Numerical modeling of mixed wet systems with a thick transition zone typically requires full hysteresis option to be invoked in the reservoir simulator. In this super giant carbonate reservoir with multi-million active cells and twelve reservoir rock-types, running the full hysteresis option proved prohibitive due to excessive run times, and in many cases the run fails. Traditionally, engineers resorted to generating scanning curves that mimic the hysteresis option manually using algorithms or spreadsheets. These scanning curves are input into the model as saturation functions. This paper aims at presenting the workflow for developing the water-oil relative permeability hysteresis for a mixed wet super-giant carbonate reservoir which optimize the 3D simulation run time.
To develop the appropriate bounding and scanning curves, three models were tested including Corey model, modified Corey, and Killough Hysteresis model. To ensure that the algorithm for each of these models resulted in reliable scanning curves, commercial simulator sector model was built and the resulted scanning curves from this sector model compared with the mathematical approach used to generate scanning curves from each of the three models over a wide range of water saturation.
Results indicate that the three models generate consistent bounding and scanning curves for the oil relative permeability. However, results for the water relative permeability differed for the three models, especially at higher water saturation –transition zone. Killough model shows unusual trend for water relative permeability scanning curves as compared with the bounding curve. Using scanning relative permeability curves show significant reduction in the simulation run times as compared with the full hysteresis option.