SELECTION OF THREE PHASE RELATIVE PERMEABILITY MODEL FOR MIXED WET RESERVOIRS

The most widely used three‑phase relative permeability models are Stone1 and Stone2. However, two more models have been developed for mixed‑wet reservoir (Blunt, 1999; Jerauld, 1997). The mixed wet condition is the most frequently encountered wetting condition in reservoirs worldwide. Blunt's model is complex to employ in simulators in contrast with the relative ease of Jerauld's model. An advantage of Jerauld'sr model is that it incorporates effects of IFT between phases. The ability to model mixed wettability and to incorporate IFT makes this an attractive option to investigate recovery in mixed wet reservoirs. In this paper Stone1 and Jerauld's models are compared. We illustrate the differences between these two models in three‑phase kro for the same two‑phase relative permeability data. Then we show how these two formulations can be cast on one another to be able to use them in commercial simulators. Recovery prediction differences as well as the effect of gas miscibility on krow are shown here. Our results show that three‑phase kro value, based on Jerauld's model, can be up to 6 times lower than those predicted by using Stone1and consequently recovery might be overestimated 6.7% at immiscible condition, while at 70% miscibility, the underestimation becomes 0.6%, if Stone1 model is used. Gas miscibility diminishes krow , resulting in lower recovery. The recovery is overestimated by 4% at 70% miscibility, if the effect of miscibility is only accounted for oil‑gas relative permeability. Here, we show how Jerauld three‑phase relative permeability model can be recast as the Stone1 model. We show the importance of using an adequate three‑phase model in addition to the effect of hysteresis in mixed wet systems. This is particularly important for mixed wet reservoir when IFT is subject to change.