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  4. Primary Drainage Saturation-Height Modeling

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- [German] So now, I'm going to switch to how we combine different pieces of special core analysis to produce these capillary pressure-derived saturation functions. So in order to model this core saturation in the direction of drainage and imbibition, a special core analysis was acquired in samples targeting each of the three depositional facies I showed you before, so deltas, shoreface, and fluvial deposits. This analysis included high-pressure mercury injection, centrifuge capillary pressure, multi-cycle stressed mercury intrusion and extrusion, and also counter-current imbibition maximum trapped gas. The capillary pressure itself was converted to the appropriate system, fluid system. For instance, mercury air was converted to gas water. And then, the non-wetting phase was corrected by clay-bound water. And finally, the air brine capillary pressure was converted to reservoir conditions. And what we basically did here is just to change the, correct the IFT by temperature, by reservoir temperature and reservoir pressure. Something to notice is that a robust resistivity-derived water saturation model was used as a reference. In this case, since there is no match clay content in the Almond, we just use an Archie water saturation model. So the upper figure, this one, displays the approach that we are taking for building the capillary pressure from special core analysis. Now, this is for primary drainage. So we basically combine the first and second stress mercury tests, which are shown by these yellow circles, yellow and orange. We're combining these pieces of mercury with the centrifuge capillary pressure, which is displayed by these green triangles, when the wetting phase saturation is lower than 40%. In other words, we are taking the mercury, stress mercury injection up to 40%, and then we are taking the water saturation from the centrifuge. And notice that, in theory, the clay-bound water corrected mercury injection, which is this one, differs from the one from the centrifuge at low wetting phase saturations. So it means that the capillary-bound water and the dead-end pore space is not associated to the clay, for which we are correcting this mercury injection data. So there is something else than clay in this pore space. A Thomeer water saturation model was used for fitting parameters, such as irreducible water saturation, entry pressure, and also the geometric factor in the capillary pressure curve. So these parameters, these parameters are correlated to routine core analysis, in order words, porosity and permeability, which are also measured in the same plug. So we are cross-plotting these three Thomeer parameters against porosity, permeability, and square root of porosity over permeability. So it's a common practice to perform this type of correlation by petrophysical rock types. But we found that if we sort samples by depositional facies, as a continuum along the rock quality, you have a better correlation. So these three plots that you see in the lower right section of the slide is the best correlation between Thomeer parameters in y-axis against porosity, permeability, or K over Phi. And you see that, what you see in green colors, are the non-marine core plugs. And what you have in red and in blue, is the marine part, in other words, the deltas and the shoreface. You see that you can improve the correlation if you do this correlation by these facies. After you find a correlation between conventional parameters and Thomeer parameters, you are going to assume a free water level. And having your contrast in densities of fluids, you are going to reconstruct your water saturation from capillary pressure using this equation. This is how we build capillary pressure-derived primary drainage model.