Mechanical Characteristics Analysis Of Downhole Safety Valve In High Temperature And High Pressure Deep Well Completion

As an essential well control tool for the integrity of oil and gas wells,the working performance and mechanical properties of downhole safety valves are critical to safe production.The safety valve is a complex structural body consisting of inner and outer tubes,valve plates,springs and other structures.The load transfer and interaction between the components is a complex mechanical problem,and the study of its overall mechanical properties has yet to be publicly reported.Based on this,the comprehensive automated analysis of the downhole safety valve,the load distribution and transfer between components,the mechanical characteristics of each element,and the drawing of the envelope curve of the downhole safety valve are investigated.Taking a deep well 88.9mm downhole safety valve in the Tarim oilfield,a three-dimensional finite element model of the safety valve,including the housing-central tube-valve plate-stop ring-force transfer cylinder and other components,is established.Four typical operating conditions and failure forms are considered.Different internal pressure,external pressure and axial force loads are applied to investigate the stress distribution pattern of the safety valve body and critical components and analyse the strength and safety of the safety valve as a whole and each member.The study shows that,through the strength and safety analysis of the downhole safety valve as a whole and its parts,the safety of the safety valve from lowest to highest is fracturing,well shutdown,well opening and seating;the minimum safety factor of the intermediate joint under fracturing conditions is 1.33,the safety factor of the central tube is 1.40,the safety factor of the upper joint is 1.90,the safety factor of the lower joint is 1.92,the safety factor of the force transmission cylinder is 1.97,and the safety factor of the stop ring is 6.42 This shows that the safety valve intermediate joint has the lowest safety factor under fracturing conditions and is the weakest part of the safety valve under fracturing conditions.The safety coefficients of the hydraulic control line under fracturing,production,well opening and seating conditions are 4.60,2.90,2.70 and 1.38,respectively,and the safety of the line under seating conditions is the lowest;comparing the results of the four operating conditions shows that appropriately increasing the annular pressure of the oil jacket and reducing the pressure difference between the inside and outside of the line can improve the overall safety performance of the line,which plays a vital role.in protecting the hydraulic control line.The single limit load and combined limit load when the main components reach the allowable stress are obtained by means of finite element simulation analysis.The line segments corresponding to the single limit load are connected to form a closed area,and the combined limit load corresponds to the inflection point of the line segment intersection,and a more complete envelope curve is drawn accordingly.Through this paper,a three-dimensional finite element model of the 88.9mm downhole safety valve has been established,the mechanical characteristics of the safety valve for four typical operating conditions have been analyzed,the hazardous operating conditions have been clarified,the weak components have been identified,recommendations for the safe operation of the liquid control line have been given,and the envelope curve drawing method for the downhole safety valve has been established,providing a way that can be used as a reference for the safety analysis of the downhole safety valve.