The Gabes aquifer system,located in southeastern Tunisia,is a crucial resource for supporting local socio-economic activities.Due to its dual porosity structure,is particularly vulnerable to pollution.This study aims ...The Gabes aquifer system,located in southeastern Tunisia,is a crucial resource for supporting local socio-economic activities.Due to its dual porosity structure,is particularly vulnerable to pollution.This study aims to develop a hybrid model that combines the Fracture Aquifer Index(FAI)with the conventional GOD(Groundwater occurrence,Overall lithology,Depth to water table)method,to assess groundwater vulnerability in fractured aquifer.To develop the hybrid model,the classical GOD method was integrated with FAI to produce a single composite index.Each parameter within both GOD and FAI was scored,and a final index was calculated to delineate vulnerable areas.The results show that the study area can be classified into four vulnerability levels:Very low,low,moderate,and high,indicating that approximately 8%of the area exhibits very low vulnerability,29%has low vulnerability,25%falls into the moderate category,and 38%is considered highly vulnerable.The FAI-GOD model further incorporates fracture network characteristics.This refinement reduces the classification to three vulnerability classes:Low,medium,and high.The outcomes demonstrate that 46%of the area is highly vulnerable due to a dense concentration of fractures,while 17%represents an intermediate zone characterized by either shallow or deeper fractures.In contrast,37%corresponds to areas with lightly fractured rock,where the impact on vulnerability is minimal.Multivariate statistical analysis was employed using Principal Components Analysis(PCA)and Hierarchical Cluster Analysis(HCA)on 24 samples across six variables.The first three components account for over 76%of the total variance,reinforcing the significance of fracture dynamics in classifying vulnerability levels.The FAI-GOD model removes the very-low-vulnerability class and expands the spatial extent of low-and high-vulnerability zones,reflecting the dominant influence of fracture networks on aquifer sensitivity.While both indices use a five-class system,FAI-GOD redistributes vulnerability by eliminating very-low-vulnerability areas and amplifying low/high categories,highlighting the critical role of fractures.A strong correlation(R2=0.94)between the GOD and FAI-GOD indices,demonstrated through second-order polynomial regression,confirms the robustness of the FAI-GOD model in accurately predicting vulnerability to pollution.This model provides a useful framework for assessing the vulnerability of complex aquifers and serves as a decision-making tool for groundwater managers in similar areas.展开更多
Fluid flow through fractured rock masses is a key process controlling the safety and performance of deep geoengineering systems,shaped by the complex interactions of thermal,hydraulic,mechanical and chemical(THMC)fiel...Fluid flow through fractured rock masses is a key process controlling the safety and performance of deep geoengineering systems,shaped by the complex interactions of thermal,hydraulic,mechanical and chemical(THMC)fields.This paper presents a systematic review of this subject with special emphasis on the multi-physics governing it.First,we elucidate the interdependent mechanisms and governing equations,highlighting the nonlinear,path-dependent,and evolving nature of the relationship between stress and permeability.Next,mainstream modeling approaches,including equivalent continuum,discrete fracture network(DFN),and dual-porosity/dual-permeability methods,are critically evaluated,and a strategy for model selection based on project scale and geological context is proposed accordingly.Moreover,experimental insights from single-fracture and triaxial flow studies are synthesized,revealing how effective stress,shear displacement,and fracture roughness control permeability evolution.In particular,the practical significance of THMC coupling is demonstrated through case studies on nuclear waste disposal,Enhanced Geothermal Systems,and tunneling projects.The reviewfurther explores AI-and machine learning-driven innovations,particularly physics-informed neural networks and hybrid modeling,which address limitations in computational efficiency,data scarcity,and physical consistency.Finally,persistent challenges,including multi-scale coupling,parameter uncertainty,and complex fracture network representation are identified and critically discussed while paying attention to future developments.展开更多
The coupled chemo-mechanical impact of supercritical CO_(2)-H_(2)O(ScCO_(2)-H_(2)O)reactions on fracture geometry and nonlinear flow regimes in deep shale under confining pressures remains inadequately quantified.This...The coupled chemo-mechanical impact of supercritical CO_(2)-H_(2)O(ScCO_(2)-H_(2)O)reactions on fracture geometry and nonlinear flow regimes in deep shale under confining pressures remains inadequately quantified.This study systematically investigates the effects of ScCO_(2)-H_(2)O-shale interactions on fracture morphology and flow properties under confining pressures from 15 MPa to 40 MPa by integrating XRD(X-ray diffraction),micro-CT,3D surface profilometry,and multistage steady-state flow experiments.The results demonstrate that ScCO_(2)-H_(2)O exposure drives pyrite/feldspar dissolution and localized clay precipitation,resulting in fracture branching and macroscopic aperture regularization.Critically,confining pressure dictates the net hydraulic response:under low confining pressure(15-25 MPa),dissolution dominates,enhancing permeability,flow efficiency(Q/VP),and pre-linear flow behavior(n<1).At high confining pressures(30-40 MPa)mechanical compaction and mineral precipitation amplify flow resistance,shifting the flow regime toward quasi-linear behavior,as inertial effects become negligible compared to dominant viscous forces and increased flow resistance.Confining pressure thus critically mediates the dissolution-precipitation balance during ScCO_(2)-H_(2)O treatment,with an optimal window of 15-25 MPa identified for enhancing conductivity while minimizing clogging risk.These findings provide a quantitative framework for predicting stress-dependent flow evolution in chemically altered shale fractures.展开更多
Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength.Nevertheless,there is a lack of potent numer...Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength.Nevertheless,there is a lack of potent numerical tools for assessing the grouting effectiveness in water-rich fractured strata.In this study,the hydro-mechanical coupled discontinuous deformation analysis(HM-DDA)is inaugurally extended to simulate the grouting process in a water-rich discrete fracture network(DFN),including the slurry migration,fracture dilation,water plugging in a seepage field,and joint reinforcement after coagulation.To validate the capabilities of the developed method,several numerical examples are conducted incorporating the Newtonian fluid and Bingham slurry.The simulation results closely align with the analytical solutions.Additionally,a set of compression tests is conducted on the fresh and grouted rock specimens to verify the reinforcement method and calibrate the rational properties of reinforced joints.An engineering-scale model based on a real water inrush case of the Yonglian tunnel in a water-rich fractured zone has been established.The model demonstrates the effectiveness of grouting reinforcement in mitigating water inrush disaster.The results indicate that increased grouting pressure greatly affects the regulation of water outflow from the tunnel face and the prevention of rock detachment face after excavation.展开更多
Predicting the productivity of multistage fractured horizontal wells plays an important role in exploiting unconventional resources.In recent years,machine learning(ML)models have emerged as a new approach for such st...Predicting the productivity of multistage fractured horizontal wells plays an important role in exploiting unconventional resources.In recent years,machine learning(ML)models have emerged as a new approach for such studies.However,the scarcity of sufficient real data for model training often leads to imprecise predictions,even though the models trained with real data better characterize geological and engineering features.To tackle this issue,we propose an ML model that can obtain reliable results even with a small amount of data samples.Our model integrates the synthetic minority oversampling technique(SMOTE)to expand the data volume,the support vector machine(SVM)for model training,and the particle swarm optimization(PSO)algorithm for optimizing hyperparameters.To enhance the model performance,we conduct feature fusion and dimensionality reduction.Additionally,we examine the influences of different sample sizes and ML models for training.The proposed model demonstrates higher prediction accuracy and generalization ability,achieving a predicted R^(2)value of up to 0.9 for the test set,compared to the traditional ML techniques with an R^(2)of 0.13.This model accurately predicts the production of fractured horizontal wells even with limited samples,supplying an efficient tool for optimizing the production of unconventional resources.Importantly,the model holds the potential applicability to address similar challenges in other fields constrained by scarce data samples.展开更多
Due to complex geological structures and a narrow safe mud density window,offshore fractured formations frequently encounter severe lost circulation(LC)during drilling,significantly hindering oil and gas exploration a...Due to complex geological structures and a narrow safe mud density window,offshore fractured formations frequently encounter severe lost circulation(LC)during drilling,significantly hindering oil and gas exploration and development.Predicting LC risks enables the targeted implementation of mitigation strategies,thereby reducing the frequency of such incidents.To address the limitations of existing 3D geomechanical modeling in predicting LC,such as arbitrary factor selection,subjective weight assignment,and the inability to achieve pre-drilling prediction along the entire well section,an improved prediction method is proposed.This method integrates multi-source data and incorporates three LC-related sensitivity factors:fracture characteristics,rock brittleness,and in-situ stress conditions.A quantitative risk assessment model for LC is developed by combining the subjective analytic hierarchy process with the objective entropy weight method(EWM)to assign weights.Subsequently,3D geomechanical modeling is applied to identify regional risk zones,enabling digital visualization for pre-drilling risk prediction.The developed 3D LC risk prediction model was validated using actual LC incidents from drilled wells.Results were generally consistent with field-identified LC zones,with an average relative error of 19.08%,confirming its reliability.This method provides practical guidance for mitigating potential LC risks and optimizing drilling program designs in fractured formations.展开更多
Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout a...Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout analyses were based on continuum mechanics.In addition to failure in intact rocks,wellbore breakouts can also be initiated along natural discontinuities,e.g.weak planes and fractures.Furthermore,the conventional models in wellbore breakouts with uniform distribution fractures could not reflect the real drilling situation.This paper presents a fully coupled hydro-mechanical model of the SB-X well in the Tarim Basin,China for evaluating wellbore breakouts in heavily fractured rocks under anisotropic stress states using the distinct element method(DEM)and the discrete fracture network(DFN).The developed model was validated against caliper log measurement,and its stability study was carried out by stress and displacement analyses.A parametric study was performed to investigate the effects of the characteristics of fracture distribution(orientation and length)on borehole stability by sensitivity studies.Simulation results demonstrate that the increase of the standard deviation of orientation when the fracture direction aligns parallel or perpendicular to the principal stress direction aggravates borehole instability.Moreover,an elevation in the average fracture length causes the borehole failure to change from the direction of the minimum in-situ horizontal principal stress(i.e.the direction of wellbore breakouts)towards alternative directions,ultimately leading to the whole wellbore failure.These findings provide theoretical insights for predicting wellbore breakouts in heavily fractured rocks.展开更多
The fractured rock mass inherently exhibits uncertainty due to the presence of pre-existing discontinuities.In this study,a particle-based model incorporating the discrete fracture network(DFN)to elucidate the dynamic...The fractured rock mass inherently exhibits uncertainty due to the presence of pre-existing discontinuities.In this study,a particle-based model incorporating the discrete fracture network(DFN)to elucidate the dynamic tensile responses and asso-ciated uncertainty of rock mass.At first,the particle-based model was used synthesize the intact rock and split Hopkinson pressure bar(SHPB)system,while the fractures were represented using the smooth fracture model(SJM).Subsequently,the samples of the fractured rock mass with varying joint geometrical configurations were conducted the dynamic tensile test using the numerical SHPB system.The simulated results demonstrate a gradual decrease in dynamic tensile strength(TS)with increasing fracture intensity and fracture length,which can be effectively described by nonlinear exponential func-tions.Additionally,the fracture orientation significantly influences the dynamic TS,however,the anisotropic characteristics gradually diminish as the deviation angle approaches 90°.Furthermore,as fracture intensity and fracture length increase,the dynamic TS variability also rises steadily.However,no noticeable pattern is seen when considering cases with varying fracture orientations.When subjected to SHPB loading,the fractured rock mass primarily exhibits a combined tensile-shear failure mode,contrasting with the pure tensile failure mode exhibited by the intact rock.These findings contribute signifi-cantly to comprehending the dynamic tensile responses of the fractured rock mass and can further enhance the stability analysis of in-situ rock engineering.展开更多
Coupled thermo-hydro-mechanical(THM)processes in fractured rock are playing a crucial role in geoscience and geoengineering applications.Diverse and conceptually distinct approaches have emerged over the past decades ...Coupled thermo-hydro-mechanical(THM)processes in fractured rock are playing a crucial role in geoscience and geoengineering applications.Diverse and conceptually distinct approaches have emerged over the past decades in both continuum and discontinuum perspectives leading to significant progress in their comprehending and modeling.This review paper offers an integrated perspective on existing modeling methodologies providing guidance for model selection based on the initial and boundary conditions.By comparing various models,one can better assess the uncertainties in predictions,particularly those related to the conceptual models.The review explores how these methodologies have significantlyenhanced the fundamental understanding of how fractures respond to fluid injection and production,and improved predictive capabilities pertaining to coupled processes within fractured systems.It emphasizes the importance of utilizing advanced computational technologies and thoroughly considering fundamental theories and principles established through past experimental evidence and practical experience.The selection and calibration of model parameters should be based on typical ranges and applied to the specificconditions of applications.The challenges arising from inherent heterogeneity and uncertainties,nonlinear THM coupled processes,scale dependence,and computational limitations in representing fieldscale fractures are discussed.Realizing potential advances on computational capacity calls for methodical conceptualization,mathematical modeling,selection of numerical solution strategies,implementation,and calibration to foster simulation outcomes that intricately reflectthe nuanced complexities of geological phenomena.Future research efforts should focus on innovative approaches to tackle the hurdles and advance the state-of-the-art in this critical fieldof study.展开更多
The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deepgeological stress for a long period of time,potentially resulting in large-scale deformations or eveninstability fail...The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deepgeological stress for a long period of time,potentially resulting in large-scale deformations or eveninstability failure of the underground engineering.Accurate characterization of the creep behavior of thesurrounding rock is essential for evaluating the long-term stability and safety of high-level radioactivewaste(HLW)disposal repositories.Although the laboratory creep tests of brittle undamaged rocks,suchas granite,have been extensively performed,the creep characteristics of fractured surrounding rockunder the multi-field coupling environment still require attention.In this study,a series of creep experimentswas conducted on Beishan granite,which was identified as the optimal candidate surroundingrock for the disposal repository in China.The effects of various factors,including inclination angle offractures,stress conditions,temperatures,and water content,were investigated.The experimental resultsshow that the axial total strain increases linearly with increasing stress level,while the lateral totalstrain,axial and lateral creep strain rates increase exponentially.The failure time of saturated specimensfractured at 45°and 60°is approximately 1.05‰and 0.84‰of that of dry specimens,respectively.Theeffect of temperature,ranging from room temperature to 120℃,is minimal,compared to the substantialvariations in strain and creep rates caused by stress and water content.The creep failure of specimensfractured at 30°is dominated by rock material failure,whereas the creep failure of specimens fractured at60°is dominated by pre-existing fracture slip.At a 45°fracture angle,a composite failure mechanism isobserved that includes both rock material failure and pre-existing fracture slip.展开更多
The shear behavior of fractured rock masses critically infuences engineering stability,particularly in slope engineering.Overcoming limitations of conventional preparation methods,this study utilizes sand-powder 3D pr...The shear behavior of fractured rock masses critically infuences engineering stability,particularly in slope engineering.Overcoming limitations of conventional preparation methods,this study utilizes sand-powder 3D printing to fabricate rocklike specimens with controlled internal fractures.Direct shear tests systematically investigate fracture radius and number efects on strength evolution under constant density,with quantitative analysis revealing their diferential contributions.The results show that:(1)The failure of sand-powder 3D-printed fractured rock-like specimens exhibits brittle characteristics.The shear stress-shear displacement relationship can be divided into fve stages:compaction,elasticity,unstable development,peak,and post-peak.Crack initiation and propagation primarily occur from the late elastic stage to the peak stage.(2)An increase in fracture radius signifcantly reduces pre-peak shear stifness,resulting in a smoother curve progression,while changes in fracture number have minimal impact on the stage-specifc characteristics of the shear curve.(3)Shear strength decreases exponentially with increasing fracture radius,whereas an increase in fracture number leads to a linear reduction in shear strength.Moreover,the weakening efect of fracture number on shear strength becomes more pronounced with larger fracture radius.(4)Quantitative analysis shows that the infuence of fracture radius on shear strength is 2.4 times greater than that of fracture number.This study broadens the understanding of the shear behaviors of fractured rock masses and reveals the key infuence mechanism of fracture density on rock mass deformation and failure,and provides theoretical guidance for slope stability analysis and rock mass engineering design.展开更多
High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock inst...High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.展开更多
Asia’s unhealed wounds and incomplete justice of WWII.WHILE Europe commemorated Nazi Germany’s defeat during the World War II in May 1945,few acknowledged that the war raged on for several more months in Asia,claimi...Asia’s unhealed wounds and incomplete justice of WWII.WHILE Europe commemorated Nazi Germany’s defeat during the World War II in May 1945,few acknowledged that the war raged on for several more months in Asia,claiming millions more lives before Japan officially signed the instrument of surrender on September 2,1945.展开更多
This manuscript introduces a new decline curve analysis(DCA) technique to analyze and predict the potentials of hydraulically fractured unconventional resources.The new approach relies on the ratenormalized flow rate ...This manuscript introduces a new decline curve analysis(DCA) technique to analyze and predict the potentials of hydraulically fractured unconventional resources.The new approach relies on the ratenormalized flow rate derivative(RNFD) concept.It uses the significant constant behavior of the RNFD that identifies the power-law type flow regime models of fractured reservoirs.This technique merges the RNFD with a new numerical model for the flow rate derivative(flow rate noise-reducing derivative model).The concept of the RNFD [1/q(txq')] is developed based on the power-law type analytical models of the flow regimes that can be characterized from the production history of gas or oil-producing wells.The production rate,cumulative production,and the calculated RNFDs from the production history are used for this purpose.The constant RNFD values and the flow rate derivative's numerical model can be used to simulate the production history or predict future performance.The impact of the skin factor is introduced to the approach by developing new RNFD models that could replace the constant pattern of RNFD when this impact does not exist.For a severe condition of skin factor,the RNFD shows a linear relationship with time instead of the constant value.The proposed approach gives an excellent match with the production history of the case studies examined in this study.The transition between flow regimes does not impact the application of the RNFD,i.e.,the calculations move very smoothly throughout the flow regime.The novelty of the proposed technique is represented by introducing an approach for the DCA that considers the observed flow regimes during the production history and the impact of the skin factor.The approach proposes new numerical flow rate and cumulative production models to predict future performance as well as new models for estimating the impact of skin factors on production history,especially for early time flow regimes.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
In this paper,according to the migration and diffusion law of MICP solution in fracture-pore medium,the migration and diffusion equation of MICP solution in loess fracture-pore medium was derived first.Then,the migrat...In this paper,according to the migration and diffusion law of MICP solution in fracture-pore medium,the migration and diffusion equation of MICP solution in loess fracture-pore medium was derived first.Then,the migration and diffusion test was carried out by using the self-made Mdevice.In the model,the apertures of the fracture of 0.5 mm,1.0 mm and 1.5 mm were selected,and the calcium ion concentrations at different points were measured by atomic absorption method,to obtain the distribution map of calcium ion concentration.According to the test results,the migration speed of calcium ions in the direction along the fracture is less than the diffusion speed of the wet peak,and the vertical fracture direction is faster than the diffusion speed of the wet peak.The distribution range of calcium ion concentration increases first and then decreases with the increase in fracture opening.COMSOL was used to compile the mathematical equation,and the whole process of MICP solution migration and diffusion was numerically simulated.The numerical calculation results are basically consistent with the experimental results,and the derived mathematical equation is reasonable.展开更多
By comprehensively considering the influences of temperature and pressure on fluid density in high temperature and high pressure(HTHP)wells in deepwater fractured formations and the effects of formation fracture defor...By comprehensively considering the influences of temperature and pressure on fluid density in high temperature and high pressure(HTHP)wells in deepwater fractured formations and the effects of formation fracture deformation on well shut-in afterflow,this study couples the shut-in temperature field model,fracture deformation model,and gas flow model to establish a wellbore pressure calculation model incorporating thermo-hydro-mechanical coupling effects.The research analyzes the governing patterns of geothermal gradient,bottomhole pressure difference,drilling fluid pit gain,and kick index on casing head pressure,and establishes a shut-in pressure determination chart for HPHT wells based on coupled model calculation results.The study results show:geothermal gradient,bottomhole pressure difference,and drilling fluid pit gain exhibit positive correlations with casing head pressure;higher kick indices accelerate pressure rising rates while maintaining a constant maximum casing pressure;validation against field case data demonstrates over 95%accuracy in predicting wellbore pressure recovery after shut-in,with the pressure determination chart achieving 97.2%accuracy in target casing head pressure prediction and 98.3%accuracy in target shut-in time.This method enables accurate acquisition of formation pressure after HPHT well shut-in,providing reliable technical support for subsequent well control measures and ensuring safe and efficient development of deepwater and deep hydrocarbon reservoirs.展开更多
Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and...Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and gas extraction.Central to this phenomenon is the transport of proppants,tiny solid particles injected into the fractures to prevent them from closing once the injection is stopped.However,effective transport and deposition of proppant is critical in keeping fracture pathways open,especially in lowpermeability reservoirs.This review explores,then quantifies,the important role of fluid inertia and turbulent flows in governing proppant transport.While traditional models predominantly assume and then characterise flow as laminar,this may not accurately capture the complexities inherent in realworld hydraulic fracturing and proppant emplacement.Recent investigations highlight the paramount importance of fluid inertia,especially at the high Reynolds numbers typically associated with fracturing operations.Fluid inertia,often overlooked,introduces crucial forces that influence particle settling velocities,particle-particle interactions,and the eventual deposition of proppants within fractures.With their inherent eddies and transient and chaotic nature,turbulent flows introduce additional complexities to proppant transport,crucially altering proppant settling velocities and dispersion patterns.The following comprehensive survey of experimental,numerical,and analytical studies elucidates controls on the intricate dynamics of proppant transport under fluid inertia and turbulence-towards providing a holistic understanding of the current state-of-the-art,guiding future research directions,and optimising hydraulic fracturing practices.展开更多
As the dominant seepage channel in rock masses,it is of great significance to study the influence of fracture roughness distribution on seepage and heat transfer in rock masses.In this paper,the fracture roughness dis...As the dominant seepage channel in rock masses,it is of great significance to study the influence of fracture roughness distribution on seepage and heat transfer in rock masses.In this paper,the fracture roughness distribution functions of the Bakhtiary dam site and Oskarshamn/Forsmark mountain were fitted using statistical methods.The COMSOL Multiphysics finite element software was utilized to analyze the effects of fracture roughness distribution types and empirical formulas for fracture hydraulic aperture on the seepage field and temperature field of rock masses.The results show that:(1)The fracture roughness at the Bakhtiary dam site and Oskarshamn/Forsmark mountain follows lognormal and normal distributions,respectively;(2)For rock masses with the same expected value and standard deviation of fracture roughness,the outflow from rock masses with lognormal distribution of fracture roughness is significantly larger than that of rock masses with normal distribution of fracture roughness;(3)The fracture hydraulic aperture,outflow,and cold front distance of the Li and Jiang model are significantly larger than those of the Barton model;(4)The outflow,hydraulic pressure distribution,and temperature distribution of the Barton model are more sensitive to the fracture roughness distribution type than those of the Li and Jiang model.展开更多
Deep underground excavation causes considerable unloading effects,leading to a pronounced bias pressure phenomenon.The deformation and seepage characteristics of rock masses under different gas and confining pressures...Deep underground excavation causes considerable unloading effects,leading to a pronounced bias pressure phenomenon.The deformation and seepage characteristics of rock masses under different gas and confining pressures were investigated via triaxial loading and unloading seepage tests.When the influential coefficient of effective confining pressure(β)is less than 0.065,the seepage force considerably weakens the strength of fractured rock masses.Conversely,whenβis greater than 0.065,the opposite is true.Moreover,the increase in the axial load leads to an increase in the precast fracture volumetric strain,which is the main reason for the increase in fracture permeability.This effect is particularly significant during the unloading stage.Based on the test results,a method for calculating the dynamic seepage evolution of rock masses,considering the effects of rock mass damage and fracture deformation,is introduced,and the effectiveness of the calculation is validated.The entire description of the seepage under loading and unloading was accomplished.The equivalent relationship between the lateral and normal stresses on fracture surfaces ranges from 0.001 to 0.1,showing an exponential variation between the lateral stress influence coefficient on normal deformation(χ)and seepage pressure.Before the failure of the rock mass,the seepage in the fractures was in a linear laminar flow state.However,after the failure,when the gas pressure reached 2 MPa,the flow state in the fractures transitioned to nonlinear laminar flow.The results are important for predicting hazardous gas leaks during deep underground engineering excavation.展开更多
文摘The Gabes aquifer system,located in southeastern Tunisia,is a crucial resource for supporting local socio-economic activities.Due to its dual porosity structure,is particularly vulnerable to pollution.This study aims to develop a hybrid model that combines the Fracture Aquifer Index(FAI)with the conventional GOD(Groundwater occurrence,Overall lithology,Depth to water table)method,to assess groundwater vulnerability in fractured aquifer.To develop the hybrid model,the classical GOD method was integrated with FAI to produce a single composite index.Each parameter within both GOD and FAI was scored,and a final index was calculated to delineate vulnerable areas.The results show that the study area can be classified into four vulnerability levels:Very low,low,moderate,and high,indicating that approximately 8%of the area exhibits very low vulnerability,29%has low vulnerability,25%falls into the moderate category,and 38%is considered highly vulnerable.The FAI-GOD model further incorporates fracture network characteristics.This refinement reduces the classification to three vulnerability classes:Low,medium,and high.The outcomes demonstrate that 46%of the area is highly vulnerable due to a dense concentration of fractures,while 17%represents an intermediate zone characterized by either shallow or deeper fractures.In contrast,37%corresponds to areas with lightly fractured rock,where the impact on vulnerability is minimal.Multivariate statistical analysis was employed using Principal Components Analysis(PCA)and Hierarchical Cluster Analysis(HCA)on 24 samples across six variables.The first three components account for over 76%of the total variance,reinforcing the significance of fracture dynamics in classifying vulnerability levels.The FAI-GOD model removes the very-low-vulnerability class and expands the spatial extent of low-and high-vulnerability zones,reflecting the dominant influence of fracture networks on aquifer sensitivity.While both indices use a five-class system,FAI-GOD redistributes vulnerability by eliminating very-low-vulnerability areas and amplifying low/high categories,highlighting the critical role of fractures.A strong correlation(R2=0.94)between the GOD and FAI-GOD indices,demonstrated through second-order polynomial regression,confirms the robustness of the FAI-GOD model in accurately predicting vulnerability to pollution.This model provides a useful framework for assessing the vulnerability of complex aquifers and serves as a decision-making tool for groundwater managers in similar areas.
文摘Fluid flow through fractured rock masses is a key process controlling the safety and performance of deep geoengineering systems,shaped by the complex interactions of thermal,hydraulic,mechanical and chemical(THMC)fields.This paper presents a systematic review of this subject with special emphasis on the multi-physics governing it.First,we elucidate the interdependent mechanisms and governing equations,highlighting the nonlinear,path-dependent,and evolving nature of the relationship between stress and permeability.Next,mainstream modeling approaches,including equivalent continuum,discrete fracture network(DFN),and dual-porosity/dual-permeability methods,are critically evaluated,and a strategy for model selection based on project scale and geological context is proposed accordingly.Moreover,experimental insights from single-fracture and triaxial flow studies are synthesized,revealing how effective stress,shear displacement,and fracture roughness control permeability evolution.In particular,the practical significance of THMC coupling is demonstrated through case studies on nuclear waste disposal,Enhanced Geothermal Systems,and tunneling projects.The reviewfurther explores AI-and machine learning-driven innovations,particularly physics-informed neural networks and hybrid modeling,which address limitations in computational efficiency,data scarcity,and physical consistency.Finally,persistent challenges,including multi-scale coupling,parameter uncertainty,and complex fracture network representation are identified and critically discussed while paying attention to future developments.
基金support from the Science and Technology Innovation Program of Hunan Province(Grant No.2023RC1021)the Natural Science Foundation of Sichuan Province(Grant No.2025YFHZ0323).-。
文摘The coupled chemo-mechanical impact of supercritical CO_(2)-H_(2)O(ScCO_(2)-H_(2)O)reactions on fracture geometry and nonlinear flow regimes in deep shale under confining pressures remains inadequately quantified.This study systematically investigates the effects of ScCO_(2)-H_(2)O-shale interactions on fracture morphology and flow properties under confining pressures from 15 MPa to 40 MPa by integrating XRD(X-ray diffraction),micro-CT,3D surface profilometry,and multistage steady-state flow experiments.The results demonstrate that ScCO_(2)-H_(2)O exposure drives pyrite/feldspar dissolution and localized clay precipitation,resulting in fracture branching and macroscopic aperture regularization.Critically,confining pressure dictates the net hydraulic response:under low confining pressure(15-25 MPa),dissolution dominates,enhancing permeability,flow efficiency(Q/VP),and pre-linear flow behavior(n<1).At high confining pressures(30-40 MPa)mechanical compaction and mineral precipitation amplify flow resistance,shifting the flow regime toward quasi-linear behavior,as inertial effects become negligible compared to dominant viscous forces and increased flow resistance.Confining pressure thus critically mediates the dissolution-precipitation balance during ScCO_(2)-H_(2)O treatment,with an optimal window of 15-25 MPa identified for enhancing conductivity while minimizing clogging risk.These findings provide a quantitative framework for predicting stress-dependent flow evolution in chemically altered shale fractures.
基金supported by the China Scholarship Council(CSC,Grant No.202108050072)JSPS KAKENHI(Grant No.JP19KK0121)。
文摘Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength.Nevertheless,there is a lack of potent numerical tools for assessing the grouting effectiveness in water-rich fractured strata.In this study,the hydro-mechanical coupled discontinuous deformation analysis(HM-DDA)is inaugurally extended to simulate the grouting process in a water-rich discrete fracture network(DFN),including the slurry migration,fracture dilation,water plugging in a seepage field,and joint reinforcement after coagulation.To validate the capabilities of the developed method,several numerical examples are conducted incorporating the Newtonian fluid and Bingham slurry.The simulation results closely align with the analytical solutions.Additionally,a set of compression tests is conducted on the fresh and grouted rock specimens to verify the reinforcement method and calibrate the rational properties of reinforced joints.An engineering-scale model based on a real water inrush case of the Yonglian tunnel in a water-rich fractured zone has been established.The model demonstrates the effectiveness of grouting reinforcement in mitigating water inrush disaster.The results indicate that increased grouting pressure greatly affects the regulation of water outflow from the tunnel face and the prevention of rock detachment face after excavation.
基金supported by the National Natural Science Foundation of China(52274055)the Shandong Provincial Natural Science Foundation(ZR2022YQ50)the Taishan Scholar Program of Shandong Province(tsqn202408088)。
文摘Predicting the productivity of multistage fractured horizontal wells plays an important role in exploiting unconventional resources.In recent years,machine learning(ML)models have emerged as a new approach for such studies.However,the scarcity of sufficient real data for model training often leads to imprecise predictions,even though the models trained with real data better characterize geological and engineering features.To tackle this issue,we propose an ML model that can obtain reliable results even with a small amount of data samples.Our model integrates the synthetic minority oversampling technique(SMOTE)to expand the data volume,the support vector machine(SVM)for model training,and the particle swarm optimization(PSO)algorithm for optimizing hyperparameters.To enhance the model performance,we conduct feature fusion and dimensionality reduction.Additionally,we examine the influences of different sample sizes and ML models for training.The proposed model demonstrates higher prediction accuracy and generalization ability,achieving a predicted R^(2)value of up to 0.9 for the test set,compared to the traditional ML techniques with an R^(2)of 0.13.This model accurately predicts the production of fractured horizontal wells even with limited samples,supplying an efficient tool for optimizing the production of unconventional resources.Importantly,the model holds the potential applicability to address similar challenges in other fields constrained by scarce data samples.
基金supported by the National Natural Science Foundation of China(No.52074312)the CNPC Science and Technology Innovation Foundation(No.2021DQ02-0505)+1 种基金the Open Fund Project of the National Key Laboratory for the Enrichment Mechanism and Efficient Development of Shale Oil and Gas(No.36650000-24-ZC0609-0006)the Major Science and Technology Project of Karamay City(No.20232023zdzx0003).
文摘Due to complex geological structures and a narrow safe mud density window,offshore fractured formations frequently encounter severe lost circulation(LC)during drilling,significantly hindering oil and gas exploration and development.Predicting LC risks enables the targeted implementation of mitigation strategies,thereby reducing the frequency of such incidents.To address the limitations of existing 3D geomechanical modeling in predicting LC,such as arbitrary factor selection,subjective weight assignment,and the inability to achieve pre-drilling prediction along the entire well section,an improved prediction method is proposed.This method integrates multi-source data and incorporates three LC-related sensitivity factors:fracture characteristics,rock brittleness,and in-situ stress conditions.A quantitative risk assessment model for LC is developed by combining the subjective analytic hierarchy process with the objective entropy weight method(EWM)to assign weights.Subsequently,3D geomechanical modeling is applied to identify regional risk zones,enabling digital visualization for pre-drilling risk prediction.The developed 3D LC risk prediction model was validated using actual LC incidents from drilled wells.Results were generally consistent with field-identified LC zones,with an average relative error of 19.08%,confirming its reliability.This method provides practical guidance for mitigating potential LC risks and optimizing drilling program designs in fractured formations.
基金supported by National Natural Science Foundation of China(Grant Nos.52074312 and 52211530097)CNPC Science and Technology Innovation Foundation(Grant No.2021DQ02-0505).
文摘Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout analyses were based on continuum mechanics.In addition to failure in intact rocks,wellbore breakouts can also be initiated along natural discontinuities,e.g.weak planes and fractures.Furthermore,the conventional models in wellbore breakouts with uniform distribution fractures could not reflect the real drilling situation.This paper presents a fully coupled hydro-mechanical model of the SB-X well in the Tarim Basin,China for evaluating wellbore breakouts in heavily fractured rocks under anisotropic stress states using the distinct element method(DEM)and the discrete fracture network(DFN).The developed model was validated against caliper log measurement,and its stability study was carried out by stress and displacement analyses.A parametric study was performed to investigate the effects of the characteristics of fracture distribution(orientation and length)on borehole stability by sensitivity studies.Simulation results demonstrate that the increase of the standard deviation of orientation when the fracture direction aligns parallel or perpendicular to the principal stress direction aggravates borehole instability.Moreover,an elevation in the average fracture length causes the borehole failure to change from the direction of the minimum in-situ horizontal principal stress(i.e.the direction of wellbore breakouts)towards alternative directions,ultimately leading to the whole wellbore failure.These findings provide theoretical insights for predicting wellbore breakouts in heavily fractured rocks.
基金supported by the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(2019ZT08G315)the National Natural Science Foundation of China(52304091,52004162 and 52274089)+1 种基金the Research Project of Education Department of Hunan Province(22B0427)the China postdoctoral science foundation(2023M741047).
文摘The fractured rock mass inherently exhibits uncertainty due to the presence of pre-existing discontinuities.In this study,a particle-based model incorporating the discrete fracture network(DFN)to elucidate the dynamic tensile responses and asso-ciated uncertainty of rock mass.At first,the particle-based model was used synthesize the intact rock and split Hopkinson pressure bar(SHPB)system,while the fractures were represented using the smooth fracture model(SJM).Subsequently,the samples of the fractured rock mass with varying joint geometrical configurations were conducted the dynamic tensile test using the numerical SHPB system.The simulated results demonstrate a gradual decrease in dynamic tensile strength(TS)with increasing fracture intensity and fracture length,which can be effectively described by nonlinear exponential func-tions.Additionally,the fracture orientation significantly influences the dynamic TS,however,the anisotropic characteristics gradually diminish as the deviation angle approaches 90°.Furthermore,as fracture intensity and fracture length increase,the dynamic TS variability also rises steadily.However,no noticeable pattern is seen when considering cases with varying fracture orientations.When subjected to SHPB loading,the fractured rock mass primarily exhibits a combined tensile-shear failure mode,contrasting with the pure tensile failure mode exhibited by the intact rock.These findings contribute signifi-cantly to comprehending the dynamic tensile responses of the fractured rock mass and can further enhance the stability analysis of in-situ rock engineering.
基金funding from the European Research Council(ERC)under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST(grant agreement No.801809)support by MICIU/AEI/10.13039/501100011033 and by"European Union Next Generation EU/PRTR"through the‘Ramón y Cajal’fellowship(reference RYC2021-032780-I)+9 种基金funding by MICIU/AEI/10.13039/501100011033 and by“ERDF,EU”through the‘HydroPoreII’project(reference PID2022-137652NBC44)support by the Institute for Korea Spent Nuclear Fuel(iKSNF)National Research Foundation of Korea(NRF)grant funded by the Korea government(Ministry of Science and ICT,MSIT)(2021M2E1A1085196)support by the Swedish Radiation Safety(SSM),Swedish Transport Administration(Trafikverket),Swedish Rock Engineering Foundation(BeFo),and Nordic Energy Research(Grant 187658)supported by the US Department of Energy(DOE),the Officeof Nuclear Energy,Spent Fuel and Waste Science and Technology Campaign,and by the US Department of Energy(DOE),the Office of Basic Energy Sciences,Chemical Sciences,Geosciences,and Biosciences Division both under Contract Number DE-AC02-05CH11231 with Lawrence Berkeley National Laboratorysupport from the US National Science Foundation(grant CMMI-2239630)funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(grant agreement No.101002507)the UK Natural Environment Research Council(NERC)for funding SeisGreen Project(Grant No.NE/W009293/1)which supported this workthe Royal Society UK for supporting this research through fellowship UF160443IMEDEA is an accredited"Maria de Maeztu Excellence Unit"(Grant CEX2021-001198,funded by MICIU/AEI/10.13039/501100011033).
文摘Coupled thermo-hydro-mechanical(THM)processes in fractured rock are playing a crucial role in geoscience and geoengineering applications.Diverse and conceptually distinct approaches have emerged over the past decades in both continuum and discontinuum perspectives leading to significant progress in their comprehending and modeling.This review paper offers an integrated perspective on existing modeling methodologies providing guidance for model selection based on the initial and boundary conditions.By comparing various models,one can better assess the uncertainties in predictions,particularly those related to the conceptual models.The review explores how these methodologies have significantlyenhanced the fundamental understanding of how fractures respond to fluid injection and production,and improved predictive capabilities pertaining to coupled processes within fractured systems.It emphasizes the importance of utilizing advanced computational technologies and thoroughly considering fundamental theories and principles established through past experimental evidence and practical experience.The selection and calibration of model parameters should be based on typical ranges and applied to the specificconditions of applications.The challenges arising from inherent heterogeneity and uncertainties,nonlinear THM coupled processes,scale dependence,and computational limitations in representing fieldscale fractures are discussed.Realizing potential advances on computational capacity calls for methodical conceptualization,mathematical modeling,selection of numerical solution strategies,implementation,and calibration to foster simulation outcomes that intricately reflectthe nuanced complexities of geological phenomena.Future research efforts should focus on innovative approaches to tackle the hurdles and advance the state-of-the-art in this critical fieldof study.
基金supported by the National Natural Science Foundation of China(Grant No.42307258)the China Atomic Energy Authority(CAEA)through the Geological Disposal Program,and the Science and Technology Department of Sichuan Province Project,China(Grant No.2023ZYD0154).
文摘The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deepgeological stress for a long period of time,potentially resulting in large-scale deformations or eveninstability failure of the underground engineering.Accurate characterization of the creep behavior of thesurrounding rock is essential for evaluating the long-term stability and safety of high-level radioactivewaste(HLW)disposal repositories.Although the laboratory creep tests of brittle undamaged rocks,suchas granite,have been extensively performed,the creep characteristics of fractured surrounding rockunder the multi-field coupling environment still require attention.In this study,a series of creep experimentswas conducted on Beishan granite,which was identified as the optimal candidate surroundingrock for the disposal repository in China.The effects of various factors,including inclination angle offractures,stress conditions,temperatures,and water content,were investigated.The experimental resultsshow that the axial total strain increases linearly with increasing stress level,while the lateral totalstrain,axial and lateral creep strain rates increase exponentially.The failure time of saturated specimensfractured at 45°and 60°is approximately 1.05‰and 0.84‰of that of dry specimens,respectively.Theeffect of temperature,ranging from room temperature to 120℃,is minimal,compared to the substantialvariations in strain and creep rates caused by stress and water content.The creep failure of specimensfractured at 30°is dominated by rock material failure,whereas the creep failure of specimens fractured at60°is dominated by pre-existing fracture slip.At a 45°fracture angle,a composite failure mechanism isobserved that includes both rock material failure and pre-existing fracture slip.
基金supported by the National Key Research and Development Program Young Scientist Project(2024YFC2911000)the Natural Science Foundation of Shandong Province(ZR2024ME031)+1 种基金National Natural Science Foundation of China(52474103)Natural Science Foundation of Shandong Province(ZR2024ZD22).
文摘The shear behavior of fractured rock masses critically infuences engineering stability,particularly in slope engineering.Overcoming limitations of conventional preparation methods,this study utilizes sand-powder 3D printing to fabricate rocklike specimens with controlled internal fractures.Direct shear tests systematically investigate fracture radius and number efects on strength evolution under constant density,with quantitative analysis revealing their diferential contributions.The results show that:(1)The failure of sand-powder 3D-printed fractured rock-like specimens exhibits brittle characteristics.The shear stress-shear displacement relationship can be divided into fve stages:compaction,elasticity,unstable development,peak,and post-peak.Crack initiation and propagation primarily occur from the late elastic stage to the peak stage.(2)An increase in fracture radius signifcantly reduces pre-peak shear stifness,resulting in a smoother curve progression,while changes in fracture number have minimal impact on the stage-specifc characteristics of the shear curve.(3)Shear strength decreases exponentially with increasing fracture radius,whereas an increase in fracture number leads to a linear reduction in shear strength.Moreover,the weakening efect of fracture number on shear strength becomes more pronounced with larger fracture radius.(4)Quantitative analysis shows that the infuence of fracture radius on shear strength is 2.4 times greater than that of fracture number.This study broadens the understanding of the shear behaviors of fractured rock masses and reveals the key infuence mechanism of fracture density on rock mass deformation and failure,and provides theoretical guidance for slope stability analysis and rock mass engineering design.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972283 and 42277182).
文摘High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.
文摘Asia’s unhealed wounds and incomplete justice of WWII.WHILE Europe commemorated Nazi Germany’s defeat during the World War II in May 1945,few acknowledged that the war raged on for several more months in Asia,claiming millions more lives before Japan officially signed the instrument of surrender on September 2,1945.
文摘This manuscript introduces a new decline curve analysis(DCA) technique to analyze and predict the potentials of hydraulically fractured unconventional resources.The new approach relies on the ratenormalized flow rate derivative(RNFD) concept.It uses the significant constant behavior of the RNFD that identifies the power-law type flow regime models of fractured reservoirs.This technique merges the RNFD with a new numerical model for the flow rate derivative(flow rate noise-reducing derivative model).The concept of the RNFD [1/q(txq')] is developed based on the power-law type analytical models of the flow regimes that can be characterized from the production history of gas or oil-producing wells.The production rate,cumulative production,and the calculated RNFDs from the production history are used for this purpose.The constant RNFD values and the flow rate derivative's numerical model can be used to simulate the production history or predict future performance.The impact of the skin factor is introduced to the approach by developing new RNFD models that could replace the constant pattern of RNFD when this impact does not exist.For a severe condition of skin factor,the RNFD shows a linear relationship with time instead of the constant value.The proposed approach gives an excellent match with the production history of the case studies examined in this study.The transition between flow regimes does not impact the application of the RNFD,i.e.,the calculations move very smoothly throughout the flow regime.The novelty of the proposed technique is represented by introducing an approach for the DCA that considers the observed flow regimes during the production history and the impact of the skin factor.The approach proposes new numerical flow rate and cumulative production models to predict future performance as well as new models for estimating the impact of skin factors on production history,especially for early time flow regimes.
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support from the Shaanxi Natural Science Basic Research Project(Grant no.2020JM-483)Investigation on the Interfacial Bonding Mechanism of Microbial Mineralization Repair Grout for Cracks in Rammed Earth Heritage(Grant no.2025JC-YBMS-551)the National Natural Science Foundation of China(NSFC)(Grant no.51408464).
文摘In this paper,according to the migration and diffusion law of MICP solution in fracture-pore medium,the migration and diffusion equation of MICP solution in loess fracture-pore medium was derived first.Then,the migration and diffusion test was carried out by using the self-made Mdevice.In the model,the apertures of the fracture of 0.5 mm,1.0 mm and 1.5 mm were selected,and the calcium ion concentrations at different points were measured by atomic absorption method,to obtain the distribution map of calcium ion concentration.According to the test results,the migration speed of calcium ions in the direction along the fracture is less than the diffusion speed of the wet peak,and the vertical fracture direction is faster than the diffusion speed of the wet peak.The distribution range of calcium ion concentration increases first and then decreases with the increase in fracture opening.COMSOL was used to compile the mathematical equation,and the whole process of MICP solution migration and diffusion was numerically simulated.The numerical calculation results are basically consistent with the experimental results,and the derived mathematical equation is reasonable.
基金Supported by the Joint Fund Key Program of the National Natural Science Foundation of China(U21B2069)Key Research and Development Program of Shandong Province(2022CXGC020407)Basic Science Center Program of the National Natural Science Foundation of China(52288101)。
文摘By comprehensively considering the influences of temperature and pressure on fluid density in high temperature and high pressure(HTHP)wells in deepwater fractured formations and the effects of formation fracture deformation on well shut-in afterflow,this study couples the shut-in temperature field model,fracture deformation model,and gas flow model to establish a wellbore pressure calculation model incorporating thermo-hydro-mechanical coupling effects.The research analyzes the governing patterns of geothermal gradient,bottomhole pressure difference,drilling fluid pit gain,and kick index on casing head pressure,and establishes a shut-in pressure determination chart for HPHT wells based on coupled model calculation results.The study results show:geothermal gradient,bottomhole pressure difference,and drilling fluid pit gain exhibit positive correlations with casing head pressure;higher kick indices accelerate pressure rising rates while maintaining a constant maximum casing pressure;validation against field case data demonstrates over 95%accuracy in predicting wellbore pressure recovery after shut-in,with the pressure determination chart achieving 97.2%accuracy in target casing head pressure prediction and 98.3%accuracy in target shut-in time.This method enables accurate acquisition of formation pressure after HPHT well shut-in,providing reliable technical support for subsequent well control measures and ensuring safe and efficient development of deepwater and deep hydrocarbon reservoirs.
基金the Australian Research Council Discovery Project(ARC DP 220100851)scheme and would acknowledge that.
文摘Particle-fluid two-phase flows in rock fractures and fracture networks play a pivotal role in determining the efficiency and effectiveness of hydraulic fracturing operations,a vital component in unconventional oil and gas extraction.Central to this phenomenon is the transport of proppants,tiny solid particles injected into the fractures to prevent them from closing once the injection is stopped.However,effective transport and deposition of proppant is critical in keeping fracture pathways open,especially in lowpermeability reservoirs.This review explores,then quantifies,the important role of fluid inertia and turbulent flows in governing proppant transport.While traditional models predominantly assume and then characterise flow as laminar,this may not accurately capture the complexities inherent in realworld hydraulic fracturing and proppant emplacement.Recent investigations highlight the paramount importance of fluid inertia,especially at the high Reynolds numbers typically associated with fracturing operations.Fluid inertia,often overlooked,introduces crucial forces that influence particle settling velocities,particle-particle interactions,and the eventual deposition of proppants within fractures.With their inherent eddies and transient and chaotic nature,turbulent flows introduce additional complexities to proppant transport,crucially altering proppant settling velocities and dispersion patterns.The following comprehensive survey of experimental,numerical,and analytical studies elucidates controls on the intricate dynamics of proppant transport under fluid inertia and turbulence-towards providing a holistic understanding of the current state-of-the-art,guiding future research directions,and optimising hydraulic fracturing practices.
基金College Students Innovation and Entrepreneurship Project of Guangzhou Railway Polytechnic(2025CXCY015)。
文摘As the dominant seepage channel in rock masses,it is of great significance to study the influence of fracture roughness distribution on seepage and heat transfer in rock masses.In this paper,the fracture roughness distribution functions of the Bakhtiary dam site and Oskarshamn/Forsmark mountain were fitted using statistical methods.The COMSOL Multiphysics finite element software was utilized to analyze the effects of fracture roughness distribution types and empirical formulas for fracture hydraulic aperture on the seepage field and temperature field of rock masses.The results show that:(1)The fracture roughness at the Bakhtiary dam site and Oskarshamn/Forsmark mountain follows lognormal and normal distributions,respectively;(2)For rock masses with the same expected value and standard deviation of fracture roughness,the outflow from rock masses with lognormal distribution of fracture roughness is significantly larger than that of rock masses with normal distribution of fracture roughness;(3)The fracture hydraulic aperture,outflow,and cold front distance of the Li and Jiang model are significantly larger than those of the Barton model;(4)The outflow,hydraulic pressure distribution,and temperature distribution of the Barton model are more sensitive to the fracture roughness distribution type than those of the Li and Jiang model.
基金supported by the National Natural Science Foundation of China(Grant No.52374079)Chongqing Graduate Research Innovation Project(Grant No.CYB22032)Chongqing Talents and Outstanding Scientists Project(Grant No.cstc2024ycjhbgzxm0032).
文摘Deep underground excavation causes considerable unloading effects,leading to a pronounced bias pressure phenomenon.The deformation and seepage characteristics of rock masses under different gas and confining pressures were investigated via triaxial loading and unloading seepage tests.When the influential coefficient of effective confining pressure(β)is less than 0.065,the seepage force considerably weakens the strength of fractured rock masses.Conversely,whenβis greater than 0.065,the opposite is true.Moreover,the increase in the axial load leads to an increase in the precast fracture volumetric strain,which is the main reason for the increase in fracture permeability.This effect is particularly significant during the unloading stage.Based on the test results,a method for calculating the dynamic seepage evolution of rock masses,considering the effects of rock mass damage and fracture deformation,is introduced,and the effectiveness of the calculation is validated.The entire description of the seepage under loading and unloading was accomplished.The equivalent relationship between the lateral and normal stresses on fracture surfaces ranges from 0.001 to 0.1,showing an exponential variation between the lateral stress influence coefficient on normal deformation(χ)and seepage pressure.Before the failure of the rock mass,the seepage in the fractures was in a linear laminar flow state.However,after the failure,when the gas pressure reached 2 MPa,the flow state in the fractures transitioned to nonlinear laminar flow.The results are important for predicting hazardous gas leaks during deep underground engineering excavation.
