An optimization approach to reduce the risk of hydrate plugging during gas-dominated restart operations

In this paper, common meta-heuristic optimization techniques are applied for the potential application of reducing the risk of hydrate plugging in gas-dominated flowlines during restart operations. Based upon a hydrodynamic approach first shown in the experimental study of Leporcher et al. (2002), a transient, gas-dominated restart operation is emulated using Computational Fluid Dynamics (CFD) for a pipe section featuring a single low-spot filled with variable heights of free water. A two-phase CFD model has been constructed and validated using OpenFOAM® to simulate the flow. A modification has been made to the solver in order to capture the interfacial area between the gas and water phases at each time step, allowing an estimation of the amount of hydrate growth to be made during the transient and steady state phases of the restart operation. A genetic algorithm has then been used on different types of surrogate models with the goal of minimizing the restart gas velocity such that a defined plugging risk is minimized. Finally, an approach to apply this methodology to actual flowlines is discussed.