The Mechanisms Behind Asphaltene Precipitation – Successfully Handled by a Classical Cubic Equation

Abstract Oil reservoir fluids may contain asphaltenes, which at high pressure are found dissolved in the oil phase. Precipitation of a separate asphaltene phase can occur when the pressure drops during production. Using fundamental thermodynamics, the paper shows that such precipitation is determined by the volumetric response of the oil phase to the pressure reduction, and that this response can be described by a classical cubic equation of state. There is no need for more complex thermodynamic models and no need to consider molecular association. This is documented through successful modeling of asphaltene precipitation data for 12 reservoir fluids from different locations around the world and with varying asphaltene contents using the Soave-Redlich-Kwong equation of state. The paper describes how to best characterize a reservoir fluid containing asphaltenes and how to assign asphaltene model parameters to a classical cubic equation of state.