The Research Of The Coiled Tubing Corrosion Life

Small footprint,economical,flexible mobility,etc.so that in the 1960 s,the coiled tubing was introduced in oilfield to produce.Since the coiled tubing bears complex stress environment in the downhole,including the effects of tension and compression,bending,torsion and other complex stress and pressure,temperature,gas and other factors,proning to breakage,buckling,corrosion and other phenomena,resulting in coiled tubing service life greatly reduced,its application is extremely limited.So,from the view of the economic and development of the field,if coiled tubing is promoted to use in large-scale in the oilfield,its life is an important factor,consequently there is important meaning to study its life.As one of the oilfields introducing coiled tubing unit in the 1990 s,there are more than 1400 times coiled tubing opreations in Tarim.All the kinds of coiled tubing failures,such as fracture,perforation,etc.are more or less related to their corrosion.Tarim Oilfield is characterized by high temperature and pressure conditions,and the downholes of a considerable part of the blocks include CO₂?H2S,etc.which easily cause coiled tubing corrosion.Thus,through the autoclave,carrying out four-point bending tests,galvanic corrosion experiments and SSC experiments to study the SSC QT900 coiled tubing corrosion reliability and estimate the remaining corrosion life,which is important significance to prevent the failure of coiled tubing,guide the application of coiled tubing in the oilfield,promote the use of the coiled tubing techonology.In this paper,QT900 coiled tubing is studied through the indoor experiment,and through the finite element simulation to predict the life.Four-point bending test,galvanic corrosion test,SSC resistance evaluation are included in the indoor experiment.?1?The main purpose of the four-point bending test is to understand to coiled tubing material corrosion situation of only bearing axial stress,by using SEM to observe the surface morphology of material,when there are corrosion products or not.EDS is used to analyze the elemental composition of the corrosion product films.XRD is used to study the main components of the corrosion products.?2?The purpose of the galvanic corrosion test is whether the coiled tubing is exposure to HP2-13 Cr to lead galvanic corrosion,EDS,SEM and other techiques are also used to study the surface.?3?SSC resistance evaluation test is to explore whther QT900 coiled tubing material can be used in H2 S environment.Finite element simulates the effection of the corrosion to the coiled tubing in the process of descending and pulling out,simulating the limit size of the coiled tubing to predict its life.