Structural Identifiability of Grid Block and Geological Parameters in Reservoir Simulation Models

It is well-known that history matching of reservoir models with production measurements is an ill-posed problem, e.g. different choices for the history matching parameters may lead to equally good history matches. We analyzed this problem using the system-theoretical concept of structural identifiability. This allows us to analytically calculate a so-called information matrix. From the information matrix we can determine an identifiable parameterization with a significantly reduced number of parameters. We apply structural identifiability analysis to single-phase reservoir simulation models and obtain identifiable parameterizations. Next, we use the parameterization in minimizing an objective function that is defined as the mismatch between pressure measurements and model outputs. We also apply the structural identifiability analysis to an object-based parameterization describing channels and barriers in the reservoir. We use the iterative procedure to determine for reservoir models with 2025 grid block permeability values a structurally identifiable parameterization of only 13 identifiable parameters. Next, we demonstrate that the parameterization leads to perfect history matches without the use of a prior model in the objective function. We also demonstrate the use of the identifiable object-based parameterization, leading to geologically more realistic history matches.