Abstract

New monoamine and diamine compounds were synthesized from dodecylamine and 1, 12-dodacanediamine, and evaluated as acid corrosion inhibitors for low-carbon steel. The inhibition behavior of these compounds was examined using gravimetric and electrochemical methods (linear polarization and Tafel plot). Weight loss tests were conducted in 1M HCl at 140oF for six hours. To simulate acid stimulation treatments, other weight loss tests were conducted using typical acid stimulation concentrations 4.1 and 7.7 M HCl, (equivalent to 15 and 28 wt%, respectively) at 140oF for two hours. The effects of corrosion inhibitor type and concentration, and acid concentration were investigated.

Experimental results indicated that examined monoamine compounds exhibited better corrosion inhibition for low-carbon steel in 1 M HCl acid solution than their corresponding diamine compounds. This behavior was clearly observed at a low corrosion inhibitor concentration of 50 ppm. Tafel Plot results suggest that the inhibition mechanism for all examined compounds involved a simple reaction site blocking. For both monoamine and diamine compounds, the inhibition performance was found to increase with increasing corrosion inhibitor concentration and decrease with acid concentration.

Aromatic and multiple bonds substituents introduced to monoamine and dimamine compounds were found to enhance inhibition performance compared to the starting materials (dodecylamine and 1, 12-dodacanediamine). This is attributed to the p-electrons present in aromatic and multiple bonds substituents. Both dodecylamine derivatives with a triple bond or an aromatic substituent exhibited excellent protection in 4.1 M HCl. However, the derivative with a triple bond showed the best protection (98%) at 7.7 M HCl. This result is very promising and suggests that this corrosion inhibitor has a good potential to be used as a corrosion inhibitor in oil/gas wells acid stimulation treatments.

Introduction

Amine-based corrosion inhibitors are widely used in the oil and gas industry. They are extensively used to protect well tubulars during matrix acidizing treatments. Stimulation treatments of oil and gas wells include the use of concentrated solutions of hydrochloric acid. This acid is employed to enhance the permeability of the reservoir rock and remove formation damage.1,2 Hydrochloric acid is selected in such treatments because the reaction products (mainly calcium chloride) are soluble in water. Hydrochloric acid corrodes steel through reaction with iron, present as the major component, as illustrated by the following chemical reactions:

Fe+2HCL*FeCl2+H2
(1)

Commercial HCl solution usually contain ferric ion, present as iron chloride which makes metals corrode much more rapidly due to availability of two cathodic reactions, hydrogen evolution and ferric ion reaction:3

Fe3+*+*eFe2+
(1)

It is reported by Alfndry et al.4 that hexamethylenetetramine protects steel in HCl, but the protection is reduced by the presence of Fe3+. The most effective type of corrosion inhibitors for well stimulation is film-forming amines and their salts.5 According to Frenier and Growcock 6, nitrogen compounds constitute the largest class of inhibitors for HCl acid. Nitrogen compounds and acetylenic alcohols are often used together to give high levels of protection at elevated temperatures (= 100oC), especially when concentrated acids are used.6 At higher temperatures, "aids" or intensifiers" must be added to the acid to improve the inhibition and to prolong the treatment time.7

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