1. A method executed by a computer, the method comprising: selecting a production workflow for a subterranean structure that comprises wells wherein the production workflow depends on availability of simulation data; responsive to selecting the production workflow, building a simplified simulation model for the subterranean structure by selecting a grid size for a grid of the simplified simulation model, the grid size greater than a grid size for a grid of an existing detailed simulation model for the subterranean structure, populating the grid of the simplified simulation model using data wherein the data comprises data from the existing detailed simulation model, generating candidate simplified simulation models using a stochastic process wherein each of the candidate simplified simulation models comprises the grid size for the grid of the simplified simulation model, performing simulation runs using each of the candidate simplified simulation models to generate candidate simulation data, after performing the simulation runs, comparing the generated candidate simulation data to measured data for the subterranean structure to rank the candidate simplified simulation models with respect to accuracy, performing a sensitivity analysis to fine tune at least a top ranked candidate simplified simulation model of the candidate simplified simulation models, and selecting a fine tuned candidate simplified simulation model of the candidate simplified simulation models; and performing one or more runs of the selected, fine tuned candidate simplified simulation model to generate the simulation data for the production workflow.