Computational Study of Water Wetting Regimes Established in Horizontal Oil-Water Flows: Flow Regime Maps and Corrosion

Internal corrosion in oil-water pipelines is generally associated with the water phase being in contact with the metal surface at the bottom of the pipe.  Prediction of phase distribution, especially the information whether oil or water wets the pipe wall is an important factor, which can affect the corrosion mitigation strategy and increase confidence in the integrity of the pipeline. There are large knowledge gaps in this area of research and consequently only empirical criteria are used in the industry.In the present work, detailed numerical study for turbulent oil-water multiphase flow is carried out in a horizontal carbon steel pipeline to predict different water wetting regimes as well as corrosion kinetics of fluid-metal interaction. Computational Fluid Dynamics simulations include Eulerian multiphase models with appropriate sub-models for interfacial forces, turbulent interaction and population balance equations. Population balance techniques identify and follow the dispersed (water) phase dynamics such as droplet breakage and coalescence in a detailed fashion. In addition, concentration equation for ferrous ion (Fe2+) is modeled to capture corrosion kinetics. The current study focuses on flow pattern computations for water cut of 20% and lower. Numerical simulations captured various water wetting regimes inclusive of intermittent, fully wetting, dispersed and semi-dispersed water-in-oil behavior. Results were in very good agreement with the experimental observation. Calculations clearly predicted that for given superficial water velocity, elevating the superficial oil velocity leads to transition of regimes from stable water wetting to intermittent water wetting and subsequently stable oil wetting scenario. Probing into the flow profile of the two-phase flows under different wetting regimes revealed the existence of severely under-developed system during a water-oil intermittent wetting regime. For a complete wetting regime, flow profile fluctuations were considerably reduced. However, fully developed oil-water flow conditions weren’t achieved. Phasic fraction and velocity distribution at different flow cross-section reveal the flow modulations as a function of the turbulence inherent to the two-phase system. Corrosion computations clearly indicate a substantial generation of Fe2+ ion under stable water wetting regime while the concentration and corrosion levels deteriorate with intermittent water wetting, an effect well characterized in flow loop tests.