Resharch Of Vibration Characteristics Of Tubing Induced By High Temperature And High Pressure Gas

In oil reservoir extraction operations,the secondary oil drive method of CO₂gas injection is usually selected.In the process of CO₂injection,the fluid-structure interaction vibration of the flow column is induced by the change of injection displacement and pressure.In this paper,we study the service safety of CO₂injection well flow column under different operating conditions,mainly calculate the flow column under periodic injection condition and pumping stop condition,and analyze the vibration law of the flow field in the tube and the flow column during high temperature and high pressure critical CO₂gas injection by numerical simulation method.Specific vibration suppression measures and reasonable design and construction suggestions are proposed for the resonance and other failure damage of the column,which provide a theoretical basis and reference standard for the evaluation of the service safety of the column in oil and gas fields.The research results show as follows:（1）The injection pressure and the internal diameter of the column are the main factors affecting the safety of the column under cyclic injection conditions,When the initial injection pressure increases,the pressure of the flow field in the tube will also increase,and the axial additional stress in the tube column will also increase accordingly.Comparing the maximum injection pressure of 30 MPa with the minimum injection pressure of 10 MPa in this paper,the flow field pressure increases by 188%and the axial stress increases by 173%.As the pipe diameter increases,the pipe pressure and flow velocity in the flow field will decrease,and the axial stress in the pipe column will increase.In the example of this paper,the maximum tube diameter of 4-¹/₂"tube column compared with the smallest 2-³/₈"tube column,the flow field pressure decreases by 3%,the flow velocity decreases by 73%,and the axial additional stress in the tube column increases by 33%.（2）Under the condition of stopping the pump,the stopping time and the stopping pressure are the main factors affecting the safety of the pipe column.The shorter the pump stopping time,the greater the pressure in the flow field,the sharper the flow velocity fluctuation,and the greater the axial additional stress in the pipe column.Compared with a pump stoppage within 3s,the pressure in the tube rises by 3%and the axial stress in the tube column rises by 3%.The higher the instantaneous tube pressure at pump stop,the faster the flow velocity of the flow field,and the faster the axial vibration velocity of the tube column,and the additional axial stress of the tube column will also increase with the increase of the pump stop pressure.When the pump was stopped at 30MPa,the wellhead flow velocity increased by 14%,the axial vibration velocity of the tubular column increased by two times,and the additional axial stress increased by 198%compared with that at 10MPa.（3）The resonance damage of the flow transmission column originates from its vibration frequency close to the intrinsic frequency,so the maximum safe column length for different pipe diameters is obtained by combining the calculation results of the vibration parameters of the flow transmission column and analyzing its intrinsic frequency distribution law,which provides a theoretical basis and reference range for the selection method of the column combination to avoid resonance in actual operation.The damage of the tubular column under pumping stoppage is more from the impact of the"water hammer"phenomenon,so the safety coefficients under different pumping stoppage lengths and different pumping stoppage pressures are calculated by combining the yield limits of the tubular column materials of gas injection wells,which provides a theoretical basis for safe operation and has good engineering practical value.