Effect of corrosion inhibitor on water wetting and carbon dioxide corrosion in oil-water two-phase flow

The internal corrosion of flowlines and pipelines made from carbon steel is encountered in the oil and gas industry. The corrosion process is primarily associated with the presence of free water in offshore or onshore production, particularly when it is accompanied by carbon dioxide gas. Corrosion inhibitor injection in oilfields is a very common and useful method for pipeline internal corrosion prevention. There is a need to understand the physics of phase wetting, carbon dioxide corrosion and the effect of corrosion inhibitor on those two processes in oil-water two-phase flow.;In this study, the flow patterns and phase wetting regimes of oil-water two-phase flow were experimentally investigated in a large scale flow loop. Five major flow patterns were observed within the test flow conditions by flow visualization. Three types of phase wetting regimes (water wetting, oil wetting and intermittent wetting) were found by using a carbon steel test section consisting of wall conductance probes, wall sampling and corrosion monitoring. Based on experimental results, phase wetting maps were generated for model oil and five crude oils in the flow loop tests.;Following the large scale flow loop tests, a small scale flow apparatus, called a doughnut cell was developed to simulate phase wetting occurring in oil-water two-phase pipe flow. Phase wetting maps were created for model oil and five crude oils in the doughnut cell tests.;Two generic inhibitors, quaternary ammonium chloride and fatty amino were studied in this work. Corrosion inhibition tests showed that a direct exposure to oil phase enhances the performance of fatty amino inhibitor. Both inhibitors produce not only a reduction in oil-water interfacial tension, which promotes easier water entrainment by the oil, but also changes the wettability of the steel surface from hydrophilic to hydrophobic, which may reduce the possibility of CO2 corrosion.;A mechanistic phase wetting prediction model was developed to predict the transition between water breakout and full water entrainment. The model was validated with the experimental results of model oil and crude oils obtained from flow loop and doughnut cell tests. The model predictions have a good agreement with empirical results of model oil, but the model overpredicts the critical oil velocity of full water entrainment for all tested crude oils. The phase wetting prediction model is also used to correct the geometry difference between doughnut cell and flow loop. A corrosion inhibition model was built based on fitting corrosion inhibition test results with the Langmuir adsorption isotherm. A strategy is proposed to predict uninhibited and inhibited CO 2 corrosion rate in oil-water two-phase pipe flow by integrating phase wetting, CO2 corrosion and inhibition models.