Study On Calculation Method Of Subsea Wellhead Fatigue Damage Considering Thermal Effect

This dissertation is supported by China Offshore Oil Research Center project “Integrity technology and its engineering application for deepwater riser-subsea wellhead system in full life”,which is a subproject of national major science and technology projects in the 13 th FiveYear Plan.In accordance with the requirement of oil and gas exploration and development in the South China Sea,a research on calculation method of subsea wellhead fatigue damage considering thermal effect is carried out firstly in domestic.Great progress has been achieved in the analysis of wellbore the temperature field,the equivalent method of subsea wellhead,the the fatigue assessment method of subsea wellhead with thermal effects,the technical countermeasures for improving the life of subsea wellhead.The study will provide technical support and guidance for the design and application of subsea wellhead system in the South China Sea,and it has good academic value and engineering application prospect.The main progress and results are summarized as follows.(1)Research on the temperature field distribution of deep water drilling wellbore,and establish the theoretical analysis model of temperature field in deep water wellbore.Because of the difference of heat transfer mechanism between ocean and formation,the numerical simulation method is used to establish the mathematical model of heat transfer in seawater and formation,and calculation program of temperature field in deepwater wellbore is compiled based on MATLAB software.The effects of riser insulation layer,drilling fluid density,drilling fluid flow rate,circulation time and seawater depth on the temperature field of deep water wellbore were analyzed.(2)Research on the equivalent method of underwater wellhead,and establish the contact relationship between the components of the subsea wellhead and the interaction between pipe and soil.The ABAQUS software is used to establish the fine finite element model of the underwater wellhead,study on the equivalent beam model and calculate the equivalent beam model parameters.The equivalent beam model and the equivalent beam model parameter calculation method are compared with the static beam,the dynamics and the overall coupling of the equivalent beam model and the subsea wellhead finite element model to verify the correctness of the equivalent beam model.(3)The influence of temperature on fatigue life of subsea wellhead is studied.By establishing the calculation model of temperature field of deep water wellhead,the temperature distribution of wellhead is applied to the fine finite element model of subsea wellhead,and the equivalent beam model of underwater wellhead is obtained by equivalent method.In the effective beam model,the equivalent beam model is substituted into the riser-wellhead coupling model to calculate the dynamic response and fatigue damage of the underwater wellhead.The influence of temperature variation on fatigue damage at fatigue hot spot of underwater wellhead during mud cycling operation was studied,and the influence of different cement heights on fatigue damage of underwater wellhead was studied.(4)To carry out research on technical countermeasures to improve the life of subsea wellhead systerm,and the influencing factors of parameters of equivalent beam model are analyzed.Then the effects of soil properties,BOP weight,conductor thickness,cement level and mud height on the parameters of the equivalent beam model of underwater wellhead were studied.Analyze and compare the effects of various factors on fatigue damage of wellhead,and the Countermeasures for improving fatigue life of subsea wellhead are put forward.