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  6. Sw Matching Exercise

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- [German] So the matching exercise, so the correlations between Thomeer and modified Brooks-Corey against petrophysical properties in core plugs are used to reproduce saturation-height models from the log-derived porosity and permeability. And again, these log-derived porosity and permeability have to be really calibrated to conventional core analysis, you know that. So the free water level for primary drainage and primary imbibition was optimized by matching the saturation-height models in reservoirs free of resistivity shoulder-bed effects. We really want to look at beds which are six feet or thicker than that. We really want to avoid shoulder-bed effects. And the history matching assumes that, so you know that there is history matching assumes that the resistivity-derived water saturation model, in this case, Archie, is a useful reference for flagging intervals with anomalous water saturation distribution with depth. Something important is that you really have to have a good handling of the resistivity-derived saturation model. In other words, you have to be really certain on water salinity, electrical properties, and, if possible, that model that's gonna be used as a reference is to be compared to direct measurements of water saturation, like Dean-Stark distillation. So I'm going to show you a couple of examples of this implementation. So in track number one, you see the gamma ray. Then you have a shallow, I hope that you can see my cursor, you have shallow and the resistivity. You have neutron density. You have porosity. You have petrophysical rock type. And what you have in this, in the last three tracks in blue, is the reference water saturation, it's the one from Archie. And what you have in red is the water saturation from capillary pressure. In red, you have drainage. And in black, you have imbibition. So you can see how, in the lower part of this well, there is a pretty decent agreement between both sources of water saturation. In all this interval, you see that there is a pretty good agreement between resistivity-derived and drainage models from cap pressure. But in the upper part, you see that if you assume the same free water level done for the lower Almond, you will see that there is some mobile water. So the water saturation from capillary pressure is lower than the one from resistivity, and the difference is approximately 20 saturation unit. So something that we tried, here, and it's shown in the far right track over here, is to try a shallower free water level. So what we did is to try something like 600 feet shallower, and you see that you have a pretty good agreement when we do that. But also, if we try an imbibition model, which is shown in this curve, we also have a decent agreement between both models. Based on this particular well, you may assume that you have a different compartment over here and you have just a different free water level for the upper part, or this reservoir was dyadically imbibed and the gas went out of the reservoir. And this is in the country transition zone 'cause this is the first example. In the second example, you see the same type of logs. You have gamma ray, resistivities, neutron density porosities. And this case, again, we kind of did a good match in the lower part of the Almond, you see that the difference in saturation models is pretty good in this lower part. But again, in this uppermost shallow marine reservoir, you always see a difference between both models, which is saturation from capillary pressure is always lower, indicating that there is some mobile water. In this case, we again tried something like a free water level shallower, and this is shown in the far right track. It's shown here. And you see that you can kind of match the upper part of these reservoirs, but the lower part is really, still really unmatched. And when we try an imbibition water saturation model, which is shown in black in this track, you see that you have almost a perfect agreement between both models. So this is the main use of this approach, I think, is, first of all, flagging mobile water or reservoirs that might be in the transition zone, and trying to guess whether, or giving you an idea of whether reservoirs are in a different compartment and you have a shallower free water level, or these reservoirs were just imbibed and you may have an imbibition, an imbibition free water level much shallower to the original one. Something that I didn't display, and I apologize for that, I didn't mention before is that all these reservoirs are charged by these cores, which are indicated by these black bars over here. So this is the middle Almond, middle Almond member. And in theory, all these cores generated the gas that is filling these reservoirs.