To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading,fatigue tests under different upper-limit stresses were carried out on salt rock,an...To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading,fatigue tests under different upper-limit stresses were carried out on salt rock,and the mesoscopic pore structures of salt rock before and after fatigue tests and under different cycle numbers were measured using CT scanning instrument.Based on the test results,the effects of the cycle number and the upper-limit stress on the evolution of cracks,pore morphology,pore number,pore volume,pore size,plane porosity,and volume porosity of salt rock were analyzed.The failure path of salt rock specimens under cyclic loading was analyzed using the distribution law of plane porosity.The damage variable of salt rock under cyclic loading was defined on basis of the variation of volume porosity with cycle number.In order to describe the fatigue deformation behavior of salt rock under cyclic loading,the nonlinear Burgers damage constitutive model was further established.The results show that the model established can better reflect the whole development process of fatigue deformation of salt rock under cyclic loading.展开更多
The paper presents the results of comprehensive studies of filtration and capacitance properties of highly porous reservoir rocks of the aquifer of an underground gas storage facility.The geomechanical part of the res...The paper presents the results of comprehensive studies of filtration and capacitance properties of highly porous reservoir rocks of the aquifer of an underground gas storage facility.The geomechanical part of the research included studying the dependence of rock permeability on the stress-strain state in the vicinity of the wells,and physical modeling of the implementation of the method of increasing the permeability of the wellbore zone-the method of directional unloading of the reservoir.The digital part of the research included computed tomography(CT)-based computer analysis of the internal structure,pore space characteristics,and filtration properties before and after the tests.According to the results of physical modeling of deformation and filtration processes,it is found that the permeability of rocks before fracture depends on the stress-strain state insignificantly,and this influence is reversible.However,when downhole pressure reaches 7-8 MPa,macrocracks in the rock begin to grow,accompanied by irreversible permeability increase.Porosity,geodesic tortuosity and permeability values were obtained based on digital studies and numerical modeling.A weak degree of transversal anisotropy of the filtration properties of rocks was detected.Based on the analysis of pore size distribution,pressure field and flow velocities,high homogeneity and connectivity of the rock pore space is shown.The absence of pronounced changes in pore space characteristics and pore permeability after non-uniform triaxial loading rocks was shown.On the basis of geometrical analysis of pore space,the reasons for weak permeability anisotropy were identified.The filtration-capacitance properties obtained from the digital analysis showed very good agreement with the results of field and laboratory measurements.The physical modeling has confirmed the efficiency of application of the directional unloading method for the reservoir under study.The necessary parameters of its application were calculated:bottomhole geometry,stage of operation,stresses and pressure drawdown value.展开更多
目的基于Markov模型评价肺结节低剂量螺旋CT(LDCT)筛查的卫生经济学。方法利用2021年—2023年北京市某三甲医院的肺结节LDCT筛查数据和部分国外临床研究数据,采用成本效用分析方法,通过增量成本效用比(ICUR)确定优势筛查策略;使用R语言...目的基于Markov模型评价肺结节低剂量螺旋CT(LDCT)筛查的卫生经济学。方法利用2021年—2023年北京市某三甲医院的肺结节LDCT筛查数据和部分国外临床研究数据,采用成本效用分析方法,通过增量成本效用比(ICUR)确定优势筛查策略;使用R语言获得转移概率参数,利用TreeAge Pro 2011软件构建Markov模型。假设以我国10万名55岁及以上人群为肺结节筛查对象,模拟其疾病发展情况,并通过敏感性分析评价该模型的稳定性。结果成本效用分析显示,该模型经20次循环后,LDCT筛查策略的总成本为3543088618元,相较于不筛查策略的总成本增加了784130651元,额外获得了7996个质量调整生命年(QALY),每获得一个QALY需多花费98059.77元。采用WHO卫生经济学评价标准,LDCT筛查策略的ICUR大于1倍人均国内生产总值(GDP)但小于3倍人均GDP,为优势策略。敏感性分析显示,各变量在其敏感性分析范围内无论如何变化,都不会对ICUR产生较大影响,表明该模型具有较好的稳定性。结论在55岁及以上人群中开展每年一次肺结节LDCT筛查的ICUR小于3倍人均GDP,具有一定的经济学效用,该筛查策略有利于肺癌的“早发现、早诊断、早治疗”。展开更多
基金supported by the National Natural Science Foundation of China(No.52178354).
文摘To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading,fatigue tests under different upper-limit stresses were carried out on salt rock,and the mesoscopic pore structures of salt rock before and after fatigue tests and under different cycle numbers were measured using CT scanning instrument.Based on the test results,the effects of the cycle number and the upper-limit stress on the evolution of cracks,pore morphology,pore number,pore volume,pore size,plane porosity,and volume porosity of salt rock were analyzed.The failure path of salt rock specimens under cyclic loading was analyzed using the distribution law of plane porosity.The damage variable of salt rock under cyclic loading was defined on basis of the variation of volume porosity with cycle number.In order to describe the fatigue deformation behavior of salt rock under cyclic loading,the nonlinear Burgers damage constitutive model was further established.The results show that the model established can better reflect the whole development process of fatigue deformation of salt rock under cyclic loading.
基金supported by the Russian Science Foundation(Grant No.22-11-00273).
文摘The paper presents the results of comprehensive studies of filtration and capacitance properties of highly porous reservoir rocks of the aquifer of an underground gas storage facility.The geomechanical part of the research included studying the dependence of rock permeability on the stress-strain state in the vicinity of the wells,and physical modeling of the implementation of the method of increasing the permeability of the wellbore zone-the method of directional unloading of the reservoir.The digital part of the research included computed tomography(CT)-based computer analysis of the internal structure,pore space characteristics,and filtration properties before and after the tests.According to the results of physical modeling of deformation and filtration processes,it is found that the permeability of rocks before fracture depends on the stress-strain state insignificantly,and this influence is reversible.However,when downhole pressure reaches 7-8 MPa,macrocracks in the rock begin to grow,accompanied by irreversible permeability increase.Porosity,geodesic tortuosity and permeability values were obtained based on digital studies and numerical modeling.A weak degree of transversal anisotropy of the filtration properties of rocks was detected.Based on the analysis of pore size distribution,pressure field and flow velocities,high homogeneity and connectivity of the rock pore space is shown.The absence of pronounced changes in pore space characteristics and pore permeability after non-uniform triaxial loading rocks was shown.On the basis of geometrical analysis of pore space,the reasons for weak permeability anisotropy were identified.The filtration-capacitance properties obtained from the digital analysis showed very good agreement with the results of field and laboratory measurements.The physical modeling has confirmed the efficiency of application of the directional unloading method for the reservoir under study.The necessary parameters of its application were calculated:bottomhole geometry,stage of operation,stresses and pressure drawdown value.
文摘目的基于Markov模型评价肺结节低剂量螺旋CT(LDCT)筛查的卫生经济学。方法利用2021年—2023年北京市某三甲医院的肺结节LDCT筛查数据和部分国外临床研究数据,采用成本效用分析方法,通过增量成本效用比(ICUR)确定优势筛查策略;使用R语言获得转移概率参数,利用TreeAge Pro 2011软件构建Markov模型。假设以我国10万名55岁及以上人群为肺结节筛查对象,模拟其疾病发展情况,并通过敏感性分析评价该模型的稳定性。结果成本效用分析显示,该模型经20次循环后,LDCT筛查策略的总成本为3543088618元,相较于不筛查策略的总成本增加了784130651元,额外获得了7996个质量调整生命年(QALY),每获得一个QALY需多花费98059.77元。采用WHO卫生经济学评价标准,LDCT筛查策略的ICUR大于1倍人均国内生产总值(GDP)但小于3倍人均GDP,为优势策略。敏感性分析显示,各变量在其敏感性分析范围内无论如何变化,都不会对ICUR产生较大影响,表明该模型具有较好的稳定性。结论在55岁及以上人群中开展每年一次肺结节LDCT筛查的ICUR小于3倍人均GDP,具有一定的经济学效用,该筛查策略有利于肺癌的“早发现、早诊断、早治疗”。
