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  8. How to Calibrate Image Logs with Core

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- [Dr. Jaffri] One of the things we talked about earlier is bringing your bore hole image logs with you when you come in to describe core. Not only just bore hole image logs, your gamma ray and everything. So I'm just gonna go through real quick, and we're gonna do some deep water sandstones as an example of how you can calibrate bore hole image log faces with core faces. Let's go through our core haul image log. This log happens to be from a well that was not cored. Okay, but you can still see some features. We can see, right here, we see a lot of convoluted lamination, okay? We see inter-collated thin sands and shales. Of course the lighter color, if you've never looked at a bore hole image log, the lighter color represents sands, whereas the darker colors represent shales. That's the standard. On the left is your static image, on the right is the dynamic. The static is normalized over the entire length of the well, whereas the dynamic is only normalized within your interval of interest. So we see lots of stuff that looks like convoluted lamination, but you want to make sure that that indeed is convoluted lamination. This core happens to be taken from a well, very close to where this bore hole image log comes from. And this is a highly likely scenario, it's a rare treat to get a bore hole image log and a core run in the same well. So in this case, let's see. And if you can see, we've got plenty of examples of soft sediment deformation throughout this core. Okay? But that is most likely what you're seeing in this zone right here. Another thing you see right there, those little horns are flames, they appear to be flame structures, but again, we want to verify all of our flame structures present in these cores. And if you look right here, you can see that there are indeed quite a few flame structures. The next thing I'd like to focus on are the trends. Okay, if you see here, you've got a sharp base, and the colors are getting darker and darker until you get that black right there. So essentially what's happening is you've got something that is normally graded. So more, it's cleaner at the base, getting more and more clear towards the top. Again, that is something that you would like to verify. And you can see plenty of examples of that in the core. So here's the base. You can see this is much cleaner. More organics and clays coming into that until you get up to the clay parting, right along which the core has broken. Okay, so that's classic, normal grading that you can see at this scale. And then you'll see the same thing in your bore hole image logs as well. Okay? So that's the first thing I do is I place my bore hole image log, I go through the core, and I interpret them independently, so I would go through, first interpret what I think is going on in the bore hole image log, and once I've done that, I'll go through my core interpreting sedimentary structures in there, and then I'll start comparing them. Okay? So that's a quick way of calibrating. The next thing you want to do is that you want to look at the larger scale patterns we have in here, which is looking at lithologies, okay? So up there, you can see it looks, it's thicker, more sand prone, versus if you look down here. This stuff tends to be a little bit more inter-collated. So you should be able to find similar faces in the core as well, and if I zoom out, right where my cell phone is at, you can see you've got pure sand, that's a lot of mass of sandstone, but look what happens here. We've got inter-collated sands, and they're not even sand, actually, they're silts. So silts and muds. And so this inter-laminated stuff you see is most likely the stuff you see here in the bore hole image log. So again, I strongly urge you, if you do have bore hole image logs, do bring them along with you when you're looking at core. Now, I'll tell you one more thing. Especially with deep water sandstones, a lot of times, your bore hole image log, because it's picking up greater sensitivities, it's gonna pick up details that your naked eye will not in the sandstones. So your bore hole image logs are a great compliment, because you're gonna pick up details that even you can't pick up with your naked eye.