Simulação numérica com aproximação unidimensional para a análise do deslocamento de fluidos imiscíveis em tubulações horizontais

Abstract

The displacement of liquid-liquid fluids, referred to as flushing, consists of substituting one fluid within a pipeline by injecting another. Flushing is a widely utilized pipeline cleaning method aimed at preventing blockages in production lines, which are commonly caused by hydrate formation, paraffin deposition, or corrosion. This procedure is extensively employed in removing liquid products, pre-commissioning, commissioning, inertization, and pipeline abandonment operations. To enhance the flushing process, it is crucial to understand the dynamics of the fluid interface and flow patterns. Consequently, parameters such as injection velocity, total displacement time, volumetric fraction, and pressure become significant for process optimization. In this context, this research presents the development of a one-dimensional mathematical and numerical model designed to simulate the displacement of immiscible fluids in horizontal pipelines. The mathematical modeling was based on the mass conservation and momentum balance equations, discretized using the Finite Volume Method (FVM). The resulting algebraic system was solved employing the TriDiagonal Matrix Algorithm (TDMA), while the coupling between pressure and velocity was addressed using the Semi-Implicit Method for Pressure-Linked Equations Revised (SIMPLER) scheme. The computational implementation was conducted in the MATrix LABoratory (MATLAB®) environment, showcasing its effectiveness in solving fluid dynamics-related problems. The model developed in this study enables users to dynamically analyze the behavior of immiscible fluid displacement through graphical representations, including illustrative videos and detailed plots that track key variables such as fluid velocity, volumetric fraction, and pressure along the pipeline during the simulation. Furthermore, the model facilitates the formulation of methodologies to optimize flushing processes in horizontal pipelines by analyzing the injection factor. To verify the consistency of the one-dimensional model, numerical simulations of cases involving water displacement by diesel oil injection were performed using commercial computational software packages ANSYS CFX® and LedaFlow®. Additionally, the model results were compared with experimental data from the literature involving mineral oil displacement through water injection. The outcomes demonstrated that the developed model consistently represented the behavior of immiscible fluid displacement, providing approximate predictions for pipeline cleaning efficiency.