The quest for efficient and scalable parallel reservoir simulators has been evolving with the advancement of high performance computing architectures. Among the various challenges of efficiency and scalability, load imbalance is a major obstacle that has not been fully addressed and solved. The reasons that cause load imbalance in parallel reservoir simulation are both static and dynamic. Robust graph partitioning algorithms are capable of handling static load imbalance by decomposing the underlying reservoir geometry to distribute a roughly equal load to each processor. However, these loads determined by a static load balancer seldom remain unchanged as the simulation proceeds in time. This so called dynamic imbalance can be further exacerbated in parallel compositional simulations. The flash calculations for equations of state in complex compositional simulations not only can consume over half of the total execution time but also are difficult to balance merely by a static load balancer.
