Mechanical Behavior And Sealing Mechanism Of Premium Connection Tubing And Casing Under Extreme Environment Gas Well

This thesis is funded by National Natural Science Foundation,“Study of behaviors of mechanics and seal mechanism of tubing and casing premium connection under the extreme conditions",(Project No.51574198).According to the tubing and casing premium connection's metal-to-metal sealing surface structure characteristics under the extreme environmental gas well,applying with theoretical modeling,experimental study,and finite element method,combining with elastoplastic theory,viscoelasticity theory,creep and relaxation,timetemperature superposition,Hertz contact mechanics,and Bezier curve designing theory,the gas leakage mechanism of premium connection is systematic investigated,which provides theoretical framework for the premium connections' structure designing and safety evaluation under the extreme environmental gas well.The main content and achievement of the thesis are as follows,(1)Based on the mechanics theory,sealing theory,finite element method,and experimental study of tubing and casing premium connections,the existing problem and development direction of the premium connections' metal sealing mechanism and gas leakage theory are analyzed,and the research approach and main content of this thesis is promoted.(2)Tubing and casing material's uniaxial tensile creep experiment is conducted under high temperature.The tubing and casing materials'creep mechanics behavior is tested under the different temperature and different tensile stress.And their creep mechanics law are investigated.Furthermore,basing on the relationship between metal material's creep and relaxation characterized,the stress relaxation mathematical model is established.Finally,the influencing rule of temperature and stress loads effecting on the tubing and casing material's stress relaxation behavior is obtained.(3)According to the tubing and casing material's creep experimental result,their viscoelastic constitutive model is established,and their relaxation modulus and Prony series are obtained.Basing on the time-temperature superposition principle,the tubing and casing material's temperature shift factor is obtained.The finite element model of premium connections sealing surface's contact stress relaxation under the extreme environment is established,and the sealing surface's contact stress changing with time is obtained,which is useful for predicting tubing and casing's service life and their material selection under the extreme environment.(4)Based on the structure of premium connection,the mechanical and mathematical model of sealing surface under static loading is established.Furthermore,the contact stress on the sealing surface's model,considering the tubing vibration with gas,is also established.And the sealing surface energy dissipation model is established in the high gas rate well.What's more,the structure of sealing surface and impacting loads on tubing effecting on the sealing surface's contact stress is analyzed.Finally,optimizing sealing surface's structure is proposed to reduce effect of tubing vibration on the premium connections' sealability.(5)Based on the micro-leakage theory of metal sealing,the gas leakage rate's mathematical model of premium connections metal-to-metal sealing surface is established,and the influence of average contact pressure on sealing surface,sealing surface's roughness,length of sealing surface on gas leakage rate is discussed,which provides theoretical bases for revealing the tubing and casing premium connections' gas sealing failure mechanism,evaluating the premium connections' gas sealability,and optimizing the structure of premium connections.(6)The finite element model of premium connections' sealing surface was established,and the distribution of contact pressure on the sealing surface was discussed.Based on the sealing contact energy theory,the structure of sealing surface's characteristic was analyzed.Aiming at the extreme environmental gas well,a novel premium sealing surface was promoted by the Bezier curve designing theory,which is verified by the finite element method.(7)The numerical simulation model of gas sealing test in the deep,ultra-deep well was established.The distribution of Von-Mises stress on tubing premium connection is investigated in the different tubing depth and different gas sealing test pressure,which provides theoretical bases for preventing premium connection fracture and gas seal failure.