Comparison of an impec and a semiimplicit formulation for compositional reservoir simulation

Abstract

In compositional reservoir simulation, a set of non-linear partial differential equations must be solved. In this work, two numerical formulations are compared. The first formulation is based on an implicit pressure and explicit composition (IMPEC) procedure, and the second formulation uses an implicit pressure and implicit saturation (IMPSAT). The main goal of this work is to compare the formulations in terms of computational times for solving 2D and 3D compositional reservoir simulation case studies. In the comparison, both UDS (Upwind difference scheme) and third order TVD schemes were used. The computational results for the aforementioned formulations and the two interpolation functions are presented for several case studies involving homogeneous and heterogeneous reservoirs. Based on our comparison of IMPEC and IMPSAT formulations using several case studies presented in this work, the IMPSAT formulation was faster than the IMPEC formulation.