01. DFIT - Lesson 1.01: Intro to DFITsOK, so let's get started with module 1, lesson 1. And here we're going to introduce the DFIT and we'll define what a different actually is and what is required during a DFIT. But we're also going to talk a little bit about some hydraulic fracture mechanics, which we'll need as we go through the course, to help understand how to analyze the DFIT.
02. IntroductionFirst, let's take a step back. And if you would have gone through petroleum engineering education in the 1970s and maybe even the early 80s, where the bulk of the material was focused on conventional reservoirs, you'd have learned that every well was going to have some sort of well test to establish the pre-stimulation reservoir pressure and permeability. And this required information would then be used to evaluate post-stimulation effectiveness.
03. What is a DFIT?OK, so what is a DFIT? It is a small volume injection of treated water or gas. It can actually be any fluid, it doesn't matter. I will talk about at the end of the course as we get to I think it's module seven, we'll talk about tests that are pumped with nitrogen. I have just recently completed an analysis of tests that were pumped with CO₂. It doesn't really matter what fluid you use as part of the injection. Had a friend of mine, a colleague when I was with Halliburton that said, "David, I'm a frac salesman. If my customer wants to pump milk and cornflakes we'll pump milk and cornflakes". And I told him, well if your customer does pump milk and cornflakes, make sure he lets me analyze the DFIT because I would like to look at that data. So the point is, it could be any fluid. There are many examples. Matter of fact, in the course I have examples of where we use lease oil to do the DFIT. Most of the time It's just water. It's fresh water or maybe some water that has a little bit of KCl in it or possibly some brine. So most of the time it's just water.
04. Before Closure AnalysisOK, so there's two portions of this falloff data that we can analyze to estimate permeability and reservoir pressure. The first is this before close your region right here. So we did this injection. And you can see the injection period, the pressures coming up, up, up and then we shut down. And then there's this falloff period.
05. After Closure AnalysisIf however, we record the data for a very, very long time, then we get out here to this after closure flow regime. And I mean a very long time. We actually recorded this data for a little over 4 hours here, but say we were to record it for 60 hours plus, then we might have been able to observe a flow regime that's called pseudo radial flow. If we observe pseudo radial flow, then we can also calculate a permeability and a reservoir pressure. We actually calculate transmissibility and then if we know some of the other variables we get permeability. But we calculate permeability and reservoir pressure from that pseudo radial flow period. If we do have pseudo radial flow, then we actually have a unique interpretation of permeability that we can use as our pre frac estimate of permeability for that reservoir. The problem is in unconventional reservoirs, we rarely, rarely see a radial flow period.