Cyclic changes in the internal pressure of compressed air energy storage reservoirs in abandoned coal mines result in complex alternating loads on the rocks surrounding the energy storage reservoirs.These complex alte...Cyclic changes in the internal pressure of compressed air energy storage reservoirs in abandoned coal mines result in complex alternating loads on the rocks surrounding the energy storage reservoirs.These complex alternating loads can be regarded as multi-stage constant-amplitude cyclic loads following simplification.In this paper,the mechanical responses and acoustic emission(AE)characteristics of red sandstone with five bedding dip angles(0°,30°,45°,60°,and 90°)under such loads are investigated,and the damage evolution processes of the five specimens are revealed from both quantitative and microscopic perspectives.The results show that the fatigue deformation characteristics of the specimens are affected by the bedding dip angle.Under cyclic loads,the axially irreversible plastic deformations of the rocks increase,their elastic stiffness increases,their crack volumetric strain increases and then decreases,and their AE cumulative count/energy curves exhibit a ladder shape.A damage evolution model based on the crack volumetric strain is proposed,and the damage evolution process is divided into two stages:a rapid increase stage and a tendency toward stabilization stage.Through cluster analysis,the AE events are used to classify the damage into three categories:small-sized localized damage,large-sized tensile damage,and large-sized shear damage.Finally,the MohreCoulomb criterion is applied to analyze the relationship between the failure modes of the red sandstone specimens and the dip angle of the bedding.The results of this study will help to predict the stability and safety of compressed air energy storage reservoirs in abandoned coal mines.展开更多
Salt cavern energy storage technology contributes to energy reserves and renewable energy scale-up.This study focuses on salt cavern gas storage in Jintan to assess the long-term stability of its surrounding rock unde...Salt cavern energy storage technology contributes to energy reserves and renewable energy scale-up.This study focuses on salt cavern gas storage in Jintan to assess the long-term stability of its surrounding rock under frequent operation.The fatigue test results indicate that stress holding significantly reduces fatigue life,with the magnitude of stress level outweighing the duration of holding time in determining peak strain.Employing a machine learning approach,the impact of various factors on fatigue life and peak strain was quantified,revealing that higher stress limits and stress holding adversely impact the fatigue index,whereas lower stress limits and rate exhibit a positive effect.A novel fatigue-creep composite damage constitutive model is constructed,which is able to consider stress magnitude,rate,and stress holding.The model,validated through multi-path tests,accurately captures the elasto-viscous behavior of salt rock during loading,unloading,and stress holding.Sensitivity analysis further reveals the time-and stress-dependent behavior of model parameters,clarifying that strain changes stem not only from stress variations but are also influenced by alterations in elasto-viscous parameters.This study provides a new method for the mechanical assessment of salt cavern gas storage surrounding rocks.展开更多
To ensure the safe implementation of underground reservoirs in abandoned coal mines,this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading....To ensure the safe implementation of underground reservoirs in abandoned coal mines,this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading.Specimens with coal-to-concrete height ratios ranging from 0.5:1 to 3:1 were tested,with damage evolution continuously monitored using acoustic emission techniques.Results indicate that while the peak strength of pure materials decreases by approximately 1 MPa under cyclic stress compared to uniaxial compression,composite specimens exhibit strength enhancements exceeding 5 MPa.However,the peak strength of composite specimens decreases with increasing coal height,from 30 MPa at CR0.5 to 20 MPa at CR3.0.The damage state was assessed using the dynamic elastic strain energy index and Felicity ratio,which revealed that composite specimens are more prone to early damage accumulation.Spatial acoustic emission localization further reveals distinct failure modes across specimens with varying height ratios.To elucidate these differences,interfacial effects were incorporated into a modified twin-shear unified strength theory.The refined model accurately predicts the internal strength distribution and failure characteristics of the composite structures.These findings provide a theoretical basis for the structural design and safe operation of underground reservoir dams.展开更多
During the development of hot dry rock,the research on thermal fatigue damage caused by thermal shock of cold and heat cycles is the basis that ensures the long-term utilization of geothermal resources,but there are n...During the development of hot dry rock,the research on thermal fatigue damage caused by thermal shock of cold and heat cycles is the basis that ensures the long-term utilization of geothermal resources,but there are not enough relevant studies at present.Based on this,the thermal damage tests of granite at different temperatures(250,350,450°C)and quenching cycles(1,5,10,15 cycles)were carried out.Preliminary reveals the damage mechanism and heat transfer law of the quenching cycle effect on hot dry rock.The results show that with the increase of temperature and cycles,the uneven thermal expansion of minerals and the thermal shock caused by quenching promote the crack development of granite,resulting in the decrease of P-wave velocity,thermal conductivity and uniaxial compressive strength of granite.Meanwhile,the COMSOL was used to simulate the heat transfer of hot dry rock under different heat treatment conditions.It concluded that the increase in the number of quenching cycles reduced the heat transfer capacity of the granite,especially more than 10 quenching cycles,which also reflects that the thermal fatigue damage leads to a longer time for the temperature recovery of the hot dry rock mass.In addition,the three-dimensional nonlinear fitting relationship among thermal conductivity,temperature and cycle number was established for the first time,which can better reveal the change rule of thermal conductivity after quenching thermal fatigue effect of hot dry rock.The research results provide theoretical support for hot dry rock reservoir reconstruction and production efficiency evaluation.展开更多
With the depletion of shallow resources,the exploration of deep earth resources has become a global strategy.The study of the different patterns in the physical mechanical properties of rocks at different occurrence d...With the depletion of shallow resources,the exploration of deep earth resources has become a global strategy.The study of the different patterns in the physical mechanical properties of rocks at different occurrence depths is the basis for exploring deep into the earth,with the core and premise being the acquisition and testing of deep in-situ core specimens.Based on the original idea of deep in-situ condition preserved coring(ICP-Coring)and testing,combined with theoretical modeling,numerical analysis,test platform development,indoor testing and engineering application,the principles and technologies of deep ICP-Coring are developed.This principle and technology consists of five parts:in-situ pressurepreserved coring(IPP-Coring),in-situ substance-preserved coring(ISP-Coring),in-situ temperaturepreserved coring(ITP-Coring),in-situ light-preserved coring(ILP-Coring),and in-situ moisturepreserved coring(IMP-Coring).The theory and technology of temperature and pressure reconstruction at different occurrence depths and in different environments are proposed,and prototype trial production was completed by following the principle of displacement and tests based on the in-situ reconstructed environment.The notable advances are as follows:(1)Deep in-situ coring system:A pressure-preserved controller with an ultimate bearing capacity greater than 140 MPa,highperformance(temperature-resistant,pressure-resistant,and low thermally conductive)temperaturepreserved materials,an active temperature control system,and high-barrier quality-preserved membrane materials were developed;a deep ICP-Coring capacity calibration platform was independently developed,a deep in-situ coring technology system was developed,and the acquisition of deep in-situ cores was realized.(2)In-situ storage displacement system:Following the dual-circuit hydraulic design idea,a single-drive source push-pull composite grabbing mechanism was designed;the design of the overall structure for the deep in-situ displacement storage system and ultrahigh pressure cabin structure was completed,which could realize docking the coring device and core displacement in the in-situ reconstructed environment.(3)Test analysis system:A noncontact acoustic-electric-magnetic test system was developed under the in-situ reconstructed environment,and the errors between the test results and traditional contact test results were mostly less than 10%;a detachable deep in-situ core true triaxial test system was developed,which could perform loading tests for deep in-situ cores.The relevant technological achievements were successfully applied to the exploration and development of deep resources,such as deep mines,deep-sea natural gas hydrates,and deep oil and gas.The research results provide technical and equipment support for the construction of a theoretical system for deep in-situ rock mechanics,the development of deep earth resources and energy,and the scientific exploration of different layers and occurrence depths(deep and ultradeep)of the Earth.展开更多
Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has b...Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has been primarily based on the assumption of smooth spherical particles to calculate the intergranular adhesion force;this approach lacks consideration for the adhesion force between irregular shaped particles.In our study,an innovative approach was established to directly measure the adhesion force between the arbitrary irregular shaped particles;the probe was modified using simulated lunar soil particles that were a typical representation of planetary regolith.The experimental results showed that for irregular shaped mineral particles,the particle size and mineral composition had no significant influence on the interparticle adhesion force;however,the complex morphology of the contact surface predominantly controlled the adhesion force.As the contact surface roughness increased,the adhesion force gradually decreased,and the rate of decrease gradually slowed;these results were consistent with the change trend predicted via the theoretical models of quantum electrodynamics.Moreover,a theoretical model to predict the adhesion force between the irregular shaped particles was constructed based on Rabinovich’s theory,and the prediction results were correlated with the experimental measurements.展开更多
The occurrence of geological hazards and the instability of geotechnical engineering structures are closely related to the time-dependent behavior of rock.However,the idealization boundary condition for constant stres...The occurrence of geological hazards and the instability of geotechnical engineering structures are closely related to the time-dependent behavior of rock.However,the idealization boundary condition for constant stress in creep or constant strain in relaxation is not usually attained in natural geological systems.Therefore,generalized relaxation tests that explore the simultaneous changes of stress and strain with time under different stress levels with constant pore-water pressure are conducted in this study.The results show that in area Ⅰ,area Ⅱ,and area Ⅲ,the stress and strain both change synchronously with time and show similar evolutionary laws as the strain-time curve for creep or the stress-time curve for relaxation.When the applied stress level surpasses the δ_(ci) or δ_(cd) threshold,the variations in stress and strain and their respective rates of change exhibit a significant increase.The radial deformation and its rate of change exhibit greater sensitivity in response to stress levels.The apparent strain deforms homogeneously at the primary stage,and subsequently,gradually localizes due to the microcrack development at the secondary stage.Ultimately,interconnection of the microcracks causes the formation of a shear-localization zone at the tertiary stage.The strain-time responses inside and outside the localization zone are characterized by local strain accumulation and inelastic unloading during the secondary and tertiary stages,respectively.The width of the shear-localization zone is found to range from 4.43 mm to 7.08 mm and increased with a longer time-to-failure.Scanning electron microscopy(SEM)reveals a dominant coalescence of intergranular cracks on the fracture surface,and the degree of physiochemical deterioration caused by water-rock interaction is more severe under a longer lifetime.The brittle sandstone’s time-dependent deformation is essentially controlled by microcrack development during generalized relaxation,and its expectancy-life is determined by its initial microstructural state and the rheological path.展开更多
Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments we...Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface(confining pressure σ_(cp)=0, room temperature(Tr)) and at depths of 1600 m(σ_(cp)=40 MPa, Ti=70 ℃) and 3300 m(σ_(cp)=80 MPa, high temperature Ti=110 ℃) in the study area.High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.展开更多
Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone(FPZ)under size effects in laminated rocks,as well as its role in rock fracturing,is crucial for various engineering ...Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone(FPZ)under size effects in laminated rocks,as well as its role in rock fracturing,is crucial for various engineering applications.In this study,three-point bending tests were conducted on shale specimens with varying bedding angles and sizes.The anisotropic characteristics and size effects of fracture parameters were revealed.A comparative analysis was performed on the evolutions of FPZs computed using size effect theory,digital image correlation(DIC),and linear elastic fracture mechanics.The results divulged that:(i)With increasing bedding angles,there is a noticeable decrease in apparent fracture toughness(KICA),apparent fracture energy(GICA),and nominal strength(σ_(Nu)).When the bedding angle of shale is less than 45°,the crack propagation and fracture parameters are mainly influenced by the matrix.Contrary,shale with bedding angles greater than 60°,the crack propagation and fracture parameters are mainly controlled by the bedding.When the bedding angle is between 45°and 60°,the fracture propagation evolves from permeating the matrix to extending along the bedding;(ii)The fracture parameters exhibit significant size dependent behavior,as KICA and GICA rise with increasing specimen size,butσNu falls with increasing specimen sizes.The fracture parameters align with the theoretical predictions of Bažant size effect law;and(iii)The lengths of DIC-based FPZ,effective FPZ,and inelastic zone follow W-shape variations with bedding angle.The dimensionless sizes of FPZ and inelastic zone decrease with specimen size,indicating a size effect.Furthermore,there is a negative relation between KICA and the dimensionless size of the FPZ,whileσNu is positively correlated to the dimensionless size of the FPZ.This highlights the essential role of the FPZ in the size effect of rock fracture.The bedding angle exerts an influence on the FPZ,subsequently affecting the anisotropic fracture and size-dependent behavior of shale.展开更多
Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite.The micromechanical behavior...Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite.The micromechanical behavior of Yanshanian granite is investigated using scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)and nanoindentation tests.The results demonstrate transitional mechanical properties at mineral interfaces.The elastic modulus and hardness exhibit intermediate values between adjacent mineral phases.The higher plasticity indices at the interfaces suggest higher plastic deformation capacity of hard-phase minerals in these regions.Additionally,fracture toughness measurements of minerals and interfaces were obtained,with interfacial values ranging from 0.90 to 1.63 MPa·m^(0.5).The analysis of mechanical property relationships shows a significant positive linear correlation between rock-scale elastic modulus and fracture toughness.However,this correlation is substantially lower at the mineral scale,demonstrating a scale effect in the relationship of different mechanical properties.展开更多
The stimulation of shale reservoirs frequently involves significant shear failure,which is crucial for creating fracture networks and enhancing permeability to boost production.As the depth of extraction increases,the...The stimulation of shale reservoirs frequently involves significant shear failure,which is crucial for creating fracture networks and enhancing permeability to boost production.As the depth of extraction increases,the impact of elevated temperatures on the anisotropic shear strength and failure mechanisms of shale becomes pronounced,yet there is a notable lack of relevant research.This study conducts,for the first time,direct shear experiment on shales at four different temperatures and seven bedding angles.By employing acoustic emission(AE)and digital image correlation(DIC)techniques,the evolution of damage and the mechanism of crack propagation under anisotropic direct shearing at varying temperatures is revealed.The results indicate that both shear displacement and strength of shale increase with temperature across different bedding angles.Additionally,shale demonstrates distinct brittle failure characteristics under various conditions during direct shearing tests.The types of anisotropic shear failure observed under the influence of temperature include central shearing fracture,central shearing with secondary fracture,and deflected slip along the bedding.Moreover,the temperature effect enhances shear-induced crack propagation along bedding planes.Shear failure in shale predominantly occurs during higher loading stages,which coincide with a substantial amount of AE signals.Finally,the introduction of the anisotropy index and temperature sensitivity coefficient further elucidates the interaction mechanism between thermal effects and anisotropy.This study offers a novel methodology to explore the anisotropic shear failure behavior of shale under elevated temperatures,and also provides crucial theoretical and experimental insights into shear failure behavior relevant to practical shale reservoir stimulation.展开更多
It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_...It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_(3))due to the influences of geological structures and engineering disturbances.It is therefore essential to study the mechanical,seepage,and dynamic disaster behaviors of deep rock under true triaxial stress to ensure the safe operation of deep rock engineering and the efficient exploitation of deep resources.In recent years,experimental techniques and research on true triaxial rock mechanics have achieved fruitful results that have promoted the rapid development of deep rock mechanics;thus,it is necessary to systematically review and summarize these developments.This work first introduced several typical true triaxial testing apparatus and then reviewed the corresponding research progress on rock deformation,strength,failure mode,brittleness,and energy as well as the 3D volumetric fracturing(dynamic disaster)properties of deep rocks under true triaxial stress.Then,several commonly used true triaxial rock strength criteria and their applicability,the permeability characteristics and mathematical models of deep reservoir rocks,and the disaster-causing processes and mechanisms of disturbed volumetric fracturing(rockburst,compound dynamic disasters)in deep rock engineering were described.This work may provide an essential reference for addressing the true triaxial rock mechanics issues involved in deep rock engineering,especially regarding the stability of surrounding rock at depth,disaster prevention and control,and oil and gas exploitation.展开更多
Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture t...Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture toughness, effective fracture energy and fracture process zone(FPZ) size of geomaterials were first analyzed by systematic size effect fracture experiments. The results showed that the nominal strength and the apparent fracture toughness decreased with increasing bedding plane inclination angle.The larger the specimen size was, the smaller the nominal strength and the larger the apparent fracture toughness was. When the bedding inclination angle increased from 0° to 90°, the effective fracture energy and the effective FPZ size both first decreased and then increased within two complex variation stages that were bounded by the 45° bedding angle. Regardless of the inherent anisotropy of geomaterials,the nominal strength and apparent fracture toughness can be predicted by the energy-based size effect law, which demonstrates that geomaterials have obvious quasi-brittle characteristics. Theoretical analysis indicated that the true fracture toughness and energy dissipation can be calculated by linear elastic fracture mechanics only when the brittleness number is higher than 10;otherwise, size effect tests should be adopted to determine the fracture parameters.展开更多
Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,...Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first time.The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior.Under a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep time.Under high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed.The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate.The applicability of the five classical empirical creep models is quantitatively evaluated.It shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep deformation.Based on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are discussed.With abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.展开更多
With the increasing scarcity of Earth’s resources and the development of space science and technology,the exploration, development, and utilization of deep space-specific material resources(minerals, water ice, volat...With the increasing scarcity of Earth’s resources and the development of space science and technology,the exploration, development, and utilization of deep space-specific material resources(minerals, water ice, volatile compounds, etc.) are not only important to supplement the resources and reserves on Earth but also provide a material foundation for establishing extraterrestrial research bases. To achieve large depth in-situ condition-preserved coring(ICP-Coring) in the extreme lunar environment, first, lunar rock simulant was selected(SZU-1), which has a material composition, element distribution, and physical and mechanical properties that are approximately equivalent to those of lunar mare basalt. Second, the influence of the lunar-based in-situ environment on the phase, microstructure, and thermal physical properties(specific heat capacity, thermal conductivity, thermal diffusivity, and thermal expansion coefficient)of SZU-1 was explored and compared with the measured lunar rock data. It was found that in an air atmosphere, low temperature has a more pronounced effect on the relative content of olivine than other temperatures, while in a vacuum atmosphere, the relative contents of olivine and anorthite are significantly affected only at temperatures of approximately-20 and 200 ℃. When the vacuum level is less than100 Pa, the contribution of air conduction can be almost neglected, whereas it becomes dominant above this threshold. Additionally, as the testing temperature increases, the surface of SZU-1 exhibits increased microcracking, fracture opening, and unevenness, while the specific heat capacity, thermal conductivity,and thermal expansion coefficient show nonlinear increases. Conversely, the thermal diffusivity exhibits a nonlinear decreasing trend. The relationship between thermal conductivity, thermal diffusivity, and temperature can be effectively described by an exponential function(R^(2)>0.98). The research results are consistent with previous studies on real lunar rocks. These research findings are expected to be applied in the development of the test and analysis systems of ICP-Coring in a lunar environment and the exploration of the mechanism of machine-rock interaction in the in-situ drilling and coring process.展开更多
In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)...In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.展开更多
Fractal theory offers a powerful tool for the precise description and quantification of the complex pore structures in reservoir rocks,crucial for understanding the storage and migration characteristics of media withi...Fractal theory offers a powerful tool for the precise description and quantification of the complex pore structures in reservoir rocks,crucial for understanding the storage and migration characteristics of media within these rocks.Faced with the challenge of calculating the three-dimensional fractal dimensions of rock porosity,this study proposes an innovative computational process that directly calculates the three-dimensional fractal dimensions from a geometric perspective.By employing a composite denoising approach that integrates Fourier transform(FT)and wavelet transform(WT),coupled with multimodal pore extraction techniques such as threshold segmentation,top-hat transformation,and membrane enhancement,we successfully crafted accurate digital rock models.The improved box-counting method was then applied to analyze the voxel data of these digital rocks,accurately calculating the fractal dimensions of the rock pore distribution.Further numerical simulations of permeability experiments were conducted to explore the physical correlations between the rock pore fractal dimensions,porosity,and absolute permeability.The results reveal that rocks with higher fractal dimensions exhibit more complex pore connectivity pathways and a wider,more uneven pore distribution,suggesting that the ideal rock samples should possess lower fractal dimensions and higher effective porosity rates to achieve optimal fluid transmission properties.The methodology and conclusions of this study provide new tools and insights for the quantitative analysis of complex pores in rocks and contribute to the exploration of the fractal transport properties of media within rocks.展开更多
Rock fracture toughness is a critical parameter for optimizing reservoir stimulation during deep resource extraction.This index characterizes the in situ resistance of rocks to fracture and is affected by high tempera...Rock fracture toughness is a critical parameter for optimizing reservoir stimulation during deep resource extraction.This index characterizes the in situ resistance of rocks to fracture and is affected by high temperature,in situ stress,thermal shock,and chemical corrosion,etc.This review comprehensively examines research on rock fracture properties in situ environments over the past 20 years,analyses the influences of various environmental factors on rock fracture,and draws the following conclusions:(i)Environmental factors can significantly affect rock fracture toughness through changing the internal microstructure and grain composition of rocks;(ii)While high temperature is believed to reduce the rock strength,several studies have observed an increase in rock fracture toughness with increasing temperature,particularly in the range between room temperature and 200℃;(iii)In addition to a synergistic increase in fracture toughness induced by both high temperature and high in situ stress,there is still a competing effect between the increase induced by high in situ stress and the decrease induced by high temperature;(iv)Thermal shock from liquid nitrogen cooling,producing high temperature gradients,can surprisingly increase the fracture toughness of some rocks,especially at initial temperatures between room temperature and 200℃;and(v)Deterioration of rock fracture toughness occurs more rapidly in acidic environments than that in alkaline environments.In addition,this review identified current research trends and suggested some potential directions to provide suggestions for deep subsurface resource extraction.展开更多
Fluidized bioleaching is an efficient,environmentally friendly,and cost-effective mining method that has been widely explored and utilized for recovering low-grade copper sulfide minerals,such as chalcopyrite.However,...Fluidized bioleaching is an efficient,environmentally friendly,and cost-effective mining method that has been widely explored and utilized for recovering low-grade copper sulfide minerals,such as chalcopyrite.However,the proliferation and apoptosis of dominant leaching bacteria,such as Acidithiobacillus ferrooxidans,within complex pore,void,and fracture structures in deep-earth environments commonly results in a dynamic bacterial community that evolves continuously.This unclear genetic-scale microbial succession often leads to low leaching reaction efficiency,undesirable reaction passivation,and poor bioleaching operations.This review integrates genetic-scale insights with industrial challenges in chalcopyrite bioleaching,proposing novel strategies for regulating microbial communities.A systematic analysis of five critical dimensions is conducted,focusing on:1)The adaptations of Acidithiobacillus spp.to high Ag^(+) stress.2)The direct,indirect,and cooperative bioleaching pathways are linked to bacterial extracellular polymer substance(EPS)and Fe/S oxidation genes.3)The passivation dynamics governed by bacterial genomics,including thiosulfate,polysulfide,and biofilm mechanisms.4)The microbial succession patterns under genetic control Hi-C sequencing-guided consortia design.5)Molecular detection methods(16S rDNA,Hi-C)for optimizing leaching efficiency.The following innovations have been identified as being of key significance:A genomic-environmental interaction model has been developed to bridge the gap between bacterial genetics and passivation dynamics.A comprehensive analysis of Ag^(+) catalysis has been conducted,resulting in a 40%reduction in jarosite formation through jar gene suppression.Practical strategies,such as thermophilic consortia engineering,have been validated in pilot trials,achieving a 32%increase in copper recovery.Additionally,this study meticulously reviews and summarizes typical potential stimulations and enhanced bioleaching methods.The genetic sequencing methods,such as 16S rDNA and Hi-C,have been shown to hold promising potential for improving bioleaching reactions and delaying the formation of passivation substances like jarosite.展开更多
Geological carbon sequestration(GCS)offers a promising approach to mitigating greenhouse gas emissions and supporting global carbon neutrality goals.Offshore GCS,which leverages subsea geological formations,provides a...Geological carbon sequestration(GCS)offers a promising approach to mitigating greenhouse gas emissions and supporting global carbon neutrality goals.Offshore GCS,which leverages subsea geological formations,provides advantages over onshore options in terms of storage capacity,public acceptance,and minimized environmental risks to populated regions,making it a socially,economically,and environmentally viable pillar of global Carbon Capture and Storage strategies.This approach involves injecting captured CO_(2)into subsea formations through wells,where it can be securely trapped via structural,residual,solubility,and mineral mechanisms over geological timescales.Successful deployment requires addressing the full GCS chain,including site selection,subsurface characterization,and engineering aspects such as platform construction,operational reliability,and risk monitoring.Despite its potential and growing attention,key technical challenges remain insufficiently addressed.This study aims to fill this gap by systematically reviewing essential geoscience and engineering elements of offshore GCS.It examines site selection,trapping efficiency,and operational issues,and provides a detailed evaluation of current and planned offshore GCS projects,with a tabulated dataset to support reference and comparison.The findings highlight research priorities and support the advancement of offshore GCS technologies toward safe and effective implementation.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52374078)the Fundamental Research Funds for the Central Universities(Grant No.2023CDJKYJH021)the Sichuan-Chongqing Science and Technology Innovation Cooperation Program Project(Grant No.2024TIAD-CYKJCXX0011).
文摘Cyclic changes in the internal pressure of compressed air energy storage reservoirs in abandoned coal mines result in complex alternating loads on the rocks surrounding the energy storage reservoirs.These complex alternating loads can be regarded as multi-stage constant-amplitude cyclic loads following simplification.In this paper,the mechanical responses and acoustic emission(AE)characteristics of red sandstone with five bedding dip angles(0°,30°,45°,60°,and 90°)under such loads are investigated,and the damage evolution processes of the five specimens are revealed from both quantitative and microscopic perspectives.The results show that the fatigue deformation characteristics of the specimens are affected by the bedding dip angle.Under cyclic loads,the axially irreversible plastic deformations of the rocks increase,their elastic stiffness increases,their crack volumetric strain increases and then decreases,and their AE cumulative count/energy curves exhibit a ladder shape.A damage evolution model based on the crack volumetric strain is proposed,and the damage evolution process is divided into two stages:a rapid increase stage and a tendency toward stabilization stage.Through cluster analysis,the AE events are used to classify the damage into three categories:small-sized localized damage,large-sized tensile damage,and large-sized shear damage.Finally,the MohreCoulomb criterion is applied to analyze the relationship between the failure modes of the red sandstone specimens and the dip angle of the bedding.The results of this study will help to predict the stability and safety of compressed air energy storage reservoirs in abandoned coal mines.
基金supported by the National Natural Science Foundation of China(Nos.52374078,U24A20616 and 52074043)the Sichuan-Chongqing Science and Technology Innovation Cooperation Program Project(No.2024TIAD-CYKJCXX0011)the Fundamental Research Funds for the Central Universities(No.2023CDJKYJH021)。
文摘Salt cavern energy storage technology contributes to energy reserves and renewable energy scale-up.This study focuses on salt cavern gas storage in Jintan to assess the long-term stability of its surrounding rock under frequent operation.The fatigue test results indicate that stress holding significantly reduces fatigue life,with the magnitude of stress level outweighing the duration of holding time in determining peak strain.Employing a machine learning approach,the impact of various factors on fatigue life and peak strain was quantified,revealing that higher stress limits and stress holding adversely impact the fatigue index,whereas lower stress limits and rate exhibit a positive effect.A novel fatigue-creep composite damage constitutive model is constructed,which is able to consider stress magnitude,rate,and stress holding.The model,validated through multi-path tests,accurately captures the elasto-viscous behavior of salt rock during loading,unloading,and stress holding.Sensitivity analysis further reveals the time-and stress-dependent behavior of model parameters,clarifying that strain changes stem not only from stress variations but are also influenced by alterations in elasto-viscous parameters.This study provides a new method for the mechanical assessment of salt cavern gas storage surrounding rocks.
基金supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(No.2024ZD1003903)National Natural Science Foundation of China(Nos.52374078,U24A20616,and 52074043)+1 种基金Sichuan-Chongqing Science and Technology Project Innovation Cooperation Program(No.2024TIAD-CYKJCXX0011)the Fundamental Research Funds for the Central Universities(No.2023CDJKYJH021).
文摘To ensure the safe implementation of underground reservoirs in abandoned coal mines,this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading.Specimens with coal-to-concrete height ratios ranging from 0.5:1 to 3:1 were tested,with damage evolution continuously monitored using acoustic emission techniques.Results indicate that while the peak strength of pure materials decreases by approximately 1 MPa under cyclic stress compared to uniaxial compression,composite specimens exhibit strength enhancements exceeding 5 MPa.However,the peak strength of composite specimens decreases with increasing coal height,from 30 MPa at CR0.5 to 20 MPa at CR3.0.The damage state was assessed using the dynamic elastic strain energy index and Felicity ratio,which revealed that composite specimens are more prone to early damage accumulation.Spatial acoustic emission localization further reveals distinct failure modes across specimens with varying height ratios.To elucidate these differences,interfacial effects were incorporated into a modified twin-shear unified strength theory.The refined model accurately predicts the internal strength distribution and failure characteristics of the composite structures.These findings provide a theoretical basis for the structural design and safe operation of underground reservoir dams.
基金supported by the Department of Science&Technology of Guangdong Province(No.2019ZT08G315)the open foundation of Key Laboratory of Deep Earth Science and Engineering(Sichuan University)+3 种基金Ministry of Education(No.DESE202102)National Natural Science Foundation of China(Nos.41972288,51804203,and 51827901)Applied Basic Research Programs of Sichuan Province(No.2021YJ0411)Shenzhen City Clean Energy Research Institute。
文摘During the development of hot dry rock,the research on thermal fatigue damage caused by thermal shock of cold and heat cycles is the basis that ensures the long-term utilization of geothermal resources,but there are not enough relevant studies at present.Based on this,the thermal damage tests of granite at different temperatures(250,350,450°C)and quenching cycles(1,5,10,15 cycles)were carried out.Preliminary reveals the damage mechanism and heat transfer law of the quenching cycle effect on hot dry rock.The results show that with the increase of temperature and cycles,the uneven thermal expansion of minerals and the thermal shock caused by quenching promote the crack development of granite,resulting in the decrease of P-wave velocity,thermal conductivity and uniaxial compressive strength of granite.Meanwhile,the COMSOL was used to simulate the heat transfer of hot dry rock under different heat treatment conditions.It concluded that the increase in the number of quenching cycles reduced the heat transfer capacity of the granite,especially more than 10 quenching cycles,which also reflects that the thermal fatigue damage leads to a longer time for the temperature recovery of the hot dry rock mass.In addition,the three-dimensional nonlinear fitting relationship among thermal conductivity,temperature and cycle number was established for the first time,which can better reveal the change rule of thermal conductivity after quenching thermal fatigue effect of hot dry rock.The research results provide theoretical support for hot dry rock reservoir reconstruction and production efficiency evaluation.
基金the National Natural Science Foundation of China(No.51827901)the Program for Guangdong Introducing Innovative and Enterpreneurial Teams(No.2019ZT08G315)Shenzhen Key Research Projects(No.JSGG20220831105002005).
文摘With the depletion of shallow resources,the exploration of deep earth resources has become a global strategy.The study of the different patterns in the physical mechanical properties of rocks at different occurrence depths is the basis for exploring deep into the earth,with the core and premise being the acquisition and testing of deep in-situ core specimens.Based on the original idea of deep in-situ condition preserved coring(ICP-Coring)and testing,combined with theoretical modeling,numerical analysis,test platform development,indoor testing and engineering application,the principles and technologies of deep ICP-Coring are developed.This principle and technology consists of five parts:in-situ pressurepreserved coring(IPP-Coring),in-situ substance-preserved coring(ISP-Coring),in-situ temperaturepreserved coring(ITP-Coring),in-situ light-preserved coring(ILP-Coring),and in-situ moisturepreserved coring(IMP-Coring).The theory and technology of temperature and pressure reconstruction at different occurrence depths and in different environments are proposed,and prototype trial production was completed by following the principle of displacement and tests based on the in-situ reconstructed environment.The notable advances are as follows:(1)Deep in-situ coring system:A pressure-preserved controller with an ultimate bearing capacity greater than 140 MPa,highperformance(temperature-resistant,pressure-resistant,and low thermally conductive)temperaturepreserved materials,an active temperature control system,and high-barrier quality-preserved membrane materials were developed;a deep ICP-Coring capacity calibration platform was independently developed,a deep in-situ coring technology system was developed,and the acquisition of deep in-situ cores was realized.(2)In-situ storage displacement system:Following the dual-circuit hydraulic design idea,a single-drive source push-pull composite grabbing mechanism was designed;the design of the overall structure for the deep in-situ displacement storage system and ultrahigh pressure cabin structure was completed,which could realize docking the coring device and core displacement in the in-situ reconstructed environment.(3)Test analysis system:A noncontact acoustic-electric-magnetic test system was developed under the in-situ reconstructed environment,and the errors between the test results and traditional contact test results were mostly less than 10%;a detachable deep in-situ core true triaxial test system was developed,which could perform loading tests for deep in-situ cores.The relevant technological achievements were successfully applied to the exploration and development of deep resources,such as deep mines,deep-sea natural gas hydrates,and deep oil and gas.The research results provide technical and equipment support for the construction of a theoretical system for deep in-situ rock mechanics,the development of deep earth resources and energy,and the scientific exploration of different layers and occurrence depths(deep and ultradeep)of the Earth.
基金supported by the National Natural Science Foundation of China(Nos.U22A20166,52104141,12172230 and U2013603)the Department of Science and Technology of Guangdong Province(No.2019ZT08G315)the Guangdong Basic and Applied Basic Research Foundation(No.2023A1515012654).
文摘Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has been primarily based on the assumption of smooth spherical particles to calculate the intergranular adhesion force;this approach lacks consideration for the adhesion force between irregular shaped particles.In our study,an innovative approach was established to directly measure the adhesion force between the arbitrary irregular shaped particles;the probe was modified using simulated lunar soil particles that were a typical representation of planetary regolith.The experimental results showed that for irregular shaped mineral particles,the particle size and mineral composition had no significant influence on the interparticle adhesion force;however,the complex morphology of the contact surface predominantly controlled the adhesion force.As the contact surface roughness increased,the adhesion force gradually decreased,and the rate of decrease gradually slowed;these results were consistent with the change trend predicted via the theoretical models of quantum electrodynamics.Moreover,a theoretical model to predict the adhesion force between the irregular shaped particles was constructed based on Rabinovich’s theory,and the prediction results were correlated with the experimental measurements.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52304099,52172625)Shenzhen Science and Technology Program(Grant No.RCYX20221008092903013).
文摘The occurrence of geological hazards and the instability of geotechnical engineering structures are closely related to the time-dependent behavior of rock.However,the idealization boundary condition for constant stress in creep or constant strain in relaxation is not usually attained in natural geological systems.Therefore,generalized relaxation tests that explore the simultaneous changes of stress and strain with time under different stress levels with constant pore-water pressure are conducted in this study.The results show that in area Ⅰ,area Ⅱ,and area Ⅲ,the stress and strain both change synchronously with time and show similar evolutionary laws as the strain-time curve for creep or the stress-time curve for relaxation.When the applied stress level surpasses the δ_(ci) or δ_(cd) threshold,the variations in stress and strain and their respective rates of change exhibit a significant increase.The radial deformation and its rate of change exhibit greater sensitivity in response to stress levels.The apparent strain deforms homogeneously at the primary stage,and subsequently,gradually localizes due to the microcrack development at the secondary stage.Ultimately,interconnection of the microcracks causes the formation of a shear-localization zone at the tertiary stage.The strain-time responses inside and outside the localization zone are characterized by local strain accumulation and inelastic unloading during the secondary and tertiary stages,respectively.The width of the shear-localization zone is found to range from 4.43 mm to 7.08 mm and increased with a longer time-to-failure.Scanning electron microscopy(SEM)reveals a dominant coalescence of intergranular cracks on the fracture surface,and the degree of physiochemical deterioration caused by water-rock interaction is more severe under a longer lifetime.The brittle sandstone’s time-dependent deformation is essentially controlled by microcrack development during generalized relaxation,and its expectancy-life is determined by its initial microstructural state and the rheological path.
基金supported by the National Natural Science Foundation of China(No.12172240).
文摘Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface(confining pressure σ_(cp)=0, room temperature(Tr)) and at depths of 1600 m(σ_(cp)=40 MPa, Ti=70 ℃) and 3300 m(σ_(cp)=80 MPa, high temperature Ti=110 ℃) in the study area.High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.
基金funded by the National Natural Science Foundation of China(Grant Nos.12172230,U22A20166)the Department of Science and Technology of Guangdong Province(Grant No.2019ZT08G315).
文摘Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone(FPZ)under size effects in laminated rocks,as well as its role in rock fracturing,is crucial for various engineering applications.In this study,three-point bending tests were conducted on shale specimens with varying bedding angles and sizes.The anisotropic characteristics and size effects of fracture parameters were revealed.A comparative analysis was performed on the evolutions of FPZs computed using size effect theory,digital image correlation(DIC),and linear elastic fracture mechanics.The results divulged that:(i)With increasing bedding angles,there is a noticeable decrease in apparent fracture toughness(KICA),apparent fracture energy(GICA),and nominal strength(σ_(Nu)).When the bedding angle of shale is less than 45°,the crack propagation and fracture parameters are mainly influenced by the matrix.Contrary,shale with bedding angles greater than 60°,the crack propagation and fracture parameters are mainly controlled by the bedding.When the bedding angle is between 45°and 60°,the fracture propagation evolves from permeating the matrix to extending along the bedding;(ii)The fracture parameters exhibit significant size dependent behavior,as KICA and GICA rise with increasing specimen size,butσNu falls with increasing specimen sizes.The fracture parameters align with the theoretical predictions of Bažant size effect law;and(iii)The lengths of DIC-based FPZ,effective FPZ,and inelastic zone follow W-shape variations with bedding angle.The dimensionless sizes of FPZ and inelastic zone decrease with specimen size,indicating a size effect.Furthermore,there is a negative relation between KICA and the dimensionless size of the FPZ,whileσNu is positively correlated to the dimensionless size of the FPZ.This highlights the essential role of the FPZ in the size effect of rock fracture.The bedding angle exerts an influence on the FPZ,subsequently affecting the anisotropic fracture and size-dependent behavior of shale.
基金funded by the National Natural Science Foundation of China(Nos.52422403 and U22A20166)the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(No.2024ZD1003903)+1 种基金the Department of Science and Technology of Guangdong Province(No.2019ZT08G315)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515012654).
文摘Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite.The micromechanical behavior of Yanshanian granite is investigated using scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)and nanoindentation tests.The results demonstrate transitional mechanical properties at mineral interfaces.The elastic modulus and hardness exhibit intermediate values between adjacent mineral phases.The higher plasticity indices at the interfaces suggest higher plastic deformation capacity of hard-phase minerals in these regions.Additionally,fracture toughness measurements of minerals and interfaces were obtained,with interfacial values ranging from 0.90 to 1.63 MPa·m^(0.5).The analysis of mechanical property relationships shows a significant positive linear correlation between rock-scale elastic modulus and fracture toughness.However,this correlation is substantially lower at the mineral scale,demonstrating a scale effect in the relationship of different mechanical properties.
基金supported by the National Natural Science Fund of China (Grant Nos.U22A20166 and 52374131)the Shenzhen Science and Technology Program (Grant No.JCYJ20220531102012028)the Young Elite Scientists Sponsorship Program by CAST.
文摘The stimulation of shale reservoirs frequently involves significant shear failure,which is crucial for creating fracture networks and enhancing permeability to boost production.As the depth of extraction increases,the impact of elevated temperatures on the anisotropic shear strength and failure mechanisms of shale becomes pronounced,yet there is a notable lack of relevant research.This study conducts,for the first time,direct shear experiment on shales at four different temperatures and seven bedding angles.By employing acoustic emission(AE)and digital image correlation(DIC)techniques,the evolution of damage and the mechanism of crack propagation under anisotropic direct shearing at varying temperatures is revealed.The results indicate that both shear displacement and strength of shale increase with temperature across different bedding angles.Additionally,shale demonstrates distinct brittle failure characteristics under various conditions during direct shearing tests.The types of anisotropic shear failure observed under the influence of temperature include central shearing fracture,central shearing with secondary fracture,and deflected slip along the bedding.Moreover,the temperature effect enhances shear-induced crack propagation along bedding planes.Shear failure in shale predominantly occurs during higher loading stages,which coincide with a substantial amount of AE signals.Finally,the introduction of the anisotropy index and temperature sensitivity coefficient further elucidates the interaction mechanism between thermal effects and anisotropy.This study offers a novel methodology to explore the anisotropic shear failure behavior of shale under elevated temperatures,and also provides crucial theoretical and experimental insights into shear failure behavior relevant to practical shale reservoir stimulation.
基金supported by the National Natural Science Foundation of China(No.52104209)the Postdoctoral Research Foundation of China(No.2021M692192)+1 种基金the National Natural Science Foundation of China(Nos.51827901 and 52174082)the Program for Guangdong Introducing Innovative and Entrepre-neurial Teams(No.2019ZT08G315).
文摘It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_(3))due to the influences of geological structures and engineering disturbances.It is therefore essential to study the mechanical,seepage,and dynamic disaster behaviors of deep rock under true triaxial stress to ensure the safe operation of deep rock engineering and the efficient exploitation of deep resources.In recent years,experimental techniques and research on true triaxial rock mechanics have achieved fruitful results that have promoted the rapid development of deep rock mechanics;thus,it is necessary to systematically review and summarize these developments.This work first introduced several typical true triaxial testing apparatus and then reviewed the corresponding research progress on rock deformation,strength,failure mode,brittleness,and energy as well as the 3D volumetric fracturing(dynamic disaster)properties of deep rocks under true triaxial stress.Then,several commonly used true triaxial rock strength criteria and their applicability,the permeability characteristics and mathematical models of deep reservoir rocks,and the disaster-causing processes and mechanisms of disturbed volumetric fracturing(rockburst,compound dynamic disasters)in deep rock engineering were described.This work may provide an essential reference for addressing the true triaxial rock mechanics issues involved in deep rock engineering,especially regarding the stability of surrounding rock at depth,disaster prevention and control,and oil and gas exploitation.
基金the National Natural Science Foundation of China(Nos.U22A20166,51904190,12172230,11872258 and U19A2098)the Department of Science and Technology of Guangdong Province(No.2019ZT08G315)MOE Laboratory of Deep Earth Science and Engineering(No.DESE202102).
文摘Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture toughness, effective fracture energy and fracture process zone(FPZ) size of geomaterials were first analyzed by systematic size effect fracture experiments. The results showed that the nominal strength and the apparent fracture toughness decreased with increasing bedding plane inclination angle.The larger the specimen size was, the smaller the nominal strength and the larger the apparent fracture toughness was. When the bedding inclination angle increased from 0° to 90°, the effective fracture energy and the effective FPZ size both first decreased and then increased within two complex variation stages that were bounded by the 45° bedding angle. Regardless of the inherent anisotropy of geomaterials,the nominal strength and apparent fracture toughness can be predicted by the energy-based size effect law, which demonstrates that geomaterials have obvious quasi-brittle characteristics. Theoretical analysis indicated that the true fracture toughness and energy dissipation can be calculated by linear elastic fracture mechanics only when the brittleness number is higher than 10;otherwise, size effect tests should be adopted to determine the fracture parameters.
基金funded by the National Natural Science Foundation of China(Grant Nos.U22A20166 and 12172230)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515012654)+1 种基金funded by the National Natural Science Foundation of China(Grant Nos.U22A20166 and 12172230)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515012654)。
文摘Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first time.The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior.Under a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep time.Under high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed.The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate.The applicability of the five classical empirical creep models is quantitatively evaluated.It shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep deformation.Based on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are discussed.With abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.
基金supported by the National Natural Science Foundation of China(Nos.U2013603 and 52225403)the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(No.2019ZT08G315)the Shenzhen National Science Fund for Distinguished Young Scholars(No.RCJC20210706091948015).
文摘With the increasing scarcity of Earth’s resources and the development of space science and technology,the exploration, development, and utilization of deep space-specific material resources(minerals, water ice, volatile compounds, etc.) are not only important to supplement the resources and reserves on Earth but also provide a material foundation for establishing extraterrestrial research bases. To achieve large depth in-situ condition-preserved coring(ICP-Coring) in the extreme lunar environment, first, lunar rock simulant was selected(SZU-1), which has a material composition, element distribution, and physical and mechanical properties that are approximately equivalent to those of lunar mare basalt. Second, the influence of the lunar-based in-situ environment on the phase, microstructure, and thermal physical properties(specific heat capacity, thermal conductivity, thermal diffusivity, and thermal expansion coefficient)of SZU-1 was explored and compared with the measured lunar rock data. It was found that in an air atmosphere, low temperature has a more pronounced effect on the relative content of olivine than other temperatures, while in a vacuum atmosphere, the relative contents of olivine and anorthite are significantly affected only at temperatures of approximately-20 and 200 ℃. When the vacuum level is less than100 Pa, the contribution of air conduction can be almost neglected, whereas it becomes dominant above this threshold. Additionally, as the testing temperature increases, the surface of SZU-1 exhibits increased microcracking, fracture opening, and unevenness, while the specific heat capacity, thermal conductivity,and thermal expansion coefficient show nonlinear increases. Conversely, the thermal diffusivity exhibits a nonlinear decreasing trend. The relationship between thermal conductivity, thermal diffusivity, and temperature can be effectively described by an exponential function(R^(2)>0.98). The research results are consistent with previous studies on real lunar rocks. These research findings are expected to be applied in the development of the test and analysis systems of ICP-Coring in a lunar environment and the exploration of the mechanism of machine-rock interaction in the in-situ drilling and coring process.
基金funded by the National Natural Science Foundation of China (No.U22A20166)Science and Technology Foundation of Guizhou Province (No.QKHJC-ZK[2023]YB074)+2 种基金Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical EngineeringInstitute of Rock and Soil MechanicsChinese Academy of Sciences (No.SKLGME022009)。
文摘In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.
基金supported by the National Natural Science Foundation of China (Nos.52374078 and 52074043)the Fundamental Research Funds for the Central Universities (No.2023CDJKYJH021)。
文摘Fractal theory offers a powerful tool for the precise description and quantification of the complex pore structures in reservoir rocks,crucial for understanding the storage and migration characteristics of media within these rocks.Faced with the challenge of calculating the three-dimensional fractal dimensions of rock porosity,this study proposes an innovative computational process that directly calculates the three-dimensional fractal dimensions from a geometric perspective.By employing a composite denoising approach that integrates Fourier transform(FT)and wavelet transform(WT),coupled with multimodal pore extraction techniques such as threshold segmentation,top-hat transformation,and membrane enhancement,we successfully crafted accurate digital rock models.The improved box-counting method was then applied to analyze the voxel data of these digital rocks,accurately calculating the fractal dimensions of the rock pore distribution.Further numerical simulations of permeability experiments were conducted to explore the physical correlations between the rock pore fractal dimensions,porosity,and absolute permeability.The results reveal that rocks with higher fractal dimensions exhibit more complex pore connectivity pathways and a wider,more uneven pore distribution,suggesting that the ideal rock samples should possess lower fractal dimensions and higher effective porosity rates to achieve optimal fluid transmission properties.The methodology and conclusions of this study provide new tools and insights for the quantitative analysis of complex pores in rocks and contribute to the exploration of the fractal transport properties of media within rocks.
基金supported by the National Natural Science Foundation of China(Grant No.12172240).
文摘Rock fracture toughness is a critical parameter for optimizing reservoir stimulation during deep resource extraction.This index characterizes the in situ resistance of rocks to fracture and is affected by high temperature,in situ stress,thermal shock,and chemical corrosion,etc.This review comprehensively examines research on rock fracture properties in situ environments over the past 20 years,analyses the influences of various environmental factors on rock fracture,and draws the following conclusions:(i)Environmental factors can significantly affect rock fracture toughness through changing the internal microstructure and grain composition of rocks;(ii)While high temperature is believed to reduce the rock strength,several studies have observed an increase in rock fracture toughness with increasing temperature,particularly in the range between room temperature and 200℃;(iii)In addition to a synergistic increase in fracture toughness induced by both high temperature and high in situ stress,there is still a competing effect between the increase induced by high in situ stress and the decrease induced by high temperature;(iv)Thermal shock from liquid nitrogen cooling,producing high temperature gradients,can surprisingly increase the fracture toughness of some rocks,especially at initial temperatures between room temperature and 200℃;and(v)Deterioration of rock fracture toughness occurs more rapidly in acidic environments than that in alkaline environments.In addition,this review identified current research trends and suggested some potential directions to provide suggestions for deep subsurface resource extraction.
基金funded by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(No.2025ZD1010904)Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities,No.FRF-IDRY-24-016)+3 种基金Beijing Natural Science Foundation(No.2232080)the National Natural Science Foundation of China(Nos.52374112,52204124,52034001,and 52304144)the State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering(No.SDGZ2517)the Shandong Provincial Natural Science Foundation(No.ZR2023QE133)
文摘Fluidized bioleaching is an efficient,environmentally friendly,and cost-effective mining method that has been widely explored and utilized for recovering low-grade copper sulfide minerals,such as chalcopyrite.However,the proliferation and apoptosis of dominant leaching bacteria,such as Acidithiobacillus ferrooxidans,within complex pore,void,and fracture structures in deep-earth environments commonly results in a dynamic bacterial community that evolves continuously.This unclear genetic-scale microbial succession often leads to low leaching reaction efficiency,undesirable reaction passivation,and poor bioleaching operations.This review integrates genetic-scale insights with industrial challenges in chalcopyrite bioleaching,proposing novel strategies for regulating microbial communities.A systematic analysis of five critical dimensions is conducted,focusing on:1)The adaptations of Acidithiobacillus spp.to high Ag^(+) stress.2)The direct,indirect,and cooperative bioleaching pathways are linked to bacterial extracellular polymer substance(EPS)and Fe/S oxidation genes.3)The passivation dynamics governed by bacterial genomics,including thiosulfate,polysulfide,and biofilm mechanisms.4)The microbial succession patterns under genetic control Hi-C sequencing-guided consortia design.5)Molecular detection methods(16S rDNA,Hi-C)for optimizing leaching efficiency.The following innovations have been identified as being of key significance:A genomic-environmental interaction model has been developed to bridge the gap between bacterial genetics and passivation dynamics.A comprehensive analysis of Ag^(+) catalysis has been conducted,resulting in a 40%reduction in jarosite formation through jar gene suppression.Practical strategies,such as thermophilic consortia engineering,have been validated in pilot trials,achieving a 32%increase in copper recovery.Additionally,this study meticulously reviews and summarizes typical potential stimulations and enhanced bioleaching methods.The genetic sequencing methods,such as 16S rDNA and Hi-C,have been shown to hold promising potential for improving bioleaching reactions and delaying the formation of passivation substances like jarosite.
基金supported by the National Natural Science Foundation of China(52304098,52106092,52474105)Shenzhen Science and Technology Program(JCYJ20220530113011027,JCYJ20220818095605012)+2 种基金Guangdong Basic and Applied Basic Research Foundation(2023A1515012761,2023A1515012316,2022A1515110338,2025A1515010748)Research Team Cultivation Program of Shenzhen University(2023QNT004)Major Science and Technology Infrastructure Project of Material Genome Big–science Facilities Platform supported by the Municipal Development and Reform Commission of Shenzhen.
文摘Geological carbon sequestration(GCS)offers a promising approach to mitigating greenhouse gas emissions and supporting global carbon neutrality goals.Offshore GCS,which leverages subsea geological formations,provides advantages over onshore options in terms of storage capacity,public acceptance,and minimized environmental risks to populated regions,making it a socially,economically,and environmentally viable pillar of global Carbon Capture and Storage strategies.This approach involves injecting captured CO_(2)into subsea formations through wells,where it can be securely trapped via structural,residual,solubility,and mineral mechanisms over geological timescales.Successful deployment requires addressing the full GCS chain,including site selection,subsurface characterization,and engineering aspects such as platform construction,operational reliability,and risk monitoring.Despite its potential and growing attention,key technical challenges remain insufficiently addressed.This study aims to fill this gap by systematically reviewing essential geoscience and engineering elements of offshore GCS.It examines site selection,trapping efficiency,and operational issues,and provides a detailed evaluation of current and planned offshore GCS projects,with a tabulated dataset to support reference and comparison.The findings highlight research priorities and support the advancement of offshore GCS technologies toward safe and effective implementation.
