Since December 2019,COVID-19 has occurred unexpectedly and emerged as a health problem worldw ide.Despite the rapidly increasing number of cases in subsequent weeks,the clinical characteristics of pediatric cases are ...Since December 2019,COVID-19 has occurred unexpectedly and emerged as a health problem worldw ide.Despite the rapidly increasing number of cases in subsequent weeks,the clinical characteristics of pediatric cases are rarely described.A cross-sectional multicenter study was carried out in 10 hospitals across Hubei province.A total of 25 confirmed pediatric cases of COVID-19 were collected.The demographic data,epidemiological history,underlying discascs,clinical mani festations,laboratory and radiological data,treatments,and outcomes were analyzcd.Of 25 hospitalized patients with COVID-19,the boy to girl ratio was 1.27:1.The median age was 3 years.COVID-19 cases in children aged<3 years,3-6 years,and≥6-years patients were 10(40%),6(24%),and 9(36%),respectively.The most common symptoms at onset of ilness were fever(13[52%]),and dry cough(11[44%]).Chest CT images showed essential normal in 8 cases(33.3%),unilateral involvement of lungs in 5 cases(20.8%),and bilateral involvement in 11 cases(45.8%).Clinical diagnoses included upper respiratory tract infection(n=8),mild pneumonia(n=15),and critical cases(n=2).Two critical cases(8%)were given invasive mechanical ventilation,corticosteroids,and immunoglobulin.The symptoms in 24(96%)of 25 patients were alleviated and one patient had been discharged.It was concluded that children were susceptible to COVID-19 like adults,while the clinical presentations and outcomes were more favorable in children.However,children less than 3 years old accounted for majority cases and critical cases lied in this age group,which demanded extra attentions during home caring and hospitalization treatment.展开更多
Drilling fluids face failure during drilling deep reservoir with high temperature and high salt.The experimental results show that high temperature and salinity reduce the negative charge on the surface of bentonite i...Drilling fluids face failure during drilling deep reservoir with high temperature and high salt.The experimental results show that high temperature and salinity reduce the negative charge on the surface of bentonite in the drilling fluid and cause the coalescence of bentonite particles.As a result,the particles coalesce,the grid structure is destroyed,and the rheological properties,rock-carrying capacity and filtration properties are lost.To resolve the foregoing,in this study,0.05-wt%carbon nanotubes are introduced into a 4%bentonite drilling fluid under conditions where the temperature and concentration of added Na Cl reach 180°C and 10 wt%,respectively.The carbon nanotubes adsorb on the bentonite surface and increase the space among bentonite particles.The steric hindrance prevents the coalescence of bentonite in high temperature and high salt environment.Thus bentonite maintains the small size distribution of bentonite and supports the bentonite grid structure in the drilling fluid.As a result,the rock-carrying capacity of the drilling fluid increases by 85.1%.Moreover,the mud cake formed by the accumulation of small-sized bentonite particles is dense;consequently,the filtration of bentonite drilling fluid reduced by 30.2%.展开更多
The well cementing is important during the extended reach well drilling and the completion, whereas the displacement efficiency and the interface stability are important to guarantee the success of the cementing. In t...The well cementing is important during the extended reach well drilling and the completion, whereas the displacement efficiency and the interface stability are important to guarantee the success of the cementing. In this paper, the interface stability of the cement slurry is simulated using the computational fluid dynamics software. The calculation results indicate that during the displacement, the length of the displacement interface increases with the increase of the deviation angle. The larger the eccentricity, the more significant the velocity difference, along with a longer displacement interface length, a less stable interface, and a lower displacement efficiency. Therefore, to guarantee the cementing quality and maintain a high displacement efficiency, the eccentricity should be controlled within 0.5. Application of a casing centralizer will dramatically improve the interface stability, decrease the dilution zone length of the interface and thus, is beneficial to the slurry cementing and displacement. The simulations are verified with an average absolute deviation less than 3.76% and the 45？ helix angle of the rigid centralizer is recommended. Combining the data of an extended reach well on-site, methods are proposed for improving the displacement efficiency and the interface stability during the well cementing and displacement with complex boreholes. These numerical methods can be used to provide some theoretical guidance for designing the cementing of an extended reach well.展开更多
文摘Since December 2019,COVID-19 has occurred unexpectedly and emerged as a health problem worldw ide.Despite the rapidly increasing number of cases in subsequent weeks,the clinical characteristics of pediatric cases are rarely described.A cross-sectional multicenter study was carried out in 10 hospitals across Hubei province.A total of 25 confirmed pediatric cases of COVID-19 were collected.The demographic data,epidemiological history,underlying discascs,clinical mani festations,laboratory and radiological data,treatments,and outcomes were analyzcd.Of 25 hospitalized patients with COVID-19,the boy to girl ratio was 1.27:1.The median age was 3 years.COVID-19 cases in children aged<3 years,3-6 years,and≥6-years patients were 10(40%),6(24%),and 9(36%),respectively.The most common symptoms at onset of ilness were fever(13[52%]),and dry cough(11[44%]).Chest CT images showed essential normal in 8 cases(33.3%),unilateral involvement of lungs in 5 cases(20.8%),and bilateral involvement in 11 cases(45.8%).Clinical diagnoses included upper respiratory tract infection(n=8),mild pneumonia(n=15),and critical cases(n=2).Two critical cases(8%)were given invasive mechanical ventilation,corticosteroids,and immunoglobulin.The symptoms in 24(96%)of 25 patients were alleviated and one patient had been discharged.It was concluded that children were susceptible to COVID-19 like adults,while the clinical presentations and outcomes were more favorable in children.However,children less than 3 years old accounted for majority cases and critical cases lied in this age group,which demanded extra attentions during home caring and hospitalization treatment.
基金financially supported by the Natural Science Foundation of China(Grants 51904328)the Natural Science Foundation of China(Grants U1762212)Fundamental Research Funds for the Central Universities(Grants 27R1702031A)
文摘Drilling fluids face failure during drilling deep reservoir with high temperature and high salt.The experimental results show that high temperature and salinity reduce the negative charge on the surface of bentonite in the drilling fluid and cause the coalescence of bentonite particles.As a result,the particles coalesce,the grid structure is destroyed,and the rheological properties,rock-carrying capacity and filtration properties are lost.To resolve the foregoing,in this study,0.05-wt%carbon nanotubes are introduced into a 4%bentonite drilling fluid under conditions where the temperature and concentration of added Na Cl reach 180°C and 10 wt%,respectively.The carbon nanotubes adsorb on the bentonite surface and increase the space among bentonite particles.The steric hindrance prevents the coalescence of bentonite in high temperature and high salt environment.Thus bentonite maintains the small size distribution of bentonite and supports the bentonite grid structure in the drilling fluid.As a result,the rock-carrying capacity of the drilling fluid increases by 85.1%.Moreover,the mud cake formed by the accumulation of small-sized bentonite particles is dense;consequently,the filtration of bentonite drilling fluid reduced by 30.2%.
基金Project supported by the National Basic Research Deve-lopment Program of China(973 Program,2015CB251200)the National Science and Technology Major Project(Grant No.2016ZX05020-006)the Changjiang Scholars and Innovative Research Team in University Project(Grant No.IRT_14R58)
文摘The well cementing is important during the extended reach well drilling and the completion, whereas the displacement efficiency and the interface stability are important to guarantee the success of the cementing. In this paper, the interface stability of the cement slurry is simulated using the computational fluid dynamics software. The calculation results indicate that during the displacement, the length of the displacement interface increases with the increase of the deviation angle. The larger the eccentricity, the more significant the velocity difference, along with a longer displacement interface length, a less stable interface, and a lower displacement efficiency. Therefore, to guarantee the cementing quality and maintain a high displacement efficiency, the eccentricity should be controlled within 0.5. Application of a casing centralizer will dramatically improve the interface stability, decrease the dilution zone length of the interface and thus, is beneficial to the slurry cementing and displacement. The simulations are verified with an average absolute deviation less than 3.76% and the 45？ helix angle of the rigid centralizer is recommended. Combining the data of an extended reach well on-site, methods are proposed for improving the displacement efficiency and the interface stability during the well cementing and displacement with complex boreholes. These numerical methods can be used to provide some theoretical guidance for designing the cementing of an extended reach well.
