst prevention by water in deep tunnels.
文摘The tight sandstone reservoirs in the first sub-member of Chang 7 member(Chang 71)of Triassic Yanchang Formation in the Jiyuan area,Ordos Basin,show significant variations in microscopic pore-throat structure(PTS)and fluid mobility due to the influences of the northeast and northwest dual provenance systems.This study performed multiple experimental analyses on nine samples from the area to determine the petrological and petrophysical properties,as well as the PTS characteristics of reservoirs in different provenance-controlled regions.On this basis,the pore-throat size distribution(PSD)obtained from high-pressure mercury injection(HPMI)was utilized to convert the NMR movable fluid T2spectrum,allowing for quantitative characterization of the full PSD and the occurrence characteristics of movable fluids.A systematic analysis was conducted on the primary controlling factors affecting fluid mobility in the reservoir.The results indicated that the lithology in the eastern and western regions is lithic arkose.The eastern sandstones,being farther from the provenance,exhibit higher contents of feldspar and lithic fragments,along with the development of more dissolution pores.The reservoir possesses good petrophysical properties,low displacement pressure,and high pore-throat connectivity and homogeneity,indicating strong fluid mobility.In contrast,the western sandstones,being nearer to the provenance,exhibit poor grain sorting,high contents of lithic fragments,strong compaction and cementation effects,resulting in poor petrophysical properties,and strong pore-throat heterogeneity,revealing weak fluid mobility.The range of full PSD in the eastern reservoir is wider than that in the western reservoir,with relatively well-developed macropores.The macropores are the primary space for occurrence of movable fluids,and controls the fluid mobility of the reservoir.The effective porosity of movable fluids(EPMF)quantitatively represents the pore space occupied by movable fluids within the reservoir and correlates well with porosity,permeability,and PTS parameters,making it a valuable parameter for evaluating fluid mobility.Under the multi-provenance system,the eastern and western reservoirs underwent different sedimentation and diagenesis processes,resulting in differential distribution of reservoir mineral components and pore types,which in turn affects the PTS heterogeneity and reservoir quality.The composition and content of reservoir minerals are intrinsic factors influencing fluid mobility,while the microscopic PTS is the primary factor controlling it.Low clay mineral content,welldeveloped macropores,and weak pore-throat heterogeneity all contribute to the storage and seepage of reservoir fluids.
基金funding support from the National Natural Science Foundation of China(Grant No.12172019).
文摘In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.
基金funded by the National Natural Scientific Foundation of China(Nos.52304008,52404038,52474043)the China Postdoctoral Science Foundation(No.2023MD734223)+1 种基金the Key Laboratory of Well Stability and Fluid&Rock Mechanics in Oil and Gas Reservoir of Shaanxi Province(No.23JS047)the Youth Talent Lifting Program of Xi'an Science and Technology Association(No.959202413078)。
文摘Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of SC-CO_(2),the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations.In this study,cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO_(2)fractu ring experiments under true-triaxial stre ss conditions.The spatial morphology and quantitative attributes of fracture induced by water and SC-CO_(2)fracturing were compared,while the impact of in-situ stress on fracture propagation was also investigated.The results indicate that the SCCO_(2)fracturing takes approximately ten times longer than water fracturing.Furthermore,under identical stress condition,the breakdown pressure(BP)for SC-CO_(2)fracturing is nearly 25%lower than that for water fracturing.A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern,with the primary fracture distribution predominantly controlled by bedding planes.In contrast,SC-CO_(2)fracturing results in a more complex fracture morphology.As the differential of horizontal principal stress increases,the BP for SC-CO_(2)fractured rock exhibits a downward trend,and the induced fracture morphology becomes more simplified.Moreover,the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO_(2)fracturing,simultaneously enhancing the development of a more conductive fracture network.These findings provide critical insights into the efficiency and behavior of SC-CO_(2)fracturing in comparison to traditional water-based fracturing,offering valuable implication for its potential applications in unconventional reservoirs.
基金supported by the National Key Research and Development Program of China(2022YFE0206700).
文摘Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.
基金supported by The National Natural Science Foundation of China(Grant Nos.12272411 and 42007259).
文摘Understanding the mesoscopic tensile fracture damage of rock is the basis of evaluating the deterioration process of mechanical properties of heat-damaged rock. For this, tensile tests of rocks under high-temperature treatment were conducted with a ϕ75 mm split Hopkinson tension bar (SHTB) to investigate the mesoscopic fracture and damage properties of rock. An improved scanning electron microscopy (SEM) experimental method was used to analyze the tensile fracture surfaces of rock samples. Qualitative and quantitative analyses were performed to assess evolution of mesoscopic damage of heat-damaged rock under tensile loading. A constitutive model describing the mesoscopic fractal damage under thermo-mechanical coupling was established. The results showed that the high temperatures significantly reduced the tensile strength and fracture surface roughness of the red sandstone. The three-dimensional (3D) reconstruction of the fracture surface of the samples that experienced tensile failure at 900 °C showed a flat surface. The standard deviation of elevation and slope angle of specimen fracture surface first increased and then decreased with increasing temperature. The threshold for brittle fracture of the heat-damaged red sandstone specimens was 600 °C. Beyond this threshold temperature, local ductile fracture occurred, resulting in plastic deformation of the fracture surface during tensile fracturing. With increase of temperature, the internal meso-structure of samples was strengthened slightly at first and then deteriorated gradually, which was consistent with the change of macroscopic mechanical properties of red sandstone. The mesoscopic characteristics, such as the number, mean side length, maximum area, porosity, and fractal dimension of crack, exhibited an initial decline, followed by a gradual increase. The development of microcracks in samples had significant influence on mesoscopic fractal dimension. The mesoscopic fractal characteristics were used to establish a mesoscopic fractal damage constitutive model for red sandstone, and the agreement between the theoretical and experimental results validated the proposed model.
基金financially supported by the National Natural Science Foundation of China(Grant No.51874207)the Natural Science Foundation of Shanxi Province(Grant Nos.202303021211042 and 202303011222006).
文摘This research employs micro-CT scanning technology to analyze the porosity,pore fractal dimension,and spatial variability of sandstone preheated to 600℃ and subsequently cooled in water at varying temperatures(20℃,60℃,100℃).The study investigates the mechanisms by which various factors influence thermal shock damage,focusing on the effects of cooling water temperature and the boiling phase transition.The objective is to develop a method for characterizing thermal shock damage that considers spatial variability.The findings indicate that thermal shock damage is limited to a shallow depth beneath the surface,with increased severity near the surface.The boiling phase transition significantly enhances the convective heat transfer coefficient,resulting in substantially higher thermal shock damage when cooled with 100℃ boiling water compared to 20℃ and 60℃ water.Furthermore,for the entire specimen,heating damage exceeds thermal shock damage,and the influence of thermal shock diminishes as specimen size increases.This study addresses the limitations of traditional methods for assessing thermal shock damage that disregard spatial variability and provides practical guidance for engineering projects to manage thermal shock damage more effectively.
基金the Helmholtz association for funding the main parts of the modeling and simulation research work under the program“MTET:38.04.04”。
文摘The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.
基金Supported by the National Natural Science Foundation of China(42372175,72088101)PetroChina Science and Technology Project of(2023DJ84)Basic Research Cooperation Project between China National Petroleum Corporation and Peking University.
文摘Existing sandstone rock structure evaluation methods rely on visual inspection,with low efficiency,semi-quantitative analysis of roundness,and inability to perform classified statistics in particle size analysis.This study presents an intelligent evaluation method for sandstone rock structure based on the Segment Anything Model(SAM).By developing a lightweight SAM fine-tuning method with rank-decomposition matrix adapters,a multispectral rock particle segmentation model named CoreSAM is constructed,which achieves rock particle edge extraction and type identification.Building upon this,we propose a comprehensive quantitative evaluation system for rock structure,assessing parameters including particle size,sorting,roundness,particle contact and cementation types.The experimental results demonstrate that CoreSAM outperforms existing methods in rock particle segmentation accuracy while showing excellent generalization across different image types such as CT scans and core photographs.The proposed method enables full-sample,classified particle size analysis and quantitative characterization of parameters like roundness,advancing reservoir evaluation towards more precise,quantitative,intuitive,and comprehensive development.
基金National Natural Science Foundation of China(Grant No.42274180)National Key Research and Development Program of China(2021YFC2902003).
文摘Evaluation of water richness in sandstone is an important research topic in the prevention and control of mine water disasters,and the water richness in sandstone is closely related to its porosity.The refl ection seismic exploration data have high-density spatial sampling information,which provides an important data basis for the prediction of sandstone porosity in coal seam roofs by using refl ection seismic data.First,the basic principles of the variational mode decomposition(VMD)method and the random forest method are introduced.Then,the geological model of coal seam roof sandstone is constructed,seismic forward modeling is conducted,and random noise is added.The decomposition eff ects of the empirical mode decomposition(EMD)method and VMD method on noisy signals are compared and analyzed.The test results show that the firstorder intrinsic mode functions(IMF1)and IMF2 decomposed by the VMD method contain the main eff ective components of seismic signals.A prediction process of sandstone porosity in coal seam roofs based on the combination of VMD and random forest method is proposed.The feasibility and eff ectiveness of the method are verified by trial calculation in the porosity prediction of model data.Taking the actual coalfield refl ection seismic data as an example,the sandstone porosity of the 8 coal seam roof is predicted.The application results show the potential application value of the new porosity prediction method proposed in this study.This method has important theoretical guiding significance for evaluating water richness in coal seam roof sandstone and the prevention and control of mine water disasters.
基金financial support from the National Natural Science Foundation of China(Grant Nos.52479108,52408391)the Fundamental Research Funds for the Central Universities(2042024kf0032)+1 种基金the Postdoctoral Fellowship Program(Grade C)of China Postdoctoral Science Foundation(Grant No.GZC20241283)the Natural Science Foundation of Hubei Province,China(No.2024AFB160)。
文摘Numerous slope failures have been reported during periods of water level fluctuations.Understanding the influence of water on the creep behavior of joints is essential for evaluating the long-term stability of slopes.This study focuses on the effects of drying-wetting cycles and soaking conditions on the long-term behavior of sandstone joints.A total of 12 multi-stage shear creep tests are carried out on sandstone joints subjected to varying drying-wetting cycles under both soaking and un-soaking conditions.Based on the experimental results,the influences of drying-wetting cycles as well as soaking conditions on the microstructure,shear creep displacement,strength,and failure morphologies of sandstone joints are investigated comprehensively.Results indicate that increasing drying-wetting cycles not only yields larger shear creep displacements but also leads to a negative exponential decrease in the strength of sandstone joints.Besides,soaking conditions strongly influence the creep behavior of sandstone joints.The failure strength and long-term strength of sandstone joints for soaked samples decrease by 13.6%–29.0%and 19.4%–37.5%,respectively,as compared to unsoaked samples.Furthermore,four distinct stages in the shear creep process were identified according to the results obtained from multi-stage shear creep tests and computerized tomography scans,and three creep failure modes of sandstone joints are thus determined.Finally,the influence mechanism of drying-wetting cycles and soaking conditions on the creep failure modes of sandstone joints is revealed.Drying-wetting cycles and soaking conditions diminish the influence of asperities on the shear creep behavior of joints,thereby reducing the resistance of joints to long-term deformation.
基金funded by the Sichuan Science and Technology Education Joint Fund,including the mechanism and characterization of CO_(2) geological storage and utilization of carbonate reservoirs in the Sichuan Basin to improve the sealing capacity of mudstone caprocks(No.2024NSFSC1981)also supported by the China Petroleum Science and Technology Innovation Fund,including the experiment of acoustic response mechanism of horizontal well fracturing and the research of DAS big data intelligent inversion method(No.2022DQ02-0305)also supported by the National Natural Science Foundation of China'Study on the mechanism of SNPs improving the sealing ability of mudstone caprock in CO_(2) geological storage(No.42272176)。
文摘As an efficient monitoring and prediction tool,chemical tracers have been widely applied in reservoir characterization,production monitoring,water resources monitoring,and various other fields.Chemical tracer technology is characterized by high efficiency,high precision,relatively simple operational procedures,and low cost.Owing to the limitations of existing tracers,such as minimal options,limited transport efficiency,and complex detection methods,this study used fluorescein isothiocyanate and a ruthenium complex(Ru(phen_(3))^(2+))to synthesize 50 nm multi-color fluorescent silica nanoparticle tracers using an improved St ober method based on fluorescence resonance energy transfer(FRET).Due to the FRET between the two compounds,the synthesized tracer exhibited the characteristics of multi-color fluorescence,and its fluorescent color varied with the mixing ratio of the two precursor solutions.The fluorescence intensity of the synthesized tracer was significantly higher than that of the monochromatic fluorescent nano-tracer.Fourier-transform infrared spectroscopy,ultraviolet spectrophotometry,and fluorescence spectrometry were used to characterize the structure,maximum absorption wavelength,and fluorescence characteristics of the synthesized tracer,respectively.The experimental results show that the synthesized tracer has a maximum absorption wavelength of 450 nm and an emission wavelength of 576 nm.Under field emission scanning electron microscopy,the tracer appears as uniformly spherical particles with a size of 50±5 nm.It exhibited good dispersibility and fluorescence characteristics in reservoir environments that varied in temperature(25-85°C)and salinity(1000-10000 mg/L).The effects of environmentally sensitive clay minerals,tracer particle size,injection concentration,fluid salinity,and flow rate on the transport characteristics(retention)of tracers in sandstone cores were studied using 12 sets of tracer breakthrough experiments.The experimental results showed that increased sensitivity to clay minerals,salinity,and tracer particle size were not conducive to tracer migration in the core.In contrast,increased tracer injection concentration and flow rate were beneficial to tracer migration in the core.
基金Anhui Natural Science Foundation Youth Program,Grant/Award Number:2208085QE142National Natural Science Foundations of China,Grant/Award Numbers:52004003,52304073Opening Foundation of Anhui Province Key Laboratory of Building Structure and Underground Engineering,Grant/Award Number:KLBSUE-2022-04。
文摘To study the energy evolution and failure characteristics of saturated sandstone under unloading conditions,rock unloading tests under different stress paths were conducted.The energy evolution mechanism of the unloading failure of saturated sandstone was systematically explored from the perspectives of the stress path,the initial confining pressure,and the energy conversion rate.The results show that(1)before the peak stress,the elastic energy increases with an increase in deviatoric stress,while the dissipated energy slowly increases first.After the peak stress,the elastic energy decreases with the decrease of deviatoric stress,and the dissipated energy suddenly increases.The energy release intensity during rock failure is positively correlated with the axial stress.(2)When the initial confining pressure is below a certain threshold,the stress path is the main factor influencing the total energy difference.When the axial stress remains constant and the confining pressure is unloading,the total energy is more sensitive to changes in the confining pressure.When the axial stress remains constant,the compressive deformation ability of the rock cannot be significantly improved by the increase in the initial confining pressure.The initial confining pressure is positively correlated with the rock's energy storage limit.(3)The initial confining pressure increases the energy conversion rate of the rock;the initial confining pressure is positively correlated with the energy conversion rate;and the energy conversion rate has a high confining pressure effect.The increase in the axial stress has a much greater impact on the elastic energy than the confining pressure.(4)When the deviatoric stress is small,the confining pressure mainly plays a protective role.Compared with the case of triaxial compression paths,the rock damage is more severe under unloading paths,and compared with the case of constant axial stress,the rock damage is more severe under increasing axial stress.
基金Projects(12072102,12102129)supported by the National Natural Science Foundation of ChinaProject(DM2022B01)supported by the Key Laboratory of Safe Mining of Deep Metal Mines,Ministry of Education,ChinaProject(JZ-008)supported by the Six Talent Peaks Project in Jiangsu Province,China。
文摘In this study,a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepage of different chemical solutions.It is observed that with the increase of confining pressure,the peak stress,dilatancy stress,dilatancy stress ratio,peak strain,and elastic modulus of the sandstone increase while the Poisson ratio decreases and less secondary cracks are produced when the samples are broken.The pore pressure and confining pressure have opposite influences on the mechanical properties.With the increase of the applied axial stress,three stages are clearly identified in the permeability evolution curves:initial compaction stage,linear elasticity stage and plastic deformation stage.The permeability reaches the maximum value when the highest volumetric dilatancy is obtained.In addition,the hydrochemical action of salt solution with pH=7 and 4 has an obvious deteriorating effect on the mechanical properties and induces the increase of permeability.The obtained results will be useful in engineering to understand the mechanical and seepage properties of sandstone under the coupled chemical-seepage-stress multiple fields.
基金Open Project of State Key Laboratory for Geomechanics and Deep Underground Engineering in CUMTB,Grant/Award Number:SKLGDUEK2023National Natural Science Foundation of China,Grant/Award Number:52204101Natural Science Foundation of Shandong Province,Grant/Award Number:ZR2022QE137。
文摘Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system.Through the combination of dynamic and static stresses,the deformation and damage of rocks under deep rock excavation and blasting were simulated.As the results show,the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases:weakening,stabilizing,and surging periods.In addition,the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases.The degree of fragmentation of specimens increases with the applied stress level;therefore,the stress level is one of the important factors influencing the damage pattern of specimens.The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting.Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz,a loading rate of 0.1 mm/min,a cyclic amplitude of 5 MPa,and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments.Among them,the fine-grained sandstones are the most sensitive to the sinusoidal cyclic perturbation,followed by the muddy siltstone and the medium-grained sandstones.On this basis,the acoustic emission energy release characteristics were analyzed,and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.
基金supported by the Postdoctoral Fellowship Program of CPSF under Grant No.GZB20230451 and 2024T170578National Natural Science Foundation of China Grant.No 52374222+1 种基金National major science and technology project for deep earth Grant No.2024ZD1003903Basic and Applied Basic Research Project of Guangdong Province(2024A1515010992).
文摘The mechanical behavior of fractured rock mass is significantly different from that of intact rock mass,and it is of great significance to study the mechanical response and damage law of crack rock to clarify the occurrence mechanism of deep geological disasters.Based on this,this paper prepared samples with cracks of different angles,simulated deep stress environment,and conducted triaxial compression test on the samples.Combined with crack strain theory and energy dissipation theory,the mechanical failure characteristics of the sample were analyzed.The results indicate that fractures significantly weaken the mechanical properties of the samples,with the strength of fractured rock decreasing by 53.85-64.67%compared to intact rock,and the strength of frac-tured sandstone samples slightly increases as the crack angle increases.The evolution of crack volume strain reflects the damage and failure processes of the rock,while the slope of the crack volume strain curve indicates the rate of crack growth.The crack initiation stress and damage stress divide the crack volume strain process into the crack closing compaction stage,linear elastic deformation stage and stable expansion stage.With the crack angle increases,both crack initiation stress and damage stress initially decrease and then increase.The sample with an angle of 45◦is the smallest,and the sample with an angle of 90◦is the largest,indicating that the sample with a prefabricated angle of 45◦is the most prone to failure.A mechanical crack propagation model was established to analyze the propagation behavior of the cracks,and the deflection propagation characteristics of the fractured sandstone are explained.Using damage mechanics and statistical theory,a multi-parameter damage evolution expression is developed.It is found that the slow damage growth stage of the sample with the crack angle of 45◦lasted the longest and exhibited the fastest damage growth rate,explaining why it is most prone to failure.The evolution trends of total absorbed energy,elastic strain energy,and dissipated strain energy closely align with the stages of microcrack evolution in the sandstone samples.The evolution of energy dissipation reflects the overall damage and failure trends of the sample,and the theoretical model developed can charac-terize the damage and failure characteristics at a certain stage.Finally,based on the law of crack volume strain,a constitutive model for specimen damage and failure is developed,which is consistent with the test results,thereby verifying its accuracy.
基金sponsored by the National Natural Science Foundation of China(Grant No.42141010).
文摘A novel fractional elastoplastic constitutive model is proposed to accurately characterize the deformation of sandstone under true-triaxial stress states.This model is founded on the yield function and the fractional flow rule.The yield function includes parameters that govern the evolution of yield surface,enabling an accurate description of three-dimensional stress states.The direction of plastic flow is governed by the two different fractional orders,which are functions of the plastic internal variable.Additionally,a detailed process is proposed for identifying the yield function parameters and fractional orders.Subsequently,the relationship between the fractional order and the direction of plastic flow in the meridian and deviatoric planes is examined,characterized by the dilation angle and the plastic deflection angle,respectively.The non-orthogonal flow rule,also referred to as the fractional flow rule,allows for a border range of plastic deflection and dilation angles compared to the orthogonal flow rule,thereby significantly enhancing its applicability.The validity and accuracy of proposed model are verified by comparing the analytical solution of the constitutive model with the experimental data.A comparison between the non-orthogonal flow rule and orthogonal flow rule is conducted in both the deviatoric and meridian planes.The further comparison of the stress-strain curves for the non-orthogonal and orthogonal flow rules demonstrates the superiority of the fractional constitutive model.
基金Projects(52279117,52325905)supported by the National Natural Science Foundation of ChinaProject(DJ-HXGG-2023-16)supported by the Technology Project of PowerChinaProject(SKLGME-JBGS2401)supported by the State Key Laboratory of Geomechanics and Geotechnical Engineering,China。
文摘During underground excavation,the surrounding rock mass is subjected to complex cyclic stress,significantly impacting its long-term stability,especially under varying water content conditions where this effect is amplified.However,research on the mechanical response mechanisms of surrounding rock mass under such conditions remains inadequate.This study utilized acoustic emission(AE)and resistivity testing to monitor rock fracture changes,revealing the rock’s damage state and characterizing the damage evolution process during uniaxial cyclic loading and unloading.First,a damage variable equation was established based on AE and resistivity parameters,leading to the derivation of a corresponding damage constitutive equation.Uniaxial cyclic loading and unloading tests were then conducted on sandstone samples with varying water contents,continuously monitoring AE signals and resistivity,along with computed tomography scans before and after failure.The predictions from the damage constitutive equation were compared with experimental results.This comparison shows that the proposed damage variable equation effectively characterizes the damage evolution of sandstone during loading and unloading,and that the constitutive equation closely fits the experimental data.This study provides a theoretical basis for monitoring and assessing the responses of surrounding rock mass during underground excavation.
基金supported by the National Natural Science Foundation of China(Grant No.51978106)China Postdoctoral Science Foundation(Grant No.2022MD723831)Graduate Research and Innovation Foundation of Chongqing(Grant No.CYB240039).
文摘The deterioration of rock mass in the Three Gorges reservoir area results from the coupled damage effects of macro-micro cracks and dry-wet cycles,and the coupled damage progression can be characterized by energy release rate.In this study,a series of dry-wet cycle uniaxial compression tests was conducted on fractured sandstone,and a method was developed for calculating macro-micro damage(D_(R))and energy release rates(Y_(R))of fractured sandstone subjected to dry-wet cycles by considering energy release rate,dry-wet damage and macro-micro damage.Therewith,the damage mechanisms and complex microcrack propagation patterns of rocks were investigated.Research indicates that sandstone degradation after a limited cycle count primarily exhibits exsolution of internal fillers,progressing to grain skeleton alteration and erosion with increased cycles.Compared with conventional methods,the D_(R) and Y_(R) methodologies exhibit heightened sensitivity to microcrack closure during compaction and abrupt energy release at the point of failure.Based on D_(R) and Y_(R),the failure process of fractured sandstone can be classified into six stages:stress adjustment(I),microcracks equal closure(II),nonlinear slow closure(III),low-speed extension(IV),rapid extension(V),and macroscopic main fracture emergence(VI).The abrupt change in damage energy release rate during stage V may serve as a reliable precursor for inducing failure.The stage-based classification may enhance traditional methods by tracking damage progression and accurately identifying rock failure precursors.The findings are expected to provide a scientific basis for understanding damage mechanisms and enabling early warning of reservoir-bank slope failure.
基金Funded by the National Natural Science Foundation of China(Nos.52174088,42277154)the Independent Innovation Research Fund Graduate Free Exploration Project for the Wuhan University of Technology(No.104972024JYS0007)。
文摘The influence of FT(freeze-thaw)cycles and average strain rate on the dynamic impact performance,energy evolution characteristics,and failure behavior of sandstone was studied through dynamic impact tests.Results displayed that the FT damage process of samples can be divided into three stages based on the changes in weight,porosity,and P-wave velocity.The dynamic peak strength,dynamic elastic modulus,and strength ratio decreased with increasing FT cycles,and increased with increasing average strain rate.Moreover,the average strain rate reduced the influence of FT cycles on dynamic peak strength.In general,the incident energy,reflected energy and dissipated energy increased with increasing average strain rate,the transmitted energy was negligibly affected by the average strain rate,and the energy dissipation ratio decreased with increasing average strain rate.In addition,the influence of FT cycles on each type of energy and energy dissipation ratio during sample failure was smaller than that of average strain rate.The average size of fragments can accurately demonstrate the impact of FT damage and average strain rate on dynamic peak strength and failure mode,and quantitatively evaluate the sample’s fragmentation degree.Fractal dimension varies with FT cycles and average strain rate,and the threshold is between 148.30 and 242.57 s^(-1).If the average strain rate is in the threshold range,the relationship between the fractal dimension and dynamic peak strength is more regular,otherwise,it will become complicated.The results reveal the dynamic failure mechanism of white sandstone samples,providing assistance for dynamic rock-breaking and disaster prevention in cold regions.
