Analysis Of Deepwater Drilling Riser Tensioner System And Recoil Control

As an important connecting device between the platform and riser,the tensioner performance analysis and coupling dynamic response analysis of platform-tensioner-riser is important to ensure the normal drilling operation.Firstly,this paper proposed the hysteretic tensioner model,and a mathematical model of direct-acting tensioner was developed to analyze the change of performance.The results from current analyses considering the effect of gas state variations in tensioner,pressure loss of hydraulic pipeline and internal friction of tensioner cylinder show that the relationship between tension and piston stroke is not a simple nonlinear relationship but a hysteretic loop relationship.Secondly,this paper analyzed the dynamic response of the platform-tensioner-riser coupling system.And the coupling system was established by implementing the tensioner model into ANSYS-AQWA through user subroutines written in PYTHON scripts.Through the coupled dynamic response analysis,it finds that the variation of vertical relative displacement between platform and riser obtained with the hysteretic tensioner model is similar to that with the nonlinear tensioner model.But the tension will has a sudden change for the hysteretic tensioner model due to the internal friction of the tensioner cylinder,which has an impact on the fatigue life of the riser and the piston rod.In addition,considering the effect of angle between the riser and tensioner,it is also finds that the tensioner not only provides the top axial tension to maintain the normal operation of riser,but also provides a large horizontal force on the top of the riser.Thirdly,this paper analyzed the overall coupled dynamic response under the riser recoil control system.In emergency disconnection mode,the riser will rapidly recoil upward and companying with drilling mud discharge.It is finds that the mud discharge velocity and discharge force increased with the mud density increasing,and it also has significant effect on the riser recoil.Based on that,the model of riser recoil control was established for suppress the riser recoil,and the dynamic response of platform-tensioner-riser coupling system was analyzed.The results showed that under the recoil control system,the pressure drop of the valve orifice increases gradually as the orifice opening of the recoil control valve decreases,thus the riser recoil movement can be effectively controlled.Finally,this paper proposed a novel riser hybrid tensioner system by integrating an electrical tensioner system into existing hydro-pneumatic tensioner system.The analysis finds that under the hybrid tensioner system,the relative movement between the platform and riser can be effectively compensated,and the electrical tensioner system and the hydro-pneumatic tensioner system also give full play to their respective performance.Then the feasibility of the hybrid tensioner system is verified.