Abstract: A method, apparatus, and program product model an Enhanced Oil Recovery (EOR) process in a subsurface volume by computer modeling a variable-concentration injection of an EOR agent in multiple grid blocks of a reservoir grid, where the variable-concentration injection includes an injection of the EOR agent at multiple injection concentrations. For a first grid block among the multiple grid blocks within which EOR agent is present, a viscous fingering effect is modeled by modifying a fluid mobility in the first grid block based at least in part upon the injection concentration of the EOR agent present in the first grid block.

Abstract: A method for operating a reservoir simulator includes performing a reservoir simulation based on a spatial reservoir model that represents a subterranean environment that includes a reservoir where, for a portion of the spatial reservoir model, the performing includes utilizing a phase model operational mode; based at least in part on a phase transition in the portion of the spatial reservoir model to a multi-phase region that includes a microemulsion, implementing a multi-phase operational mode; and, based at least in part on a phase transition in the portion of the spatial reservoir model from the multi-phase region to a different phase region, implementing the phase model operational mode for the portion of the spatial reservoir model.

Abstract: A method, apparatus, and program product model an Enhanced Oil Recovery (EOR) process in a subsurface volume by computer modeling a variable-concentration injection of an EOR agent in multiple grid blocks of a reservoir grid, where the variable-concentration injection includes an injection of the EOR agent at multiple injection concentrations. For a first grid block among the multiple grid blocks within which EOR agent is present, a viscous fingering effect is modeled by modifying a fluid mobility in the first grid block based at least in part upon the injection concentration of the EOR agent present in the first grid block.