Modifying the gas-oil ratio and water cut of a PVT lookup table using correlations for fluid volatility

Abstract

PVT lookup tables with fixed fluid composition are widely used by simulation software packages to model complex multiphase flow in petroleum production systems. These tables contain pre-calculated values of various fluid properties, including phase fractions, densities, viscosities, and other properties that are relevant to fluid behaviour. The pre-calculated values are based on a given set of pressures, temperatures, and composition. The tables enable efficient and accurate simulations by reducing computational load. However, they are created for fluids with fixed total composition, which limits their use for modelling fluids with varying gas-oil ratios and water cuts.To address this limitation, this work introduces a novel methodology for adjusting the gas-oil ratio and water cut within a given PVT table without changing the composition of the fluid. The methodology relies on correlations developed for volatility, estimating bubble- and dewpoint pressures when adjusting gas-oil ratio and water cut. The model demonstrates remarkable efficacy, achieving excellent agreement with bubble- and dewpoint pressures, yielding average absolute relative errors of only 0.85% and 0.68% respectively for gas-oil ratio adjustments, and 0.97% for water cut adjustments. It is further demonstrated that the new model accurately predicts phase fractions of typical volatile oils below the critical temperature and black oils when adjusting the gas-oil ratio and water cut. Additionally, the model can provide rough estimates for volatile oils above the critical temperature and for gas condensates. Moreover, model reliability is expected if the gas-oil ratio and water cut adjustments are kept within a range of 20–180% of the original values.The work provides a valuable approach to improve the flexibility of fixed composition PVT lookup tables for simulating multiphase production systems.