Since some years back a new class of Oilfield corrosion inhibitors have been available on the market, oligomeric film-forming inhibitors. In contrast to the standard cationic surfactant type, these chemistries contain multiple positively charged hydrophilic headgroups. These amine-based inhibitors have proven to be broadly applicable, and compatibility studies have shown some of these active bases to be extremely flexible in formulation, allowing a wide range of corrosion inhibition solutions. Further, some of these novel products also fulfill North Sea environmental criteria for offshore application allowing use globally in environmentally restricted areas. The purpose of this paper is to outline and summarize the performance of this inhibitor class under different conditions and how these materials are meeting the diverse challenges connected to use in the oilfield area. This includes e.g. sweet and sour corrosion, severe brines and various compatibility issues.
The standard type of chemicals long used as oilfield corrosion inhibitors are so-called film-forming molecules carrying a positive net charge. More specifically, these additives belong to e.g. the classes fatty amines, alkoxylated fatty amines, amidoamines, imidazolines, pyridinium quats, and quarternary ammonium compounds like alkyl benzyl quats1. Anionic molecules, predominantly phosphate esters, may sometimes also be used as stand-alone inhibitors or as enhancers in formulations with a base inhibitor of the abovementioned type1-3.
A common feature of these chemicals is that they are surface-active. This property is inherently required by the application where key elements include the correct distribution between oil- and water phases and a good attachment to metal surfaces, enabling the creation of a water-repelling film. A second characteristic is that they are monomeric, and normally contain one, or (rarely) two hydrophilic headgroups and similarly one or two hydrophobic alkyl chains.
However, over the past few years a new type of corrosion inhibitor chemistry has appeared on the market. The differentiating feature of these novel molecules compared to the traditional type is that they contain multiple hydrophilic (positively charged) headgroups, and in some cases, also multiple hydrophobic alkyl chains. An obvious advantage of this structure is that it enables several potential points of adhesion to the metal surface. Since these structures have a higher molecular weight than the common types, and frequently consist of a few repetitive structure elements, but still cannot be correctly classified as "polymeric", they will be referred to as "oligomeric" in this paper. These oligomeric inhibitors also, in line with the "standard monomeric type", carry surface active properties4. The aim of this paper is to summarize experiments with this novel chemistry to meet the diverse corrosion inhibition challenges connected to the use in oilfield applications area including e.g. sweet and sour corrosion, difficult brines and diverse compatibility issues.
