Efficient multiphysics models that can adapt to the varying complexity ofphysical processes in space and time are desirable for modeling fluid migrationin the subsurface. Vertical equilibrium (VE) models are simplified mathematicalmodels that are computationally efficient but rely on the assumption of instantgravity segregation of the two phases, which may not be valid at all times orat all locations in the domain. Here, we present a multiphysics model thatcouples a VE model to a full multidimensional model that has no reduction indimensionality. We develop a criterion that determines subdomains where the VEassumption is valid during simulation. The VE model is then adaptively appliedin those subdomains, reducing the number of computational cells due to thereduction in dimensionality, while the rest of the domain is solved by the fullmultidimensional model. We analyze how the threshold parameter of the criterioninfluences accuracy and computational cost of the new multiphysics model andgive recommendations for the choice of optimal threshold parameters. Finally,we use a test case of gas injection to show that the adaptive multiphysicsmodel is much more computationally efficient than using the fullmultidimensional model in the entire domain, while maintaining much of theaccuracy.
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