Research On Casing Corrosion Mechanism And Corrosion Inhibitor Optimization Under Air Foam Flooding Conditions

It is difficult for recovery efficiency to break through by the conventional displacement to the late production owing to the more water injection flow rate,low recovery ratio for low permeability light oil reservoir.Air-foam flooding gathers the advantages of air injection and foam flooding,which can not only profile control,but also displace oil.With the prominent increase of production,low cost,extensive source,therefore,this technology is widely applied into low permeability light oil reservoir.However,a lot of oxygen is carried into injection system during air injection,giving rise to serious corrosion of oil casing steel in injection well.In order to the safety production of oil field,taking efficient control measures,the study of oil casing steel corrosion in air foam flooding is indispensable.Ganguyi Oilfield is the typical "Three Low Character" reservoirs".For this experiment,simulating the field conditions indoors,the weight loss method was used to systematically analyze corrosion rules of J55 oil casing steel for six corrosion influential factors,including alternating injection frequency of foam liquid and air,oxygen concentration of air,temperature,pressure,humility and velocity of foam liquid.The results show that corrosion rate of oil casing steel increases in various degrees with the rise of the values of corrosion factors,respectively.In addition,the grey relational degree of each corrosion factor for corrosion rate was calculated with grey relation analysis,and the order of importance for the corrosion influential factors to corrosion rate,in sequence,is the factor air-foam alternating frequency,oxygen content,temperature,pressure,humidity and foam liquid velocity.Further,alternating injection frequency of foam liquid and air,oxygen concentration of air and temperature are principal factors,and others are secondary factors.The electrochemical corrosion method was utilized to analyze the Tafel polarization curve,electrochemical impedance,and simulate the equivalent circuit for three principal corrosion factors.The results show that electrochemical corrosion rate of oil casing steel increases with the increase of alternating injection frequency of foam liquid and air,temperature.In addition,low oxygen concentration promotes corrosion,but high oxygen concentration restrains corrosion.In the condition of alternating frequency,electrochemical impedance spectrum presents two time constant,that is,capacitive impedance loop in high and low frequency.Then,circuit is controlled by the charge transfer process.For the oxygen concentration factor,electrochemical impedance spectrum show high frequency capacity reactance arc and a line approximation into 45 degree with the horizontal axis under low frequency.Circuit is controlled by the charge transfer and diffusion process.Under the different temperature condition,electrochemical impedance spectrum presents a single capacitive impedance loop and circuit is controlled by the charge transfer process.At the same time,the Tafel polarization curve was measured on the secondary corrosion factors for pressure and humidity.The experiment results show that electrochemical corrosion rate increases with the rise of pressure below 10MPa,but the oil casing steel corrosion is restrained for pressure lOMPa to 12MPa.Corrosion of oil casing steel is susceptible to much more severity with the increasing of humidity of air.Further,the surface micro-topography,elementary composition and structural analysis of corrosion products,deriving from injection well casing wall oil field locale,weightless test and electrochemical experiment,were characterized by SEM,EDS,XRD,respectively.The results show that corrosion products of the oil casing steel in air-foam flooding exists dehydration and oxidation during multiple alternating injection foam liquid and air,which contributes to better understanding for corrosion mechanism.Finally,corrosion weight loss method and electrochemical corrosion were investigated to evaluate the corrosion inhibitors.It can draw a conclusion that the inhibitor rate of corrosion inhibitor HY802 and HY506B reached 94.21%,82.34%under the concentration of 120mg/L,respectively.Above two inhibitors belong to cathode and anode mixed type.To the study of the oil casing steel corrosion in air-foam flooding,is conducive to provide a reference to further understand the corrosion mechanism of air-foam flooding and put forward relevant control countermeasure,and enlarge the application for this technology in low permeability light oil reservoir.