Evaluation And Analysis Of The Adaptability Of Premium Connection Of Tubing In An Oilfield

The bottom hole pressure of natural gas wells reaches 110 MPa in the certain area,and the bottom hole temperature exceeds 170°C.The harsh downhole conditions bring severe challenges to the strength and sealing performance of premium connection.According to the ISO 13679 specification,the evaluation of the tubing premium connection can not fully meet the needs of the premium connection used in the oil field.This paper explores a evaluation and selection method for the premium connection that is suitable for the region.The paper is based on the actual mechanics and temperature load conditions of the oilfield wellbore,through the combination of the physical experiment that including the shackle test,the composite load envelope test and the limit load test and the finite element method,that analyzes and evaluates type A and type B premium connection.Through physical experiments,it is found that the premium connection of type A and type B have not structural damage and leakage failure in the shackle test and composite load envelope experiment;the two structures are intact during the test load envelope tests,and no leakage occurs;the type A premium connection didn’t leak during the internal pressure with the compression increasing to failure tests.When the tensile load was increased to 1382 kN under the condition of high internal pressure,the external thread of the tubing A end has broken and failed.It indicates that the externally threaded end of the tubing end A is the weak point of strength of the B type premium connection.During the failure test of B type premium connection,the internal pressure increased to 96.3MPa and no leakage occurred during the 10 min maintenance period.When the internal pressure increased to 127 MPa,the B-type premium connection A end tube blast compression instability Invalid.According to the results of finite element analysis,the stress distribution of the connection n is relatively uniform.The thread segment of the pipe string and the apex of the end face of the pipe string was yielded in a local area.Appropriate increase of internal pressure load can improve the sealing performance of the connection;the stress level of the external thread is higher than the stress value of the coupling,indicating that the external thread of the pipe is easy to fail compared with the coupling,which is consistent with the previous test results.It is found that the two premium connections have good sealing and integrity under the given test load and working conditions of the paper,which can basically meet the normal production requirements of high pressure gas wells in area A,but their adaptability to extremely complex working conditions still needs to be tested.The research recognizes that combined with the evaluation scheme established by the experimental method and the finite element method,the premium connection can be evaluated effectively,which provides a method for reference for the selection of premium connection in oilfield.