As we are running out of oil, and the oil price is reaching new hights, the oil industry is increasing the focus on exploration and production of heterogeneous reservoirs. In this paper we focus on the rock physics of shaly sands, and how different types of clay configurations will affect the rock stiffness and pore fluid sensitivity. Laminated sands and shaly sands with pore-filling clays will have different fluid sensitivity. We find that lamination will increase the Vp/Vs ratio for gas saturated sands compared to clean sands, in contrary to sands with pore-filling clay, where the Vp/Vs ratio will be relatively less affected by the clay content. This is related to the reduced shear effect induced by the micro-scale clay lamina. Next, we study the effect of net-to-gross and scale on fluid sensitivity using the Backus Average method. Here we also observe an increase in Vp/Vs ratio. Gas saturated thin-bedded sands will have Vp/Vs ratios similar to oil-saturated clean, homogeneous sands. This is related to the patchy saturation induced by the geologic heterogeneities. We also study the effect of anisotropy on the fluid sensitivity of heterogeneous reservoirs.


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