The accurate simulation of complex subsurface reservoirs, such as those found in onshore Abu Dhabi, presents significant computational challenges, particularly when dealing with high-resolution models. Fully implicit solvers are traditionally used in reservoir simulation due to their robustness and stability, especially when handling non-linearities associated with multiphase flow in heterogeneous porous media. However, their computational cost increases dramatically with the size and complexity of the model, causing challenges for the simulation of high-resolution models.
To address these limitations, the industry has seen the development and integration of the multiscale sequential fully implicit (SFI) method for reservoir and streamline simulation. The SFI method is a flexible and configurable framework that leverages a sequential solution approach to apply different custom solvers for the pressure and transport calculations separately, for example the Algebraic Multiscale Solver (AMS) (Zhou and Tchelepi, 2012; Wang et al., 2014; Manea et al., 2016, 2017) and the Multiscale Restricted
Smoothed Basis (MsRSB) method that enhanced the pressure calculations (Møyner and Lie, 2016a, b; Møyner and Tchelepi, 2018; Kozlova et al., 2016a, b; Lie et al., 2017). Recent work on the original implementation of the MsRSB solver in the commercial simulator (Watanabe et al., 2023) provided significant improvement to the linear and non-linear convergence in heterogeneous models with high permeability contrast. Fig. 1 shows schematic to compare between multiscale SFI & fully implicit (Schlumberger, 2024).