Horizontal wells in the anisotropic reservoirs can be stimulated by hydraulic fracturing in order to create multiple finite-conductivity vertical fractures. Several methods for evaluating the productivity of the horiz...Horizontal wells in the anisotropic reservoirs can be stimulated by hydraulic fracturing in order to create multiple finite-conductivity vertical fractures. Several methods for evaluating the productivity of the horizontal wells have been presented in the literature. With such methods, however, it is still difficult to obtain an accurate result. This paper firstly presents the dimensionless conductivity theory of vertical fractures. Then models for calculating the equivalent wellbore radius and the skin factor due to flow convergence to the well bore are proposed after analyzing the steady-state flow in porous reservoirs. By applying the superposition principle to the pressure drop, a new method for evaluating the productivity of horizontal wells intercepted by multiple finite-conductivity fractures is developed. The influence of fracture conductivity and fracture half length on the horizontal well productivity is quantitatively analyzed with a synthetic case. Optimum fracture number and fracture space are further discussed in this study. The results prove that the method outlined here should be useful to design optimum fracturing of horizontal wells.展开更多
As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks...As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage road- way in a certain coal mine is so broken and loose that the supporting is very difficult. Based on compre- hensive anal[ysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks, Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture dewelopment. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.展开更多
Multi-stage volume fracturing of horizontal wells is the main means to develop tight gas reservoirs.Complex fracture networks of various shapes are generated around the wellbore after volume fracturing.At present,howe...Multi-stage volume fracturing of horizontal wells is the main means to develop tight gas reservoirs.Complex fracture networks of various shapes are generated around the wellbore after volume fracturing.At present,however,most of the well test models suitable for fracturing horizontal wells take all hydraulic fractures as single main fractures,which results in a large error between well test interpretation result and actual situation.As a result,the fracture network characteristic parameters of the stimulated areas cannot be obtained accurately.To this end,a well test model for complex fracture networks in tight-gas fracturing horizontal wells was established on the basis of the non-structural discrete fracture model.Then,this model was solved by using thefinite element method with combined triangular elements and linear elements.And accordingly,the well test type curves of a horizontal well under different fracture network patterns(rectangular,elliptical and hyperbolic)were prepared.Based on this,well test type curves were analyzed from the aspects of characteristics and influential factors and were compared with those obtained from the conventional single-fracture model.Finally,the new model was applied in well test interpretation of one multi-stage volume fracturing horizontal well in the gas reservoir of Permian Shan 1 formation in the Qingyang Gas Field of the Ordos Basin.And the following research results were obtained.First,the biggest difference of well test type curve between the fracture network model and the conventional single-fracture model occurs in the early stage,the characteristics offirst linearflow regime are replaced with the characteristics of pseudo-radialflow regime in the stimulated area.Second,the end time of the pseudo-radialflow regime in the stimulated area is mainly dominated by the size and shape of the stimulated area.The larger the stimulated area is,the longer the pseudo-radialflow regime lasts.As the shape of the stimulated area approaches to be elongated,the characteristics of the well test type curve obtained by the new model are more consistent with those by the single-fracture model.Third,the pressure derivative value of the pseudo-radialflow regime in the stimulated area is mainly dependent on the conductivity and density of the fracture network.The higher the density or the conductivity of fracture network in the stimulated area is,the earlier the wellbore storage effect regime ends,the lower the pressure derivative value of the pseudo-radialflow regime in the stimulated area is and the more obvious the characteristics of the horizontal line are.In conclusion,case study results confirm that the new model is reliable and practical and can provide accurate reservoir parameters as well as the size of the effectively stimulated area by volume fracturing and the conductivity of fracture network,which is conducive to evaluating the stimulation effect of volume fracturing and predicting the postfrac production performance.展开更多
This study aims to elucidate the dynamic evolution mechanism of the fracturing fracture system during the exploration and development of complex oil and gas reservoirs.By integrating methods of rock mechanical testing...This study aims to elucidate the dynamic evolution mechanism of the fracturing fracture system during the exploration and development of complex oil and gas reservoirs.By integrating methods of rock mechanical testing,logging calculation,and seismic inversion technology,we obtained the current insitu stress characteristics of a single well and rock mechanical parameters.Simultaneously,significant controlling factors of rock mechanical properties were analyzed.Subsequently,by coupling hydraulic fracturing physical experiments with finite element numerical simulation,three different fracturing models were configured:single-cluster,double-cluster,and triple-cluster perforations.Combined with acoustic emission technology,the fracture initiation mode and evolution characteristics during the loading process were determined.The results indicate the following findings:(1)The extension direction and length of the fracture are significantly controlled by the direction of the maximum horizontal principal stress.(2)Areas with poor cementation and compactness exhibit complex fracture morphology,prone to generating network fractures.(3)The interlayer development of fracturing fractures is controlled by the strata occurrence.(4)Increasing the displacement of fracturing fluid enlarges the fracturing fracture length and height.This research provides theoretical support and effective guidance for hydraulic fracturing design in tight oil and gas reservoirs.展开更多
To explore the treatment methods for scapular fractures associated with clavicle fractures.Methods Of 23 cases with scapular fractures associated with clavicle fractures,13 treated conservatively took the function exe...To explore the treatment methods for scapular fractures associated with clavicle fractures.Methods Of 23 cases with scapular fractures associated with clavicle fractures,13 treated conservatively took the function exercise of shoulder joint after two months and 10 treated with open reduction and plate fixation reconstruction began the function exercise of shoulder joint four weeks after operation.The follow up averaged 12 months.Results All patients were healed up.18 cases were followed up,of them 8 cases were treated surgically,10 cases,conservatively.Of eight cases treated surgically,seven got excellent functional recovery of the shoulder joint and one satisfactory.In the meantime,of 10 cases treated conservatively,the recovery of shoulder joint was excellent in six,good in three and poor in one.Conclusion As for scapular fractures with associated clavicle fractures,open reduction and plate fixation reconstruction is a good treatment method for it can keep the stability and the balance of shoulder joint and is helpful for early functional exercise and recovery of the shoulder joint.7 refs,5 figs.展开更多
This study investigates the fracture behavior of clay-rich mudstone under varying temperature and pressure conditions,which is crucial for the safety of geological structures.It focuses on three fracture types:pure mo...This study investigates the fracture behavior of clay-rich mudstone under varying temperature and pressure conditions,which is crucial for the safety of geological structures.It focuses on three fracture types:pure mode I tensile fractures,pure mode II tensile fractures,and shear fractures,examining specimens at room temperature(RT)and after thermal treatments at 250 and 500℃.The findings reveal that increasing temperatures makes the mudstone more brittle,enhancing fracture velocity,toughness,load-bearing capacity,roughness,and the fracture process zone(FPZ)radius.Notably,tensile fractures induced under pure mode II displayed the highest velocities,while shear fractures exhibited the lowest velocities,smoothest surfaces,and greatest resistance to failure.The application of a confining pressure of 4 MPa significantly improved shear fracture toughness by 119.7%,98.5%and 71.9%at RT,250℃and 500℃,respectively,and reduced roughness by 8.2%,22.4%and 30.4%.This research offers a novel,comprehensive view of how temperature and pressure impact fractures in mudstone sensitive to temperature due to its high clay content and water affinity.The findings provide valuable insights applicable to geothermal energy,oil and gas exploration,and underground construction,thereby enhancing the understanding of fracture mechanics in geological contexts.展开更多
Before 1980s,the circular suspension spring in automobile subjected to torsion fatigue load,under the cyclic normal tensile stresses,the majority of fatigue fracture occurred was in normal tensile fracture mode（NTFM...Before 1980s,the circular suspension spring in automobile subjected to torsion fatigue load,under the cyclic normal tensile stresses,the majority of fatigue fracture occurred was in normal tensile fracture mode（NTFM）and the fracture surface was under 45°diagonal.Because there exists the interaction between the residual stresses induced by shot peening and the applied cyclic normal tensile stresses in NTFM,which represents as＂stress strengthening mechanism＂,shot peening technology could be used for improving the fatigue fracture resistance（FFR）of springs.However,since 1990s up to date,in addition to regular NTFM,the fatigue fractures occurred of peened springs from time to time are in longitudinal shear fracture mode（LSFM）or transverse shear fracture mode（TSFM）with the increase of applied cyclic shear stresses,which leads to a remarkable decrease of FFR.However,LSFM/TSFM can be avoided effectively by means of shot peening treatment again on the peened springs.The phenomena have been rarely happened before.At present there are few literatures concerning this problem.Based upon the results of force analysis of a spring,there is no interaction between the residual stresses by shot peening and the applied cyclic shear stresses in shear fracture.This;means that the effect of＂stress strengthening mechanism＂for improving the FFR of LSFM/TSFM is disappeared basically.During shot peening,however,both of residual stress and cyclic plastic deformed microstructure are induced synchronously like＂twins＂in the surface layer of a spring.It has been found for the first time by means of force analysis and experimental results that the modified microstructure in the＂twins＂as a＂structure strengthening mechanism＂can improve the FFR of LSFM/TSFM.At the same time,it is;also shown that the optimum technology of shot peening strengthening must have both＂stress strengthening mechanism＂and＂structure strengthening mechanism＂simultaneously so that the FFR of both NTFM and LSFM/TSFM can be improved by shot peening.展开更多
To deal with the stress interference caused by simultaneous propagation of multiple fractures and the wettability reversal and physical property changes of the reservoir caused by fracturing fluid getting in during la...To deal with the stress interference caused by simultaneous propagation of multiple fractures and the wettability reversal and physical property changes of the reservoir caused by fracturing fluid getting in during large-volume fracturing of tight oil reservoirs through a horizontal well, a non-planar 3D fracture growth model was built, wettability reversal characterizing parameters and change of relative permeability curve were introduced to correct the production prediction model of fractured horizontal well, a fracturing design optimization software(Fr Smart) by integrating geological and engineering data was developed, and a fracturing design optimization approach for tight oil reservoirs based on fracture control was worked out. The adaptability of the method was analyzed and the fracture parameters of horizontal wells in tight oil reservoirs were optimized. The simulation results show that fracturing technology based on fracture control is suitable for tight oil reservoirs, and by optimizing fracture parameters, this technology makes it possible to produce the maximum amount of reserves in the well-controlled unit of unconventional reservoirs. The key points of fracturing design optimization based on fracture control include increasing lateral length of and reducing the row spacing between horizontal wells, increasing perforation clusters in one stage to decrease the spacing of neighboring fractures, and also avoiding interference of old and new fracturing wells. Field tests show that this technology can increase single well production and ultimate recovery. Using this technology in developing unconventional resources such as tight oil reservoirs in China will enhance the economics significantly.展开更多
An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1....An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar （SHPB） apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMnSiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor （DSIF） and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experimentsneed to be performed in a comparatively large striker velocity range.展开更多
To obtain the fracture parameters of concrete, fracture tests were conducted with three-point bending beam method aiming at 30 concrete beams with different sizes and different intensity. The concrete specimen with pr...To obtain the fracture parameters of concrete, fracture tests were conducted with three-point bending beam method aiming at 30 concrete beams with different sizes and different intensity. The concrete specimen with prefabricated crack to determine the fracture parameters of concrete were conducted and the fracture performance of the specimen was analyzed. The test results show that, initial fracture toughness is unrelated to the size of specimens; while unstable fracture toughness is related to the size of specimens. As for specimens of bastard size, when concrete intensity is relatively low, unstable fracture toughness increases along with the increase of intensity; when concrete intensity is relatively high, unstable fracture toughness will decrease; when concrete intensity increases continuously, unstable fracture toughness will further increase somewhat. As for specimens of standard size, unstable fracture toughness will increase along with the increase of intensity. Aiming at concrete beam specimens, we conducted two-dimensional non-linear finite element analysis, obtained the stress intensity factor, and carried out contrastive analysis with the experimental results.展开更多
The high-resolution azimuthal resistivity laterolog response in a fractured formation was numerically simulated using a three-dimensional finite element method. Simulation results show that the azimuthal resistivity i...The high-resolution azimuthal resistivity laterolog response in a fractured formation was numerically simulated using a three-dimensional finite element method. Simulation results show that the azimuthal resistivity is determined by fracture dipping as well as dipping direction, while the amplitude differences between deep and shallow laterolog resistivities are mainly controlled by the former. A linear relationship exists between the corrected apparent conductivities and fracture aperture. With the same fracture aperture, the deep and shallow laterolog resistivities present small values with negative separations for low-angle fractures, while azimuthal resistivities have large variations with positive separations for high-angle fractures that intersect the borehole. For dipping fractures, the variation of the azimuthal resistivity becomes larger when the fracture aperture increases. In addition, for high-angle fractures far from the borehole, a negative separation between the deep and shallow resistivities exists when fracture aperture is large as well as high resistivity contrast exists between bedrock and fracture fluid. The decreasing amplitude of dual laterolog resistivity can indicate the aperture of low-angle fractures, and the variation of the deep azimuthal resistivity can give information of the aperture of high-angle fractures and their position relative to the borehole.展开更多
Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconventional hydrocarbon or geothermal reservoirs by hydraulic fracturing. Fracture propagation in isotropic material is we...Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconventional hydrocarbon or geothermal reservoirs by hydraulic fracturing. Fracture propagation in isotropic material is well understood but strictly isotropic rocks are rarely found in nature. This study aims at the examination of fracture initiation and propagation processes in a highly anisotropic rock, specifically slate. We performed a series of tensile fracturing laboratory experiments under uniaxial as well as triaxial loading. Cubic specimens with edge lengths of 150 mm and a central borehole with a diameter of13 mm were prepared from Fredeburg slate. An experiment using the rather isotropic Bebertal sandstone as a rather isotropic rock was also performed for comparison. Tensile fractures were generated using the sleeve fracturing technique, in which a polymer tube placed inside the borehole is pressurized to generate tensile fractures emanating from the borehole. In the uniaxial test series, the loading was varied in order to observe the transition from strength-dominated fracture propagation at low loading magnitudes to stress-dominated fracture propagation at high loading magnitudes.展开更多
A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with doub...A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double edge-notches.The interference effects of two cracks/notches are investigated through varied ligament angles and crack lengths.It is shown that shear fracturing paths change remarkably with the initial ligament angles and crack lengths.The cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.展开更多
The 0.2-0.3mm thick cold-rolled sheets and annealed sheets of high silicon steel were produced by rolling process,then punching tests were carried out at room temperature to 150℃.The punchability and punching fractur...The 0.2-0.3mm thick cold-rolled sheets and annealed sheets of high silicon steel were produced by rolling process,then punching tests were carried out at room temperature to 150℃.The punchability and punching fracture behavior were investigated by means of scanning electron microscope（SEM）and electron back-scattered diffraction（EBSD）.It is found that cold-rolled sheets of high silicon steel show good punchability under the condition of 0.01 mm punch-die clearance and at the temperature of 100℃;the punchability of annealed sheets with fine grain size is better than that of annealed sheets with coarse grain size;the punching temperature of 150℃is suitable for annealed high silicon steel sheets especially with coarse grain size on account of punching edge quality.The major cleavage planes of annealed high silicon steel sheets are{100}crystallographic planes on which brittle fracture occurs at low temperatures.The cleavage systems include{100}〈110〉and{100}〈100〉,and cleavage fracture is completed by one or both of them.The punchability of high silicon steel sheets is related with punching temperature,grain size and ordering degree.Reducing ordering degree,increasing punching temperature,as well as refining grain size can improve the ductility and punchability of high silicon steel sheets.展开更多
In this study, our objective was to evaluate effects of leptin on fracture healing in rats. Seventy two male SpragueDawley（SD） rats were randomized into 3 groups. Standardized femoral fractures were created in all t...In this study, our objective was to evaluate effects of leptin on fracture healing in rats. Seventy two male SpragueDawley（SD） rats were randomized into 3 groups. Standardized femoral fractures were created in all the rats. Group A was treated with 1 mL normal saline（NS）, group B with 0.3μg/kg leptin in 1 mL NS, and group C with 0.5μg/kg leptin in 1 mL NS for 2 weeks intraperitoneally. Each group was divided into three subgroups including 8 rats for evaluation at 2, 4 and 8 weeks. Radiological evaluation showed that callus formation of group B and C was all significantly higher than group A at 8 weeks（P=0.04 and P = 0.013, respectively）. There was no statistically significant difference in fracture healing between group B and group C at 8 weeks（P = 0.197）. Histological evaluation revealed fracture healing of group B and C was better than group A at 4 weeks（P=0.01 and P= 0.002,respectively） and 8 weeks（P = 0.008 and P= 0.003, respectively）. Micro-computed tomography（Micro-CT） analysis demonstrated that greater amounts of bony callus and evidence of bone fusion were observed in group B and C at 4 weeks（P = 0.02 and P = 0.04, respectively） and 8 weeks（P= 0.005 and P = 0.001, respectively） compared to group A. Group C also had better fracture healing than group B at 8 weeks（P = 0.01）. In conclusion, leptin has a positive effect on rat femoral fracture healing.展开更多
The paper is discussing problems connected with embedment of the incubation time criterion for brittle fracture into finite element computational schemes. Incubation time fracture criterion is reviewed; practical ques...The paper is discussing problems connected with embedment of the incubation time criterion for brittle fracture into finite element computational schemes. Incubation time fracture criterion is reviewed; practical questions of its numerical implementation are extensively discussed. Several examples of how the incubation time fracture criterion can be used as fracture condition in finite element computations are given. The examples include simulations of dynamic crack propagation and arrest, impact crater formation （i.e. fracture in initially intact media）, spall fracture in plates, propagation of cracks in pipelines. Applicability of the approach to model initiation, development and arrest of dynamic fracture is claimed.展开更多
On the basis of analysis of low carbon steel fracture macro-features and micro-processes at low temperature,the definition was given of the characteristic transition temperature of brittleness,T_(pm),and its physical ...On the basis of analysis of low carbon steel fracture macro-features and micro-processes at low temperature,the definition was given of the characteristic transition temperature of brittleness,T_(pm),and its physical meaning was expounded.Discussion was carried out of phys- ical characteristic of variation at T_(pm) in respect of the fracture toughness and property of crack arrest.In addition,research was made on the application of T_(pm),which can give infor- mation about the transition of the fracture toughness,the property of crack arrest and critical crack size,to estimation the brittleness of low carbon steel at low temperatures.展开更多
The main task of fracture mechanics of rock masses is the study on the propagating mechanism of fractures in rock masses , which can be efficiently conducted by discontinuty displacement (DD) numerical evaluation . Fi...The main task of fracture mechanics of rock masses is the study on the propagating mechanism of fractures in rock masses , which can be efficiently conducted by discontinuty displacement (DD) numerical evaluation . Firstly ,the element stress and displacement are analysed and the principle and steps of the numerical calculation of stress intensity factor and fracture extension force are introduced .The numerical results of parallel and echelon fracture systems ,which are compared with real field fractures .are presented. Finally . a simple engineering application example is presented .展开更多
Forearm fractures are prevalent which include radius fractures,ulna fractures,or both radius and ulna fractures.Proximal radius fractures combined with dislocations of the radial heads are rare and easily misdiagnosed...Forearm fractures are prevalent which include radius fractures,ulna fractures,or both radius and ulna fractures.Proximal radius fractures combined with dislocations of the radial heads are rare and easily misdiagnosed.The authors present and discuss a case of proximal radius fractures associated with radial head dislocations.A 36 years old male was admitted to the hospital due to pain and activity limitation in his left elbow for 7 hours due to a car accident.An X-ray of the left elbow joint revealed a“left radius fracture with surrounding soft tissue edema”.During the procedure,the radial head was found to be dislocated forward.A 3.0 mm anchor was used to fix the annular ligament.Radius fractures combined dislocations of the radial heads are rare and may be missing the diagnosis.Before undergoing surgery,the possibility of elbow dislocation should be evaluated.Wire anchors can provide reliable fixation.展开更多
Normal-pressure shale gas is an important object of shale gas reserves and production increasewith broad resource prospects in China,but its large-scale benefit development is still confronted with technical bottlenec...Normal-pressure shale gas is an important object of shale gas reserves and production increasewith broad resource prospects in China,but its large-scale benefit development is still confronted with technical bottlenecks.To promote the large-scale benefit development of normal-pressure shale gas,this paper systematically sorts out and summarizes the research achievements and technological progresses related to normal-pressure shale gas from the aspects of accumulation mechanism,enrichment theory,percolation mechanism,development technology,and low-cost engineering technology,and points out the difficulties and challenges to the benefit development of normal-pressure shale gas in the complex structure zones of southern China,by taking the shale gas in the Southeast Chongqing Area of the Sichuan Basin as the research object.In addition,the research direction of normal-pressure shale gas exploration and development is discussed in terms of sweet spot selection,development technology policy,low-cost drilling technology and high-efficiency fracturing technology.And the following research results are obtained.First,the accumulation mechanism of normal-pressure shale gas is clarified from the perspective of geological exploration theory;the hydrocarbon accumulation model of generation,expulsion,retention and accumulation is established;the enrichment theory of“three-factor controlling reservoir”is put forward;and the comprehensive sweetspot target evaluation system is formed.Second,as for development technology,the development technology policies of“multiple series of strata,variable well spacing,long horizontal section,small included angle,low elevation difference,strong stimulation and pressure difference controlling”are formulated.Third,as for drilling engineering,the optimal fast drilling and completion technology with“secondary structureþradical parameterþintegrated guidanceþunpressured leak-proof cementing”as the core is formed.Fourth,as for fracturing engineering,the low-cost and high-efficiency fracturing technology with“multi-cluster small-stageþlimited-entry perforatingþdouble temporary blockingþhigh-intensity sand injectionþfully electric”as the core is formed.Fifth,normal-pressure shale gas is characterized by complex geological conditions,low pressure coefficient and gas content,poor resource endowment and so on,but its resource utilization still faces a series of challenges,such as uncertain productivity construction positions,low single-well productivity and ultimate recoverable reserve,high investment cost and poor economic benefit.In conclusion,the key research directions to realize the large-scale benefit development of low-grade normal-pressure shale gas are to deepen the research on the enrichment and high yield mechanism and sweet spot selection of normal-pressure shale gas,strengthen the research on the benefit development technology policy based on percolation mechanism and the key technologies for low-cost drilling,accelerate the research and devel-opment of the key technologies for low-cost and high-efficiency fracturing,and implement cost reduction and efficiency improvement continuously.展开更多
文摘Horizontal wells in the anisotropic reservoirs can be stimulated by hydraulic fracturing in order to create multiple finite-conductivity vertical fractures. Several methods for evaluating the productivity of the horizontal wells have been presented in the literature. With such methods, however, it is still difficult to obtain an accurate result. This paper firstly presents the dimensionless conductivity theory of vertical fractures. Then models for calculating the equivalent wellbore radius and the skin factor due to flow convergence to the well bore are proposed after analyzing the steady-state flow in porous reservoirs. By applying the superposition principle to the pressure drop, a new method for evaluating the productivity of horizontal wells intercepted by multiple finite-conductivity fractures is developed. The influence of fracture conductivity and fracture half length on the horizontal well productivity is quantitatively analyzed with a synthetic case. Optimum fracture number and fracture space are further discussed in this study. The results prove that the method outlined here should be useful to design optimum fracturing of horizontal wells.
基金provided by the National Natural Science Foundation of China (No. 50974118)the Program for New Century Excellent Talents in University (No. NCET-09-0727)+1 种基金the Program for Post graduates Research Innovation in Universities of Jiangsu Province (No. CX10B_149Z)the Priority Academic Program Development of Jiangsu Higher Education Institutions and the State Key Laboratory of Coal Resources and Mine Safety (No.SKLCRSM08X04)
文摘As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage road- way in a certain coal mine is so broken and loose that the supporting is very difficult. Based on compre- hensive anal[ysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks, Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture dewelopment. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.
文摘Multi-stage volume fracturing of horizontal wells is the main means to develop tight gas reservoirs.Complex fracture networks of various shapes are generated around the wellbore after volume fracturing.At present,however,most of the well test models suitable for fracturing horizontal wells take all hydraulic fractures as single main fractures,which results in a large error between well test interpretation result and actual situation.As a result,the fracture network characteristic parameters of the stimulated areas cannot be obtained accurately.To this end,a well test model for complex fracture networks in tight-gas fracturing horizontal wells was established on the basis of the non-structural discrete fracture model.Then,this model was solved by using thefinite element method with combined triangular elements and linear elements.And accordingly,the well test type curves of a horizontal well under different fracture network patterns(rectangular,elliptical and hyperbolic)were prepared.Based on this,well test type curves were analyzed from the aspects of characteristics and influential factors and were compared with those obtained from the conventional single-fracture model.Finally,the new model was applied in well test interpretation of one multi-stage volume fracturing horizontal well in the gas reservoir of Permian Shan 1 formation in the Qingyang Gas Field of the Ordos Basin.And the following research results were obtained.First,the biggest difference of well test type curve between the fracture network model and the conventional single-fracture model occurs in the early stage,the characteristics offirst linearflow regime are replaced with the characteristics of pseudo-radialflow regime in the stimulated area.Second,the end time of the pseudo-radialflow regime in the stimulated area is mainly dominated by the size and shape of the stimulated area.The larger the stimulated area is,the longer the pseudo-radialflow regime lasts.As the shape of the stimulated area approaches to be elongated,the characteristics of the well test type curve obtained by the new model are more consistent with those by the single-fracture model.Third,the pressure derivative value of the pseudo-radialflow regime in the stimulated area is mainly dependent on the conductivity and density of the fracture network.The higher the density or the conductivity of fracture network in the stimulated area is,the earlier the wellbore storage effect regime ends,the lower the pressure derivative value of the pseudo-radialflow regime in the stimulated area is and the more obvious the characteristics of the horizontal line are.In conclusion,case study results confirm that the new model is reliable and practical and can provide accurate reservoir parameters as well as the size of the effectively stimulated area by volume fracturing and the conductivity of fracture network,which is conducive to evaluating the stimulation effect of volume fracturing and predicting the postfrac production performance.
基金supported by the Major Scientific and Technological Projects of CNPC under grant ZD2019-183-006the National Science and Technology Major Project of China(2016ZX05014002-006)the National Natural Science Foundation of China(42072234)。
文摘This study aims to elucidate the dynamic evolution mechanism of the fracturing fracture system during the exploration and development of complex oil and gas reservoirs.By integrating methods of rock mechanical testing,logging calculation,and seismic inversion technology,we obtained the current insitu stress characteristics of a single well and rock mechanical parameters.Simultaneously,significant controlling factors of rock mechanical properties were analyzed.Subsequently,by coupling hydraulic fracturing physical experiments with finite element numerical simulation,three different fracturing models were configured:single-cluster,double-cluster,and triple-cluster perforations.Combined with acoustic emission technology,the fracture initiation mode and evolution characteristics during the loading process were determined.The results indicate the following findings:(1)The extension direction and length of the fracture are significantly controlled by the direction of the maximum horizontal principal stress.(2)Areas with poor cementation and compactness exhibit complex fracture morphology,prone to generating network fractures.(3)The interlayer development of fracturing fractures is controlled by the strata occurrence.(4)Increasing the displacement of fracturing fluid enlarges the fracturing fracture length and height.This research provides theoretical support and effective guidance for hydraulic fracturing design in tight oil and gas reservoirs.
文摘To explore the treatment methods for scapular fractures associated with clavicle fractures.Methods Of 23 cases with scapular fractures associated with clavicle fractures,13 treated conservatively took the function exercise of shoulder joint after two months and 10 treated with open reduction and plate fixation reconstruction began the function exercise of shoulder joint four weeks after operation.The follow up averaged 12 months.Results All patients were healed up.18 cases were followed up,of them 8 cases were treated surgically,10 cases,conservatively.Of eight cases treated surgically,seven got excellent functional recovery of the shoulder joint and one satisfactory.In the meantime,of 10 cases treated conservatively,the recovery of shoulder joint was excellent in six,good in three and poor in one.Conclusion As for scapular fractures with associated clavicle fractures,open reduction and plate fixation reconstruction is a good treatment method for it can keep the stability and the balance of shoulder joint and is helpful for early functional exercise and recovery of the shoulder joint.7 refs,5 figs.
基金Projects(19300604,19300751)supported by the ORSP at Abu Dhabi University,UAE。
文摘This study investigates the fracture behavior of clay-rich mudstone under varying temperature and pressure conditions,which is crucial for the safety of geological structures.It focuses on three fracture types:pure mode I tensile fractures,pure mode II tensile fractures,and shear fractures,examining specimens at room temperature(RT)and after thermal treatments at 250 and 500℃.The findings reveal that increasing temperatures makes the mudstone more brittle,enhancing fracture velocity,toughness,load-bearing capacity,roughness,and the fracture process zone(FPZ)radius.Notably,tensile fractures induced under pure mode II displayed the highest velocities,while shear fractures exhibited the lowest velocities,smoothest surfaces,and greatest resistance to failure.The application of a confining pressure of 4 MPa significantly improved shear fracture toughness by 119.7%,98.5%and 71.9%at RT,250℃and 500℃,respectively,and reduced roughness by 8.2%,22.4%and 30.4%.This research offers a novel,comprehensive view of how temperature and pressure impact fractures in mudstone sensitive to temperature due to its high clay content and water affinity.The findings provide valuable insights applicable to geothermal energy,oil and gas exploration,and underground construction,thereby enhancing the understanding of fracture mechanics in geological contexts.
文摘Before 1980s,the circular suspension spring in automobile subjected to torsion fatigue load,under the cyclic normal tensile stresses,the majority of fatigue fracture occurred was in normal tensile fracture mode（NTFM）and the fracture surface was under 45°diagonal.Because there exists the interaction between the residual stresses induced by shot peening and the applied cyclic normal tensile stresses in NTFM,which represents as＂stress strengthening mechanism＂,shot peening technology could be used for improving the fatigue fracture resistance（FFR）of springs.However,since 1990s up to date,in addition to regular NTFM,the fatigue fractures occurred of peened springs from time to time are in longitudinal shear fracture mode（LSFM）or transverse shear fracture mode（TSFM）with the increase of applied cyclic shear stresses,which leads to a remarkable decrease of FFR.However,LSFM/TSFM can be avoided effectively by means of shot peening treatment again on the peened springs.The phenomena have been rarely happened before.At present there are few literatures concerning this problem.Based upon the results of force analysis of a spring,there is no interaction between the residual stresses by shot peening and the applied cyclic shear stresses in shear fracture.This;means that the effect of＂stress strengthening mechanism＂for improving the FFR of LSFM/TSFM is disappeared basically.During shot peening,however,both of residual stress and cyclic plastic deformed microstructure are induced synchronously like＂twins＂in the surface layer of a spring.It has been found for the first time by means of force analysis and experimental results that the modified microstructure in the＂twins＂as a＂structure strengthening mechanism＂can improve the FFR of LSFM/TSFM.At the same time,it is;also shown that the optimum technology of shot peening strengthening must have both＂stress strengthening mechanism＂and＂structure strengthening mechanism＂simultaneously so that the FFR of both NTFM and LSFM/TSFM can be improved by shot peening.
基金Supported by China National Science and Technology Major Project(2016ZX05023,2017ZX05013-005)
文摘To deal with the stress interference caused by simultaneous propagation of multiple fractures and the wettability reversal and physical property changes of the reservoir caused by fracturing fluid getting in during large-volume fracturing of tight oil reservoirs through a horizontal well, a non-planar 3D fracture growth model was built, wettability reversal characterizing parameters and change of relative permeability curve were introduced to correct the production prediction model of fractured horizontal well, a fracturing design optimization software(Fr Smart) by integrating geological and engineering data was developed, and a fracturing design optimization approach for tight oil reservoirs based on fracture control was worked out. The adaptability of the method was analyzed and the fracture parameters of horizontal wells in tight oil reservoirs were optimized. The simulation results show that fracturing technology based on fracture control is suitable for tight oil reservoirs, and by optimizing fracture parameters, this technology makes it possible to produce the maximum amount of reserves in the well-controlled unit of unconventional reservoirs. The key points of fracturing design optimization based on fracture control include increasing lateral length of and reducing the row spacing between horizontal wells, increasing perforation clusters in one stage to decrease the spacing of neighboring fractures, and also avoiding interference of old and new fracturing wells. Field tests show that this technology can increase single well production and ultimate recovery. Using this technology in developing unconventional resources such as tight oil reservoirs in China will enhance the economics significantly.
基金supported by the 111 Project (B07050)the National Natural Science Foundation of China (10932008)
文摘An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar （SHPB） apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMnSiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor （DSIF） and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experimentsneed to be performed in a comparatively large striker velocity range.
基金Funded by the National Natural Science Foundation of China(No.51279111)The Non-profit Industry Financial Program by the Ministry of Water Resources in2012(No.201201038)
文摘To obtain the fracture parameters of concrete, fracture tests were conducted with three-point bending beam method aiming at 30 concrete beams with different sizes and different intensity. The concrete specimen with prefabricated crack to determine the fracture parameters of concrete were conducted and the fracture performance of the specimen was analyzed. The test results show that, initial fracture toughness is unrelated to the size of specimens; while unstable fracture toughness is related to the size of specimens. As for specimens of bastard size, when concrete intensity is relatively low, unstable fracture toughness increases along with the increase of intensity; when concrete intensity is relatively high, unstable fracture toughness will decrease; when concrete intensity increases continuously, unstable fracture toughness will further increase somewhat. As for specimens of standard size, unstable fracture toughness will increase along with the increase of intensity. Aiming at concrete beam specimens, we conducted two-dimensional non-linear finite element analysis, obtained the stress intensity factor, and carried out contrastive analysis with the experimental results.
基金co-funded by the National Natural Science Foundation of China(41174099,41474100)the Fundamental Research Funds for the Central Universities (14CX06077A)National Major Science & Technology Projects of China(2011ZX05003,2011ZX05009,2011ZX05020,2011ZX 05035)
文摘The high-resolution azimuthal resistivity laterolog response in a fractured formation was numerically simulated using a three-dimensional finite element method. Simulation results show that the azimuthal resistivity is determined by fracture dipping as well as dipping direction, while the amplitude differences between deep and shallow laterolog resistivities are mainly controlled by the former. A linear relationship exists between the corrected apparent conductivities and fracture aperture. With the same fracture aperture, the deep and shallow laterolog resistivities present small values with negative separations for low-angle fractures, while azimuthal resistivities have large variations with positive separations for high-angle fractures that intersect the borehole. For dipping fractures, the variation of the azimuthal resistivity becomes larger when the fracture aperture increases. In addition, for high-angle fractures far from the borehole, a negative separation between the deep and shallow resistivities exists when fracture aperture is large as well as high resistivity contrast exists between bedrock and fracture fluid. The decreasing amplitude of dual laterolog resistivity can indicate the aperture of low-angle fractures, and the variation of the deep azimuthal resistivity can give information of the aperture of high-angle fractures and their position relative to the borehole.
基金funded by the German Federal Ministry for Economic Affairs(FKZ 0325279B)
文摘Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconventional hydrocarbon or geothermal reservoirs by hydraulic fracturing. Fracture propagation in isotropic material is well understood but strictly isotropic rocks are rarely found in nature. This study aims at the examination of fracture initiation and propagation processes in a highly anisotropic rock, specifically slate. We performed a series of tensile fracturing laboratory experiments under uniaxial as well as triaxial loading. Cubic specimens with edge lengths of 150 mm and a central borehole with a diameter of13 mm were prepared from Fredeburg slate. An experiment using the rather isotropic Bebertal sandstone as a rather isotropic rock was also performed for comparison. Tensile fractures were generated using the sleeve fracturing technique, in which a polymer tube placed inside the borehole is pressurized to generate tensile fractures emanating from the borehole. In the uniaxial test series, the loading was varied in order to observe the transition from strength-dominated fracture propagation at low loading magnitudes to stress-dominated fracture propagation at high loading magnitudes.
基金Project supported by Iran's National Elites Foundation(INEF)Partial supports of center of excellent for structures and earthquake engineering at Sharif University of technology
文摘A simultaneous experimental and numerical study of shear fracture of concrete-like materials is carried out using Brazilian disc specimens with initial double edge cracks and fourpoint bending beam specimens with double edge-notches.The interference effects of two cracks/notches are investigated through varied ligament angles and crack lengths.It is shown that shear fracturing paths change remarkably with the initial ligament angles and crack lengths.The cracked specimens are numerically simulated by an indirect boundary element method.A comparison between the numerical results and the experimental ones shows good agreement.
基金Sponsored by National High Technology Research and Development Program of China(2012AA03A505)
文摘The 0.2-0.3mm thick cold-rolled sheets and annealed sheets of high silicon steel were produced by rolling process,then punching tests were carried out at room temperature to 150℃.The punchability and punching fracture behavior were investigated by means of scanning electron microscope（SEM）and electron back-scattered diffraction（EBSD）.It is found that cold-rolled sheets of high silicon steel show good punchability under the condition of 0.01 mm punch-die clearance and at the temperature of 100℃;the punchability of annealed sheets with fine grain size is better than that of annealed sheets with coarse grain size;the punching temperature of 150℃is suitable for annealed high silicon steel sheets especially with coarse grain size on account of punching edge quality.The major cleavage planes of annealed high silicon steel sheets are{100}crystallographic planes on which brittle fracture occurs at low temperatures.The cleavage systems include{100}〈110〉and{100}〈100〉,and cleavage fracture is completed by one or both of them.The punchability of high silicon steel sheets is related with punching temperature,grain size and ordering degree.Reducing ordering degree,increasing punching temperature,as well as refining grain size can improve the ductility and punchability of high silicon steel sheets.
文摘In this study, our objective was to evaluate effects of leptin on fracture healing in rats. Seventy two male SpragueDawley（SD） rats were randomized into 3 groups. Standardized femoral fractures were created in all the rats. Group A was treated with 1 mL normal saline（NS）, group B with 0.3μg/kg leptin in 1 mL NS, and group C with 0.5μg/kg leptin in 1 mL NS for 2 weeks intraperitoneally. Each group was divided into three subgroups including 8 rats for evaluation at 2, 4 and 8 weeks. Radiological evaluation showed that callus formation of group B and C was all significantly higher than group A at 8 weeks（P=0.04 and P = 0.013, respectively）. There was no statistically significant difference in fracture healing between group B and group C at 8 weeks（P = 0.197）. Histological evaluation revealed fracture healing of group B and C was better than group A at 4 weeks（P=0.01 and P= 0.002,respectively） and 8 weeks（P = 0.008 and P= 0.003, respectively）. Micro-computed tomography（Micro-CT） analysis demonstrated that greater amounts of bony callus and evidence of bone fusion were observed in group B and C at 4 weeks（P = 0.02 and P = 0.04, respectively） and 8 weeks（P= 0.005 and P = 0.001, respectively） compared to group A. Group C also had better fracture healing than group B at 8 weeks（P = 0.01）. In conclusion, leptin has a positive effect on rat femoral fracture healing.
基金supported by RFBR research (10-01-00810-a,11-01-00491-a,10-01-91154-GFEN a),Russian Federation State contracts and academic programs of the Russian Academy of Sciences
文摘The paper is discussing problems connected with embedment of the incubation time criterion for brittle fracture into finite element computational schemes. Incubation time fracture criterion is reviewed; practical questions of its numerical implementation are extensively discussed. Several examples of how the incubation time fracture criterion can be used as fracture condition in finite element computations are given. The examples include simulations of dynamic crack propagation and arrest, impact crater formation （i.e. fracture in initially intact media）, spall fracture in plates, propagation of cracks in pipelines. Applicability of the approach to model initiation, development and arrest of dynamic fracture is claimed.
文摘On the basis of analysis of low carbon steel fracture macro-features and micro-processes at low temperature,the definition was given of the characteristic transition temperature of brittleness,T_(pm),and its physical meaning was expounded.Discussion was carried out of phys- ical characteristic of variation at T_(pm) in respect of the fracture toughness and property of crack arrest.In addition,research was made on the application of T_(pm),which can give infor- mation about the transition of the fracture toughness,the property of crack arrest and critical crack size,to estimation the brittleness of low carbon steel at low temperatures.
基金The research is supported by the National Nature Science Foundation of China
文摘The main task of fracture mechanics of rock masses is the study on the propagating mechanism of fractures in rock masses , which can be efficiently conducted by discontinuty displacement (DD) numerical evaluation . Firstly ,the element stress and displacement are analysed and the principle and steps of the numerical calculation of stress intensity factor and fracture extension force are introduced .The numerical results of parallel and echelon fracture systems ,which are compared with real field fractures .are presented. Finally . a simple engineering application example is presented .
基金The authors acknowledge the financially support received from the Medicine and Health Project of Zhejiang Province(2022KY1288,2022KY1313)General Research Project of Zhejiang Provincial Department of Education(LY202043116,Y202145976)Science and Technology Project of Shaoxing City(2020A13011).
文摘Forearm fractures are prevalent which include radius fractures,ulna fractures,or both radius and ulna fractures.Proximal radius fractures combined with dislocations of the radial heads are rare and easily misdiagnosed.The authors present and discuss a case of proximal radius fractures associated with radial head dislocations.A 36 years old male was admitted to the hospital due to pain and activity limitation in his left elbow for 7 hours due to a car accident.An X-ray of the left elbow joint revealed a“left radius fracture with surrounding soft tissue edema”.During the procedure,the radial head was found to be dislocated forward.A 3.0 mm anchor was used to fix the annular ligament.Radius fractures combined dislocations of the radial heads are rare and may be missing the diagnosis.Before undergoing surgery,the possibility of elbow dislocation should be evaluated.Wire anchors can provide reliable fixation.
基金supported by the National Science and Technology Major Project of China"Demonstrative project of normal-pressure shale gas exploration and development in the Pengshui area"(No.2016ZX05061)the Sinopec Scientific Research Projects"Evaluation of normal-pressure shale gas enrichment and production mechanisms and targets in Nan-chuan-Wulong"(No.P21087-6)"Evaluation of shale gas enrichment and targets in the East China exploration area in Sichuan Basin and its periphery"(No.P20059-6).
文摘Normal-pressure shale gas is an important object of shale gas reserves and production increasewith broad resource prospects in China,but its large-scale benefit development is still confronted with technical bottlenecks.To promote the large-scale benefit development of normal-pressure shale gas,this paper systematically sorts out and summarizes the research achievements and technological progresses related to normal-pressure shale gas from the aspects of accumulation mechanism,enrichment theory,percolation mechanism,development technology,and low-cost engineering technology,and points out the difficulties and challenges to the benefit development of normal-pressure shale gas in the complex structure zones of southern China,by taking the shale gas in the Southeast Chongqing Area of the Sichuan Basin as the research object.In addition,the research direction of normal-pressure shale gas exploration and development is discussed in terms of sweet spot selection,development technology policy,low-cost drilling technology and high-efficiency fracturing technology.And the following research results are obtained.First,the accumulation mechanism of normal-pressure shale gas is clarified from the perspective of geological exploration theory;the hydrocarbon accumulation model of generation,expulsion,retention and accumulation is established;the enrichment theory of“three-factor controlling reservoir”is put forward;and the comprehensive sweetspot target evaluation system is formed.Second,as for development technology,the development technology policies of“multiple series of strata,variable well spacing,long horizontal section,small included angle,low elevation difference,strong stimulation and pressure difference controlling”are formulated.Third,as for drilling engineering,the optimal fast drilling and completion technology with“secondary structureþradical parameterþintegrated guidanceþunpressured leak-proof cementing”as the core is formed.Fourth,as for fracturing engineering,the low-cost and high-efficiency fracturing technology with“multi-cluster small-stageþlimited-entry perforatingþdouble temporary blockingþhigh-intensity sand injectionþfully electric”as the core is formed.Fifth,normal-pressure shale gas is characterized by complex geological conditions,low pressure coefficient and gas content,poor resource endowment and so on,but its resource utilization still faces a series of challenges,such as uncertain productivity construction positions,low single-well productivity and ultimate recoverable reserve,high investment cost and poor economic benefit.In conclusion,the key research directions to realize the large-scale benefit development of low-grade normal-pressure shale gas are to deepen the research on the enrichment and high yield mechanism and sweet spot selection of normal-pressure shale gas,strengthen the research on the benefit development technology policy based on percolation mechanism and the key technologies for low-cost drilling,accelerate the research and devel-opment of the key technologies for low-cost and high-efficiency fracturing,and implement cost reduction and efficiency improvement continuously.
