On the injectivity estimation in foam EOR

Abstract

In this work, we study injectivity issues caused by the use of the Peaceman equation in the numerical simulation of chemical enhanced oil recovery (EOR) processes aimed at reducing fluid mobility, such as foam injection, on coarse grids. Employing analytical solutions, we demonstrate that the Peaceman equation, commonly applied to mathematical modeling of the injectivity in commercial simulators, leads to errors of more than two orders of magnitude in the injection well pressure drop when the foam flow effects near the well are considered for assuming homogeneous mobility in a coarse-well block. To circumvent this issue, we investigate numerical treatments focused on the grid of well blocks through local grid partitioning strategies (radial and Cartesian) to improve the injection well bottom-hole pressure (BHP) estimation. This methodology does not change the input data nor the injectivity model characteristics of the commercial simulator. It does not significantly affect the computational cost of the simulation, since the grid treatment occurs only in the blocks containing the wells. Thus, the radial and Cartesian grid partitioning for the well block are compared using the STARS simulator. Our results show the clear capability of the methodology to reduce the well BHP overestimation, mitigating the errors caused by the Peaceman equation. Indeed, in some simulated scenarios, the BHP overestimation was reduced a hundredfold after applying the partitioning technique. Furthermore, we discuss the choice of simulation parameters leading to more accurate and numerically stable results.