A Solid Corrosion And Scale Inhibitor With High Temperature Resistance

During the process of oil and gas production, it is a common mean to prevent corrosion and scale by adding the liquid inhibitor into the oil well. But there are many problems in this way, for example: The effective protection period of liquid inhibitor is shorter for it is very easily brought out by the produced fluid that is bulk and very high velocity. It's very hard for liquid inhibitor to get the well below the working valve so that 30-50% pipes are not protected. Much equipment, such as high-pressure filling pump, vessel, transports, are need for adding the liquid inhibitor, so it is very inconvenient for administration. Aside there is inevitable loss of inhibitor for its adhesion to the oil pipe. The preparation of environmental friendly corrosion and scale inhibitor with high temperature resistance was discussed in detail. The inhibitor was mainly composed of polyaspartic acid used as major scale inhibitor, and imidazolines as main corrosion inhibitor. And its properties such as dissolution and dispersion ability in water, high temperature resistance, scale and corrosion inhibition efficiencies were studied. Also its adsorption and desorption behaviors were studied by electrochemical methods.Experiments results illustrate that the inhibitor has good dissolution and dispersion abilities, and can be dissolved completely for 30 days while immersed in aqueous solution at 90℃.Also the results show that the inhibitor possesses good scale inhibition ability to calcite. At a very low concentration of 5mg/L, the scale inhibition efficiency reaches 86.96% at 60℃, and 68.53% at 90℃. With the concentration of 10mg/L, the scale inhibition efficiency is 91.03% at 60℃, and about 82.52% at 90℃.The influences of salts such as sodium chloride, sodium nitrate and ammonium nitrate on the scale inhibition were also conducted. Results indicate that all salts have synergistic effect on the inhibitor, and the effect is in the order of NaCl>NH4NO3>NaNO3.On the other hand, the inhibitor also exhibits good corrosion inhibition ability for A3 steel in 1% NaCl solution. At 40℃, the inhibition efficiency is about 80.68%, 72.82% at 60℃, and 61.92% at 80℃.Also, the inhibitor has very good inhibition efficiency over A3 steel when it is mixed with Zn2+ of 2mg/L. When the concentration of inhibitor is 50mg/L, the inhibition efficiency is about 80.00% after mixed, while the inhibition efficiency is about 62.55% before mixed.Polarization tests demonstrate that the inhibitor is an anodic adsorption type corrosion inhibitor, which retards effectively the anodic process of corrosion.In the Nyquist plots of A3 steel with inhibitor at 30℃, the capacitive loop at high frequency part means the film covering the anode, and the line at low frequency part means the diffusion-controlled reaction, and exhibits the characteristic of Warburg impedance. The scale inhibition mechanisms of inhibitor are the cooperation of chelation, interface adhesion, dispersion, threshold effect, etc.Based on the theory of corrosion electrochemistry and the experimental results, the adsorption behavior of inhibitor obeys the Langmuir isotherm as following: where,, C is the concentration of inhibitor in mg/L, and is the inhibition efficiency (%).