Numerical Challenges in Simulation of Foam for Enhanced Oil Recovery
Time: 12:45 – 13:30, June 27
Numerical simulation of foam enhanced oil recovery faces serious challenges. Foam responds in an abrupt, nonlinear way to changes in water saturation, surfactant concentration, and oil saturation, in ways that cause fluxes to fluctuate in time and space. As the grid is refined these effects have smaller impact on the overall process but execution of the simulation slows. Models for the effect of oil on foam lead to instabilities, and the naming of the nonaqueous phase (as gas or oil) in a miscible flood can greatly affect predictions of the simulator. Numerical dispersion of surfactant concentration is a problem, but attempts to minimize its effect can lead to other numerical artifacts. "Population-balance" foam simulators, which represent the complex dynamics of bubble creation and destruction along with the effect of foam on gas mobility, face additional challenges with instability and slow run times, especially for models that represent the multiple steady states seen in the laboratory. We collect and review the various numerical challenges to foam simulation. Some of these problems are largely cosmetic, giving for instance fluctuating fluxes and pressure gradient but no significant effect on final recovery. Others do severely influence the whole progress of the flood. Slow-moving waves propagating from an injection well can have huge effects on injectivity and are difficult to simulate accurately. We discuss the origin of the challenges, how to recognize them, how they can be mitigated, and whether they arise from a correct representation of foam physics or the unintended result of attempts to solve other numerical problems.