Flow diagnostics refers to a set of simple and controlled numerical flow experiments that are run to probe a reservoir model, establish connections and basic volume estimates, compute dynamic heterogeneity measures, and and quickly provide a qualitative picture of the flow patterns in the reservoir. Flow diagnostics can also be used to compute simplified forecasts of fluid displacement and perform what-if and sensitivity analyzes in parameter regions surrounding preexisting simulations. The module offers a computationally inexpensive alternative to performing full-featured multiphase simulations to rank, compare, and validate reservoir models, upscaling procedures, and optimize production scenarios.