Simulation of Dynamic Foam-Acid Diversion Processes

Summary A new simulator for foam-acid diversion is described. The simulator explicitly accounts for the first time for the effects of gas trapping on gas mobility in foam and in liquid injected after foam and for the effects of pressure gradient on gas trapping. The foam model fits steady-state foam behavior in both high- and low-quality flow regimes and steady-state liquid mobility after foam. Previous laboratory experiments suggested that a relatively slow transition between steady states during foam and acid injection may control the diversion process in the field. The simulator fits this transition period in laboratory corefloods qualitatively with no additional adjustable parameters. Simulations and new data agree that the transition is faster at higher pressure (with lower gas compressibility) and that response to a shut-in period depends on how much gas escapes during the shut-in (i.e., on how long the shut-in lasts). Simulations and data suggest that a dead volume present upstream of the core in previous studies strongly affects the transition period seen in those experiments.