Study On Recoil Control And Application Of Riser Tensioner System In Deep Water Drilling

The riser is an key equipment in offshore oil and gas engineering.The subsea wellhead and the drilling platform are connected by the riser during normal drilling operations.However,the marine environment is complex and changeable.It is inevitable to encounter emergency situations which require emergency evacuation.The connector between the lower marine riser package(LMRP)and the blowout preventer(BOP)should be quickly disconnected.Once the riser is disconnected from the subsea wellhead,the riser quickly moves upward under the action of the top tensioner and enters a recoil process.If the riser recoil process is not controlled,accidents can occur that results in loss of life and property.The recoil control of deepwater drilling riser system is an urgent problem to be solved in offshore oil and gas engineering.The research work is summarized as follows:(1)The recoil dynamic model of deepwater drilling riser-tensioner system is established.After analyzing the recoil process of the riser system and the structure and working principle of the riser-tensioner system,the tensioner model,the riser string model and the drilling mud discharge model were established respectively.The riser string model uses the concentrated mass method,the drilling mud discharge model uses the whole fluid column model and the tensioner model is linearized.Considering the coupling relationship between riser,tensioner and drilling mud,the recoil dynamic model is obtained.(2)Based on the optimal control theory,a riser recoil control method is designed.The established riser-tensioner model has multiple degrees of freedom and the control problem of multi-degree of freedom system is usually solved by modern control theory.Firstly,according to the analysis results of riser system recoil process and summarized characteristics of riser system recoil process,the control strategy of riser recoil is put forward.Then,the recoil control strategy is combined with the optimal control theory,and the LQR control algorithm is used to design the recoil controller of the riser system which takes the displacement and velocity of the equivalent mass blocks of the riser system as the state variables.Finally,the recoil response of riser system without controller and with controller is compared and analyzed by using Simulink programming.The results show that the LQR controller can control the riser recoil process.(3)A method of riser recoil control is designed by using fuzzy control theory.Aiming at the problem that the recoil controller designed by the optimal control theory is highly dependent on the system model,the fuzzy control theory is used to design the recoil controller.The recoil control law of riser system is summarized and the summarized recoil control law is combined with fuzzy control theory.The recoil controller of riser system is designed based on Mamdani fuzzy model.Using Simulink as a simulation calculation platform.A comparative study on the recoil dynamics of riser system without controller and with controller is carried out.The results show that the peak value of the riser recoil response decreases obviously after using the controller,and the recoil response valley value increases obviously.The control effect of the riser recoil process is obvious.(4)The characteristics of two recoil control methods are compared and analyzed.The possibility of the recoil control method in engineering application is studied.The adaptive analysis of the controller with good application is carried out and the control effect of the controller under different riser system configuration on changing the platform motion amplitude,platform motion period and pressure of high pressure air vessel is studied.The results show that the fuzzy controller has better application and adaptability.