How many relative permeability measurements do you need? A case study from a North African reservoir

While there are published methods for estimating the appropriate number of samples for estimating the mean permeability within a workable tolerance, there exist no formal guidelines for the selection of the number of relative permeability samples. In this paper, we examine this issue for a clastic reservoir in North Africa. Rock properties (essentially the porosity and permeability relationships) are adequately characterized by a number of rock types in the glaciomarine reservoir. For this reservoir, seven have been found appropriate, using either Hydraulic Unit or Winland criteria. In a sector simulation model, the impact of the different relative permeability curves is examined. The simulation models showed less than 5% variation in total oil production for all the relative permeability scenarios investigated. This shows that, for this field, the selection of relative permeability curves from the more important rock types, defined as those making up the dominant transmissive and storage units in the reservoir, can be sufficient. The timing of the modeling study may also be important. If a screening or scoping study is required, this could be reduced to just two sets of curves. The approach to studying the number of relative permeability curves required, based on geological analysis, rock typing, heterogeneity analysis, and flow simulation is considered to be a framework for the selection of the appropriate material for special core analysis.