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Steady state vs transient physics-based models Physics-based simulation models may use correlations to describe certain phenomena, like bubble and droplet entrainment in multiphase flow or the inflow from a reservoir. In practice, many flow simulation tools use a combination of correlations and physics-based models. Here, we can distinguish between steady state physics-based models and transient physics-based models. Physics-based models are instead based on fundamental physical principles, like the conservation of mass, energy and momentum. This means that correlations may only be applicable for a limited range of systems and conditions. Correlations are relationships between two or more physical variables, generally obtained by curve-fitting to a set of observed data (measurements). The tools that are available for predicting the behavior and conditions of multiphase flow in wells and pipes may be divided into two core categories: correlations and physics-based models. More importantly, transient simulations may even be required under steady-state conditions! Correlations vs physics-based modelsīut let’s take a step back. However, as computers have evolved, transient simulators for realistic field operations have become much more accessible, even in real-time. Steady state simulations of multiphase flow are widely used in the petroleum industry, partly because calculations are generally quick and require less information than the more computationally intensive transient evaluations. By Torgeir Vanvik, Principal Project Engineer