Research On Recoil Mechanism And Control Strategy Of Emergency Release Of Deepwater Drilling Riser

In deep water drilling operation,in order to avoid the possible vortex induced vibration damage,instability and excessive lateral deformation under the action of self weight,the drilling riser needs to maintain the tension state under the action of the top tensioner,and the size of the top tension becomes an important parameter affecting the safety of the riser.When the drilling platform encounters severe sea conditions or the positioning equipment failure which is difficult to be eliminated,the drilling operation needs to be interrupted and the connection between the bottom assembly of the riser and the BOP needs to be released urgently.At this time,the huge potential energy stored in the riser is released instantaneously,the riser will recoil upward,which seriously threatens the safety of the riser.According to the longitudinal vibration response equation of riser under different conditions after release,the differential equation of longitudinal vibration response of riser after release is first obtained by using the method of separation of variables.;on this basis,the differential equation of the longitudinal vibration response of the riser under the joint action of the riser and the tensioner is obtained;considering the influence of the inertial load of the platform,the differential equation of the longitudinal vibration response of the riser under the coupling action of the inertial load of the riser and the platform is obtained A more accurate boundary condition of the effective axial force at the bottom of the riser is proposed,and the differential equation of the vertical vibration response of the riser is obtained considering the influence of the axial force and the inertial load of the platform.Combined with the characteristics of the rigid suspension of the riser during evacuation and navigation,the differential equation of the vertical vibration response of the riser is solved,which is described more carefully The longitudinal vibration response of riser during emergency release and hard suspension evacuation is described.Based on Orca Flex software and the actual situation of a deepwater drilling platform operating in the South China Sea,an analysis model of riser emergency release and recoil response is established,and the influence of riser tension,platform heave motion and release time selection on riser backflushing is discussed in detail.The results show that the reasonable setting of tension before release is very important for the safe release of riser.If the tension setting is too small,the release may fail.If the tension setting is too large,the recoil response may damage the tensioner.In addition,when the amplitude of platform heave is small,it is more advantageous to release the riser at the peak.Finally,the coupling analysis model of drilling platform and riser system is established,and the influence of wave height,wind direction,wind speed and speed on riser safety under the mode of hard suspension evacuation is compared with the actual environmental conditions of a well in South China Sea.The results show that the safety of riser is more sensitive to the change of angular displacement between riser and universal joint than the maximum equivalent stress of suspension point.