The rigid-plastic assumption has greatly simplified the theoretical analysis of dynamic plastic response of structures.Within this framework,a common tool is the modal technique using approximate independent yield cri...The rigid-plastic assumption has greatly simplified the theoretical analysis of dynamic plastic response of structures.Within this framework,a common tool is the modal technique using approximate independent yield criteria,which leads to upper-and lower-bound solutions,but usually with poor accuracy.In this paper,by utilizing the membrane factor method(MFM),the large-deflection dynamic plastic response of square plates subjected to exponentially decaying pulse loading is analyzed by taking both the transient response phase and the exact yield criterion into account.Based on the combination of saturation analysis(SA)and MFM,the complete solutions and regressive formulae of saturated deflection and saturated impulse are obtained.As the dynamic behavior of plates under rectangular pulse loading serves as a benchmark of pulse-equivalent techniques,the large plastic deformation of square plates under short-duration rectangular pulse is also analyzed in detail.Moreover,by comparing the SA results of pulse-loaded square plates with different boundary conditions,it is found that the saturated deflection and saturated impulse of the fully clamped and simply supported square plates both increase linearly with the pulse amplitude,and the slopes are approximately the same,so the conversion between the SA quantities of plates with different boundary conditions can be easily achieved.展开更多
When using the plug pulse decay method to measure shale permeability,a comprehensive analysis of various factors influencing the measurement and analysis precision is conducive to improving the accuracy of the test re...When using the plug pulse decay method to measure shale permeability,a comprehensive analysis of various factors influencing the measurement and analysis precision is conducive to improving the accuracy of the test result.A great number of nano-scale pores are developed in shale,so the lower the test pressure is,the more easily the non-Darcy flow tends to emerge.In order to ensure the gas is in the form of Darcy flow in the process of measurement,we put forward the lower pressure limit of Darcy flow in pores according to the definition of Knudsen number.Then,the gas desorption-flow coupling model for the gas flow process during the plug pulse decay measurement was established by considering the effects of gas on the adsorption in organic pores.After the partial differential equation set was solved and derived,the corresponding permeability calculation method was proposed.Finally,after the plug pulse decay measurement,the supporting nitrogen isothermal adsorption test and methane isothermal adsorption test were conducted on shale samples.And the following research results were obtained.First,during the plug pulse decay measurement,the flow of gas in rock samples is one-dimensional linear,so when establishing the flow equation,the gas pseudopressure can be replaced with the gas pressure to simplify the calculation.Second,the adsorption of nitrogen in shale is much less than that of methane in shale,so the influence of nitrogen desorption on the flow is negligible when the pressure difference(i.e.<5%)of upstream and downstream changes within 5%of the initial pore pressure.In conclusion,the available industrial standards don't take into consideration the influence of gas adsorption,but the shale permeability measurement can still satisfy the accuracy requirement.展开更多
Permeability is a key parameter to describe fluid transport properties of porous medium; however, the permeability measurement is extremely difficult for tight porous medium, e.g. fine-grained rock or dense soil. In t...Permeability is a key parameter to describe fluid transport properties of porous medium; however, the permeability measurement is extremely difficult for tight porous medium, e.g. fine-grained rock or dense soil. In this paper, three methods for gas permeability measurement, i.e. steady state method, pulse decay method(PDM) and pressure oscillation method(POM), are first reviewed and then their advantages and drawbacks are discussed. Both analytical and numerical solutions of gas permeability are presented for the tight porous medium. The results show that the analytical method is relatively simple but only valid under certain conditions, whilst the numerical method is more robust and generic, which can take into account several factors such as porosity, saturation, gas leakage, and unconventional boundary conditions. The influence of the effective porosity on the permeability determination is further analyzed using the proposed numerical method. In this study, new pressure data interpretation procedures for PDM and POM are proposed, and the obtained results can serve as a guidance to define a proper method for permeability measurement of the tight porous medium.展开更多
基金the support of the Wuhan University of Technology start-up fund for Distinguished Professors(No.471-40120163)the China Scholarship Council(CSC).
文摘The rigid-plastic assumption has greatly simplified the theoretical analysis of dynamic plastic response of structures.Within this framework,a common tool is the modal technique using approximate independent yield criteria,which leads to upper-and lower-bound solutions,but usually with poor accuracy.In this paper,by utilizing the membrane factor method(MFM),the large-deflection dynamic plastic response of square plates subjected to exponentially decaying pulse loading is analyzed by taking both the transient response phase and the exact yield criterion into account.Based on the combination of saturation analysis(SA)and MFM,the complete solutions and regressive formulae of saturated deflection and saturated impulse are obtained.As the dynamic behavior of plates under rectangular pulse loading serves as a benchmark of pulse-equivalent techniques,the large plastic deformation of square plates under short-duration rectangular pulse is also analyzed in detail.Moreover,by comparing the SA results of pulse-loaded square plates with different boundary conditions,it is found that the saturated deflection and saturated impulse of the fully clamped and simply supported square plates both increase linearly with the pulse amplitude,and the slopes are approximately the same,so the conversion between the SA quantities of plates with different boundary conditions can be easily achieved.
基金supported by the National Major Science and Technology Project under the 13th Five-year Plan“Development of large oil/gas fields and coalbed methane”(No.:2016ZX05034-002-006 and 2016ZX05066003-003).
文摘When using the plug pulse decay method to measure shale permeability,a comprehensive analysis of various factors influencing the measurement and analysis precision is conducive to improving the accuracy of the test result.A great number of nano-scale pores are developed in shale,so the lower the test pressure is,the more easily the non-Darcy flow tends to emerge.In order to ensure the gas is in the form of Darcy flow in the process of measurement,we put forward the lower pressure limit of Darcy flow in pores according to the definition of Knudsen number.Then,the gas desorption-flow coupling model for the gas flow process during the plug pulse decay measurement was established by considering the effects of gas on the adsorption in organic pores.After the partial differential equation set was solved and derived,the corresponding permeability calculation method was proposed.Finally,after the plug pulse decay measurement,the supporting nitrogen isothermal adsorption test and methane isothermal adsorption test were conducted on shale samples.And the following research results were obtained.First,during the plug pulse decay measurement,the flow of gas in rock samples is one-dimensional linear,so when establishing the flow equation,the gas pseudopressure can be replaced with the gas pressure to simplify the calculation.Second,the adsorption of nitrogen in shale is much less than that of methane in shale,so the influence of nitrogen desorption on the flow is negligible when the pressure difference(i.e.<5%)of upstream and downstream changes within 5%of the initial pore pressure.In conclusion,the available industrial standards don't take into consideration the influence of gas adsorption,but the shale permeability measurement can still satisfy the accuracy requirement.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 41572290, 51479190 and 51879260)the Chinese Fundamental Research (973) Program (Grant No. 2015CB057906)Hubei Provincial Natural Science Foundation of China (Grant No. 2018CFA012)
文摘Permeability is a key parameter to describe fluid transport properties of porous medium; however, the permeability measurement is extremely difficult for tight porous medium, e.g. fine-grained rock or dense soil. In this paper, three methods for gas permeability measurement, i.e. steady state method, pulse decay method(PDM) and pressure oscillation method(POM), are first reviewed and then their advantages and drawbacks are discussed. Both analytical and numerical solutions of gas permeability are presented for the tight porous medium. The results show that the analytical method is relatively simple but only valid under certain conditions, whilst the numerical method is more robust and generic, which can take into account several factors such as porosity, saturation, gas leakage, and unconventional boundary conditions. The influence of the effective porosity on the permeability determination is further analyzed using the proposed numerical method. In this study, new pressure data interpretation procedures for PDM and POM are proposed, and the obtained results can serve as a guidance to define a proper method for permeability measurement of the tight porous medium.
