Two mechanically ventilated cases of COVID-19 successfully managed with a sequential ventilation weaning protocol: Two case reports

BACKGROUND Patients with critical coronavirus disease 2019(COVID-19),characterized by respiratory failure requiring mechanical ventilation(MV),are at high risk of mortality.An effective and practical MV weaning protocol is needed for these fragile cases.CASE SUMMARY Here,we present two critical COVID-19 patients who presented with fever,cough and fatigue.COVID-19 diagnosis was confirmed based on blood cell counts,chest computed tomography(CT)imaging,and nuclei acid test results.To address the patients’respiratory failure,they first received noninvasive ventilation(NIV).When their condition did not improve after 2 h of NIV,each patient was advanced to MV[tidal volume(Vt),6 mL/kg ideal body weight(IBW);8-10 cmH2 O of positive end-expiratory pressure;respiratory rate,20 breaths/min;and 40%-80%FiO2]with prone positioning for 12 h/day for the first 5 d of MV.Extensive infection control measures were conducted to minimize morbidity,and pharmacotherapy consisting of an antiviral,immune-enhancer,and thrombosis prophylactic was administered in both cases.Upon resolution of lung changes evidenced by CT,the patients were sequentially weaned using a weaning screening test,spontaneous breathing test,and airbag leak test.After withdrawal of MV,the patients were transitioned through NIV and high-flow nasal cannula oxygen support.Both patients recovered well.CONCLUSION A MV protocol attentive to intubation/extubation timing,prone positioning early in MV,infection control,and sequential withdrawal of respiratory support,may be an effective regimen for patients with critical COVID-19.

Influencing factors and prevention measures of casing deformation in deep shale gas wells in Luzhou block,southern Sichuan Basin,SW China

Based on structural distribution and fault characteristics of the Luzhou block,southern Sichuan Basin,as well as microseismic,well logging and in-situ stress data,the casing deformation behaviors of deep shale gas wells are summarized,and the casing deformation mechanism and influencing factors are identified.Then,the risk assessment chart of casing deformation is plotted,and the measures for preventing and controlling casing deformation are proposed.Fracturing-activated fault slip is a main factor causing the casing deformation in deep shale gas wells in the Luzhou block.In the working area,the approximate fracture angle is primarily 10°-50°,accounting for 65.34%,and the critical pore pressure increment for fault-activation is 6.05-9.71 MPa.The casing deformation caused by geological factors can be prevented/controlled by avoiding the faults at risk and deploying wells in areas with low value of stress factor.The casing deformation caused by engineering factors can be prevented/controlled by:(1)keeping wells avoid faults with risks of activation and slippage,or deploying wells in areas far from the faulting center if such avoidance is impossible;(2)optimizing the wellbore parameters,for example,adjusting the wellbore orientation to reduce the shear force on casing to a certain extent and thus mitigate the casing deformation;(3)optimizing the casing program to ensure that the curvature radius of the curved section of horizontal well is greater than 200 m while the drilling rate of high-quality reservoirs is not impaired;(4)optimizing the fracturing parameters,for example,increasing the evasive distance,lowering the single-operation pressure,and increasing the stage length,which can help effectively reduce the risk of casing deformation.

Hydraulic fracturing induced casing shear deformation and a prediction model of casing deformation

To study the casing deformation(CD)in shale gas well fracturing caused by natural fracture slip,a fracture face stress model is built based on stress analysis,and a CD prediction model is established based on complex function to analyze factors affecting wellbore shear stress and CD.(1)The fracture and wellbore approach angles have significant impacts on the wellbore shear stress.In Weiyuan shale gas field,Sichuan Basin,under the common wellbore approach angle of nearly 90°,the wellbore is subjected to large shear stress and high risk of CD at the fracture approach angle range of 20° to 55° or its supplementary angle range.(2)When the fracture is partially opened,the wellbore shear stress is positively correlated with the fluid pressure,and negatively correlated with the fracture friction coefficient;when the fracture is fully opened,the wellbore shear stress is positively correlated with the natural fracture area.(3)The lower the elastic modulus and the longer the fracture length,the more serious the CD will be,and the Poisson’s ratio has a weak influence on the CD.The deformation first increases and then decreases with the increase of fracture approach angle,and reaches the maximum when the fracture approach angle is 45°.(4)At a given fracture approach angle,appropriately adjusting the wellbore approach angle can avoid high shear stress acting on wellbore,and reasonable control of the fluid pressure in the fracture can reduce the CD risk.The shear stress acting on casing is usually much greater than the shear strength of casing,so increasing casing strength or cementing quality have limited effect on reducing the risk of CD.Caliper logging data has verified that the CD prediction model is reliable,so the model can be used to establish risk analysis chart and calculate deformation value,to provide a reference for quick CD risk prediction in fracturing design.