Research On The Corrosion Behavior Of P110 Steel In Two Typical Solutions

The oilfield environment is becoming more and more complicated with the oilfield production period goes on, and corrosion of casing pipe is much worse now. P110 steel is one kind of casing pipe steel and its usage increases with time. However, few researches show great concern on the corrosion behavior of P110 steel in well drilling solutions and alkali-surfactant-polymer (ASP) solutions. So it is very important to study the corrosion behavior of P110 steel in these two solutions, which can attribute to the development of the theory and application of P110 steel in oilfield.In this study, the corrosion of P110 steel in well drilling solutions and ASP solutions was tested by the dynamicpotential polarization curve, linear polarization and electrochemical impedance spectroscopy (EIS). The influence of different concentrations, temperature and cation type of well drilling solutions was analysed. Also, the effect of ASP composition, concentration and temperature of ASP solutions on P110 steel was obtained. After corrosion immersion test, the corrosion products and mechanism were concluded by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD).The results indicated that the corrosion rate of P110 steel increased with the increasing of temperature (high to 80℃) of well drilling solutions. There was a critical value between concentration of salt containing well drilling solutions and corrosivity, which the corrosivity reached to a maximum when the concentration of salt solutions was 3%. The types of cations showed different influence on the corrosion behavior of P110 steel, which the cations of Ca2+, Mg2+ improved the corrosion-resistance of P110 steel by forming compact and adhesive corrosion products film on the surface of P110 steel. The corrosion rate of P110 steel in three different cations solutions was in the order of NaCl, MgCl2 and CaCl2 solution. The corrosion-resistance of P110 steel was susceptible to the compositions of ASP solutions. The corrosion rates of P110 steel increased by the sequence of ASP, AS, A and AP solution. The corrosion rules of P110 steel in weak base and strong base ASP flooding exhibit the different trend, which the corrosion rate increases with the increasing of concentration of weak alkali. The concentration of strong base ASP flooding has noticeable effect on the number of corrosion potential. The phenomenon of three corrosion potentials was firstly observed in potentiodynamic polarization curve for P110 steel in strong base ASP flooding which indicated that it is an unstable system. At D(A:0.6%, S:1000 mg/L, P:800 mg/L)< strong base ASP concentration≤E(A:1.0%, S:1200 mg/L, P:1000 mg/L), three corrosion potentials were observed which decreased to two high than the concentration E, and decrease further to one less than concentration D. The corrosion mechanism differs from each other, which the P110 steel can passive in strong base ASP flooding and possess the stability of passive film than weak base ASP flooding. The corrosion resistance increases with the addition of surfacant, and there exhibits the same corrosion trend in strong base ASP flooding as in the weak base ASP flooding. Besides, there exists a critical value between the concentration of polyacrylamide and the corrosion resistance, which the corrosion resistance decreases when the concentration of polyacrylamide reaches to 800 mg/L. Also, the corrosion rates of P110 steel in two ASP solutions decreased with the the increasing of temperature.The corrosion rates calculated from the corrosion immersion test was consistent to the results of electrochemical corrosion tests. The forming of corrosion products on the surface of P110 steel in well drilling solution was closely related to the concentration of NaCl after analysed by SEM and EDS. The average corrosion rate of P110 steel increased firstly and then decreased with the increasing of the concentration of NaCl, which was reached to a maximum when the concentration of NaCl was 3%. The quantities and forms of corrosion products exerted great influence on the corrosion process of P110 steel, which the compact and adhesive corrosion products could prevent corrosion further. EDS results showed the main elements in corrosion product of P110 steel in 3% NaCl well drilling solution were Fe, O, C, Cl, Cr and that mainly composed of Fe3O4 as the result of XRD.