Geologically based estimation of k v / k h ratios: an example from the Garn Formation, Tyrihans Field, Mid-Norway

Abstract

During reservoir model building, one encounters several stages where upscaling or averaging of petrophysical data is required; core plug data have to be compared to wireline measurements and wireline measurements are averaged to the scale of building-size reservoir grid cells. Simple averaging does not, in most cases, give representative values, since the property in question is very scale-dependent. This is especially true for permeability and permeability anisotropy ( k v / k h ). For the case of a reservoir model of the Garn Formation (Middle Jurassic) in the Tyrihans Field, a simple geologically based upscaling method including the use of the SBED TM software package has been developed. Small-scale models of near well-bore geology are upscaled using single-phase flow simulation to obtain directional-dependent permeabilities for facies with different mud contents and style. The resulting k v / k h estimation curve has been implemented in the reservoir model by modelling V shale as a continuous parameter and applying the function to derive upscaled horizontal and vertical permeability grids. Upscaled permeabilities were found to closely match the well test data. This approach gives a more realistic k v / k h ratio than traditional methods involving simple averaging, or arbitrary guesses, of vertical permeability.