Preparation And Evaluation Of New Compound Scale Corrosion Inhibitor

In the process of petroleum production, carbon dioxide in oilfield produced water often causes severe corrosion of carbon steel, resulting in huge economic losses and threaten production safety, but also cause certain environmental pollution. Meanwhile, due to the changes in temperature, pressure, etc, it is easily for inorganic salts to deposited in the casing, underground facilities and gathering pipeline, which can cause obstruction, affecting crude oil production.Adding scale corrosion inhibitor is an effective way to solve the problem of corrosion and scaling. Single inhibitor usually have shortages more or less, and it often can not be solved the corrosion and scaling simultaneously or have a poor performance. By combine two or more of the scale inhibitor and corrosion inhibitor together, it can achieve synergistic effect between the various components, which can not only improve the effect of corrosion inhibition and scale inhibition but also reduce the dosage of inhibitions. In order to get a new kind of phosphorus and environment-friendly scale corrosion inhibitor, the three-element compound based the imidazoline-ammonium-salt, polyaspartic acid and 1-diphosphonic acid were studied. At the same time, the mechanism of compound scale corrosion inhibitor were studied to provide the support for the practical application of scale corrosion inhibitor.The main findings are as follows:(1) Imidazoline-ammonium-salt has a good effect of corrosion inhibition, while HEDP and PASP have a good effect of scale inhibition in a small amount, they also have a certain effect of corrosion inhibition. The optimal concentration ratio of compound corrosion scale inhibitor is A:HEDP:PASP=100:3:2, that is the best formula is a3b2C1.(2) At the temperature of 25℃,40℃,60℃,80℃, the inhibition efficiency increases with the concentration of inhibitors, after reaching a certain concentration, the inhibition efficiency remained unchanged or declined slightly. Under the four temperature, scale inhibition increases with the concentration of inhibitors, and the scale inhibition reached a higher value at the concentration of 150 mg·L-1. Based on the economic considerations and ensure the corrosion and scale inhibition efficiency, selected 120 mg·L-1 as the best working concentration.(3) The inhibition mechanism of compound scale corrosion inhibitor were studied by methods of polarization curves, AC impedance spectroscopy and SEM.The results of polarization curves show that:after added the compound scale corrosion inhibitor, the potential of X65 steel shift towards the positive direction significant, and the value of the shift increases with the increasing concentration of scale corrosion inhibitor. The reactions coefficient of anodic and cathodic are both less than 1, and the reactions coefficient of anodic is much smaller than that of the cathodic, indicating that the compound scale corrosion inhibitor is a typical type of anodic inhibitor.AC impedance results show that:at the temperature of 25 ℃,40℃,60℃,80℃, the compound scale corrosion inhibitor can be adsorbed on the surface of X65 steel and formed a protective film, inhibited the corrosion of X65 steel effectively. The AC impedance results of different immersion time indicated that the adsorbed film formed on the surface of X65 steel comes through a process of growth and decay.The SEM analysis of X65 steel show that:the corrosion of X65 steel was worst at 60℃ among the 25℃,40℃,60℃ and 80℃, the scale corrosion inhibitor can play a protective role for X65 steel when it was added.(4) The scale mechanism of compound scale corrosion inhibitor were studied by methods of conductivity, SEM and XRD.The experimental results of the conductivity show that:the crystallization process of calcium carbonate can be divided into two process:nucleation and grain growth. The scale corrosion inhibitor can extend the time of induction, and primarily control the formation of calcium carbonate through inhibited the process of nucleation however, it has less impact on the process of grain growth.The SEM analysis results of CaCO3 show that:the crystals of calcium carbonate were transformed from calcite to aragonite and vaterite after the addition of compound scale corrosion inhibitor.The XRD analysis results of CaCO3, show that:the scale corrosion inhibitor can promote the formation of aragonite and vaterite while inhibit the formation of calcite at the same time, in order to change the polymorphs of calcium carbonate and inhibit the formation of scale.