The gas kick represents a major risk in deepwater oil and gas exploration.Understanding the dynamics of gas kick evolution and the associated pressure response characteristics is critical for effective well control.In...The gas kick represents a major risk in deepwater oil and gas exploration.Understanding the dynamics of gas kick evolution and the associated pressure response characteristics is critical for effective well control.In this paper,we introduce a transient wellbore multiphase flow model specifically developed to simulate gas kick in deepwater dual-gradient drilling,incorporating a downhole separator.The model accounts for the variable mass flow within the annulus and heat exchange between the annular fluid and the formation.Using this model,we analyzed the multiphase flow and thermodynamic behavior during the gas kick.Simulation results reveal a progressive increase in bottom-hole temperature,underscoring its potential as a key indicator for gas kick early detection.Additionally,variable gradient parameters affect not only the annular equivalent circulating density(ECD)profile but also the evolution of the gas kick.The inclusion of a downhole separator alters the annular ECD profile,creating a“broken line”shape,which enhances adaptability to the multi-pressure systems typically encountered in deepwater forma-tion.By adjusting factors such as hollow sphere concentration,separator position,and separation effi-ciency,the annular ECD profile can be effectively customized.This study provides important theoretical insights and practical applications for utilizing dual-gradient drilling technology to address challenges in deepwater formation drilling.展开更多
Equivalent circulating density(ECD)denotes the density of drilling mud during circulation within a well.It is determined by integrating the equivalent static density with the pressure loss attributable to friction bet...Equivalent circulating density(ECD)denotes the density of drilling mud during circulation within a well.It is determined by integrating the equivalent static density with the pressure loss attributable to friction between the flowing mud and the geological formation.The effective management of ECD is imperative during drilling operations,as it plays a critical role in preventing kicks and minimising mud losses.Mud ECD has undergone extensive investigation through laboratory experiments,field measurements,and predictive modelling.Nevertheless,a comprehensive review of the various predictive models associated with ECD remains absent.The objective of this study is to review and critique existing correlations for estimating ECD.To accomplish this,a thorough bibliometric analysis was performed,focusing on peer-reviewed journals,mud manuals,and oil and gas conference papers.For the sake of clarity,existing models were categorized into tables,with their principal features highlighted.A critique of each model was subsequently provided.In total,45 models related to ECD were identified,reviewed,and critiqued.The findings reveal that over 44%of the models are based on machine learning(ML),27%are analytical models,16%are regression based models,and 13%are simulator-related.Although there is no universally accepted model for ECD,there is an observable trend towards the utilization of ML algorithms for ECD estimation due to their predictive capabilities.However,the interpretability of these ML-based models remains a significant concern.This review serves as a comprehensive source of information on ECD for both readers and industry practitioners.Additionally,it directs researchers towards areas requiring further exploration and aids drilling professionals in selecting appropriate ECD models.展开更多
A dimensionless load-displacement model based on the energy-density equivalence principle is proposed to obtain the stress-strain relationships of metallic materials under monotonic indentations with various diameters...A dimensionless load-displacement model based on the energy-density equivalence principle is proposed to obtain the stress-strain relationships of metallic materials under monotonic indentations with various diameters of spherical indenters.Finite element simulations are carried out to verify the constitutive relations from the new model,involving indentations made with various spherical indenters.For each indenter,some quasi-static spherical indentation tests are conducted on the materials with 40 preset constitutive relationships.The results indicate that the stress-strain curves predicted by the model align with the preset curves under 200 loading conditions.Moreover,the goodness-of-fit between the predicted stress-strain curves and the preset curves exceeds0.96 for all indenters and materials.In the end,the indentation tests are conducted by the spherical indenters with the diameters of 1.587 mm for fifteen metallic materials and1 mm for eight metallic materials.The results show that the stress-strain curves obtained by the spherical indentation based on the new model closely match those obtained from the uniaxial tensile tests.The relative errors for both the proof strength at 0.2%plastic extension and the tensile strength are below 5%.展开更多
Considering that we still do not fully understand the behavior of air pockets trapped in rainstorm systems and water flow changes inside pipes,the study of actual geysers presents many challenges.In this study,three-d...Considering that we still do not fully understand the behavior of air pockets trapped in rainstorm systems and water flow changes inside pipes,the study of actual geysers presents many challenges.In this study,three-dimensional numerical models were developed to investigate the mechanisms of geyser events triggered by rapid filling flows at different scales.The results showed that,in the first stage of the water–air mixture of the prototype model,a large amount of air was released quickly,and the subsequent overflow lasted for a more extended period.The transport capacity of the downstream pipe,as a critical factor,significantly influenced the water–air interaction of the geyser.Restricting the outlet area and increasing the outlet pressure simultaneously resulted in a stronger geyser.The equivalent density of the water–air mixture increased as the scale decreased during the geyser event.展开更多
The electromagnetic field under applied AC and DC current in round and rectangular pipe was systematically investigated, then a concept of 'equivalent current density' was proposed for evaluating the inhomogen...The electromagnetic field under applied AC and DC current in round and rectangular pipe was systematically investigated, then a concept of 'equivalent current density' was proposed for evaluating the inhomogeneous electromagnetic pinch force, and the mono-component removal efficiency and the overall removal efficiency of inclusion were formulated. It is founded that flat pipe is superior to round pipe for the electromagnetic removal of inclusion, and DC current can get a higher removal efficiency than A C current due to absence of skin phenomenon. Under usual condition, a removal efficiency of 52% for 10μm inclusion or more than 92% for 20μm inclusion can be achieved by imposing a current density of 3×106A/m2 in a flat pipe.展开更多
Although there are methods for testing the stress-strain relation and strength,which are the most fundamental and important properties of metallic materials,their application to small-volume materials and tube compone...Although there are methods for testing the stress-strain relation and strength,which are the most fundamental and important properties of metallic materials,their application to small-volume materials and tube components is lim-ited.In this study,based on energy density equivalence,a new dimensionless elastoplastic load-displacement model for compressed metal rings with isotropy and constitutive power law is proposed to describe the relations among the geometric dimensions,Hollomon law parameters,load,and displacement.Furthermore,a novel test method was developed to determine the elastic modulus,stress-strain relation,yield and tensile strength via ring compression test.The universality and accuracy of the method were verified within a wide range of imaginary materials using finite element analysis(FEA),and the results show that the stress-strain curves obtained by this method are consistent with those inputted in the FEA program.Additionally,a series of ring compression tests were performed for seven metallic materials.It was found that the stress-strain curves and mechanical properties predicted by the method agreed with the uniaxial tensile results.With its low material consumption,the ring compression test has the potential to be as an alternative to traditional tensile test when direct tension method is limited.展开更多
LS-SVM （least squares support vector machines） are a class of kemel machines emphasizing on primal-dual aspects in a constrained optimization framework. LS-SVMs aim at extending methodologies typical of classical su...LS-SVM （least squares support vector machines） are a class of kemel machines emphasizing on primal-dual aspects in a constrained optimization framework. LS-SVMs aim at extending methodologies typical of classical support vector machines for problems beyond classification and regression. This paper describes a methodology that was developed for the prediction of the critical flashover voltage of polluted insulators by using a LS-SVM. The methodology uses as input variables characteristics of the insulator such as diameter, height, creepage distance, form factor and equivalent salt deposit density. The estimation offlashover performance of polluted insulators is based on field experience and laboratory tests are invaluable as they significantly reduce the time and labour involved in insulators design and selection. The majority of the variables to be predicted are dependent upon several independent variables. The results from this work are useful to predict the contamination severity, critical flashover voltage as a function of contamination severity, arc length, and especially to predict the flashover voltage. The validity of the approach was examined by testing several insulators with different geometries. Moreover, the performance of the proposed approach with other intelligence method based on ANN （artificial neural networks） is compared. It can be concluded that the LS-SVM approach has better generalization ability that assist the measurement and monitoring of contamination severity, flashover voltage and leakage current.展开更多
The first principal stress plays a key role in ductile fracture processes.Investigation of the distribution and evolution of the first principal stress at the crack tip is essential for exploring elastoplastic fractur...The first principal stress plays a key role in ductile fracture processes.Investigation of the distribution and evolution of the first principal stress at the crack tip is essential for exploring elastoplastic fracture behaviors.A semi-analytical model was developed in this study to determine the maximal first principal stress at the mode I crack tip with 3D constraints for materials following the Ramberg-Osgood law.The model,based on energy density equivalence and dimensional analysis,was validated through finite element analysis(FEA)of various materials and geometric dimensions of specimens with mode I cracks,under over 100 different types of working conditions.The dimensionless curves of maximal first principal stress versus load,as predicted by the model,agreed well with the FEA results,demonstrating the accuracy and applicability of the model.This research can provide a basis for future theoretical predictions of crack initiation and propagation.展开更多
To investigate the fouling characteristics of the composite insulator surface under the salt fog environment,the FXBW-110/120-2 composite insulator was taken as the research object.Based on the field-induced charge me...To investigate the fouling characteristics of the composite insulator surface under the salt fog environment,the FXBW-110/120-2 composite insulator was taken as the research object.Based on the field-induced charge mechanism,the multi-physical field coupling software COMSOL was used to numerically simulate the fouling characteristics,explored the calculation method of ESDD,and demonstrated its rationality.Based on this method,the pollution characteristics of the composite insulator under the pollution fog environment were studied,and the influence of wind speed,droplet size,and voltage type on the pollution characteristics of the composite insulator was analyzed.The results showed that:with the increase in wind speed,the amount of accumulated pollution of insulator increases in the range of droplet size,and the relationship between wind speed and accumulated pollution is approximately linear;at the same wind speed,the amount of accumulated pollution increases with the increase of droplet size under the action of DC voltage;when there is no voltage,the amount of dirt on the upper surface of the insulator is more than that on the lower surface,while it is the opposite under DC voltage.展开更多
The problems in calculating parameters of equivalent collection area,earth resistivity and lightning protection category as well as their effects on lightning disaster risk assessment were analyzed,and practical examp...The problems in calculating parameters of equivalent collection area,earth resistivity and lightning protection category as well as their effects on lightning disaster risk assessment were analyzed,and practical examples proved the effects of those differences on lightning protection identification,intercept efficiency calculation in evaluating lightning disaster risk. In the meantime,several new concepts,such as the height of buildings for lightning protection were defined,and a fixed radius value was set to the ground flash density for calculation,establishing the ground flash density formula to solve the problems in parameter calculation,which would be beneficial to promote the standardization of lightning disaster risk assessment.展开更多
A triboelectric nanogenerator （TENG） with an organic nanocomposite electret thin film as the triboelectric layer for mechanical energy harvesting was investigated systematically. In combination with corona charging,...A triboelectric nanogenerator （TENG） with an organic nanocomposite electret thin film as the triboelectric layer for mechanical energy harvesting was investigated systematically. In combination with corona charging, a TENG was fabricated by using embedded-nanocapacitor-structure polytetrafluoroethylene （PTFE） impregnated with gold nanoparticles （Au-NPs）. The output performances, stability, and durability of the TENGs with Au-PTFE nanocomposite films were characterized after being washed in water. It was found that the output current increases by 70% and the equivalent surface charge density （ESCD） reaches 85 μC/m^2 in comparison to the virgin PTFE film. Such outstanding performance is likely due to the equivalent nanocapacitors between the Au-NPs and PTFE molecules, which serve as nano charge traps in the nanocomposite electret film under negative high-voltage corona charging. This work not only expands the practical applications of TENGs, but also opens up new possibilities for the development of high performance triboelectric materials.展开更多
基金supported by the Postdoctoral Fellow-ship Program of CPSF(Grant No.GZC20233105)the Science Foundation of China University of Petroleum,Beijing(Grant No.2462024XKBH006)+2 种基金the China Postdoctoral Science Foundation(Grant No.2024M753615)the Major Scientific Research Instrument Development Program of National Natural Science Foundation of China(Grant No.52227804)the Youth Science Foundation Program of National Natural Science Foundation of China(Grant No.52404012).
文摘The gas kick represents a major risk in deepwater oil and gas exploration.Understanding the dynamics of gas kick evolution and the associated pressure response characteristics is critical for effective well control.In this paper,we introduce a transient wellbore multiphase flow model specifically developed to simulate gas kick in deepwater dual-gradient drilling,incorporating a downhole separator.The model accounts for the variable mass flow within the annulus and heat exchange between the annular fluid and the formation.Using this model,we analyzed the multiphase flow and thermodynamic behavior during the gas kick.Simulation results reveal a progressive increase in bottom-hole temperature,underscoring its potential as a key indicator for gas kick early detection.Additionally,variable gradient parameters affect not only the annular equivalent circulating density(ECD)profile but also the evolution of the gas kick.The inclusion of a downhole separator alters the annular ECD profile,creating a“broken line”shape,which enhances adaptability to the multi-pressure systems typically encountered in deepwater forma-tion.By adjusting factors such as hollow sphere concentration,separator position,and separation effi-ciency,the annular ECD profile can be effectively customized.This study provides important theoretical insights and practical applications for utilizing dual-gradient drilling technology to address challenges in deepwater formation drilling.
文摘Equivalent circulating density(ECD)denotes the density of drilling mud during circulation within a well.It is determined by integrating the equivalent static density with the pressure loss attributable to friction between the flowing mud and the geological formation.The effective management of ECD is imperative during drilling operations,as it plays a critical role in preventing kicks and minimising mud losses.Mud ECD has undergone extensive investigation through laboratory experiments,field measurements,and predictive modelling.Nevertheless,a comprehensive review of the various predictive models associated with ECD remains absent.The objective of this study is to review and critique existing correlations for estimating ECD.To accomplish this,a thorough bibliometric analysis was performed,focusing on peer-reviewed journals,mud manuals,and oil and gas conference papers.For the sake of clarity,existing models were categorized into tables,with their principal features highlighted.A critique of each model was subsequently provided.In total,45 models related to ECD were identified,reviewed,and critiqued.The findings reveal that over 44%of the models are based on machine learning(ML),27%are analytical models,16%are regression based models,and 13%are simulator-related.Although there is no universally accepted model for ECD,there is an observable trend towards the utilization of ML algorithms for ECD estimation due to their predictive capabilities.However,the interpretability of these ML-based models remains a significant concern.This review serves as a comprehensive source of information on ECD for both readers and industry practitioners.Additionally,it directs researchers towards areas requiring further exploration and aids drilling professionals in selecting appropriate ECD models.
基金Project supported by the National Natural Science Foundation of China(Nos.11872320 and 12072294)。
文摘A dimensionless load-displacement model based on the energy-density equivalence principle is proposed to obtain the stress-strain relationships of metallic materials under monotonic indentations with various diameters of spherical indenters.Finite element simulations are carried out to verify the constitutive relations from the new model,involving indentations made with various spherical indenters.For each indenter,some quasi-static spherical indentation tests are conducted on the materials with 40 preset constitutive relationships.The results indicate that the stress-strain curves predicted by the model align with the preset curves under 200 loading conditions.Moreover,the goodness-of-fit between the predicted stress-strain curves and the preset curves exceeds0.96 for all indenters and materials.In the end,the indentation tests are conducted by the spherical indenters with the diameters of 1.587 mm for fifteen metallic materials and1 mm for eight metallic materials.The results show that the stress-strain curves obtained by the spherical indentation based on the new model closely match those obtained from the uniaxial tensile tests.The relative errors for both the proof strength at 0.2%plastic extension and the tensile strength are below 5%.
基金supported by the National Key Laboratory of Water Disaster Prevention(Grant No.2021492011)the Natural Science Foundation of Zhejiang Province(Grant No.LQ22E090002).
文摘Considering that we still do not fully understand the behavior of air pockets trapped in rainstorm systems and water flow changes inside pipes,the study of actual geysers presents many challenges.In this study,three-dimensional numerical models were developed to investigate the mechanisms of geyser events triggered by rapid filling flows at different scales.The results showed that,in the first stage of the water–air mixture of the prototype model,a large amount of air was released quickly,and the subsequent overflow lasted for a more extended period.The transport capacity of the downstream pipe,as a critical factor,significantly influenced the water–air interaction of the geyser.Restricting the outlet area and increasing the outlet pressure simultaneously resulted in a stronger geyser.The equivalent density of the water–air mixture increased as the scale decreased during the geyser event.
文摘The electromagnetic field under applied AC and DC current in round and rectangular pipe was systematically investigated, then a concept of 'equivalent current density' was proposed for evaluating the inhomogeneous electromagnetic pinch force, and the mono-component removal efficiency and the overall removal efficiency of inclusion were formulated. It is founded that flat pipe is superior to round pipe for the electromagnetic removal of inclusion, and DC current can get a higher removal efficiency than A C current due to absence of skin phenomenon. Under usual condition, a removal efficiency of 52% for 10μm inclusion or more than 92% for 20μm inclusion can be achieved by imposing a current density of 3×106A/m2 in a flat pipe.
基金Supported by National Natural Science Foundation of China(Grant Nos.11872320 and 12072294)
文摘Although there are methods for testing the stress-strain relation and strength,which are the most fundamental and important properties of metallic materials,their application to small-volume materials and tube components is lim-ited.In this study,based on energy density equivalence,a new dimensionless elastoplastic load-displacement model for compressed metal rings with isotropy and constitutive power law is proposed to describe the relations among the geometric dimensions,Hollomon law parameters,load,and displacement.Furthermore,a novel test method was developed to determine the elastic modulus,stress-strain relation,yield and tensile strength via ring compression test.The universality and accuracy of the method were verified within a wide range of imaginary materials using finite element analysis(FEA),and the results show that the stress-strain curves obtained by this method are consistent with those inputted in the FEA program.Additionally,a series of ring compression tests were performed for seven metallic materials.It was found that the stress-strain curves and mechanical properties predicted by the method agreed with the uniaxial tensile results.With its low material consumption,the ring compression test has the potential to be as an alternative to traditional tensile test when direct tension method is limited.
文摘LS-SVM （least squares support vector machines） are a class of kemel machines emphasizing on primal-dual aspects in a constrained optimization framework. LS-SVMs aim at extending methodologies typical of classical support vector machines for problems beyond classification and regression. This paper describes a methodology that was developed for the prediction of the critical flashover voltage of polluted insulators by using a LS-SVM. The methodology uses as input variables characteristics of the insulator such as diameter, height, creepage distance, form factor and equivalent salt deposit density. The estimation offlashover performance of polluted insulators is based on field experience and laboratory tests are invaluable as they significantly reduce the time and labour involved in insulators design and selection. The majority of the variables to be predicted are dependent upon several independent variables. The results from this work are useful to predict the contamination severity, critical flashover voltage as a function of contamination severity, arc length, and especially to predict the flashover voltage. The validity of the approach was examined by testing several insulators with different geometries. Moreover, the performance of the proposed approach with other intelligence method based on ANN （artificial neural networks） is compared. It can be concluded that the LS-SVM approach has better generalization ability that assist the measurement and monitoring of contamination severity, flashover voltage and leakage current.
基金supported by the National Natural Science Foundation of China(Grant No.11872320)Sichuan Province Science and Technology Support Program(Grant No.2023NSFSC1296).
文摘The first principal stress plays a key role in ductile fracture processes.Investigation of the distribution and evolution of the first principal stress at the crack tip is essential for exploring elastoplastic fracture behaviors.A semi-analytical model was developed in this study to determine the maximal first principal stress at the mode I crack tip with 3D constraints for materials following the Ramberg-Osgood law.The model,based on energy density equivalence and dimensional analysis,was validated through finite element analysis(FEA)of various materials and geometric dimensions of specimens with mode I cracks,under over 100 different types of working conditions.The dimensionless curves of maximal first principal stress versus load,as predicted by the model,agreed well with the FEA results,demonstrating the accuracy and applicability of the model.This research can provide a basis for future theoretical predictions of crack initiation and propagation.
文摘To investigate the fouling characteristics of the composite insulator surface under the salt fog environment,the FXBW-110/120-2 composite insulator was taken as the research object.Based on the field-induced charge mechanism,the multi-physical field coupling software COMSOL was used to numerically simulate the fouling characteristics,explored the calculation method of ESDD,and demonstrated its rationality.Based on this method,the pollution characteristics of the composite insulator under the pollution fog environment were studied,and the influence of wind speed,droplet size,and voltage type on the pollution characteristics of the composite insulator was analyzed.The results showed that:with the increase in wind speed,the amount of accumulated pollution of insulator increases in the range of droplet size,and the relationship between wind speed and accumulated pollution is approximately linear;at the same wind speed,the amount of accumulated pollution increases with the increase of droplet size under the action of DC voltage;when there is no voltage,the amount of dirt on the upper surface of the insulator is more than that on the lower surface,while it is the opposite under DC voltage.
文摘The problems in calculating parameters of equivalent collection area,earth resistivity and lightning protection category as well as their effects on lightning disaster risk assessment were analyzed,and practical examples proved the effects of those differences on lightning protection identification,intercept efficiency calculation in evaluating lightning disaster risk. In the meantime,several new concepts,such as the height of buildings for lightning protection were defined,and a fixed radius value was set to the ground flash density for calculation,establishing the ground flash density formula to solve the problems in parameter calculation,which would be beneficial to promote the standardization of lightning disaster risk assessment.
文摘A triboelectric nanogenerator （TENG） with an organic nanocomposite electret thin film as the triboelectric layer for mechanical energy harvesting was investigated systematically. In combination with corona charging, a TENG was fabricated by using embedded-nanocapacitor-structure polytetrafluoroethylene （PTFE） impregnated with gold nanoparticles （Au-NPs）. The output performances, stability, and durability of the TENGs with Au-PTFE nanocomposite films were characterized after being washed in water. It was found that the output current increases by 70% and the equivalent surface charge density （ESCD） reaches 85 μC/m^2 in comparison to the virgin PTFE film. Such outstanding performance is likely due to the equivalent nanocapacitors between the Au-NPs and PTFE molecules, which serve as nano charge traps in the nanocomposite electret film under negative high-voltage corona charging. This work not only expands the practical applications of TENGs, but also opens up new possibilities for the development of high performance triboelectric materials.
