Abstract
We present a general framework for flow-based coarsening of grid models, in which blocks in the coarse grid are formed by amalgamation of cells from an underlying fine grid. The amalgamation process is steered by a set of admissible directions that determine the basic shapes of the grid blocks (defined based on topology, geological parameters, etc) and a set of feasible directions that determine how the grid adapts to the flow field (defined based on a set of indicator functions). The framework is flexible and enables the user to create many different types of fit-for-purpose grids. This is illustrated through several examples.