Responding to feedback from our viewers, this week Luke pulls one of his old tricks out of his sleeve: how he blends multiple vertical curves together to produce a coherent three-dimensional trend model. Enjoy!
If you'd like to explore this week's whiteboard, click the image below to get a closer look.
Juggling Multiple Vertical Facies Proportional Curves
Hello, and welcome back to The Cognitive Whiteboard. My name is Luke and, today, this is the third video we're filming around facies modelling. I was planning on talking more about methodology at this point, but there was so much interest in how I blend multiple vertical curves together into a coherent three-dimensional trend model, that I thought I'd show you exactly how I do that. So let's get started.
WELL DATA AND VERTICAL CURVES
What we want to do is have a conceptual depositional model in mind. So this is something you have built up from your field data and analogous nearby data sets so that you understand how the facies might be brought together in the overall system of that formation. And we’ll take a look at the wells that we've acquired and see where they cluster inside that depositional model. Because, what we're going to do, is say that these clusters of data give us some observed information, but it's an incomplete set. We need it to represent that depositional suite in a more robust fashion.
So we're going to cluster our wells together. In this case, I've got three particular groups that I've used that represent my depositional model, and I'm also concerned that there might be another set of facies that hasn't been sampled by my wells.
So when I start with my data, I've upscaled the facies logs three different times for different groups of wells, and now I'm going to build some vertical proportion curves. And I'm going to use some detective work to understand how to take this observed set, that has a terrible sample rate, to construct something that represents that depositional region of the model. We're going to do that for each one of the scenarios that we want to carry, including the one that we haven't sampled, so that we're going to really base this entirely upon depositional concepts. And we're going to build vertical curves four times over, and these will exist there, and every IJ column of your grid will have these percentages of these particular facies types.
Now, obviously, this is tremendously uncertain at this stage, so it's well worth considering; does this need to be analysed multiple times so that you're representing your uncertainty appropriately? But let's say for now these are the trends that we want to do. So, essentially, we have picked up the vertical trends out of our depositional model linked to the wells, but that's really where it's coming from, so that we come down and say, "How are we going to distribute this geological behaviour onto that grid?"
MAPS AND EQUATIONS
What I do then is I construct some simple two-dimensional maps that overlay the reservoir. So I can now map out where vertical curve one will exist, where two, where three, and where four should be on a map-based sense. This is simply a surface that goes literally from value one to value four, and I've sculpted that myself using geological intuition.
So for example, I want to say, "What if this carbonite facies exists?" Perhaps it could be in this corner of the map or the other corner, or perhaps along the entire edge. And I want to see, does this change the answer for the particular business decision that I'm facing next. And I can simply blend together these four properties that are the same everywhere in three-dimensional space into a model that has different vertical curves in every point in space by using this equation here.
So you have to increment that for each one of the trends that you're doing and, obviously, you could combine one and four if you wanted to think about how you could do that mathematics; you could obviously change the numbers around a little bit. But in doing so, you can blend these curves together so that if you're 30% of the way between one and two on this map, the vertical curve you'll get will have 70% of this facies assemblage and 30% of that facies assemblage with those same vertical patterns. And in doing so, you can really take control of the way your facies models appear, and I find this a fantastic way to generate very different geological scenarios and test what's going to change my next business decision.
I hope this is helpful, and I'd love to hear some critique on the method. So please, feed back in the comments and let me know what you think.