The invention relates to a method of simulating operations of an oilfield, which has process facilities and wellsite operatively connected, each wellsite having a wellbore penetrating a subterranean formation for extracting fluid from an underground reservoir. The method steps include selecting simulators for modeling the oilfield with at least one of the simulators having functionality to model fluid injection, selectively coupling each of the simulators according to a predefined configuration, and modeling an injection operation of the oilfield by selectively communicating between the simulators.