Modelling of Multiscale Structures in Flow Simulations for Petroleum Reservoirs

Flow in petroleum reservoirs occurs on a wide variety of physical scales. This poses a continuing challenge to modelling and simulation of reservoirs since fine-scale effects often have a profound impact on flow patterns on larger scales. Resolving all pertinent scales and their interaction is therefore imperative to give reliable qualitative and quantitative simulation results. To overcome the problem of multiple scales it is customary to use some kind of upscaling or homogenisation procedure, in which the reservoir properties are represented by some kind of averaged properties and the flow is solved on a coarse grid. Unfortunately, most upscaling techniques give reliable results only for a limited range of flow scenarios. Increased demands for reservoir simulation studies have therefore led researchers to develop more rigorous multiscale methods that incorporate subscale effects more directly. In the first part of the paper, we give an overview of some of the many scales that are considered important for flow simulations. Next, we present and discuss several upscaling approaches that have played a role in the history of reservoir simulation. In the final part, we present some more recent approaches for modelling scales in the flow simulations based upon the multiscale paradigm. We conclude with a discussion of benefits and disadvantages of using multiscale methods, rather than using traditional upscaling techniques, in reservoir simulation.