China is rich in ultra-deep oil and gas resources.In the development process of ultra-deep oil and gas,the integrated string is often used for perforating-testing-acidizing operation.In the process of this operation,however,the dynamic load of perforating impact in ultra-deep well frequently causes packer fracture failure.In order to solve this problem,this paper carries out the finite element simulation of transient impact dynamics of absorber string on the RTTS packer(fully-open hook wall packer)used for perforating in Well X1 in Xinjiang,based on the elastic-plastic finite element method,combined with the actually measured boundary conditions of the transient impact dynamic load at the moment of perforating string detonation.Based on this,a second-order damping mass-spring mechanical system model of shock absorber is established.In addition,the damping effect of double shock absorbers and the reliability of finite element analysis results are theoretically analyzed and compared.And the following research results are obtained.First,at the time of 0.09 s and 0.21 s of perforation detonation,two peak stresses of 805.4 MPa and 925.1 MPa appear at the thread of the central pipe joint,respectively,exceeding the yield strength and tensile strength of the pipe.Moreover,the alternating stress caused by the shock wave induces local crack failure,and the cracks gradually expand to the entire section,causing the failure of the threaded joint.Second,the calculation results of the simulation model and the structure size of the central pipe show that the structure size of the threaded part is so small that the peak stress exceeds its tensile strength,causing fracture failure.Third,it is suggested to adopt the improvement plan of upsetting 2-3 mm at the upper threaded connection of the central pipe,which can reduce the maximum stress by more than 27%and improve the structural strength.Fourth,the application of the double shock absorbers can effectively reduce the impact load on the upper part of the perforating string.Theoretical calculation results show that the amplitude of double shock absorbers is reduced by about 50%compared with single shock absorber,and the maximum stress is reduced by about 42%.In conclusion,the research results can provide theoretical and technical support for the safe perforating operation of the RTTS packer string in ultra-deep wells,and will powerfully promote the efficient exploration and development of ultra-deep oil and gas resources in China.
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