The effects of relative permeability and capillary pressure curves on a 2D karst reservoir model

Much of the world's remaining oil resides in carbonate reservoirs which are challenging to model. In particular, karst reservoirs are very complex to construct and simulate due to extreme heterogeneity. The aim of this work is to study a water flood of a carbonate paleokarst system, and investigate the effect of petrophysical properties such as matrix permeability and wettability which influences relative permeability and capillary pressure. A 2D water-oil model was created from a conceptual model. A total of twelve cases were considered with four combinations of relative permeability and capillary pressure, and three different matrix permeability cases. The results highlighted the possibility of early breakthrough and bypassed oil due to high permeability layers acting as thieve zones. This occurred in intermediate permeability case where viscous and capillary forces dominated over gravity forces. On the contrary, the high permeability case promoted gravity slumping giving rise to early breakthrough. In addition, the results showed that a water-wet system (positive Pc) dispersed the flood front, which was not the case in the oil-wet system. To conclude, it is worth remarking on a previously unobserved effect, namely that the karstic features such as caves and conduits acted as a source points.