Sensitivity of Steamflood Model Results to Grid and Timestep Sizes

Abstract

Abstract Numerical simulation of complex processes in oil reservoirs has become a standard tool. The grid size and timestep sensitivity of a simulator are of prime concern in reaching the correct conclusions in any study. This paper presents an analysis of the sensitivity to timestep and grid size of a one-dimensional (1D) and two-dimensional (2D) compositional multiphase steamflood model used to simulate a heavy-oil reservoir. The behavior of primary variables before breakthrough in the 1D and 2D cases is presented for clearer understanding of steamflooding heavy-oil reservoirs. The peculiar features exhibited by primary variables of the production and injection blocks for the 1D reservoir plus timestep and grid-size effects on primary variables for 2D cases studied are discussed. Sensitivity studies of grid and timestep size are meaningful only if each is carried out while the other variable has minimum truncation error. The recovery performance parameters are less sensitive to timestep size than to grid size. They are also less sensitive in the 2D runs than in the 1D runs. The time/pore-volume-injected (PVI) relationship is very sensitive to grid size, and to a lesser extent, to timestep size.