1. A computer-implemented method of simulating fluid production in a multi-reservoir system with a common surface network, the method comprising: matching equation of state (EOS) characterization of fluids with a delumped EOS model for each of a plurality of reservoirs within the multi-reservoir system, the delumped EOS model representing different components of the fluids for each reservoir; simulating fluid production in the multi-reservoir system for at least one simulation point in the common surface network, based in part on the delumped EOS model for each of the plurality of reservoirs; determining whether or not fluids produced during the simulation at the simulation point are mixed fluids from different reservoirs in the plurality of reservoirs; when the fluids at the simulation point are determined not to be mixed fluids produced from different reservoirs in the plurality of reservoirs, calculating properties of the fluids using the delumped EOS model corresponding to one of the plurality of reservoirs from which the fluids are produced; and when the fluids at the simulation point are determined to be mixed fluids produced from different reservoirs: generating one or more interpolation tables representing the mixed fluids produced from the different reservoirs via the common surface network, based on the corresponding delumped EOS model for each of the different reservoirs; and calculating properties of the mixed fluids based on the one or more interpolation tables.