Fluid Characterization for Miscible Floods

Abstract The compositional simulation of a miscible gas injection process depends on an equation of state (EOS) model. An EOS model should not only predict traditional black oil PVT experiments for reservoir fluids but also experiments that give gas-oil compositional information, such as swelling tests, multi-contact tests, and slim-tube MMP. The two most common methods used to estimate MMP with an EOS model are traditional slim-tube simulation and, more recently, the analytical tie-line method. In most cases, the MMP computed from a slim tube simulation agrees well with the analytical tie-line method, but on some occasions, the MMP computed from the analytical method differs significantly from the value derived from slim-tube simulation. Additionally, for some gas floods, slim-tube simulation seems to identify an apparent MMP, but the analytical tieline method fails to give a solution. In this paper, we identify the reason behind these apparent discrepancies: physical dispersion and phase behavior. Thereafter, we propose a reservoir fluid characterization procedure for miscible gas floods that more accurately represents the interaction of flow and phase behavior. We demonstrate this approach for two different gas floods.