To counter the strength problem of drill string in well of large curvature and small diameter, well axis was taken as datum mis. Based on description of deflection of well an's and on analysis of three dimensional...To counter the strength problem of drill string in well of large curvature and small diameter, well axis was taken as datum mis. Based on description of deflection of well an's and on analysis of three dimensional forces of a small section of drill string, equilibrium differential equations of large deflection drill string were established. The internal forces were found by Longe-Kutta method. The stresses were found by using them and the strength prerequisite was established. Stresses of drill string in lateral horizontal well H767 were computed. The results are in agreement with those of finite element model and soft-rope rigidified model. But the method is simpler for computation than finite element model and is more perfect than soft-rope rigidified model. Curvature of the well is too large and there is stress concentration so that the fraction accident of drill string occurs.展开更多
Improper drilling parameters may cause severe vibration of drill string which leads to reduce the rate of penetration and drilling tool premature failure accidents in the drilling process of ultra-deep well.The study ...Improper drilling parameters may cause severe vibration of drill string which leads to reduce the rate of penetration and drilling tool premature failure accidents in the drilling process of ultra-deep well.The study on dynamic characteristics of drill string plays an important role in increasing the safety of drilling tool and optimizing the drilling parameters.Considering the influences of real borehole trajectory,interaction between bit and formation,contact between drill string and borehole wall,stiction of drilling fluid and other factors,a comprehensive drill string dynamic model was established to simulate the changes of wellhead hook load,torque,equivalent stress of drill string and BHA(bottomhole assembly)section acceleration and motion trajectory with time at different WOBs(weights on bit)and rotary speeds.The safety factor and overpull margin of wellhead drill string were calculated and the strength of drilling tool in ultra-deep well was checked using the fourth strength theory.The analysis results show that,in the drilling process of ultra-deep well,the transverse motion amplitude of the drill string near the wellhead is relatively small and vibration of drill string mainly occurs in the lower well section.As the rotary speed increases,the number of collision between lower drilling tool and borehole wall increases,wellhead transverse stress increases,change in torque is not large and change in wellhead equivalent stress is relatively small.As the WOB increases,wellhead torque will increase,axial load and equivalent stress will decrease and vibration acceleration of BHA will increase sharply.Wellhead overpull margin and safety factor will decrease with the increase of rotary speed and increase with the increase of WOB.Wellhead safety factor of S135 drilling tool in an F190.5 mm ultra-deep well on the south margins of Junggar basin changes around 1.8.The drilling tool is safe and has relatively sufficient ability to deal with the downhole accidents if a large size high steel grade drill string(F139.7 mm S135)is used.However,in view of BHA safety,neither rotary speed shall be too high nor WOB shall be too large.展开更多
文摘To counter the strength problem of drill string in well of large curvature and small diameter, well axis was taken as datum mis. Based on description of deflection of well an's and on analysis of three dimensional forces of a small section of drill string, equilibrium differential equations of large deflection drill string were established. The internal forces were found by Longe-Kutta method. The stresses were found by using them and the strength prerequisite was established. Stresses of drill string in lateral horizontal well H767 were computed. The results are in agreement with those of finite element model and soft-rope rigidified model. But the method is simpler for computation than finite element model and is more perfect than soft-rope rigidified model. Curvature of the well is too large and there is stress concentration so that the fraction accident of drill string occurs.
基金This work is financially supported by National Natural Science Foundation of China(Grant No.52104006 and Grant No.51674215).
文摘Improper drilling parameters may cause severe vibration of drill string which leads to reduce the rate of penetration and drilling tool premature failure accidents in the drilling process of ultra-deep well.The study on dynamic characteristics of drill string plays an important role in increasing the safety of drilling tool and optimizing the drilling parameters.Considering the influences of real borehole trajectory,interaction between bit and formation,contact between drill string and borehole wall,stiction of drilling fluid and other factors,a comprehensive drill string dynamic model was established to simulate the changes of wellhead hook load,torque,equivalent stress of drill string and BHA(bottomhole assembly)section acceleration and motion trajectory with time at different WOBs(weights on bit)and rotary speeds.The safety factor and overpull margin of wellhead drill string were calculated and the strength of drilling tool in ultra-deep well was checked using the fourth strength theory.The analysis results show that,in the drilling process of ultra-deep well,the transverse motion amplitude of the drill string near the wellhead is relatively small and vibration of drill string mainly occurs in the lower well section.As the rotary speed increases,the number of collision between lower drilling tool and borehole wall increases,wellhead transverse stress increases,change in torque is not large and change in wellhead equivalent stress is relatively small.As the WOB increases,wellhead torque will increase,axial load and equivalent stress will decrease and vibration acceleration of BHA will increase sharply.Wellhead overpull margin and safety factor will decrease with the increase of rotary speed and increase with the increase of WOB.Wellhead safety factor of S135 drilling tool in an F190.5 mm ultra-deep well on the south margins of Junggar basin changes around 1.8.The drilling tool is safe and has relatively sufficient ability to deal with the downhole accidents if a large size high steel grade drill string(F139.7 mm S135)is used.However,in view of BHA safety,neither rotary speed shall be too high nor WOB shall be too large.
