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  5. Carbonate Unconventional Reservoirs

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- [Voiceover] The Bakken and the Niobrara are two examples of carbonate reservoirs that are undergoing active development right now. Both produced from carbonate intervals a lot of the, especially financial community, think the Bakken is a shale clay and it isn't, it's a carbonate clay, at least as we speak carbonate sand clay actually. Okay going back in time to conventional reservoirs our model petrophysically was sort of like this, a simple model of matrix, porosity, an shale. We sort of disregarded the shale they were a nuisance, a nuisance because they became unstable, they might swell and mess up the reservoir but essentially they weren't part of the intricate analytical sequence. Most of it was oriented towards the effective porosity. Now if we look at what is now the unconventional system you can see a lot more elements, we're not just looking at matrix, effective porosity, and shale, we're trying to distinguish TOC, total organic carbons, clay water effective porosity and what we have done is also to attempt, I think successfully, to look at what we are calling free shale porosity. It's porosity of the shale that is not TOC it's not clay, it is maybe fractures or organic material or something but it is available to contain free hydrocarbons as opposed to the TOC which is adsorbed. So what we've done then is to concentrate on defining these four porosity components as well as calculating adsorbed hydrocarbons from the TOC and free hydrocarbons that reside in the effective porosity and free shale porosity. Here is an example from the Niobrara and I'd like you to draw your attention to the middle two panels, those are showing the four porosity components, red, effective porosity, clay in gray, TOC in dark brown and free shale in yellow. I should say that these porosity scales are facing one another so the TOC is going from right to left as is the clay. Then also our pay flag is showing the pay in the clean formation, and this is probably the B bench of the Niobrara a lot of pay right in there, but then also right next to it is showing a resource of potential free hydrocarbons in adjacent shaley intervals, so it's giving you an idea of the total resource not just what is in the clean formation. Now this is a modified lorenz plot showing cumulative adsorbed oil in the vertical axis, cumulative free oil on the horizontal axis and highlighted are two intervals where the curve is vertical suggesting that is totally adsorbed oil in the Niobrara. The next one is from the Bakken and again we can see the Bakken dolomite where the pay is, that's what's been completed, the Bakken shale on top of it has got very high TOC values and again pay in the clean formation and then potential pay in the shales. And again now cumulative plot highlighting the adsorbed oil in the Bakken shale.