Polymeric Corrosion Inhibitors - a New Class of Versatile Oilfield Formulation Bases
Authors: Hellberg Per-Erik , Zuberbuehler Adrian 
Published: May 2016

Produced (oilfield) brines are rich in dissolved salts and thus have high ionic strength as well as conductivity. Further, they are in contact with ferrous metals used for oil- and gasfield installations. Thus, the potential for electro-chemical corrosion reactions in these environments is high. The latent consequences are e.g. general metal wastage, pitting, embrittlement and cracking which all can lead to equipment failure, or even catastrophic results like major oil spills. One of the most abundant methods to mitigate such events is the use of organic corrosion inhibitors (CIs). No doubt, film-forming organic CIs are one of the most important oilfield production chemicals as ranked by volumes used globally. There is a constant need to develop new chemistry in this field, driven by requirements for more environmentally adapted products, lower dosages, higher performance and meeting new compatibility and high temperature/high pressure (HTHP) challenges. The development and testing of of corrosion inhibitors for oil- and gasfield (offshore) use has been thoroughly reviewed (1).

1 Organic Film-forming Oilfield Corrosion Inhibitors

The most common classes of chemicals used today for this application are fatty amines, alkoxylated fatty amines, amidoamines, imidazolines, pyridinium quats and quarternary ammonium compounds like alkyl benzyl quats.

All of these are surface active compounds, a property which is inherently required by the application where correct distribution between oil- and water phases as well as good attachment to metal surfaces and the creation of a water-repelling film are key elements. Another common feature is that they are monomeric, and normally contain one, or maybe two hydrophilic headgroups and similarly one or possibly two hydrophobic alkyl chains.

These film-forming corrosion inhibitors are always formulated in order to get the highest possible effect at the lowest cost and to facilitate transport, handling and dosage. Formulation is also needed in order to adapt to different water-to-oil ratios, the presence of solid materials (like sand), corrosive gases etc. in pipelines and other crude oil- and gas transporting and treatment equipment. Formulating an effective corrosion inhibitor can be a complex task. Many amines are neutralized with an organic acid when they are formulated in order to make them more water soluble. Further, a "synergist" is many times added to enhance the performance of the primary inhibitor. It is not unusual for formulations to contain 7–8 different components, including 3–4 active CIs. Requirements to include more than one type of production chemical in a single formulation, or to guarantee compatibility with certain materials under HTHP conditions can pose further challenges.

2 General Properties of the New Oligomeric/Polymeric Corrosion Inhibitors

A new class of oilfield corrosion inhibitors has now been developed. The differentiating feature of these novel molecules compared to the traditional type previously described is that they contain multiple hydrophilic head groups and in some cases multiple hydrophobic alkyl chains also. An obvious advantage of this structure is that it enables several potential points of adhesion to the metal surface. However, a number of other interesting attributes for these chemistries have been found as well, which will be described in detail in this paper.

In order to simplify the presentation, these products be called "polymeric", although there clearly may also be arguments to classify them as "oligomeric".