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  1. Introduction

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- [Voiceover] Hello, this is Susan Nash with AAPG and I'm happy to be here today to talk to you a little bit about mini fracs and sweet spots, what we know now and as you might guess since I'm looking at the topic from basically an integrated point of view, I'm going to be looking primarily at the geology and it might be a little bit different than what you've been looking at from the point of view of Geo-mechanics or engineering but I hope that it's very useful to you especially as you work in teams. As I mentioned earlier, this is a geology-centric presentation and what is basically the theme of my presentation is that geology matters. I know we all realize that because after all, oil is found in rocks and geology is all about the rocks. Well I'd like to say that in this presentation we are gonna focus on sweet spot identification, reservoir characterization for optimization and finally sedimentological analysis to understand depositional environment so you can ask okay what does this have to do with hydraulic fracturing and refracturing and in a nutshell, what it is is that in order to really optimize the fracturing and that includes selecting the frac fluid, selecting the propent and also more than anything determining where exactly to frac and why. You really need to have a detailed understanding of the geology. One of the good places to get started with the geology is before you even start drilling and before you even start looking at the history, the depositional history where the base and setting or any of the geological history, it's good to take a look at the rocks themselves and focus on the fractures and also the mechanical elements of the rock and what we see here in the slide is an example of La Boca sandstone which is in Mexico and one of the things that has been done is there has been an analysis of the core. Now Bob Jacoby has done quite a bit of work on the Utica in upstate New York and especially in the Finger Lake District and what he has looked at is the out crop of the Utica, the same Utica that produces oil and gas in Ohio and he's taken a look at natural fractures and to see the extent of it and also just to see the frequency and to analyze the types of fractures, the natural fractures. Are they open or are they closed? He has also looked at what has happened within the fractures. Is there any delematization? Do you see any tiny little crystals of dual light? Has there been hydro thermal alteration and have liquid or minerals rich liquids intruded and filled up the natural fractures with say sparry calcite. If so, it's really really useful to know that. Now in terms of the Geo-mechanical properties Bob Jacoby issues a giant caveat and cautionary tale. He says that it's really important to take into consideration that the pressures at depth are not the pressures on the surface and so what you might have are changes in the fractures as the burial, as the rock is unburied so to speak and comes up on surface and rebounds or changes because there is not that sort of hydro static pressure and there's not the pressure on top of all the burial. Also he says it's good to look at fractures in conjunction with any well logs that may be near by. If we're looking at an outcrop, there's not gonna be too many well logs of the same thing but of the interval it's very useful to just line up the core with the image logs and also the other sweet of triple combo logs and take a look to see okay what exactly are the porosity differences, the permeability. Just and also maybe elements of other mineralogy, all very useful.