Lesson 1.01 Course Introduction

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01. Lesson 1.1: Flowback & Early Time Production Data Analysis of Unconventional Reservoirs

Hi I'm Chris Clarkson and I'll be presenting: Flowback and Early Time Production Data Analysis of Unconventional Reservoirs. This topic will be the subject of an upcoming Society of Petroleum Engineers Monograph on Hydraulic Fracturing.Hydraulic Fracturing: Fundamentals and Advancements. Jennifer Miskimins, Editor-in-Chief. 2019 795 pp.; Hardcover ISBN: 978-1-61399-719-2 The chapter will be co-authored by Jesse Williams Kovacs, or as the folks at SAGA like to say Jesse Williams "Flowbacks". So I'm going to start by answering a couple of questions.

02. What is FBA?

First of all what is flowback analysis or FBA? Well simply stated flowback analysis is rate transient analysis of flowback data or that early time production data that's gathered immediately after a well is hydraulically fractured. So as such there's various inputs to the models that we need to consider such as the fluid production (water gas and oil rates), bottomhole flowing pressure, fluid properties (PVT). In some cases we require the number of fractures. Petrophysical properties such as reservoir porosity, saturation and initial pressures. In addition to this there's various data that we can use to supplement the analysis such as surveillance data collected during the hydraulic fracture stimulation and after. We can also use laboratory data, geomechanical data to constrain certain inputs, geochemical data etc.
With flowback analysis we can then derive various outputs, the primary ones being those related to hydraulic fracture characterization. For example hydraulic fracture half-length, before and after breakthrough. So BBT and ABT refer to before and after breakthrough of reservoir fluids to the hydraulic fracture. And we'll get into those definitions a little bit later in the course. We can also obtain properties such as the fracture permeability or fracture conductivity, skin. In some instances the reservoir permeability and various other properties that we can derive. Now RTA of flowback can differ quite substantially from RTA of online production. Because of the physics of the problem we may see single-phase flow followed by multiphase flow. The dynamics of the fracture come into play and therefore our models have to account for these effects which will be a big point of importance that we'll talk about later in the course.

03. Why Perform FBA? - Background

So why would we perform flowback analysis? What's so important about analyzing this early time production data? Well I'm going to give you a little bit of background before I answer that question.
First as Dave Anderson had suggested in his RTA in Unconventionals Course, multi-fractured horizontal wells are the most common technology used to exploit tight and shale reservoirs today.Link to Dave Anderson's RTA for Unconventionals Course These wells require massive stimulation treatments that allow us to maximize the contact with the reservoir providing a high permeability conduit to the well.
These fracture network characteristics are important for driving productivity, the ultimate recovery of the well and the development scheme and how we optimize that development scheme.
So predicting hydraulic fracture properties has become of great importance for optimizing production but it's very challenging. Therefore a premium has been placed in recent years on early time assessments.
Now the issue is that most early time data acquisition methods, microseismic being one of them, are very costly. Sometimes unreliable and impractical in certain scenarios, when it comes to application to tight rock.
RTA of online production, as was the subject of Dave Anderson's RTA course has proved useful for reservoir hydraulic fracture characterisation that ties directly to well performance. However in order to perform a meaningful analysis of online production we typically require 6 - 12 months of production data.
Now the issue of course is that analysis cannot be made in a timely fashion to allow us to adjust the completions during a drilling campaign i.e. on the next well or the next pad.
It's also very difficult in certain instances to separate out reservoir and hydraulic fracture properties in the analysis.

04. Why Perform FBA?

So that leads us to why perform flowback analysis? Well, I would argue that it's a relatively inexpensive routine method that allows us to perform early hydraulic fracture characterization.
Flowback data is relatively inexpensive to acquire and it's typically collected with I'd say relatively high resolution on most multi-fractured horizontal wells. So that addresses the cheap and routine aspect.
During flowback the hydraulic fracture is the primary porous medium that's being analyzed as opposed to the reservoir during online production. So this is the concept or the paradigm shift that one has to make when performing flowback analysis is that it's the hydraulic fracture that's the poorest medium that's under study here.
As a result RTA performed on flowback data provides a unique opportunity to perform early hydraulic fracture property assessment. Which in turn enables us to optimize stimulation treatments in future wells, as I said the next well or the next pad.
Some additional benefits of performing flowback analysis include aiding a proper flowback choke management strategy. We have seen that improper choke management can actually damage hydraulic fractures leading to productivity losses. So the parameters that we derive from quantitative flowback analysis can allow us to properly design that scheme to mitigate any sort of damage that occurs to the well.
And then lastly, and further benefit to quantitative flowback analysis is that we can populate a forward model that can be used to generate forecasts which in turn can be used for various purposes such as reserves assessment and development planning.

05. Course Outline - Introduction

So with that I'd like to move on to the outline for the course. And as you'll see each of these different sections will be covered in different modules or sub modules in the course. We're going to start today with the introduction. And in the introduction we'll provide some very high level facts on unconventional reservoirs. Some definitions of unconventional reservoirs that we'll use in place and contexts what we'll cover in this course. We'll discuss reservoir and hydraulic fracture characterization methods. We'll see flowback analysis is one tool in our tool kit and is one tool in a suite of reservoir and hydraulic fracture characterization methods that we're going to cover. We'll then launch into a discussion of rate transient analysis of flowback in online production. So we'll distinguish flowback in online production, we'll show you some typical signatures for both of those. We'll talk a little bit about the RTA models that we use for model inversion to extract properties of interest from flowback data. And then that'll lead us to our problem statement. And I'll spend a bit of time at the end of this module talking about course learning objectives that will carry through the rest of the course.

06. Course Outline - Workflow for RTA of Flowback & Early Time Production Data"

We'll then launch into a discussion of a workflow that we have used for quantitative rate transient analysis of flowback and early time production data. Each of these steps that are illustrated here will be the subject of separate modules. Steps #1 through #3 are all about assessing the data quality and viability so that we can determine whether or not we should even be performing a model based analysis. Step #4 is identifying flow regimes, a critical early step that allows us to select the model that's used for rate transient analysis. We'll then discuss in steps #5 through #6, the model inversion techniques where we are extracting information from the model for rate transient analysis. And then a critical step for flowback assessment is comparing the results of flowback in online production. We'll see that fracture properties are very dynamic. So there's a lot of information that can be gleaned from analyzing flowback and online results and then comparing the two.

07. Course Outline - Additional Workflow Examples

Now in our workflow we will be using tight oil shale gas examples to illustrate each step. However we want to demonstrate that this workflow works for wells, in addition to the ones that are used as an example there. So we've got some additional workflow examples; a multi-fractured horizontal well in a shale oil reservoir and a multi-fractured horizontal well completed in a shale gas reservoir to provide supplemental examples. Again those will be separate modules for this course.

08. Course Outline - Case Studies

And then lastly and very importantly we have some case studies that we'll go through that are designed to address some of the biggest issues that are facing flowback analysis today.
Case Study #1 will address the all important issue of what is the initial condition on flowback? So in other words what are the initial pressures and saturations in the reservoir immediately adjacent to the fracture at the initiation of flowback. It's a critical step because those initial conditions have a huge influence on the analysis.
Case Study #2 will address the all important issue of multi-well communication. We know that in current operations that instances of inter well communication through frac hits or more sustained communication are occurring more and more frequently in the field. And the issue is that most RTA models are applied as a single well analysis tool. And this case study will address forward modeling in the face of multi-well communication and how do we account for that.
And then the last case study is focused on online production addressing the all important issue of multiphase flow. And we'll show you how we correct for multiphase flow and the impact that that has on analysis of online production.
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Flowback Analysis (FBA) Course
Chapter 1 - FBA: Introduction (2:06:09)
Chapter 2 - FBA: Straight Line Analysis (SLA) (2:39:09)
Chapter 3 - FBA: Type-Curve Analysis (TCA) (1:09:41)
Chapter 4 - FBA: Examples and Case Studies (3:32:16)