SPE 159869

Thermodynamics of Multiphase Flow in Unconventional Liquids-Rich Reservoirs


The average pore size in currently producing unconventional, liquids-rich reservoirs is estimated to be less than 100 nm. At this nano-pore scale, capillary and surface disjoining force interactions (like van der Waals, structural, and adsorption) play an important role on phase behavior that is not considered in conventional PVT studies. In this paper, a comprehensive discussion of thermodynamics required to adequately model phase behavior that can impact multiphase flow in unconventional, liquids-rich reservoirs is presented. Three oil samples from different unconventional reservoirs are used to generate results. The impact of confinement manifests itself in the form of reduction (suppression) of the liquid pressure that the first bubble can form when compared to the bulk fluid measurements that are conducted in PVT cells. It is shown that the suppression of the bubble-point pressure impacts saturated portion of the liquid formation volume factor and extends the undersaturated portion of the curve. The gas composition is different for each supersaturation level and the gas is composed of lighter components as the supersaturation (bubble point suppression) increases