Numerical effects of fluid flow modelling in surfactant chemical flooding

Numerical simulation of surfactant flooding using conventional reservoir simulation models can lead to unreliable forecasts and bad decisions due to the appearance of numerical effects. The simulations solve systems of nonlinear partial differential equations describing the physical behavior of surfactant flooding by combining multiphase flow in porous media with surfactant transport. The simulations approximate the solutions by discretization of time and space which can lead to spurious oscillations, instabilities or deviations in the model outcome. In this work, the black oil decoupled implicit method was used to carry out simulations at various altered conditions (with dimensions at the reservoir scale) so as to investigate the model behavior in comparison with the analytical solution obtained from fractional flow theory. Various conditions were examined including changes to cell size and time step as well as the properties of the surfactant and how it affects miscibility and flow. The main aim of this study was to identify if oscillations occur, why and when they occur. The results show spurious oscillations occur at the surfactant flood water bank and removed after the adsorption rate increased by 25% at its initial value of 0.0002kg/kg. While the oscillation was negligible after grid refinement of 5000 grid block set-up in the x-axis. The results also show aqueous phase velocity and pressure drop contributed significantly to the appearance of oscillation. The oscillation was not totally removed by the implementation of a sudden transition in the relative permeabilities around the surfactant front. The oscillations induced earlier solution miscibility that caused a misleading prediction of improved oil recovery in comparison to the solution without numerical effect. Thus, it is important to improve existing models and use appropriate guidelines to stop oscillations and remove errors.