The Anderson's model can be applied only to elastic homogeneous deformation and cannot explain complicated phenomena of natural faults, which to a large degree limits the model to practical application. By combing...The Anderson's model can be applied only to elastic homogeneous deformation and cannot explain complicated phenomena of natural faults, which to a large degree limits the model to practical application. By combing the Coulomb-Mohr Criterion with the sandbox modeling and considering non-homogeneous deformation, mechanisms of how basement pre-existing fabrics control fault formation and evolution are analyzed and a mechanical factor, activation-coefficient (faS) of pre-existing fabrics, is proposed. It is determined by the attitude and mechanical properties of pre-existing fabric, and the stress state (the magnitudes and directions of the three principal stresses). The coefficient has taken the heterogeneity of rocks into account and may serve as a criterion for evaluating the activity of a pre-existing fabric. The Mohr-Coulomb Criterion is expanded to non-homogeneous deformation domain in terms of activation-coefficient (faS) of pre-existing fabrics, the general law of the activity of a pre-existing fabric is predicted, the fault complexity real of rift basin is revealed in theory, and the controlling law of basement pre-existing faults to fault formation and evolution is determined, and checked with sandbox modeling. A new way is provided for in-depth study of faulting.展开更多
A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strai...A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.展开更多
Fault formation and evolution in the presence of multiple pre-existing weaknesses has not been investigated extensively in rift basins. The fault systems of Weixinan Sag, Beibuwan Basin of China, which is fully covere...Fault formation and evolution in the presence of multiple pre-existing weaknesses has not been investigated extensively in rift basins. The fault systems of Weixinan Sag, Beibuwan Basin of China, which is fully covered with high-precision 3-D seismic data and is rich in oil-gas resources, have been successfully reproduced by sandbox modeling in this study with inclusion of multiple pre-existing weaknesses in the experimental model. The basic characteristics of fault formation and evolution revealed by sandbox modeling are as follows. 1） Weakness-reactivation faults and weakness-related faults are formed much earlier than the distant-weakness faults （faults far away from and with little or no relationship to the weakness）. 2） Weakness-reactivation faults and weakness-related faults develop mainly along or parallel to a pre-existing weakness, while distant-weakness faults develop nearly perpendicular to the extension direction. A complicated fault system can be formed in a fixed direction of extension with the existence of multiple pre-existing weaknesses, and the complicated fault system in the Weixinan Sag formed gradually in a nearly N-S direction with multiple pre-existing weaknesses. 3） The increase in the length and number of faults is closely tied to the nature of pre-existing weaknesses. The sandbox model may provide a new clue to detailed fault system research for oil and gas exploration in rift basins.展开更多
Through fault structure analysis and chronology study, we discuss the origin and growth mechanisms of strike-slip faults in the Tarim Basin.(1) Multiple stages strike-slip faults with inherited growth were developed i...Through fault structure analysis and chronology study, we discuss the origin and growth mechanisms of strike-slip faults in the Tarim Basin.(1) Multiple stages strike-slip faults with inherited growth were developed in the central Tarim cratonic basin. The faults initiation time is constrained at the end of Middle Ordovician of about 460 Ma according to U-Pb dating of the fault cements and seismic interpretation.(2) The formation of the strike-slip faults was controlled by the near N-S direction stress field caused by far-field compression of the closing of the Proto-Tethys Ocean.(3) The faults localization and characteristics were influenced by the pre-existing structures of the NE trending weakening zones in the basement and lithofacies change from south to north.(4) Following the fault initiation under the Andersonian mechanism, the strike-slip fault growth was dominantly fault linkage, associated with fault tip propagation and interaction of non-Andersonian mechanisms.(5) Sequential slip accommodated deformation in the conjugate strike-slip fault interaction zones, strong localization of the main displacement and deformation occurred in the overlap zones in the northern Tarim, while the fault tips, particularly of narrow-deep grabens, and strike-slip segments in thrust zones accumulated more deformation and strain in the Central uplift. In conclusion, non-Andersonian mechanisms, dominantly fault linkage and interaction, resulted in the small displacement but long intraplate strike-slip fault development in the central Tarim Basin. The regional and localized field stress, and pre-existing structures and lithofacies difference had strong impacts on the diversity of the strike-slip faults in the Tarim cratonic basin.展开更多
This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how c...This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how coplanar flaw angle and load type impact the strength and deformation behavior and microscopic damage mechanism.Results indicated that being fluctuated before rising with increasing fissure angle under monotonic loading,the peak strength of the specimen first increased slowly and then steeply under cyclic loading.The effect of multilevel cyclic loading on the mechanical parameters was more significant.For a single fatigue stage,the specimen underwent greater deformation in early cycles,which subsequently stabilized.Similar variation pattern was also reflected by AE count/energy/b-value.Crack behaviors were dominated by the fissure angle and load type and medium-scale crack accounted for 74.83%–86.44%of total crack.Compared with monotonic loading,crack distribution of specimen under cyclic loading was more complicated.Meanwhile,a simple model was proposed to describe the damage evolution of sandstone under cyclic loading.Finally,SEM images revealed that the microstructures at the fracture were mainly composed of intergranular fracture,and percentage of transgranular fracture jumped under cyclic loading due to the rapid release of elastic energy caused by high loading rate.展开更多
Physical model tests have been conducted by various researchers to investigate fault rupture propagation and ground deformation induced by bedrock faulting. However, the effects of pre-existing fracture on ground defo...Physical model tests have been conducted by various researchers to investigate fault rupture propagation and ground deformation induced by bedrock faulting. However, the effects of pre-existing fracture on ground deformation are not fully understood. In this work, six centrifuge tests are reported to investigate the influence of pre-existing fracture on ground deformation induced by normal faulting in sand, clay and nine-layered soil with interbedded sand and clay layers. Shear box tests were conducted to develop a filter paper technique, which was adopted in soil model preparation to simulate the effects of pre-existing fracture in centrifuge tests. Centrifuge test results show that ground deformation mechanism in clay, sand and nine-layered soil strata is classified as a stationary zone, a shearing zone and a rigid body zone. Inclination of the strain localization is governed by the dilatancy of soil material. Moreover, the pre-existing fracture provides a preferential path for ground deformation and results in a scarp at the ground surface in sand. On the contrary, fault ruptures are observed at the ground surface in clay and nine-layered soil strata.展开更多
Crack closure is one of the reasons inducing changes of P-wave velocity of rocks under compression.In this context,a method is proposed to investigate the relationships among P-wave velocity,pre-existing cracks,and co...Crack closure is one of the reasons inducing changes of P-wave velocity of rocks under compression.In this context,a method is proposed to investigate the relationships among P-wave velocity,pre-existing cracks,and confining pressure based on the discrete element method(DEM).Pre-existing open cracks inside the rocks are generated by the initial gap of the flat-joint model.The validity of the method is evaluated by comparing the P-wave velocity tested on a sandstone specimen with numerical result.As the crack size is determined by the diameter of particles,the effects of three factors,i.e.number,aspect ratio,and orientation of cracks on the P-wave velocity are discussed.The results show that P-wave velocity is controlled by the(i.e.number) of open micro-cracks,while the closure pressure is determined by the aspect ratio of crack.The reason accounting for the anisotropy of P-wave velocity is the difference in crack number in measurement paths.Both of the number and aspect ratio of cracks can affect the responses of P-wave velocity to the applied confining pressure.Under confining pressure,the number of open cracks inside rocks will dominate the lowest P-wave velocity,and the P-wave velocity of the rock containing narrower cracks is more sensitive to the confining pressure.In this sense,crack density is difficult to be back-calculated merely by P-wave velocity.The proposed method offers a means to analyze the effect of pre-existing cracks on P-wave velocity.展开更多
Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out tru...Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic(brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence: when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis(such as σ2=σ3=0 MPa); conversely, the failure surface is parallel to the z axis(such as σ2=20 MPa, σ3=0 MPa).展开更多
In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution ...In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution characteristics for rock similar materials with pre-existing cracks of varying length under uniaxial compression load.The equipment used in this study is the self-developed YYW-Ⅱ strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission monitoring system.Results show that,as the length of pre-existing crack increases:(1) the peak and residual strength reduces,and the peak axial strain and the strain during the initial compression phase increases;(2) the major failure mode is changed from shear failure to tensile failure along a vertical plane that passes the middle of the pre-existing crack;(3) The damage increases during the stable and accelerated development stage,and the effect of the pre-existing cracks is more during the accelerated development stage than the stable development stage.展开更多
In the mammalian heart,cardiomyocytes are forced to withdraw from the cell cycle shortly after birth,limiting the ability of the heart to regenerate and repair.The development of multimodal regulation of cardiac proli...In the mammalian heart,cardiomyocytes are forced to withdraw from the cell cycle shortly after birth,limiting the ability of the heart to regenerate and repair.The development of multimodal regulation of cardiac proliferation has verified that pre-existing cardiomyocyte proliferation is an essential driver of cardiac renewal.With the continuous development of genetic lineage tracking technology,it has been revealed that cell cycle activity produces polyploid cardiomyocytes during the embryonic,juvenile,and adult stages of cardiogenesis,but newly formed mononucleated diploid cardiomyocytes also elevated sporadically during myocardial infarction.It implied that adult cardiomyocytes have a weak regenerative capacity under the condition of ischemia injury,which offers hope for the clinical treatment of myocardial infarction.However,the regeneration frequency and source of cardiomyocytes are still low,and the mechanism of regulating cardiomyocyte proliferation remains further explained.It is noteworthy to explore what force triggers endogenous cardiomyocyte proliferation and heart regeneration.Here,we focused on summarizing the recent research progress of emerging endogenous key modulators and crosstalk with other signaling pathways and furnished valuable insights into the internal mechanism of heart regeneration.In addition,myocardial transcription factors,non-coding RNAs,cyclins,and cell cycle-dependent kinases are involved in the multimodal regulation of pre-existing cardiomyocyte proliferation.Ultimately,awakening the myocardial proliferation endogenous modulator and regeneration pathways may be the final battlefield for the regenerative therapy of cardiovascular diseases.展开更多
The activation coefficient equations in the"activation criterion of pre-existing weakness"are relatively complex and not easy to apply to specific applications.The relative activity of pre-existing weaknesse...The activation coefficient equations in the"activation criterion of pre-existing weakness"are relatively complex and not easy to apply to specific applications.The relative activity of pre-existing weaknesses is often critical in geological analysis.The Mohr circle can be used only in two-dimensional stress analysis.By applying the"activation criterion of pre-existing weakness"and combining it with numerical analysis,we establish the correspondence between the pole(n,n)of a pre-existing weakness plane and its orientation in"Mohr space".As a result,the normal stress(n)and shear stress(n)of a pre-existing weakness plane can be readily expressed in Mohr space.Furthermore,we introduce the method and procedures for predicting the activation and relative activation of pre-existing weaknesses in Mohr space.Finally,we apply the Mohr space method and compare the predictions to sandbox modeling results and 3D seismic data.The results show that Mohr space can be used in stress analysis to estimate the activation of a pre-existing weakness in any triaxial stress state.展开更多
This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins.A series of unconfined compression tests was performed on specimens of two types of ...This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins.A series of unconfined compression tests was performed on specimens of two types of sandstones,argillite and basalt that contain open and filled cracks.It was found that the presence of cracks tends to decrease the overall strength for all studied rocks;however,the magnitude of strength reduction is related to the property of rock.The larger strength decrease was observed for the relatively harder argillite and basalt,compared to the softer sandstone.It was also found that the infill material could increase the strength of rock specimens,while the obtained strength depended on the characteristics of the fill material.展开更多
The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determinati...The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.展开更多
A transfer zone in rift basins preserves important information on regional tectonic evolution and plays significant roles in hydrocarbon accumulation.Based on the systematic analysis of 3D seismic data and hydrocarbon...A transfer zone in rift basins preserves important information on regional tectonic evolution and plays significant roles in hydrocarbon accumulation.Based on the systematic analysis of 3D seismic data and hydrocarbon accumulation conditions,the geometry,kinematics,and reservoir control of a large synthetic overlapping transfer zone in the south of the Wenchang A subsag in the Zhujiang(Pearl)River Mouth basin were investigated.Results indicate that the development and evolution of the transfer zone was controlled by the interaction between pre-existing faults and regional stress transformation.The intense rifting of the main faults of the transfer zone controlled the development of source rocks and faultcontrolled slope break paleogeomorphology.The strike-slip overprint since the Oligocene is conducive to the formation of a large-scale fault-anticline trap,and the secondary faults in the transfer zone contribute to the hydrocarbon transportation.The conjugate intersection area of the NE-and NW-trending faults offers more opportunity for hydrocarbon migration and accumulation.展开更多
History of upper respiratory tract infection in the mother or siblings was associated with higher risk of acute lower respiratory tract infection in cases. Most upper respiratory tract infections were caused by viral ...History of upper respiratory tract infection in the mother or siblings was associated with higher risk of acute lower respiratory tract infection in cases. Most upper respiratory tract infections were caused by viral pathogens and likely to occur in many members of the family. The study aimed to determine the existence and pattern of relationship between risk of acute respiratory infection (ARI) among infants and exposure to pre-existing maternal/caregiver acute respiratory tract infection. The study was designed as a community-based Nested case-control study of 1100 infants randomly selected from 12 communities out of 6 Local Government Areas of the 3 senatorial districts of Rivers State. A multistage random sampling technique was used in selecting the subjects up to the community level. Descriptive method was used to represent the characteristics of the subjects and the differences in ARI between exposed and unexposed infants were tested in a bivariate logistics regression at 5% level of significance. Odds ratio (OR) was used to interpret the size effect measures of ARI on exposure to pre-existing maternal/caregiver ARI differences. A total of 275 Cases of ARI and 825 controls were included in the study. Among exposed infants (N = 104), ARI cases were found to be higher n = 80 (76.9%) than in control n = 24 (23.1%). Whereas, among unexposed infants N = 991, ARI cases were found to be lower n = 195 (19.7%) than in control n = 796 (80.3%). For the exposed infants, the odds for ARI were 13.5 times significantly higher compared to those of their unexposed counterparts (OR-Unadjusted = 13.52, (p < 0.0001, 95% CI = 0.047 - 0.121)). The findings will widen the horizon in the etiological consideration of ARI among infants vis-à-vis exposure potential to pre-existing maternal/caregiver ARI via nursing care. Therefore, community-based sensitization programme on barrier nursing care techniques and personal hygiene practices should be on focus.展开更多
Investigations of the growth,interaction,and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better ...Investigations of the growth,interaction,and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better estimations of the strength and stiffness of a rock material.Understanding the coalescence mechanism is useful for justifying the mechanism of continental crustal deformation,evaluating the structural failure of slopes with rock bridges,and analyzing the stability of tunnels when a mode I or mix mode failure mechanism is involved.The evaluation of crack growth can provide valuable information about the mechanism for the formation of new geological structures,and the formation,evolution,and growth of faults.This paper reports the results of diametrical compression tests on rocklike disk-shaped specimens.Each specimen contained two pre-existing open or closed flaws.The growth,interaction,and coalescence of the pre-existing flaws were investigated both physically and numerically.A hybrid bonded particle-finite element system was used in the numerical simulation.The results of the physical and numerical studies were in good agreement.In particular,the induced crack patterns showed close agreement in the physical and numerical tests.Digital microscope image processing was used in the physical tests to study the dislocations along the initial flaws.It was shown that wing crack formation was responsible for the failure of the specimen when flaws were inclined with respect to the loading direction.The crack growth and linkage were shown to be affected by the friction between faces of the flaws.In addition,the slip distributions at the flaws surfaces were illustrated and examined to understand the crack propagation mechanism.The effects of the flaws on the disk failure loads were assessed both numerically and experimentally as well.展开更多
Based on 3D seismic data, the evolution mechanism and characteristics of faults were investigated to reveal the structural origin and its control on differential hydrocarbon accumulation through comprehensive analyses...Based on 3D seismic data, the evolution mechanism and characteristics of faults were investigated to reveal the structural origin and its control on differential hydrocarbon accumulation through comprehensive analyses, including structure style analysis, fault activity analysis, analogue modelling and comparison among the wells. The complex fault system with differently trending faults resulted from strike-slip and rifting in Paleogene was partly activated, developed successively and stretched obliquely by the near-NS extensional stress field in Neogene. In the area little affected by pre-existing faults, new faults nearly perpendicular to the extension direction developed. The structural development in the study area was not caused by transpressional strike slip. Under the oblique extension effect of pre-existing faults, if the angle between the strike of pre-existing fault and the extensional direction is different, the strike-slip and extensional stresses are different in ratio. The larger the angle between the two is, the stronger the extensional component, the poorer the sealing ability of the fault, and the stronger the oil and gas migration capacity will be. Conversely, the smaller the angle between the two is, the stronger the strike-slip component, the better the sealing ability of the fault, and the poorer the oil and gas migration capacity will be. The accumulation condition analysis results considering the fault trend are in good agreement with the oil and gas shows in wells drilled in this area.展开更多
基金supported by National Natural Science Foundation of China (Grant No.40772086)Oil and Gas Exploration Projects in Common Ahead of China National Petroleum Corporation (Grant No.07-01C-01-04)
文摘The Anderson's model can be applied only to elastic homogeneous deformation and cannot explain complicated phenomena of natural faults, which to a large degree limits the model to practical application. By combing the Coulomb-Mohr Criterion with the sandbox modeling and considering non-homogeneous deformation, mechanisms of how basement pre-existing fabrics control fault formation and evolution are analyzed and a mechanical factor, activation-coefficient (faS) of pre-existing fabrics, is proposed. It is determined by the attitude and mechanical properties of pre-existing fabric, and the stress state (the magnitudes and directions of the three principal stresses). The coefficient has taken the heterogeneity of rocks into account and may serve as a criterion for evaluating the activity of a pre-existing fabric. The Mohr-Coulomb Criterion is expanded to non-homogeneous deformation domain in terms of activation-coefficient (faS) of pre-existing fabrics, the general law of the activity of a pre-existing fabric is predicted, the fault complexity real of rift basin is revealed in theory, and the controlling law of basement pre-existing faults to fault formation and evolution is determined, and checked with sandbox modeling. A new way is provided for in-depth study of faulting.
基金Project(BK20150005) supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars,ChinaProject(2014YC10) supported by the Fundamental Research Funds for the Central Universities,China
文摘A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.
基金supported by China National Major Project of Oil and Gas (2011ZX05023-004-012, 2011ZX05006-006-02-01)China Natural Science Foundation (Grant No. 40772086)
文摘Fault formation and evolution in the presence of multiple pre-existing weaknesses has not been investigated extensively in rift basins. The fault systems of Weixinan Sag, Beibuwan Basin of China, which is fully covered with high-precision 3-D seismic data and is rich in oil-gas resources, have been successfully reproduced by sandbox modeling in this study with inclusion of multiple pre-existing weaknesses in the experimental model. The basic characteristics of fault formation and evolution revealed by sandbox modeling are as follows. 1） Weakness-reactivation faults and weakness-related faults are formed much earlier than the distant-weakness faults （faults far away from and with little or no relationship to the weakness）. 2） Weakness-reactivation faults and weakness-related faults develop mainly along or parallel to a pre-existing weakness, while distant-weakness faults develop nearly perpendicular to the extension direction. A complicated fault system can be formed in a fixed direction of extension with the existence of multiple pre-existing weaknesses, and the complicated fault system in the Weixinan Sag formed gradually in a nearly N-S direction with multiple pre-existing weaknesses. 3） The increase in the length and number of faults is closely tied to the nature of pre-existing weaknesses. The sandbox model may provide a new clue to detailed fault system research for oil and gas exploration in rift basins.
基金Supported by the National Natural Science Foundation of China(91955204)PetroChina-Southwest Petroleum University Innovation Consortium Science and Technology Cooperation Project(2020CX010101)。
文摘Through fault structure analysis and chronology study, we discuss the origin and growth mechanisms of strike-slip faults in the Tarim Basin.(1) Multiple stages strike-slip faults with inherited growth were developed in the central Tarim cratonic basin. The faults initiation time is constrained at the end of Middle Ordovician of about 460 Ma according to U-Pb dating of the fault cements and seismic interpretation.(2) The formation of the strike-slip faults was controlled by the near N-S direction stress field caused by far-field compression of the closing of the Proto-Tethys Ocean.(3) The faults localization and characteristics were influenced by the pre-existing structures of the NE trending weakening zones in the basement and lithofacies change from south to north.(4) Following the fault initiation under the Andersonian mechanism, the strike-slip fault growth was dominantly fault linkage, associated with fault tip propagation and interaction of non-Andersonian mechanisms.(5) Sequential slip accommodated deformation in the conjugate strike-slip fault interaction zones, strong localization of the main displacement and deformation occurred in the overlap zones in the northern Tarim, while the fault tips, particularly of narrow-deep grabens, and strike-slip segments in thrust zones accumulated more deformation and strain in the Central uplift. In conclusion, non-Andersonian mechanisms, dominantly fault linkage and interaction, resulted in the small displacement but long intraplate strike-slip fault development in the central Tarim Basin. The regional and localized field stress, and pre-existing structures and lithofacies difference had strong impacts on the diversity of the strike-slip faults in the Tarim cratonic basin.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.42077231 and 51574156).
文摘This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how coplanar flaw angle and load type impact the strength and deformation behavior and microscopic damage mechanism.Results indicated that being fluctuated before rising with increasing fissure angle under monotonic loading,the peak strength of the specimen first increased slowly and then steeply under cyclic loading.The effect of multilevel cyclic loading on the mechanical parameters was more significant.For a single fatigue stage,the specimen underwent greater deformation in early cycles,which subsequently stabilized.Similar variation pattern was also reflected by AE count/energy/b-value.Crack behaviors were dominated by the fissure angle and load type and medium-scale crack accounted for 74.83%–86.44%of total crack.Compared with monotonic loading,crack distribution of specimen under cyclic loading was more complicated.Meanwhile,a simple model was proposed to describe the damage evolution of sandstone under cyclic loading.Finally,SEM images revealed that the microstructures at the fracture were mainly composed of intergranular fracture,and percentage of transgranular fracture jumped under cyclic loading due to the rapid release of elastic energy caused by high loading rate.
基金Project supported by the Earthquake Administration of Beijing Municipality and the National Development and Reform Commission of ChinaProject(IRT1125) supported by the program for Changjiang Scholars and Innovative Research Team in University, China
文摘Physical model tests have been conducted by various researchers to investigate fault rupture propagation and ground deformation induced by bedrock faulting. However, the effects of pre-existing fracture on ground deformation are not fully understood. In this work, six centrifuge tests are reported to investigate the influence of pre-existing fracture on ground deformation induced by normal faulting in sand, clay and nine-layered soil with interbedded sand and clay layers. Shear box tests were conducted to develop a filter paper technique, which was adopted in soil model preparation to simulate the effects of pre-existing fracture in centrifuge tests. Centrifuge test results show that ground deformation mechanism in clay, sand and nine-layered soil strata is classified as a stationary zone, a shearing zone and a rigid body zone. Inclination of the strain localization is governed by the dilatancy of soil material. Moreover, the pre-existing fracture provides a preferential path for ground deformation and results in a scarp at the ground surface in sand. On the contrary, fault ruptures are observed at the ground surface in clay and nine-layered soil strata.
基金partially supported by the National Natural Science Foundation of China(Grant Nos.41872210 and 51674238)the Open Research Fund of the State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.Z017006)。
文摘Crack closure is one of the reasons inducing changes of P-wave velocity of rocks under compression.In this context,a method is proposed to investigate the relationships among P-wave velocity,pre-existing cracks,and confining pressure based on the discrete element method(DEM).Pre-existing open cracks inside the rocks are generated by the initial gap of the flat-joint model.The validity of the method is evaluated by comparing the P-wave velocity tested on a sandstone specimen with numerical result.As the crack size is determined by the diameter of particles,the effects of three factors,i.e.number,aspect ratio,and orientation of cracks on the P-wave velocity are discussed.The results show that P-wave velocity is controlled by the(i.e.number) of open micro-cracks,while the closure pressure is determined by the aspect ratio of crack.The reason accounting for the anisotropy of P-wave velocity is the difference in crack number in measurement paths.Both of the number and aspect ratio of cracks can affect the responses of P-wave velocity to the applied confining pressure.Under confining pressure,the number of open cracks inside rocks will dominate the lowest P-wave velocity,and the P-wave velocity of the rock containing narrower cracks is more sensitive to the confining pressure.In this sense,crack density is difficult to be back-calculated merely by P-wave velocity.The proposed method offers a means to analyze the effect of pre-existing cracks on P-wave velocity.
基金Project(51021004)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China
文摘Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic(brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence: when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis(such as σ2=σ3=0 MPa); conversely, the failure surface is parallel to the z axis(such as σ2=20 MPa, σ3=0 MPa).
基金This paper is an extended version of a published conference paper Li et al.(2017)this paper gets its funding from Project(51734007)+1 种基金supported by National Natural Science Foundation of ChinaWe would also like to acknowledge the editor-in-chief,editors and the anonymous reviewers for their valuable comments,which have greatly improved this paper.
文摘In order to further study the damage and failure mechanism for rock similar materials,this study investigated the mechanical properties and failure characteristics,law of damage space development,and damage evolution characteristics for rock similar materials with pre-existing cracks of varying length under uniaxial compression load.The equipment used in this study is the self-developed YYW-Ⅱ strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission monitoring system.Results show that,as the length of pre-existing crack increases:(1) the peak and residual strength reduces,and the peak axial strain and the strain during the initial compression phase increases;(2) the major failure mode is changed from shear failure to tensile failure along a vertical plane that passes the middle of the pre-existing crack;(3) The damage increases during the stable and accelerated development stage,and the effect of the pre-existing cracks is more during the accelerated development stage than the stable development stage.
基金supported by the National Natural Science Foundation of China(No.82070314,81600244)the Natural Science Foundation of Shandong Province,China(No.ZR2021MC189).
文摘In the mammalian heart,cardiomyocytes are forced to withdraw from the cell cycle shortly after birth,limiting the ability of the heart to regenerate and repair.The development of multimodal regulation of cardiac proliferation has verified that pre-existing cardiomyocyte proliferation is an essential driver of cardiac renewal.With the continuous development of genetic lineage tracking technology,it has been revealed that cell cycle activity produces polyploid cardiomyocytes during the embryonic,juvenile,and adult stages of cardiogenesis,but newly formed mononucleated diploid cardiomyocytes also elevated sporadically during myocardial infarction.It implied that adult cardiomyocytes have a weak regenerative capacity under the condition of ischemia injury,which offers hope for the clinical treatment of myocardial infarction.However,the regeneration frequency and source of cardiomyocytes are still low,and the mechanism of regulating cardiomyocyte proliferation remains further explained.It is noteworthy to explore what force triggers endogenous cardiomyocyte proliferation and heart regeneration.Here,we focused on summarizing the recent research progress of emerging endogenous key modulators and crosstalk with other signaling pathways and furnished valuable insights into the internal mechanism of heart regeneration.In addition,myocardial transcription factors,non-coding RNAs,cyclins,and cell cycle-dependent kinases are involved in the multimodal regulation of pre-existing cardiomyocyte proliferation.Ultimately,awakening the myocardial proliferation endogenous modulator and regeneration pathways may be the final battlefield for the regenerative therapy of cardiovascular diseases.
基金supported by the China Major National Science & Technology Program of Oil and Gas (Grant Nos. 2011ZX05023-004-012, 2011ZX05006-006-02-01)the National Natural Science Foundation of China (Grant Nos. 41272160, 40772086)
文摘The activation coefficient equations in the"activation criterion of pre-existing weakness"are relatively complex and not easy to apply to specific applications.The relative activity of pre-existing weaknesses is often critical in geological analysis.The Mohr circle can be used only in two-dimensional stress analysis.By applying the"activation criterion of pre-existing weakness"and combining it with numerical analysis,we establish the correspondence between the pole(n,n)of a pre-existing weakness plane and its orientation in"Mohr space".As a result,the normal stress(n)and shear stress(n)of a pre-existing weakness plane can be readily expressed in Mohr space.Furthermore,we introduce the method and procedures for predicting the activation and relative activation of pre-existing weaknesses in Mohr space.Finally,we apply the Mohr space method and compare the predictions to sandbox modeling results and 3D seismic data.The results show that Mohr space can be used in stress analysis to estimate the activation of a pre-existing weakness in any triaxial stress state.
基金The authors would like to acknowledge Mr.Beau McDonald for his invaluable help with laboratory testing.
文摘This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins.A series of unconfined compression tests was performed on specimens of two types of sandstones,argillite and basalt that contain open and filled cracks.It was found that the presence of cracks tends to decrease the overall strength for all studied rocks;however,the magnitude of strength reduction is related to the property of rock.The larger strength decrease was observed for the relatively harder argillite and basalt,compared to the softer sandstone.It was also found that the infill material could increase the strength of rock specimens,while the obtained strength depended on the characteristics of the fill material.
基金supported by the National Natural Science Foundation of China(Grant No.42174118)a research grant(Grant No.ZDJ 2020-7)from the National Institute of Natural Hazards,Ministry of Emergency Management of China.
文摘The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.
基金Supported by the National Natural Science Foundation of China(Nos.42302155,42072169,42072235)the Natural Science Foundation of Shandong Province(No.ZR2023QD016)+2 种基金the China Postdoctoral Science Foundation(No.2022M713461)the Qingdao Postdoctoral Application Research Funds(No.QDBSH20220202067)the Fundamental Research Funds for the Central Universities(No.22CX06005A)。
文摘A transfer zone in rift basins preserves important information on regional tectonic evolution and plays significant roles in hydrocarbon accumulation.Based on the systematic analysis of 3D seismic data and hydrocarbon accumulation conditions,the geometry,kinematics,and reservoir control of a large synthetic overlapping transfer zone in the south of the Wenchang A subsag in the Zhujiang(Pearl)River Mouth basin were investigated.Results indicate that the development and evolution of the transfer zone was controlled by the interaction between pre-existing faults and regional stress transformation.The intense rifting of the main faults of the transfer zone controlled the development of source rocks and faultcontrolled slope break paleogeomorphology.The strike-slip overprint since the Oligocene is conducive to the formation of a large-scale fault-anticline trap,and the secondary faults in the transfer zone contribute to the hydrocarbon transportation.The conjugate intersection area of the NE-and NW-trending faults offers more opportunity for hydrocarbon migration and accumulation.
文摘History of upper respiratory tract infection in the mother or siblings was associated with higher risk of acute lower respiratory tract infection in cases. Most upper respiratory tract infections were caused by viral pathogens and likely to occur in many members of the family. The study aimed to determine the existence and pattern of relationship between risk of acute respiratory infection (ARI) among infants and exposure to pre-existing maternal/caregiver acute respiratory tract infection. The study was designed as a community-based Nested case-control study of 1100 infants randomly selected from 12 communities out of 6 Local Government Areas of the 3 senatorial districts of Rivers State. A multistage random sampling technique was used in selecting the subjects up to the community level. Descriptive method was used to represent the characteristics of the subjects and the differences in ARI between exposed and unexposed infants were tested in a bivariate logistics regression at 5% level of significance. Odds ratio (OR) was used to interpret the size effect measures of ARI on exposure to pre-existing maternal/caregiver ARI differences. A total of 275 Cases of ARI and 825 controls were included in the study. Among exposed infants (N = 104), ARI cases were found to be higher n = 80 (76.9%) than in control n = 24 (23.1%). Whereas, among unexposed infants N = 991, ARI cases were found to be lower n = 195 (19.7%) than in control n = 796 (80.3%). For the exposed infants, the odds for ARI were 13.5 times significantly higher compared to those of their unexposed counterparts (OR-Unadjusted = 13.52, (p < 0.0001, 95% CI = 0.047 - 0.121)). The findings will widen the horizon in the etiological consideration of ARI among infants vis-à-vis exposure potential to pre-existing maternal/caregiver ARI via nursing care. Therefore, community-based sensitization programme on barrier nursing care techniques and personal hygiene practices should be on focus.
文摘Investigations of the growth,interaction,and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better estimations of the strength and stiffness of a rock material.Understanding the coalescence mechanism is useful for justifying the mechanism of continental crustal deformation,evaluating the structural failure of slopes with rock bridges,and analyzing the stability of tunnels when a mode I or mix mode failure mechanism is involved.The evaluation of crack growth can provide valuable information about the mechanism for the formation of new geological structures,and the formation,evolution,and growth of faults.This paper reports the results of diametrical compression tests on rocklike disk-shaped specimens.Each specimen contained two pre-existing open or closed flaws.The growth,interaction,and coalescence of the pre-existing flaws were investigated both physically and numerically.A hybrid bonded particle-finite element system was used in the numerical simulation.The results of the physical and numerical studies were in good agreement.In particular,the induced crack patterns showed close agreement in the physical and numerical tests.Digital microscope image processing was used in the physical tests to study the dislocations along the initial flaws.It was shown that wing crack formation was responsible for the failure of the specimen when flaws were inclined with respect to the loading direction.The crack growth and linkage were shown to be affected by the friction between faces of the flaws.In addition,the slip distributions at the flaws surfaces were illustrated and examined to understand the crack propagation mechanism.The effects of the flaws on the disk failure loads were assessed both numerically and experimentally as well.
基金Supported by the China National Science and Technology Major Project(2016ZX05024-002-006)
文摘Based on 3D seismic data, the evolution mechanism and characteristics of faults were investigated to reveal the structural origin and its control on differential hydrocarbon accumulation through comprehensive analyses, including structure style analysis, fault activity analysis, analogue modelling and comparison among the wells. The complex fault system with differently trending faults resulted from strike-slip and rifting in Paleogene was partly activated, developed successively and stretched obliquely by the near-NS extensional stress field in Neogene. In the area little affected by pre-existing faults, new faults nearly perpendicular to the extension direction developed. The structural development in the study area was not caused by transpressional strike slip. Under the oblique extension effect of pre-existing faults, if the angle between the strike of pre-existing fault and the extensional direction is different, the strike-slip and extensional stresses are different in ratio. The larger the angle between the two is, the stronger the extensional component, the poorer the sealing ability of the fault, and the stronger the oil and gas migration capacity will be. Conversely, the smaller the angle between the two is, the stronger the strike-slip component, the better the sealing ability of the fault, and the poorer the oil and gas migration capacity will be. The accumulation condition analysis results considering the fault trend are in good agreement with the oil and gas shows in wells drilled in this area.
