Accurate extraction of pores and fractures is a prerequisite for constructing digital rocks for physical property simulation and microstructural response analysis.However,fractures in CT images are similar in grayscal...Accurate extraction of pores and fractures is a prerequisite for constructing digital rocks for physical property simulation and microstructural response analysis.However,fractures in CT images are similar in grayscale to the rock matrix,and traditional algorithms have difficulty to achieve accurate segmentation results.In this study,a dataset containing multiscale fracture information was constructed,and a U-Net semantic segmentation model with a scSE attention mechanism was used to classify shale CT images at the pixel level and compare the results with traditional methods.The results showed that the CLAHE algorithm effectively removed noise and enhanced the fracture information in the dark parts,which is beneficial for further fracture extraction.The Canny edge detection algorithm had significant false positives and failed to recognize the internal information of the fractures.The Otsu algorithm only extracted fractures with a significant difference from the background and was not sensitive enough for fine fractures.The MEF algorithm enhanced the edge information of the fractures and was also sensitive to fine fractures,but it overestimated the aperture of the fractures.The U-Net was able to identify almost all fractures with good continuity,with an MIou and Recall of 0.80 and 0.82,respectively.As the image resolution increases,more fine fracture information can be extracted.展开更多
In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels...In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.展开更多
Introduction: Intra-articular distal radial fractures in young patients occur in high energy trauma which can lead to a combination of bone and ligaments lesions. An articular step superior to 2 mm is pejorative, for ...Introduction: Intra-articular distal radial fractures in young patients occur in high energy trauma which can lead to a combination of bone and ligaments lesions. An articular step superior to 2 mm is pejorative, for that an adequate radiologic analysis is necessary accessing to the best surgical treatment. The purpose of our study was to investigate this type of fracture and expose radiologic analysis (radiograph and CT-scan) of bone and ligamentous associated lesions of this specific twisted lunate facet fracture for recognizing it and accessing to the best surgical treatment. Patients and Methods: Seven patients with severely displaced type 4 articular fractures of the distal radius whose wrists had been exposed to violent compression are reported in our series, they are required open treatment for the reduction and fixation of disrupted articular surfaces by using an antero-medial approach which allows direct access to the fragment of the lunate facet and easier visualization of the distal radio-ulnar joint. Results: All the patients were clinically examined with antero-posterior and lateral X ray, completed by a CT scan, all the fractures were type IV according to Melone classification. In all of our seven cases there was a lesion of the distal radioulnar joint (DRUJ) identified in the CT scan. The CT scan allowed us to individualize well the void of the lunate fossa and calculate his exact degree of rotation, which is very important for planning therapeutic management. Discussion: In all of our cases the CT scan was to expose all of the osseous and ligamentous injuries;in the sagittal reconstruction we were able to objectify and calculate the exact degree of the rotation of the lunate fossa fragment;in the frontal reconstruction the void of the lunate fossa is visible and in the axial reconstruction we can determine the incongruence of the distal radio-ulnar joint (DRUJ). Intra-articular involvement has long been recognized as a poor prognostic factor in fractures of the distal radius. However, despite early studies reporting poor results with non operative treatment for these injuries, most authors opposed operative intervention, due to lack of a good radiological analysis and the CT scan;knowledge that a number of studies have shown that inadequate reduction of intra-articular distal radius fractures leads to the development of arthritis.展开更多
Tortuous hydraulic fractures(HFs) are likely to be created in heterogeneous formations such as conglomerates, which may cause sand plugging, ultimately resulting in poor stimulation efficiency. This study aims to expl...Tortuous hydraulic fractures(HFs) are likely to be created in heterogeneous formations such as conglomerates, which may cause sand plugging, ultimately resulting in poor stimulation efficiency. This study aims to explore HF growth behavior in conglomerate through laboratory fracturing experiments under true tri-axial stresses combined with computed tomography scanning and acoustic emission(AE) monitoring. The effects of gravel size, horizontal differential stress, and AE focal mechanisms were examined. Especially, the injection pressure and the AE response features during HF initiation and propagation in conglomerate were analyzed. Simple HFs with narrow microfractures are created in conglomerate when the gravels are considerably smaller than the specimen, whereas complex fractures are created when the gravels are similar in size to the specimen, even under high horizontal differential stresses. Breakdown pressure and AE rates are high when a HF is initiated from the high-strength gravel. A large pressure decline after the breakdown may indicate the creation of a planar and wide HF. Analyzing the focal mechanism indicates that the shear mechanism generally dominates with an increase in the HF complexity. Tensile events are likely to occur during HF initiation and are located around the wellbore. Shear events occur mainly around the nonplanar and complex matrix/gravel interfaces.展开更多
Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness...Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.展开更多
Despite lots of techniques in improving the heap leaching performance,many constraints on the industrial applications remain.We proposed a correspondingly effective and new idea of introducing forced aeration to impro...Despite lots of techniques in improving the heap leaching performance,many constraints on the industrial applications remain.We proposed a correspondingly effective and new idea of introducing forced aeration to improve the bad permeability and leaching effect of Yangla Copper Mine(YCM)during heap leaching.The dual-media theory was employed to study the impact mechanism of forced aeration on the variations of porous and fractured media during the column leaching experiments.An X-Ray Computed Tomography(CT)set was utilized to perform the pore imaging of the specimens and the fracture morphology of the particles within the columns was analyzed by Scanning Electron Microscope(SEM)as aeration rate(AR)changed.The results show that there exists copious fine particles within the heap of YCM,the particle size distribution of which is not reasonable.The forced aeration can not only promote the development of the porous and fractured structures but effectively break the blocked seepage paths.Then the leaching degree is improved and the seepage performance of the solute within the solution is enhanced.Therefore,the forced aeration is probable of making the leaching performance greatly improved.展开更多
目的验证基于临床CT的数字体相关(digital volume correlation,DVC)方法在测量股骨内部变形场时的准确性,并通过DVC进一步测量股骨在跌倒情况下的内部变形,验证基于临床CT的有限元分析方法(finite element analysis,FEA)在计算股骨内部...目的验证基于临床CT的数字体相关(digital volume correlation,DVC)方法在测量股骨内部变形场时的准确性,并通过DVC进一步测量股骨在跌倒情况下的内部变形,验证基于临床CT的有限元分析方法(finite element analysis,FEA)在计算股骨内部变形场的准确性。方法使用猪股骨,模拟侧向跌倒姿态,进行分步力学加载实验,同步进行多次CT成像。通过重复扫描和虚拟位移验证DVC方法的准确性。DVC以子体积作为配准两组图像的研究对象,分别设置8、12、16和20 mm的子体积进行测试。量化误差指标包括位移系统误差-平均值(mean)、位移随机误差-标准差(standard deviation,SD)、应变准确度-平均绝对误差(mean absolute error,MAER)和应变精确度-标准差误差(standard deviation of the error,SDER)。基于CT图像建立股骨有限元模型,模拟实验条件,计算股骨内部位移,与DVC测量的内部变形场对比验证。结果基于临床CT的DVC方法重复扫描位移偏差小于0.013 mm,MAER和SDER均小于200με;虚拟位移偏差小于0.098 mm,MAER为1093~1687με,SDER为604~1267με,远小于骨组织屈服应变。FEA计算的位移和DVC测量的位移之间具有较强的相关性(R^(2)≥0.76,P<0.05)。结论基于临床CT的DVC方法可以准确测量股骨内部变形场,并且基于临床CT的有限元模型可以准确计算股骨内部变形场。展开更多
基金funded by the Natural Science Basis Research Plan in Shaanxi Province of China(No.2022JM-147).
文摘Accurate extraction of pores and fractures is a prerequisite for constructing digital rocks for physical property simulation and microstructural response analysis.However,fractures in CT images are similar in grayscale to the rock matrix,and traditional algorithms have difficulty to achieve accurate segmentation results.In this study,a dataset containing multiscale fracture information was constructed,and a U-Net semantic segmentation model with a scSE attention mechanism was used to classify shale CT images at the pixel level and compare the results with traditional methods.The results showed that the CLAHE algorithm effectively removed noise and enhanced the fracture information in the dark parts,which is beneficial for further fracture extraction.The Canny edge detection algorithm had significant false positives and failed to recognize the internal information of the fractures.The Otsu algorithm only extracted fractures with a significant difference from the background and was not sensitive enough for fine fractures.The MEF algorithm enhanced the edge information of the fractures and was also sensitive to fine fractures,but it overestimated the aperture of the fractures.The U-Net was able to identify almost all fractures with good continuity,with an MIou and Recall of 0.80 and 0.82,respectively.As the image resolution increases,more fine fracture information can be extracted.
基金This work was financially supported by the National Natural Science Foundation of China(No.52074041)the Chongqing Talent Program(No.cstc2022ycjh-bgzxm0077)the Postgraduate Research and Innovation Foundation of Chongqing,China(No.CYS23060).
文摘In coal mining,rock strata are fractured under cyclic loading and unloading to form fracture channels.Fracture channels are the main flow narrows for gas.Therefore,expounding the flow conductivity of fracture channels in rocks on fluids is significant for gas flow in rock strata.In this regard,graded incremental cyclic loading and unloading experiments were conducted on sandstones with different initial stress levels.Then,the three-dimensional models for fracture channels in sandstones were established.Finally,the fracture channel percentages were used to reflect the flow conductivity of fracture channels.The study revealed how the particle size distribution of fractured sandstone affects the formation and expansion of fracture channels.It was found that a smaller proportion of large blocks and a higher proportion of small blocks after sandstone fails contribute more to the formation of fracture channels.The proportion of fracture channels in fractured rock can indicate the flow conductivity of those channels.When the proportion of fracture channels varies gently,fluids flow evenly through those channels.However,if the proportion of fracture channels varies significantly,it can greatly affect the flow rate of fluids.The research results contribute to revealing the morphological evolution and flow conductivity of fracture channels in sandstone and then provide a theoretical basis for clarifying the gas flow pattern in the rock strata of coal mines.
文摘Introduction: Intra-articular distal radial fractures in young patients occur in high energy trauma which can lead to a combination of bone and ligaments lesions. An articular step superior to 2 mm is pejorative, for that an adequate radiologic analysis is necessary accessing to the best surgical treatment. The purpose of our study was to investigate this type of fracture and expose radiologic analysis (radiograph and CT-scan) of bone and ligamentous associated lesions of this specific twisted lunate facet fracture for recognizing it and accessing to the best surgical treatment. Patients and Methods: Seven patients with severely displaced type 4 articular fractures of the distal radius whose wrists had been exposed to violent compression are reported in our series, they are required open treatment for the reduction and fixation of disrupted articular surfaces by using an antero-medial approach which allows direct access to the fragment of the lunate facet and easier visualization of the distal radio-ulnar joint. Results: All the patients were clinically examined with antero-posterior and lateral X ray, completed by a CT scan, all the fractures were type IV according to Melone classification. In all of our seven cases there was a lesion of the distal radioulnar joint (DRUJ) identified in the CT scan. The CT scan allowed us to individualize well the void of the lunate fossa and calculate his exact degree of rotation, which is very important for planning therapeutic management. Discussion: In all of our cases the CT scan was to expose all of the osseous and ligamentous injuries;in the sagittal reconstruction we were able to objectify and calculate the exact degree of the rotation of the lunate fossa fragment;in the frontal reconstruction the void of the lunate fossa is visible and in the axial reconstruction we can determine the incongruence of the distal radio-ulnar joint (DRUJ). Intra-articular involvement has long been recognized as a poor prognostic factor in fractures of the distal radius. However, despite early studies reporting poor results with non operative treatment for these injuries, most authors opposed operative intervention, due to lack of a good radiological analysis and the CT scan;knowledge that a number of studies have shown that inadequate reduction of intra-articular distal radius fractures leads to the development of arthritis.
基金supported by the Major National Science and Technology Projects of China (No. 2016ZX05046004002 No. 2017ZX05039002-003)the National Basic Research Program of China (No. 2015CB250903)
文摘Tortuous hydraulic fractures(HFs) are likely to be created in heterogeneous formations such as conglomerates, which may cause sand plugging, ultimately resulting in poor stimulation efficiency. This study aims to explore HF growth behavior in conglomerate through laboratory fracturing experiments under true tri-axial stresses combined with computed tomography scanning and acoustic emission(AE) monitoring. The effects of gravel size, horizontal differential stress, and AE focal mechanisms were examined. Especially, the injection pressure and the AE response features during HF initiation and propagation in conglomerate were analyzed. Simple HFs with narrow microfractures are created in conglomerate when the gravels are considerably smaller than the specimen, whereas complex fractures are created when the gravels are similar in size to the specimen, even under high horizontal differential stresses. Breakdown pressure and AE rates are high when a HF is initiated from the high-strength gravel. A large pressure decline after the breakdown may indicate the creation of a planar and wide HF. Analyzing the focal mechanism indicates that the shear mechanism generally dominates with an increase in the HF complexity. Tensile events are likely to occur during HF initiation and are located around the wellbore. Shear events occur mainly around the nonplanar and complex matrix/gravel interfaces.
基金the National Natural Science Foundation of China fund (Project number: 52174045 and No. 52104011)Research Foundation of China University of Petroleum-Beijing at Karamay (No. XQZX20210001)PetroChina Innovation Foundation (2020D50070207)。
文摘Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.
基金the National Natural Science Foundation of China(No.51374035)the Foundation for the Author of National Excellent Doctoral Dissertation of PR China(No.201351)the Program for New Century Excellent Talents in University of China(No.NCET-13-0669).
文摘Despite lots of techniques in improving the heap leaching performance,many constraints on the industrial applications remain.We proposed a correspondingly effective and new idea of introducing forced aeration to improve the bad permeability and leaching effect of Yangla Copper Mine(YCM)during heap leaching.The dual-media theory was employed to study the impact mechanism of forced aeration on the variations of porous and fractured media during the column leaching experiments.An X-Ray Computed Tomography(CT)set was utilized to perform the pore imaging of the specimens and the fracture morphology of the particles within the columns was analyzed by Scanning Electron Microscope(SEM)as aeration rate(AR)changed.The results show that there exists copious fine particles within the heap of YCM,the particle size distribution of which is not reasonable.The forced aeration can not only promote the development of the porous and fractured structures but effectively break the blocked seepage paths.Then the leaching degree is improved and the seepage performance of the solute within the solution is enhanced.Therefore,the forced aeration is probable of making the leaching performance greatly improved.
文摘目的验证基于临床CT的数字体相关(digital volume correlation,DVC)方法在测量股骨内部变形场时的准确性,并通过DVC进一步测量股骨在跌倒情况下的内部变形,验证基于临床CT的有限元分析方法(finite element analysis,FEA)在计算股骨内部变形场的准确性。方法使用猪股骨,模拟侧向跌倒姿态,进行分步力学加载实验,同步进行多次CT成像。通过重复扫描和虚拟位移验证DVC方法的准确性。DVC以子体积作为配准两组图像的研究对象,分别设置8、12、16和20 mm的子体积进行测试。量化误差指标包括位移系统误差-平均值(mean)、位移随机误差-标准差(standard deviation,SD)、应变准确度-平均绝对误差(mean absolute error,MAER)和应变精确度-标准差误差(standard deviation of the error,SDER)。基于CT图像建立股骨有限元模型,模拟实验条件,计算股骨内部位移,与DVC测量的内部变形场对比验证。结果基于临床CT的DVC方法重复扫描位移偏差小于0.013 mm,MAER和SDER均小于200με;虚拟位移偏差小于0.098 mm,MAER为1093~1687με,SDER为604~1267με,远小于骨组织屈服应变。FEA计算的位移和DVC测量的位移之间具有较强的相关性(R^(2)≥0.76,P<0.05)。结论基于临床CT的DVC方法可以准确测量股骨内部变形场,并且基于临床CT的有限元模型可以准确计算股骨内部变形场。
