DFIT-FBA: Methodology and Innovative Applications / Chapter 1 - Introduction to DFIT-FBA

Lesson 01-01 - Course Overview

Transcript

01. Lesson 1.01: Course Overview 02. Outline 03. Diagnostic Fracture Injection Test: Overview 04. Diagnostic Fracture Injection Test: Overview (2)05. Diagnostic Fracture Injection Test: Overview (3)

01. Lesson 1.01: Course Overview

Hello, I'm Chris Clarkson and in this course, we're going to cover diagnostic fracture injection test flowback analysis or DFIT-FBA, and we'll cover methodology and innovative applications.
So we've been working on this DFIT method for probably 4 or 5 years now. It was first initiated with work that I did with Behnam Zanganeh, a former PhD student. That work has been carried on by Danial Zeinabady, also a former PhD student in our group. And currently we have Sadjad Haqparast, a PhD student that continues to develop this technology.

02. Outline

So I'll begin with an outline, talk a little bit about what you'll learn in this course. In the introduction, we'll first introduce the conventional DFIT and then talk aboutflowback DFITs and in particular, the new DFIT-FBA, and we'll compare and contrast the different techniques.
In the next lesson, we'll talk about theory and methods where we'll introduce an analytical model that can be used to rationalize pressure changes that occur during DFIT-FBA. And we'll also introduce a workflow for quantitative DFIT-FBA analysis and a straight-line analysis technique that can be used to extract permeability.
In the next lesson after that, we'll provide an example of practical application using a field case and we'll demonstrate the DFIT-FBA is very fast and we believe also accurate for obtaining properties of interest.
And that will lead the discussion of the next lesson which is on applications of DFIT-FBA, where we're able to apply DFIT-FBA to scenarios that we couldn't previously apply conventional DFITs to.
And then we'll wrap up the course with some key takeaways right at the end.

03. Diagnostic Fracture Injection Test: Overview

So let's first start with a discussion of the conventional diagnostic fracture injection test (DFIT). So we also call this a pump-in/shut-in DFIT. And what is conventionally done today in unconventional reservoirs is we'll perform a conventional DFIT on the toe of a long horizontal well, as illustrated here on the left. We first pump in with water-based fluids. We achieve breakdown pressure. And we continue pumping, propagate our mini-fracture into the reservoir. And then we shut down and measure pressures over time for various properties of interest, one of them being ISIP (or instantaneous shut-in pressure). With continued fall-off, we achieve closure. So we obtain a fracture closure pressure estimate which is a proxy for in-situ stress. And then after mechanical closure of the fracture, we may see reservoir flow regimes such as linear flow and radial flow. So simply stated, we can subdivide a conventional DFIT into 2 periods of interest; the before-closure period and the after-closure period.
From before-closure analysis, we can obtain estimates of breakdown pressure, ISIP, and closure pressure or proxy for minimum in-situ stress. And we can use this information to help design hydraulic fracturing treatments. We can use it for caprock integrity evaluation. If we look at after-closure analysis, this is really the domain of reservoir engineers so we can obtain initial pore pressure estimates and permeability estimates. And of course, this is important information to populate simulation models to forecast production, evaluate injection schemes, etc. So that's the conventional diagnostic fracture injection test, again, what we refer to is a pump-in/shut-in test.

04. Diagnostic Fracture Injection Test: Overview (2)

And so now what we want to do is contrast that with the flowbackDFIT. So again, with a pump-in/shut-in test, we're primarily relying on a long falloff to obtain the pressures and properties of interest.
In the late 1970s, an alternative DFIT was introduced by Nolte. Nolte being a completions engineer. And how this particular DFIT works is, just like a conventional DFIT, we again pump in. We achieve breakdown pressure. We propagate our mini-fracture. But instead of extending a long falloff, what we do is briefly shut-in and then we flowback after that brief shut-in period. Now importantly, what we can do with this DFIT is analyze the flowing pressure data during the flowback period to obtain properties of interest such as the minimum in-situ stress.
Now with Nolte's design, because he was a completion engineer, he was mostly interested in obtaining quick estimates of closure pressure and minimum in-situ stress, not really interested in the reservoir side. So they flowed back at relatively high rates. And the issue with this from a reservoir point of view is that would tend to slam the mini-fracture closed very quickly and we'd lose connectivity between the reservoir and the wellbore. As an alternative, what Benham Zanganeh proposed in our group is to flowback at smaller rates. Sorry, that didn't come across that well. We flowback at a fraction of the flowback rate that Nolte proposed. And what this would achieve is our ability to maintain connectivity between the fracture and the reservoir, so we can now get reservoir information from the flowback test.
So after we realized that we could maintain this connectivity, we started to look at this idea of analyzing the flowback rates and flowing pressures quantitatively using rate transient analysis techniques. So on the right here, we're showing you a log-log diagnostic rate normalized pressure and it's derivative vs.material balance time. And you can see here, just like with conventional rate transient analysis, we can identify flow regimes and we can actually use these flow regimes to directly obtain information from the flowback DFIT test. But beyond that, we can also identify periods that we can analyze using straight line techniques, for example, for permeability. So we call this version of the flowback DFIT, the DFIT-FBA where FBA stands for flowback analysis. As you've seen in a previous course that we've done for SAGA, we can analyze flowback data quantitatively using rate transient analysis techniques. So we're applying that concept here now to the flowback data associated with this DFIT. That's really the premise of the new method and the innovation that we brought to the table.

05. Diagnostic Fracture Injection Test: Overview (3)

So let's now compare these 3 types of DFITs that we've been talking about. So on the left side of this table are some properties of interest that we commonly try to obtain from a conventional DFIT, including ISIP (or instantaneous shut-in pressure), minimum in-situ stress, reservoir pressure, reservoir permeability. And we can see that with the conventional DFIT, the first DFIT column here, we can obtain all of these properties from the fall-off test, but the limitation is that it can take days, weeks, or in some cases even months if we have very low-permeability reservoirs to obtain these after-closure reservoir flow regimes that are used to extract reservoir pressure and permeability.
As an alternative, with the pump-in flowback tests that Nolte has proposed, they're relatively quick, but we only obtain estimates of minimum in-situ stress. That's because, again, these tests were designed to accelerate the estimates of closure pressure. They weren't designed to obtain reservoir information. So we can't get reservoir pressure and we can't get reservoir permeability.
With DFIT-FBA, over the past few years, we've been able to demonstrate that we can obtain all the same parameters as a conventional DFIT, but in a matter of hours. So we can typically flowback a well for about 3 - 4 hours after the DFIT portion and obtain all these properties of interest.
So in the next lesson, we're going to provide some theory and discuss some methods for obtaining these properties that I've listed. So stay tuned for that.