A recurrent issue when performing an up-scaling workflow is to assign representative values for the small scale petrophysical anisotropy ratio kV/kH. Most of the time the data provided by the plugs is not appropriate due to the absence of vertical sampling or to problems of representativeness. Where plug data is available kV/kH ratios are often found to be close to one, a value too high to be realistic when considering geological heterogeneity at small scale.
A methodology is proposed in order to give more appropriate ranges of values for the small scale permeability anisotropy ratio (kV/kH) as an input during the up-scaling workflow. When a well test with partial penetration interpretation is available, it is possible to use the large scale anisotropy ratio Kv/Kh obtained from spherical flow equations and thus constrain the small scale anisotropy ratio kV/kH.
The approach consists in: 1) building a fine scale grid whose size is consistent with the well test investigation radius, 2) populating the grid with facies and petrophysical characteristics observed at the well, and 3) up-scaling the fine scale grid so as to compare the upscaled anisotropy ratio Kv/Kh with the one derived from the well test interpretation.
The method was successfully tested on different field cases in turbidite and carbonate environments. Reference values of kV/kH ratios associated to facies have been determined and can be used, as an initial starting point during the up-scaling process. Guide lines for matching the parameters are also provided.