The corrosion phenomenon is a severe problem in many industries. Metallurgical corrosion issues in the oil industry are frequently related to aggressive environments such as high H2S content (sour environment), HCl plus atmospheric oxygen (acidic interventions) or high CO2 flows, combined with high pressures, high temperatures, and high salinity conditions faced by materials in all oil wells. Additionally, the entire value chain —from drilling, production, and transportation to refinery processes— is affected by internal corrosion problems [[1], [2], [3], [4]]. The global cost of corrosion problems in the oil industry is estimated at 3–4 % of each nation's gross domestic product, equivalent to approximately US$375–875 billion annually [5]. To address this challenge, it is important to focus on researching and developing viable corrosion-inhibitors technologies that are both technically and economically feasible. From a chemical perspective, many researchers have focused on synthesizing compounds to prevent the corrosion of pristine steel or to halt further oxidation on surfaces already passivated by iron oxide, including propargyl alcohol [6], Mannich bases [7], trans-cinnamaldehyde [8], and other alloys used in the oil industry.

Corrosion in the oil and gas industry, particularly in oil wells, is caused by environmental conditions (humidity, temperature, flow, pressure, and atmospheric oxygen), the composition of the oil well fluids (oil, sediments, brines, emulsions, and associated gases), microorganisms, pH, and artificial chemical interventions previously applied [9]. During conventional hydrocarbon extraction processes in mature Mexican fields, several types of degraded iron —such as pyrite (FeS2), hematite (Fe2O3), and siderite (FeCO3)— are observed in the pipes or other metallic components of oil-well installations. These compounds are formed by aggressive environments containing either high concentrations of H2S, HCl combined with atmospheric oxygen, or high CO2 flows (Fig. 1).

In addition, crude oils with high naphthenic acid content and sour sulfide compounds become significantly more corrosive to iron alloys. When oil well metal components undergo the oxidation processes mentioned above, the reservoir wall also suffers from plugging due to asphaltene and resin accumulation. Consequently, oil wells require stimulation to improve hydrocarbon flow.

Acid stimulation through HCl flooding is a common technique in the oil and gas industry. In this process, HCl mixed with water and additives (including corrosion inhibitors) is pumped into the wellbore, where it reacts with formation rock, dissolving minerals such as calcium carbonate and limestone. This creates flow channels, increasing rock porosity and permeability to enhance oil and gas production. This stimulation method is most effective in carbonate formations (e.g., limestone and dolomite), though it can also be used in sandstone formations to remove scale and other damage [10].

However, HCl is highly corrosive and can damage wellbore equipment by attacking metallic surfaces. The corrosion mechanism involves formation of Fe2+ cations from neutral Fe atoms through the reaction:Fes+2HClaq→FeCl2aq+H2g

The resulting Fe2+ subsequently reacts with water and atmospheric oxygen, H2S or CO2 to form corroded surfaces of pyrite, hematite, and siderite, respectively (Fig. 1). To mitigate this corrosion, inhibitors are used to passivate internal pipeline surfaces that transport HCl-containing well fluids.

Preventing and controlling pipeline corrosion in the oil industry can be better achieved through understanding the phenomenon at the molecular level. Computational chemistry serves as a powerful tool for designing new chemical inhibitors to protect metallic surfaces, including pure iron, iron alloys, aluminum, cobalt, copper, Cu2O, Fe2O3, and FeS2 [11,12].

Many of the common commercial chemicals used as corrosion inhibitors in the oil and gas industry based on organic compounds with nitrogen, oxygen, and sulfur, for instance, azole, benzotriazole, and pyrimidine families [13] damage the environment and are toxic [5]. Likewise, some green-based corrosion inhibitors obtained from natural extracts or biomimetic versions of biological compounds have been developed to be non-toxic and environmentally friendly compared with commercial inhibitors [10]. Other examples are the polymeric inhibitors, which are effectively adsorbed on metallic surfaces due to their ability to form numerous interactions: polyanilines, polyamides, polyimines, polyvinyl pyridines, polyvinyl pyrrolidines, poly(acrylic acids), polyacrylamides, cellulose-carboxy methyl cellulose, polyvinyl acetates, polyvinyl benzenes, and polyalcohols [14].

It should be noted that polymeric corrosion inhibitors are particularly important in the oil industry due to their stability under high pressure (5000 to 10,000 psi) and high temperature (200–400 °C) conditions. Some examples of polymers stable under these extreme conditions include polysulfide phosphate esters and polyisobutylene succinic esters [15]. The structure-activity relationship reveals that effective polymeric corrosion inhibitors contain heteroatoms (P, S, N, and O) in their molecular structure. Likewise, studies have identified that polymer physisorption on metallic surfaces plays an important role, while their elastic properties enable integration with various chemicals to enhance corrosion-inhibition performance [16].

Corrosion inhibitors must comply with strict eco-friendly regulations regarding toxicity and biodegradability to minimize environmental damage. In this context, amino acid-derived corrosion inhibitors are particularly eco-friendly for use in different media in contact with copper, aluminum, iron, and its alloys. These compounds are notably nontoxic, biodegradable, soluble in both aqueous and oil media (due to their zwitterionic properties), relatively inexpensive, and easy to produce [17].

In the present work, we demonstrate the computational chemistry-based design and experimental performance of a novel bio-inspired polymeric-zwitterionic corrosion inhibitor (PZCI). This compound features two alkyl-substituted quaternary-amine/carboxylic-acid zwitterionic polar heads linked by a polyethylene glycol bridge, whose synthesis and low environmental impact were previously reported [18]. We study PZCI's capability to protect metallic surfaces in Mexican oil well installations that are corroded into the aforementioned iron oxide surfaces. Using ab initio Density Functional Theory (DFT), we gain insights into PZCI's performance in forming protective thin films and its potential to prevent and control the corrosion problem.