Performance evaluation of miscible and near-miscible gas injection processes is available through conventional finite difference (FD) compositional simulation. The Finite-difference method is widely used for solving large-scale multiphase displacement problems (e.g. displacement of oil by water/gas in heterogeneous petroleum reservoirs). While FD simulation has many advantages, it also suffers from some disadvantages. These include numerical dispersion, grid orientation, small time step size and excessive computation time. However, and specifically for compositional simulation, low-resolution compositional simulation is adversely affected by numerical dispersion and may fail to represent geological heterogeneities adequately, while high-resolution simulation may be expensive in computation time. The number of fluid components can possibly be reduced but only at the price of less accurate representation of phase behavior.
Streamline methods have been developed in which fluid is transported along the streamlines instead of the finite difference grid. In streamline-based simulation, a 3D flow problem is decoupled into a set of 1D problems solved along streamlines, reducing simulation time and suppressing any numerical dispersion. Larger time steps and higher spatial resolution can be achieved in these simulations. Streamline-based reservoir simulation, being orders of magnitude faster than the conventional finite difference methods, may mitigate many of the challenges noted above.
In this paper a detailed comparison is given between the results of conventional FD simulation and the streamline approach for Gas Displacement processes (including miscible processes). Different sensitivities on several resolutions of the dynamic grid is presented. Finally, guidelines are given on how streamline can be potentially used to good effect for Gas displacement processes.