Wellhead Stability Study Of Gas Hydrate Production Considering Multi-Phase Flow Dynamic Load In Wellbore

With the rapid development of domestic economy,the demand for oil and gas is greatly increased.It has become an inevitable trend that oil and gas exploitation gradually moves from land to shallow water and from shallow water to deep water.As a potential replacement energy source,more and more attention has been paid to the exploration of Marine gas hydrate.However,due to the complex mining environment,the stability of the seabed wellhead has potential safety hazards.The dynamic load of multiphase flow in the exploitation of natural gas hydrate will cause the vibration of the pipe string and affect the stability of the seabed wellhead.In present,there are few studies on the vibration of production string in the process of deep water hydrate development under the dynamic load of multiphase flow.Therefore,this study has certain academic value and practical significance.In this paper,the multiphase flow theory and pipeline vibration theory are analyzed firstly,and the principles of Olga and ANSYS software are introduced,which provides a foundation for the analysis of multiphase flow dynamic load and pipeline vibration law.The multiphase flow model in the production string isestablished by using Olga software,and the influence of gas production and pipe diameter on the multiphase flow law is analyzed.The fluid-structure coupling model of production string and multiphase flow is established with ANSYS software,and the force on the top of production string is analyzed and calculated.Wellhead stability considering vibration load caused by multiphase flow in production string is analyzed.With ABAQUS software.The results show that slug flow is not easily generated when gas production is too large or too small,and the liquid carrying capacity of pipe string increases with the decrease of pipe diameter.When the flow pattern is slug flow,the vibration of production string is more likely to be caused,and the effect is most obvious when the slug flow frequency is about 1 Hz.The maximum dynamic load of supporting reaction force under different gas production conditions is obtained by simulation method.When the size of conductor and casing is small,wellhead instability is easy to happen.The influence law of the production string on the stability of the subsea wellhead due to the vibration of the slug flow is obtained by simulation analysis.The greater the vibration load is,the greater the maximum displacement and stress of the pipe and casing are.In order to increase wellhead stability and reduce the risk of string yield failure,suction anchors and wellhead chassis are recommended to enhance wellhead and string stability.