Transient multiphase flow modeling and validation in a real production system with high CO2 content using the drift-flux model

This study presents a transient multiphase flow simulator based on the non-isothermal Drift-Flux model that aims to reproduce oil and gas production systems. The mathematical model consists of three mass conservation equations, one equation for the momentum mixture and one equation to reproduce the energy conservation of the gas-liquid-liquid mixture, assuming mass transfer between the produced liquid and gas phases and neglecting the slip between the liquid phases. The solver utilizes the finite volume method with a semi-implicit approach making use of the upwind first order scheme with staggered grid. Liquid holdup and liquid amount between the liquid phases are evaluated explicitly whereas the coupling between velocities and pressure fields is implicit by building a global matrix. The temperature field is obtained in an uncoupled way after the volumetric fraction, mass flow rates and pressure calculus. For the sake of validation of the solver, the simulated profiles of pressure, temperature and liquid holdup along the production line are compared with those given by the reference benchmark for multiphase flow simulation in the Oil & Gas industry, OLGA® (OiL and GAs simulator), and real field data in the steady-state regime of an offshore oil producer well with high CO2 content. The influence of input parameters on the simulation results is investigated. A sensitivity analysis is performed on the fluid modeling, considering the Black-Oil model making use of two different Rs correlations and the compositional approach. The influence of drift parameters on the numerical solutions is also verified. Liquid holdup, pressure and temperature trends are analyzed upstream and downstream of the master valve as well as in the well bottom and on the separator regions. Finally, important production procedures such as well shutdown and start-up are analyzed. The main motivation is to verify the solver capability to reproduce the multiphase flow behavior during the oil and gas production, especially for a fluid with high GOR and high amount of CO218