Study On Corrosion Inhibitors For Saturated Saltwater Drilling Fluids

In well-drilling projects, the corrosion of drill pipe is ubiquitous phenomena; moreover, it becomes more serious along with the development of deep wells and high-speed wells and it becomes more urgent because of rise in price of drill pipe in recent years. Lately, Jiangsu oil field drills lots of salt wells locating in Hongze and Huaiyin, saturated saltwater drilling fluids is used, the concentration of Cl- is very high; various additives are added into the drilling fluids; the conductance of drilling fluids is high; the temperature of wells is high(80℃~90℃ );Dissolved oxygen exists in it; so, the corrosion of drill pipe is more serious.In this work, by the method of EDS analysis of drill pipe corrosion production, we can conclude that the corrosion of drill pipe is mainly caused by the depolarization of dissolved oxygen; anode process: Fe-2e→Fe2+, cathode process: O2+2H2O+4e→ 4OH-, the whole process: 2Fe+3/2O2+H2O→2FeOOH→Fe2O3+H2O.Potentiodynamic polarization test results show: nitrogen containing compound A can apparently enhance G105 steel's pitting potential in saturated saltwater among oxidation-type corrosion inhibitors; so does silicon containing compound B among deposition-type inhibitors; organic amine C also works a lot among adsorption-type inhibitors; then, by the method of orthogonal experiments we picked out composite inhibitor: 1%A+0.5%B +0.5%C.Laboratory dynamic simulation test results show: the inhibition efficiency of composite inhibitor is above 95%, which is superior to single inhibitors; Spot evaluation test, which was carried out by the method of corrosion test ring, results show: composite inhibitor is consistent to saturated saltwater drilling fluids, its inhibition efficiency is about 90%.X-ray photoelectron spectroscopy (XPS) was used to study the composition of G105 steel passive film formed in saturated saltwater. Results show that the major elements in the passive film are Fe, C and O; and that there are two oxides of iron( gamma -FeOOH, FeO) in the film. After adding composite inhibitor, the content of gamma-FeOOH in the film is increased, so, the ability of resistance of Cl- pitting corrosion is enhanced.