How Do Inhibitors Mitigate Corrosion in Oil-Water Two-Phase Flow Beyond Lowering the Corrosion Rate?

Corrosion inhibitors are commonly used to mitigate corrosion in oil and gas pipelines, and the choice of inhibitor for a particular oil field depends on the conditions of the field (oil chemistry, water chemistry, temperature, etc.). To find the optimum formulation for each field condition, extensive laboratory tests are carried out, which include corrosion inhibitor performance, foaming, and emulsification, to name a few. However, corrosion inhibitors can have the additional advantage of altering the wettability of the steel surface from hydrophilic (water wet) to hydrophobic (oil wet) by forming a hydrophobic adsorption layer on the steel surface. In the current work, the ability of chemicals to alter the wettability of the steel is investigated by measuring the static contact angle in a goniometer, as well as the dynamic wetting with a small scale flow apparatus called a doughnut cell, especially designed for this purpose. The doughnut cell makes it possible to measure the water and oil wetting of a steel surface using flush-mounted conductivity pins that detect whether water (conductive fluid) or oil (non-conductive fluid) are covering the surface. The two generic compounds tested here, a quaternary ammonium chloride and a fatty amine, lowered the corrosion rate, altered the surface wetting from hydrophilic (mostly water wet) to hydrophobic (mostly oil wet), and lowered the oil-water interfacial tension, facilitating water entrainment in the oil. A doughnut cell was used to map out how an inhibitor can increase the oil-wetting regime for a given water cut. It is a practical tool that can be used to help optimize the inhibitor dosage and maximize its value. It can also be used in new field development, where enhanced oil wetting could be factored into the corrosion allowance calculation.