Drillworks Geostress: Tutorial

Drillworks Geostress
version 3.0
TUTORIAL
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Document Information
Title: Drillworks Geostress ver 3.0Tutorial
Description: Step-by-step exercise for wellbore stability analysis
Author(s): Linda Murdock
Reviewer(s): Gemma Keaney
Document Version: 1.0 Sources Used: ver 2.1
Creation Date: 12/7/00 Last Date Modified: 1/6/05
Will be sent to: all Drillworks Geostress customers
Document Number: 2004-000233
Knowledge Systems ©2005

Table of Contents
Table of Contents
PART 1: GETTING STARTED ................................................................1
Introduction ..................................................................................... 1
Purpose and Scope............................................................................. 1

Conventions ..................................................................................................... 1
Typographical .............................................................................................. 1
Graphical....................................................................................................... 2
PART 2: NAVIGATING THE TUTORIAL ...............................................3
Geostress Analysis Overview ....................................................... 3
Basic Wellbore Stability Analysis ..................................................... 3

Shear Failure Gradient ................................................................................... 4
Specifying Rock Strength Parameters .......................................................... 4
Advanced Wellbore Stability Analysis ............................................. 4

Well Orientation .............................................................................................. 5
Failure Criteria ................................................................................................. 5
Stress Distribution ........................................................................................... 5
Safe Operating ................................................................................................. 5
Strength Analysis ............................................................................................ 6
PART 3: THE TUTORIAL .......................................................................7
Basic Wellbore Stability Analysis ............................................... 7
Shear Failure Gradient Analysis....................................................... 7

Displaying the Results .................................................................................. 17
Creating and Editing Rock Strengths in Lithology Columns ........ 23

Creating a Lithology Column ...................................................................... 24
Editing a Lithology Column ........................................................................ 27
Displaying the Lithology Column .............................................................. 28
Advanced Wellbore Stability Analysis .................................... 33
The Component Windows............................................................... 33
Wellbore Orientation Component................................................... 33
Tutorial Knowledge Systems iii

Table of Contents
The Basic Input Panel ................................................................................... 34

Maximum Horizontal Stress Option....................................................... 35
Rock Strength Input Panel ........................................................................... 35
Advanced Settings Input Panel ................................................................... 35
The Plotting Area .......................................................................................... 36
Saving the View and Specifying the Scale Options .............................. 37
Displaying the View .................................................................................. 38
Changing the Display................................................................................ 38
Failure Criteria Component ............................................................ 39

Inclination and Azimuth Section............................................................. 40
Reference Mud Weight Option................................................................ 40
Advanced Input Panel .................................................................................. 41
Stress Distribution Component ...................................................... 43

Mud Weight Option .................................................................................. 45
Advanced Input Panel .................................................................................. 46
Safe Operating Mud Weight Component ....................................... 48

Minimum Horizontal Stress Option ....................................................... 49
Input for Advanced Panel ............................................................................ 51
Viewing the Results in 3D ........................................................................ 51
Saving the View and Specifying Scale Options..................................... 52
Strength Analysis Component........................................................ 53

iv Knowledge Systems Copyright©2005

Table of Contents
Mud Weight Option .................................................................................. 55

Rock Strength Display Properties ........................................................... 55
Input for Advanced Panel ............................................................................ 56
Saving the View and Specifying Scale Options..................................... 56
PART 4: APPENDIX .............................................................................59
Terminology ................................................................................... 59
Tutorial Knowledge Systems v

vi Knowledge Systems Copyright©2005
INTRODUCTION
Purpose and Scope
PART 1: GETTING STARTED
Introduction
Thank you for choosing Drillworks Geostress, the wellbore stability software
program that is fully integrated with Drillworks Predict. In directional and
abnormally-pressured wells, borehole instability is a critical problem. The
drilling costs associated with wellbore instabilities can be decreased
significantly if problems are anticipated. Geostress is a tool designed to help
drilling engineers plan mud programs and/or wellbore trajectories to
minimize any surprises associated with instabilities.
Geostress calculates the minimum mud weights required to maintain a stable
wellbore given information about in situ stress conditions (vertical and
horizontal stresses and the pore pressure), the wellbore trajectory, and
relevant rock strength parameters. It can also be used to estimate stress
conditions and/or rock strengths from existing well performance data.
Purpose and Scope

This tutorial is designed to help you get started with Drillworks Geostress by
allowing you to explore a case study through the various analyses functions.
Conventions
Document conventions explain how the tutorial was written using standards
and special ways of writing or representing text.
Typographical
The following typographical conventions are used in this document:
Menu selections on the toolbar are written as: To print, select File > Print on
the menu bar.
Tutorial Knowledge Systems 1

INTRODUCTION
Purpose and Scope
File is the top level of the menu (located on the menu bar); ">" is used to
separate the next level; Print is the next level of the menu (located under the
menu selection).
Terminology used in Drillworks Geostress and explanations of acronyms or
abbreviations are capitalized. For example, OBG stands for Overburden
Gradient. You can also refer to Terminology on page 59 for other definitions.
All keyboard keys, menu items, windows/dialog box titles, labels found in
windows/dialog boxes, components of the program, and buttons are
capitalized to help distinguish the text.
Drillworks Geostress is sometimes referred to as Geostress.
User input entered in the program is shown in this format.
Graphical
The following icons represent different types of information:
Represents something important, a warning or precaution that

needs to be taken.
Is a helpful tip you can use.
Means that it is a self test which allows you to stop and do some
steps on your own.
Geostress Analysis Overview on page 3
2 Knowledge Systems Copyright©2005

GEOSTRESS ANALYSIS OVERVIEW
Basic Wellbore Stability Analysis
PART 2: NAVIGATING THE TUTORIAL
Geostress Analysis Overview

The example discussed in the tutorial is from a generic deepwater well. Data
is provided as a sample project in Drillworks Predict and in Drillworks
Geostress software. The following modes and analyses may be performed to
develop wellbore stability profiles as needed. Some calculations may require
data developed in previous analyses.
See also
Basic Wellbore Stability Analysis on page 7
Advanced Wellbore Stability Analysis on page 33

Geostress analyses assume datasets for overburden gradient, pore pressure
and fracture gradient (assumed to be minimum stress in this example) have
been developed in Predict. The basic wellbore stability analysis is run from
Predict.
To import the Geostress Tutorial project

Open Predict and select Project > Import from the menu bar.
Step 1 - Specify Source Location
1 Choose the Project directory location.
2 Click the Browse button to navigate through Windows folders and files to
the Project folder, which is usually located in C:\Program
Files\Drillworks 2005\Samples\Projects
3 Select the Geostress Tutorial sub-folder from the displayed list an click
OK.
4 The projects listed in the folder are displayed in the list of box. Select the
Geostress Tutorial and click Next.
Step 2 - Specify Import Options

Advanced Wellbore Stability Analysis
5 Enter Geostress Tutorial for the name of the project and accept the
default import options. See Drillworks 2005 Help files for more
information on setting import options.
6 Click Finish and the project is imported.
An overview of the available analyses follows:
Shear Failure Gradient

Minimum mud weight required to prevent wellbore shear failures (Shear
Failure Gradient (SFG) versus depth is calculated along the entire length of
the wellbore. This calculation can be made in realtime or in a post-drill
analysis. The tutorial uses a post-drill case.
See Shear Failure Gradient Analysis on page 7
Specifying Rock Strength Parameters

In this tutorial we will use two methods to estimate rock strengths:
• sonic to rock strength correlations
• a lithology column dataset
A lithology column dataset includes geological, lithological, and strength
data, and are one option for specifying rock strengths needed in a Geostress
analysis.
See Creating and Editing Rock Strengths in Lithology Columns on page 23

To begin, open Predict and from the menu bar choose Project > Open and
select the Geostress Tutorial project to load the required log, survey and
related well data for the tutorial. See To import the Geostress Tutorial
project on page 3 for instructions if the tutorial project is not listed.
Begin the Advanced Wellbore Stability Analysis by selecting Analyze > Start
Drillworks Geostress. Note that the Drilling/Monitoring Mode must be run
at least once prior to performing all analyses available in the Design/Analysis
Mode.
An overview of the five Design/Analysis Components follows:

Well Orientation
Calculations assess the dependence of Shear Failure Gradient (SFG) on well
orientation at a fixed depth.
See Wellbore Orientation Component on page 33
Failure Criteria
Calculations show how the shear stress (maximum shear stress for the Mohr-
Coulomb criterion, octahedral shear stress for Drucker-Prager and Stassi-
d’Alia criteria and Lade shear stress for the Modified Lade criterion varies
around the circumference of one-half of the wellbore, not just at the critical
point, when wellbore pressure is at shear failure gradient (minimum mud
weight required to prevent shear failure) and some user-specified increment
from that value. This function allows the analyst to check the solution's
sensitivity to variations in mud weight. These calculations are performed at a
fixed depth.
See Failure Criteria Component on page 39
Stress Distribution
Calculations show how the various wellbore stresses vary around the
circumference of one-half of the wellbore (the other half is the same) at a fixed
depth. The wellbore mud pressure may be varied. This component allows the
analyst to determine the most likely location for wellbore failures to assist in
calibration of rock strengths and in situ stresses and to identify the effect of
changes in wellbore pressure and the various wellbore stresses.
See Stress Distribution Component on page 43
Safe Operating
Summarizes the results of Predict and Geostress analyses to show the range
of safe operating mud weights that can be used to exceed the pore pressure
and shear failure gradient, whichever is the greatest, and which is less than
the minimum stress. These calculations are performed at a fixed depth.
See Safe Operating Mud Weight Component on page 48

Strength Analysis
Calculations of the critical shear stress (maximum shear stress for the Mohr-
Coulomb criterion, octahedral shear stress for Drucker-Prager and Stassi-
d’Alia criteria and Lade stress for the Modified Lade criterion) over a
specified depth range given the in situ stress conditions and a mud weight.
This allows the analyst to determine empirically the effective strength of a
rock formation that experienced wellbore instability. This information can
then be used in analyses of subsequent development wells in the same field.
This assumes that the user has constrained the maximum horizontal stress
magnitude and azimuth. Otherwise, this component can also be used to
assess or constrain the value of this stress.
See Strength Analysis Component on page 53

BASIC WELLBORE STABILITY ANALYSIS
Shear Failure Gradient Analysis
PART 3: THE TUTORIAL

This analyis is accessed from the regular Predict window.
Choose Project > Open and select the Geostress Tutorial project to load the
required log, survey and related well data for the tutorial. Note that the data
in this project has already been "prepared" for use in Geostress. Normally,
you would work in Predict first before working in Geostress. This tutorial
uses the same well and data that was used in the Predict tutorial.
NOTE: See the To import the Geostress Tutorial project on page 3 for
instructions.
The following analyses are available and discussed in this section:

Choose Analyze > Shear Failure Gradient to activate the shear failure
analysis and determine the minimum mud weight required to prevent shear
failure based on different failure criteria. See Shear Failure Gradient
Analysis on page 7.
Choose Data > Create Lithology Column to create and edit rock strengths in
Lithology Columns for formations and develop lithology datasets to use with
the Advanced Wellbore Stability Analysis. See Creating and Editing Rock
Strengths in Lithology Columns on page 23.
Wellbore stability in realtime analysis is accessed from the regular Predict
window. See the Drillworks 2005 Help files for further information.

Geostress basic wellbore stability analysis analyses are made in Predict.
To perform a shear failure gradient analysis.

1 From the Predict menu bar, select Analyze > Shear Failure Stress
Gradient. The Step 1 - Select a Method dialog box displays.

2 Choose the Use Mohr-Coulomb failure condition option.

3 Click Next. The Step 2 - Select a Well dialog box displays.
4 In the Well Name list box, select ANALOGUE.

5 Click Next. The Step 3 - Collect Survey Parameters Information dialog box
displays.

6 In the Inclination and Azimuth section, select the Use Well's Survey Data
option. Well inclination and azimuth data can be defined from either a
well survey file or assumed constant values.
7 Click Next. The Step 4 - Collect Parameter Information dialog box displays.
The minimum mud weight required to prevent shear failure versus depth
along the well path is calculated based on the defined input parameters.
This dialog box is used to define all analyses input variables.
8 Choose the datasets:

• In the Overburden Gradient (OBG) dataset drop-down list, select

OBG rhob.
• In the Pore Pressure (PP) Gradient dataset drop-down list, select PP
dt Bowers.
• In the Minimum. Horizontal. Stress Gradient (ShG) Dataset drop-
down list, select FG MK K0 Sh. This is a Matthews and Kelly method
fracture gradient dataset calibrated to minimum stress measurements
from Leak Off Tests (LOTs).
NOTE: If the dataset is not found in the list, make sure that the correct
datasets are filtered for the drop-down list. Click Filter and choose the correct
datatype (e.g., OBG datatype). This displays all datasets using the selected
datatype.
9 In the Maximum Horizontal Stress Gradient (SHG) Option section choose

the formula option.
• Select SHG = ShG + k * (OBG - ShG)
• Specify the horizontal stress increment factor k as 0.5.
10 Select the check box to create a SHG dataset. This will create an additonal
dataset.
11 In the Max. Horizontal Stress Azimuth field, select 0. The azimuth is
defined as the direction of the maximum horizontal stress relative to true
North, i.e., 0 is North-South, 90 is East-West.
12 Click Advanced Settings.
13 In the Poisson’s ratio settings section:

• For this tutorial, choose Use Constant. The rock's drained Poisson's
ratio is the default of 0.25, which is appropriate for most shales. Note:
This value is unrelated to the pseudo-Poisson's ratios published by
Eaton.
• Other options include using a dataset for the Poisson's ratio.
14 In the Wellbore PP settings section:
• Choose the Equal to far field pore pressure option for the tutorial.
This is the default setting and assumes there are no chemical or
hydraulically induced changes in the near wellbore pressure.
• Chemical effects - Use this option to account for near wellbore stress
changes induced by differences in the mud and pore fluid salinity.
You can specify Biot’s effective stress coefficient directly (alpha) or
add values of Kb and Ks to calculate. You can specify the value for
Delta P directly (select the appropriate pressure unit) or add values to
account for mud and pore fluid activites (AwDF and AwS) and the
membrane efficiency (q). With this option, you will need to specify a
temperature value and unit.
• Hydraulic communication effects - Use this option in cases where the
near wellbore formation pressures are higher than the far field pore
pressure due to invasion of drilling mud in the near wellbore
formation. You can specify Biot’s effective stress coefficient directly
(alpha) or add values of Kb and Ks to calculate.
15 In the Other settings section:
• Breakout angle (degrees) option defaults to 0 and means that
Geostress will calculate the minimum mud weight to prevent zero
amount of shear failure on either side of the wellbore wall.
• Make shear failure stress value no less than PP Value checkbox is
unchecked by default. If left blank, the minimum shear failure stress
required to prevent shear failure will be recorded even if it is less
than the pore pressure. In this tutorial, leave the box unchecked.
16 Click OK to close the Advanced Settings dialog box.
17 Click Next on the Step 4 - Collect Parameter Information dialog box. The Step
5 - Collect Strength Parameter Information dialog box displays.

18 Select the Use a correlation dataset option. This will require additional
inputs.
19 Accept the default values of 1 for the Friction Angle and Cohesion
Strength calibration factors.
NOTE: The strength calibration factors provide a means of adjusting the

selected strength values (defined by the chosen option) by a constant ratio to
calibrate to local conditions. Calibration factors less than one reduce the
defined or predicted strength and vice versa.
20 Click Next. The Step 6 - Collect Correlation Information dialog box appears.

21 In the Options section select Apply a single correlation to both sand and
shale for this tutorial.
22 In the Inputs section, select Lal’s law from the drop-down list.
23 Select the DT Merged SHPTs and Chk Shot dataset from the drop-down
list for the sonic/velocity dataset.
Other options include applying a single correlation to shale only and
using a lithology discriminating datset. You can apply different correla-
tion laws to shale and sand and use shale and sand baselines to discrimi-
nate.
24 Select the check box to create rock mechanical property datasets. Later
steps will create the Friction Angle and Cohesive Strength datasets.
25 Click Next. The Step 7 - Collect New SHG Dataset Information dialog box
displays.

26 The first dataset to name is the Shear Failure Gradient dataset.The system
will automatically name a new dataset based on the source datasets and/
or method used. In this case, accept the default name of SFG Mohr-
Coulomb.
27 You can enter an optional description.
28 Choose True vertical depth from the drop-down list in the Index type
section.
29 In the Display Attributes section, click on the drop-down arrow at the
color button and select a maroon (dark red) color from the color picker.
Make the line style a heavier line.
30 The Depth Interval field is used for establishing datapoint intervals in the
new dataset. Leave this value set at 5.
31 Keep the default Units set at ppg.
32 Click Next. The Step 8 - Collect New SHG Dataset Information dialog
displays.

33 This dialog displays in response to the selection to Create a SHG dataset

in step 10. The system will name the dataset based on the source datasets
and/or method used. In this case, SHG from ShG and OBG. Accept the
default name.
34 Enter an optional description.
35 Select True vertical depth from the drop-down list for the Index type.
36 For this tutorial, accept the default color and line style for the display
attributes.
37 Select the unit, ppg.
38 Accept the default interval of 5.
39 Click Next and the Step 9 - Collect New FA Dataset Information dialog box
displays.

40 This dialog is in response to the selection to create a Friction Angle

dataset in step 24. The system will name the dataset based on the source
dataset and/or method used. In this case, FA from DT. Accept the name
for this tutorial.
42 Select True vertical depth from the drop-down list as the Index type.
43 Accept the default display attributes or change the color and line style.
44 Click Next. The Step 10 - Collect New CS Dataset Information dialog box
displays.

45 This dialog is in response to the selection to create a Cohesive Strength

dataset in step 24. The system will name the dataset based on source
dataset and/or method used. In this case, the name is CS from DT. Accept
the name.
47 Select True vertical depth from from the drop-down list in the Index type
section.
48 Change the display color to Yellow and make the line weight heavier.
49 Change the units to psi.
50 Click Finish. You can now display the results of the shear failure analysis
on Predict tracks.
NOTE: The rock mechanical property datasets (the FA and CS datasets )

created in this analysis will be used in the Advanced Wellbore Stability Anal-
ysis section of the Tutorial.
Displaying the Results

To display the results
1 Make sure the Geostress PPFG SFG view has been selected from the
drop-down list on the Predict toolbar. Your view should show the
gamma ray wireline dataset in the first track, accoustical datasets in the
third track and the overburden, pore pressure, LOTs and MDTs in the
fifth track. These are the datasets created in the Predict Tutorial.
The other tracks will be used later in the tutorial.

2 Right-click on the fourth track from the left.

3 From the pop-up menu, choose Add Datasets.
4 The Add Datasets to the Track dialog box displays.

5 Make sure the ANALOGUE well is selected. Scroll down to select the CS
from DT and the FA from DT datasets.
6 Click Apply and then Close. The two datasets are displayed on the track.
You can drag and drop datasets from the Project Explorer to a
track. Toggle the Project Explorer on (View > Project Explorer) from the
Drillworks Predict menu bar. Click on the Data tab to display the wells in
your project. Expand the well listing by clicking on the plus sign and select a
dataset from the list. Hold down the left mouse button and drag the dataset to
the desired track.
7 Now we will change the display range for the datasets. Right-click on the
track and select Dataset Properties from the pop-up menu.

8 The Dataset Properties dialog box displays. Select the CS from DT

(ANALOGUE) dataset first and verify the display range is 0 - 2000.
9 Select the FA from DT (ANALOGUE) dataset and change the display
range to 0 - 50.
10 Click Apply and Close. The scale is changed for the FA dataset.
The datasets made in the original Predict tutorial are displayed on the
fifth track from the left. We will add the Shear Failure Gradient datasets
made in the first part of this tutorial together with the calibrated Fracture
Gradient dataset, and a MW and Casing dataset for reference.
11 Right-click on the fifth track and select Add Datasets from the pop-up
menu. The Add Datasets to Track dialog box displays.
12 Make sure the ANALOGUE well is selected. Choose the CSG, FG MK K0
Sh, (if not displayed) MW, SFG Mohr-Coloumb, and SHG from ShG and
OBG datasets from the list.
13 Click Apply and Close.
14 Right-click on the track and select Dataset Properties from the pop-up
menu.
15 In the Dataset Properties dialog box, verify the display range of the
displayed datasets. All should have a display range of 8 - 18.
The Overburden Gradient is shown in Pink, Fracture Gradient in Blue,
Pore Pressure Gradient in Green, Shear Failure Gradient (SFG) in Maroon
(dark red), Maximum Horizontal Stress Gradient (SHG) and MW in
Brown-Green, LOTs in Blue Squares, and MDTs in Black Diamonds.
As the last step in displaying the results, we will add datasets to the sixth
track.
16 Right-click on the sixth (the farthest right track). Select Add Datasets
from the pop-up menu.

17 The Add Datasets to Track dialog box displays.

18 Make sure the ANALOGUE well is selected.
19 Select the BS (bit size) and Caliper datasets and click Apply, then Close.
20 The datasets are displayed on the track. Right-click on the track and select
Dataset Properties from the pop-up menu.
21 Change the display range for both datasets to 5 - 15.
Now, we will add shading to better see the comparison between the bit
size and caliper.
22 Right-click on the sixth track with the BS and Caliper datasets. Select
Shade Datasets from the pop-up menu.
23 The Shade Datasets dialog box displays.
24 Click on the Plus button. The Dataset Shading dialog box displays.

25 Select the BS dataset for Dataset A and the Caliper dataset for Dataset B.
26 Select red for the shading pattern and specify the Between A and B
option.
27 Click OK to close the Shading Datasets dialog box.
28 Click Close on the Shade Datasets dialog box. The shading is applied.
The Geostress PPFG SFG view should look like this:

Creating and Editing Rock Strengths in Lithology Columns
Experiment with viewing the datasets created in the Shear Failure

Analysis.
See Geostress Analysis Overview on page 3 to choose a new analysis option.
Creating and Editing Rock Strengths in Lithology

Columns
One of the enhanced features of Drillworks 2005 is the ability to associate rock
strength parameters with a lithology or a depth range within a lithology

column dataset. In this part of the tutorial, you will create a lithology column
dataset to use in the Geostress component analyses.
The rock strength parameters are cohesion (C), friction angle (FA),
unconfined compressive strength (UCS) and tensile strength (TS). Note that
even though the UCS and TS can be related to Cohesion and FA, they are
treated as independent parameters.
When you specify Geostress to use a lithology column dataset in order to
derive rock strengths, Geostress assumes that the specified rock strength
parameters are constant over any particular lithology's depth interval.
Creating a Lithology Column

1 Select Data > Create a Lithology Column from the Predict menu bar. The
Step 1 - Input General Information dialog box displays.
2 In the Name field, enter Rock Strength. The description field is optional.
3 The Bottom depth is taken from the Well Properties information.
4 Enter a Top and Bottom Age in million of years for the entire lithology
column. In this tutorial enter 0.01 for the Top and 5 for the Bottom.
5 Enter the two way time, if available. In this tutorial, you can leave it
blank.

6 The Depth reference can be changed. In this tutorial, select Mean Sea
Level.
NOTE: Predict allows the user to create system Geological Ages and sys-
tem Formation Groups that can be copied to a new lithology column. See the
System Manager section of the Drillworks 2005 Help files for details of creat-
ing system defaults. In this tutorial, these features are not used.
7 Click Next. The Step 2 - Input Formation Record Information dialog box
displays.
8 Enter the data for a formation specifying the top depth, geological age
and choosing a display lithology using the data in the table below:
Formation Start Geological Lithology Friction Cohesive Tensile Unconfined

Name Depth Age in mil- Angle Strength Strength Compressive
lion of years Strength
Upper Shale 4668 0.01 yellow light 25.00 200.00 100.00 800.00
Middle Shale 8000 0.9 grey medium 20.00 200.00 0.0 1000.00
Weak Shale 14000 2.0 orange light 20.00 150.00 0.0 1000.00
Lower Shale 16000 2.5 grey green 25.00 300.00 100.00 700.00
9 When the data entry is complete for a formation, click Add and the data is
added to the named dataset in the Lithology Column dialog box.

10 Repeat this process for as many formations as required.
NOTE: Formations may be added in any order, but may not overlap. See
Drillworks 2005’s Help files for more information on changing lithology and
age information (i.e. the appearance or naming of the lithologies).
11 Click Next and the Step 3 - Input Lithology Record Information dialog box
displays.
12 Select a lithology in the list box and enter the values for the Friction
Angle, Cohesive Strength, Tensile Strength and Unconfined Strength
according to the chart above.
13 Click Update to enter the information.
You can scroll to the right to see the columns that are hidden. Click
on the column header to sort by that column’s data values.
14 Select another record and repeat steps 12 and 13 until all records have
been updated with the rock strength data.
15 Click Finish. The Next button displays dialog boxes that are used to
define Geological Ages and Formations units and are not used in this
tutorial.

Editing a Lithology Column

If you find that you need to edit or correct the formation in the lithology
column, you can follow this procedure.
1 Select Data > Edit a Lithology Column from the Predict menu bar to
display the Select a Dataset dialog box.
2 Choose the ANALOGUE well and Rock Strength dataset and click OK.
The Edit a Lithology Column dialog box displays.

3 The Lithology tab allows you to change the display color, top depth and /
or the rock strength parameters. Select a record, change the desired
parameters and click Update.
Displaying the Lithology Column

1 Right-click in the second track from the left and choose Add Datasets
from the pop-up menu. The Add Datasets to Track dialog box appears.
NOTE: Lithology Column datasets are indicated by a tri-color icon to

distinguish them from other datasets.

2 Select the ANALOGUE from the well list and scroll down to find the
check box for Rock Strength in the Select Datasets list box.
3 Click Apply and then Close. The Lithology Column is displayed on the
track.
You can drag and drop datasets from the Project Explorer to a
track. Toggle the Project Explorer on (View > Project Explorer) from the
Predict menu bar. Select a dataset and hold down the left mouse button while
dragging to the desired track.

In this tutorial, the lithology is shown on a separate track. If you display the
lithology on the same track as other datasets, there may be an overlap. This
can be adjusted.
To change the display properties

1 Right-click on a formation of the lithology column and choose Properties
from the pop-up menu. The Lithology Column Properties dialog box
displays.

2 The Display tab controls the starting postion of the Lithology Column
display on the track. You can adjust the position of the Lithology Column
as well as the text labels.
3 After making changes, click Apply and the display is adjusted
accordingly.
Experiment with changing the Lithology Column display

properties and observe the changes on a Track.


ADVANCED WELLBORE STABILITY ANALYSIS
The Component Windows

To start the Advanced Wellbore Stability Analysis mode of Geostress, choose
Analyze > Start Drillworks Geostress from the Predict menu bar.
One of the five Advanced Wellbore Stability Component windows will
appear. From the Geostress menu bar, choose Analyze to see the menu for the
five components.
The Component Windows

Each component has an input panel on the left side for analysis. The right side
displays the results graphically. Windows may be resized by grabbing a side
or corner of the window with the left mouse button depressed and moving to
the desired size.
Panes within the windows may be resized. Place the cursor over a pane you
want to adjust. The cursor turns into a line with arrows on each end. Press the
left mouse button and drag left or right. The pane maintains the new settings
until you change them.
See also
Wellbore Orientation Component on page 33
Failure Criteria Component on page 39
Stress Distribution Component on page 43
Safe Operating Mud Weight Component on page 48
Strength Analysis Component on page 53
Wellbore Orientation Component

Choose Analyze > Well Orientation on the menu bar or click on the
toolbar.
Calculations in this window assess the dependence of Shear Failure Gradient
on well orientation at a fixed depth. There are two parts to the window:
• Input Panel (to the left of the window)
• Plotting Area (to the right of the window)

The Basic Input Panel

Make sure that you have opened the tutorial project in Geostress. If the
project is open, the Project name is in the title bar. If not, select Project > Open
from the Geostress menu bar and choose the Geostress Tutorial from the
Open a Project dialog list box.
Data required for the calculations are specified in the panel at the left.
1 The display screen on the right will show no data until you adjust the
depth to an appropriate depth where sufficient data is available to
calculate a shear failure gradient. In the Depth field of the input panel,
enter 14000 and make sure that TVD is selected. Notice that the display
on the right updates according to the data that you enter.
2 In the Method drop-down list, select Modified Lade.
NOTE: If the Recalculate box is checked, any changes made to the input
panel will be shown on the plotting area as entered. If left blank, check the
Recalculate box when all variables are entered to view the new plot.
3 Make sure the well name is ANALOGUE.

4 From the Output Unit drop-down list, select ppg.

5 In the OBG drop-down list, make sure that OBG rhob is selected.
6 In the PP drop-down list, make sure that PP dt Bowers is selected.
7 In the Min. Horiz. Stress drop-down list, make sure that FG MK K0 Sh is
selected.
Maximum Horizontal Stress Option

1 The maximum horizontal stress can be determined from
• a dataset
• a formula
In this tutorial, we use a calculation from OBG and the minimum hori-
zontal stress:
2 Choose SHG = ShG + k * (OBG - ShG) formula from the drop-down list.
3 Specify an horizontal stress increment factor of 0.5.
4 The maximum horizontal stress azimuth is required. Use 0 for this
tutorial.
5 Click the Rock Strength tab at the bottom of the Input panel.
Rock Strength Input Panel

1 The rock shear strength parameters can be determined from
• rock strength correlation laws
• user supplied strength datasets appropriate to the selected failure
criterion
• constant values appropriate to the selected failure criterion
• a formation column dataset
In this tutorial, we use constant values:
2 Choose constant values for the Friction Angle of 25.
3 Choose the Cohesive strength of 200 psi.
4 Accept the default values of 1 for the Friction Angle and Cohesion
Strength Calibration factors.
5 Click Advanced Settings tab.
Advanced Settings Input Panel

The Advanced Settings Input Panel allows specification of the near wellbore
pore pressure settings, Poisson's ratio, and breakout angle.
1 In the Near wellbore PP settings section the following options are
available:

• Equal to far field pore pressure. This is the default setting and assumes
there is no pressure communication between the wellbore mud
pressure and the near wellbore formation pressure.
• Chemical effects. Use this option to account for near wellbore stress
You can specify Biot’s effective stress coefficient directly (alpha) or
add values of Kb and Ks. You can specify the value for Delta P
directly (select the appropriate pressure unit) or add values to
account for mud and pore fluid activites (AwDF and AwS) and the
membrane efficiency (q). With this option, you will need to specify a
• Hydraulic communication effects. Use this option in cases where the
(alpha) or add values of Kb and Ks.
For this tutorial, choose the default setting of Equal to far field pore pres-
sure.
2 In the Poisson's ratio field, keep the default at 0.25, which is suitable for
most shales. You also have the option of specifying a dataset for Poisson's
ratio.
NOTE: This value is unrelated to the pseudo-Poisson's ratios published

by Eaton.
3 In the Other setting section

• Enter 0 for the breakout angle.
• Leave the Make shear failure stress value no less than Pore Pressure
value unchecked.
The Plotting Area

The results are plotted in what is termed a "lower hemisphere plot" by
structural geologists. Wellbore orientation is shown by a single point on this
plot; its azimuth is plotted from 0° to 360° around the circumference while its
inclination is defined along any radial line from 0° to 90°.
• The scale is determined by the system or specified by the user. In this
case, let the system decide.
• The arrows on the outer circle indicate the direction of the maximum and
minimum horizontal stress.
• Shear Failure Gradient at any point is defined by the color contours.

The current inclination and azimuth location is shown on the plotting area as
a black diamond. To toggle this display, select or unselect the Show current
inclination and azimuth location check box at the bottom of the input panel.
Click the Basic tab to access the Multiple Views feature. Select the check box
and choose a parameter (other than Depth) from the drop-down list.
Change the failure conditions, vary the depth and observe the
changes to the plot.
Saving the View and Specifying the Scale

Options
Each case (the data input and the diagram) that is investigated can be saved
as a view. As the datasets used with each Advanced Wellbore Stability
Analysis option are stored in the Predict project, changing the design
parameters and values result in a different visual plot that can be saved and
recalled by name.
1 First, select View > Save from the menu bar or click on the toolbar.
This saves the parameters and values that compose the view.
2 Name the current view Orientation ML 14000.

3 Keep the Let System Decide Option selected.
4 Click OK.

To save the view under a different name, select View > Save As from
the menu bar. The Save As dialog box displays. Enter a new name for the
view and click OK.
Displaying the View

In the upper part of the window, select the view name in the drop-down
menu on the Geostress toolbar and press Enter.
Changing the Display

Choose either View > Properties from the Geostress menu bar or right-click
on the plotting area and choose Properties from the pop-up menu to access
the Properties dialog box.
1 In the Properties dialog box, choose the Well Orientation tab to change
the color scale.
2 Use double buffer may be checked if using a low-resolution monitor to
improve the graphics appearance.
3 Change the Color Scale option to Green, Red, Blue.
4 The Display tab allows you to change the font choice and size for the
labels, as well as change the grid style on the plot. Leave the options as
they are.
5 The View tab shows the name of the current view and allows you to
change the scale of the plotted results.
6 Click Apply to activate any changes. Click OK to close the dialog box.
Back to the top of Wellbore Orientation Component on page 33

Failure Criteria Component
Back to The Component Windows on page 33

Choose Analyze > Failure Criteria from the menu or click on the
toolbar.
Analysis results show the wellbore shear stress relative to the rock's failure
criterion at each point around one-half of the wellbore wall when the mud
weight equals
• a shear failure gradient
• the mud weight used
• an absolute mud weight value
• some specified increment (+ or -) from the shear failure gradient.
There are two parts to the window:


Make sure that you have opened the project in Geostress. If the project is
open, the Project name is in the title bar. If not, select Project > Open from the
Geostress menu bar and choose the Geostress Tutorial from the Open a
Project dialog list box.
1 The display screen will show no data in it until you adjust the depth to an
appropriate value. In the Depth field of the Basic input panel, enter 13000
and make sure that the ANALOGUE well and TVD is selected. Notice
that the display on the right updates according to the data that you enter.
2 In the Method drop-down list, select Stassi d' Alia.

4 From the Output Unit drop-down list, select psi.
selected.
Inclination and Azimuth Section

8 The Inclination and Azimuth can be determined from
• survey data
• constants
9 In this tutorial choose the Use survey data option.
Reference Mud Weight Option

10 The reference mud weight can be determined from
• the value in a specific dataset
• an absolute value
• an increment
11 In this tutorial choose to specify an increment and enter -1 and select ppg
as the unit.


• a dataset
• a formula
zontal stress:
13 Choose SHG = k * (OBG - ShG)
14 Specify an horizontal stress increment factor of 0.5
tutorial.
16 Click the Rock Strength tab.

• rock strength correlation laws
criterion
• constant values appropriate to the selected failure criterion
• a formation column dataset
2 Select the Constant option and enter constant values for the UC strength
of 1000 psi
3 Enter a Tensile strength of 200 psi.
4 Accept the default value of 1 for the UC Strength and Tensile Strength
calibration factors.
5 Click the Advanced tab.
Advanced Input Panel

The Advanced Settings panel allows specification of near wellbore pore
pressure settings, the Poisson's ratio, and breakout angle.
1 In the Near Wellbore PP Settings section
• Equal to far field pore pressure. This is the default setting and assumes
there is no pressure communication between the wellbore mud
pressure and the near wellbore formation pressure.
• Chemical effects. Use this option to account for near wellbore stress
You can specify Biot’s effective stress coefficient directly (alpha a) or
add values of Kb and Ks. You can specify the value for P directly

(select the appropriate pressure unit) or add values to account for

mud and pore fluid activites (AwDF and AwS) and the membrane
efficiency (q). With this option, you will need to specify a
• Hydraulic communication effects. Use this option in cases where the
(alpha) or add values of Kb and Ks.
Choose the default setting of Equal to far field pore pressure.
most shales. You have the option to choose a Predict dataset for the
Poisson's ratio.

by Eaton.
3 In the Other Settings section, set the Breakout Angle to 0.

4 Leave the check box for Make shear failure stress value no less than Pore
Pressure unchecked for this tutorial.
The Plotting Area

The default results plotted assume that the wellbore pressure equals the
minimum required to prevent wellbore shear failure (Shear Failure Gradient)
for the defined in situ stresses, pore pressures and rock strengths.
Stress states which occur above the failure envelope indicate that the wellbore
has failed in 'shear'. Stress states below the failure envelope have not failed in
shear.
Change the mud weight increment to see how wellbore stresses

change with small mud weight changes. Also change the failure criterion,
vary the depth and other parameters and observe the changes to the plot.

Options
All views are saved in the same manner.

Stress Distribution Component
1 To save an initial view,select View > Save from the menu bar or click
on the toolbar. This saves the current View and displays a dialog to
name the view.
2 Enter a name for the view. For this tutorial enter SA-1 13000.
3 Choose Let the System decide the scale.
4 Click OK.
To save the view under a different name, select View > Save As from
view and click OK.
Displaying the View

In the upper part of the window, select the name in the drop-down menu on
the Geostress menu bar and press Enter.

1 Choose either View > Properties from the Geostress menu bar or right-
click on the plotting area and choose Properties from the pop-up menu to
access the Properties dialog box.
2 In the Properties dialog box, choose the Failure Criteria tab.
3 For the Failure Criteria Curve color, change it to Black.
4 Shading is shown on the Plotting Screen via the Use Shading check box.
NOTE: Selecting the Shading option here also applies shading to the
Strength Analysis display.
they are for this tutorial.
6 Click Apply to accept the changes, and OK to close the dialog box.
Back to the top of Failure Criteria Component on page 39

Choose Analyze > Stress Distribution or click on the Geostress toolbar.

The Stress Distribution Component allows the analyst to see how the various
wellbore stresses change around the wellbore circumference and assess the
angular extent of a potential failed zone. The plot displays a variety of
different stresses at the upper half of the wellbore wall as a function of
angular position (stresses on the lower half of the wellbore are the same). The
"zero" angular position is at the most extreme left when looking down the
wellbore.
There are two parts to the window:

Data required for the calculations are specified in the panels at the left.

1 The display screen will show no data in it until you adjust the depth to an
appropriate value. Make sure the ANALOGUE well is selected and enter
14000 in the Depth field. TVD should be selected. Notice that the right
hand display updates according to the data that you enter.

3 From the Output Unit drop-down list, select psi.
6 In the Min. Horz. Stress drop-down list, make sure that FG MK K0 Sh is
selected.
NOTE: In all the Component Windows the shaded fields to the right of
the selected datasets or parameters display the value at the selected depth.

• survey data
• constants
8 In this tutorial choose the Use survey data option.
Mud Weight Option

9 The mud weight option can be set by
• a dataset
• a specific value
10 For this tutorial, select the Use Dataset option.
11 Choose MW from the drop-down list. This is the Mud Weight analysis
used to drill the well. The dataset has been provided as part of the
tutorial.

• a dataset
• a formula

zontal stress:
13 Choose SHG = ShG k * (OBG - ShG) from the drop-down list.
tutorial.
16 Select the check box for showing the breakout location.
17 Enter 60 for the angular extent of the breakout. This is how much angular
extent of the wellbore is broken out. This information was interpreted
from bore hole image data and is used as a calibration for stress
correction.
18 Enter 30 for the angular location of the breakout. This is the angular
location on the wellbore wall of the center of the breakout.
Notice the shaded area of the breakout on the Plotting Area.

Increase the value of the maximum horizontal stress azimuth and watch the
Maximum Tangential Stress curve (shown in Red) on the plot until the peak is
centered in the shaded breakout area.
Advanced Input Panel

The Advanced Input Panel allows specification of the Poisson's ratio.
• In the Poisson's ratio field, keep the default at 0.25, which is suitable for
most shales. You also have the option of using a Predict dataset.

by Eaton.
The Plotting Area

The axial, circumferential and radial stresses are the normal stresses
associated with the local cylindrical coordinate system defined by the
wellbore. The radial stress is a principal stress in all cases. The maximum and
minimum tangential principal stress will be different in general from the axial
and circumferential stresses but they both act tangential to the wellbore wall.

Change the Mud Weight values, vary the depth and other
parameters and observe the changes to the plot.

Options
name the view.
2 Enter a name for the view. For this tutorial enter Stress Dist 14000.
3 Choose Let the System decide the scale.
4 Click OK.
To rename the saved view, select View > Save As from the menu bar.
The Save As dialog box displays. Enter a new name for the view and click
OK.
Displaying the View


2 In the Properties dialog box, choose the Stress Distribution tab to change
the color scale.
3 For the Mean color, change it to Gray.
they are.
5 Click OK
Back to top of Stress Distribution Component on page 43

Safe Operating Mud Weight Component

Choose Analyze > Safe Operating on the menu bar, or click on the
toolbar.
This is the plot of the safe operating mud weight window (the range of mud
weights that will either exceed the pore pressure or Shear Failure Gradient,
whichever is greater, and be less than the minimum stress). These
calculations are performed at a fixed depth. There are two parts to the
window:


Data required for the calculations are specified in the panel at the left
1 The screen will show no data in it until you adjust the depth to an
appropriate value. Make sure the ANALOGUE well is selected and enter
16000 in the Depth field. TVD should be is selected. The display updates
according to the data that you enter during the following steps.
2 From the Method drop-down list, select Drucker-Prager.

3 From the Output Unit drop-down list, select ppg.
4 From the OBG drop-down list, make sure that OBG rhob is selected.
When a velocity dataset is used to calculate the strength properties, the calcu-
lated results are shown in the shaded fields normally used to show the Fric-
tion Angle and the Cohesive Strength.
Minimum Horizontal Stress Option

6 The minimum horizontal stress can be determined from ShG or FG
dataset calibrated to minimum horizontal stress and either
• a value at the current depth
• a minimum value from a previous casing point
7 In this tutorial, choose the FG MK K0 Sh dataset and the Use minimum
value from previous casing point option.
8 Enter 15000 as the value.

• a dataset
• a formula
zontal stress:
10 Choose SHG = ShG + k * (OBG - ShG) from the drop-down list.


tutorial.

13 The maximum principal horizontal stress can be determined from either
• survey data
• constants
In this tutorial
14 Choose the Use survey data option.
15 Select the check box to Show stress/strength ratio information.
16 The Show more information check box can be selected to show values on
the plotting area for selected datasets. In this tutorial, select the check box
and the MW dataset. Notice the Mud Weight value is shown on the
Plotting Area.
17 To better observe the data, right-click on the Plotting Area and choose
Properties from the pop-up menu.
18 On the View tab select the Specify option in the Scale section.
19 Enter 12 for the Min X value and 16 for the Max X value and click Apply
and OK. Notice the display changes in the Plotting Area.
20 For now skip the section for 3D view. We will come back to this section
when viewing the results.
21 Click the Rock Strength tab.

• rock strength correlation laws.
criterion.
• constant values appropriate to the selected failure criterion.
• a formation column dataset.
2 Choose constant values for the Friction Angle of 25
3 Choose a Cohesive strength of 200 psi.
4 Accept the default value of 1 for the Friction Angle and Cohesion
Strength calibration factors.

Input for Advanced Panel

The Advanced Input Panel allows specification of the Poisson's ratio.
most shales. You may also choose a dataset for the Poisson's ratio.

by Eaton.
2 Select the Make shear failure stress no less than pore pressure check box.
The Plotting Area

Calculations in the window investigate the value of the maximum shear
stress measure divided by rock strength as a function of mud weight, as
shown by the blue line on the plot. Shear failures do not occur when this ratio
is less than one; and if shear failure were the only criterion for a stable
wellbore, any mud weight that produced a ratio less than one would be a
"safe" mud weight.
However, mud weights are limited at the upper bound by the value of the
minimum horizontal stress as shown by the vertical black line. Sometimes the
minimum mud weight will be limited by the pore pressure as shown on the
on the view by the black line at 12.66 ppg.
Regardless, the safe operating mud weight range is shown by the vertical
shaded band that is limited at the higher mud weight by the minimum stress
and at the lower mud weight by either the pore pressure or the case when the
stress to strength ratio is less than one, i.e the shear failure pressure.
Change the Failure criteria, vary the depth and other parameters
and observe the changes to the plot.
Viewing the Results in 3D

1 Click the Basic tab at the bottom of the Input Panels.
2 Select the 3D view check box. Notice the Plotting Area shows No data is
available. You must enter an End Depth to display the 3D view.
3 Enter an End depth of 17000 near the top of the Panel.
4 The Safe Operating display is now shown as a 3D cube.
5 Use the slider located at the bottom of the panel to zoom in on the cube.

6 You can rotate the 3D view by clicking on the display and moving the
cursor in any direction.
7 Use the Span buttons in the desired plane to move the openings closer
together or further apart
8 Use the Slide buttons in the desired plane to move the opening in the
direction of the specified plane.
9 Clear the check box labeled 1 to remove half of the cube display and
observe the interior of the cube.
Saving the View and Specifying Scale Options

Each case (the data input and the diagram) that is investigated can be saved
as a view. As the datasets used with each Design Analysis Option are stored
in the Predict project, changing the design parameters and values result in a
different visual plot that can be saved and recalled by name.
1 To save an initial view,select View > Save from the menu bar or click the
button on the toolbar. This saves the current View and displays a
dialog to name the view.

Strength Analysis Component
2 Enter a name for the view. For this tutorial enter DP 16000.
3 Click OK.
To save the view with a different name, select View > Save As from
view and click OK.
Displaying the View


click on the plotting area and choose Properties to access the Properties
dialog box.
2 In the Properties dialog box, choose the Safe Operating tab.
3 For the Safe Zone color, change it to Green.
labels, as well as change the grid style on the plot (if applicable).
5 Click Apply and then OK.
Back to the top of Safe Operating Mud Weight Component on page 48
Back The Component Windows on page 33

Choose Analyze > Strength Analysis from the Geostress menu bar or click
on the toolbar.
This option allows the analyst to use well performance data (that is, mud
weights and depth ranges where failures occurred) to back-calculate the
effective rock strength of a specified depth interval. There are two parts to the
window:
• 2- tabbed Input Panel (to the left of the window)


1 The screen will show no data in it until you adjust the depth to an
appropriate value. Make sure the well ANALOGUE is selected and in the
Start and End Depth fields, enter 14000 and 16000 respectively (we are
assuming that well failures occurred over this depth range). Notice that
the right hand display updates according to the data that you enter.
2 From the Method drop-down list, select Stassi d'Alia.

3 From the Stress Unit drop-down list, select psi.


selected.

• survey data
• constants
In this tutorial
8 Choose the Use survey data option.
Mud Weight Option

9 The mud weight option can be set by
• a dataset
• a specific value
10 Select the Use Dataset option.
11 Choose the MW dataset from the drop-down list.

• a dataset
• a formula
zontal stress:
13 Choose SHG = ShG + k * (OBG - ShG) from the drop-down list.
tutorial.
Rock Strength Display Properties

16 In the UC Strength field, enter 1450 psi.
17 In the Tensile Strength field, enter 0 psi.
18 Accept the default values of 1 for the UC Strength and Tensile Strength
calibration factors.

Input for Advanced Panel

The Advanced Settings Panel allows specification of Poisson's ratio.
• In the Poisson's ratio field, keep the default at 0.25, which is suitable for
most shales. You also have the option to select a dataset for the Poisson's
ratio.

by Eaton.
The Plotting Area

The tutorial calculations illustrated in this case assume the ANALOGUE well
experienced wellbore instabilities over a depth range of 14000 to 16000 ft
when the mud weight was 12.89 to 12.97 ppg. The red data points in the
upper right of the view are the calculated wellbore stress conditions over that
depth interval for the given input parameters.
The black parabolic line (for the Stassi-d'Alia failure criterion) is a plot of the
failure criterion for the input UCS and TS. The objective is to change the rock
strength parameters until the wellbore stress conditions intercept the failure
criterion over the depth interval where failure occured. The failure criterion
line changes automatically each time the analyst changes the shear strength
parameters.
Change the shear strength values, the failure conditions, vary the
depth and other parameters and observe the changes to the plot.
Saving the View and Specifying Scale Options

name the view.
2 Enter a name for the view. For this tutorial enter SdA 1-14000-16000.
3 Select the Specify option and enter Min Y as 0, Max Y as 2000, Min X as 0
and Max X as 2500.

4 Click OK.
To save the view with a different name, select View > Save As from
view and click OK.
Displaying the View

In the upper part of the window, highlight the name in the drop-down menu
on the Geostress menu bar and press Enter.

2 In the Properties dialog box, choose the Strength Analysis tab.

3 For the Failure Criteria Curve color, change it to Blue.
4 The Use Shading option applies to both the Strength Analysis
Component and the Failure Criteria Component. For example, if you
turned on Shading in an earlier tutorial exercise, the option will apply in
this component as well.
labels, as well as change the grid style on the plot. The Show Grid option
can be enabled only if Use Shading is turned off.
6 Click Apply and then OK.
Back to the top of Strength Analysis Component on page 53


TERMINOLOGY
PART 4: APPENDIX
PART 4: APPENDIX
Terminology
This list briefly describes terms and concepts used in Drillworks Geostress.
.
Term Description
cohesion (C) Cohesion (C) is the intercept on the shear stress axis of a straight-line
Mohr-Coulomb envelope. In physics, cohesion is described as ‘the force
that holds together molecules or like particles within a substance’. Since it
is easier to make the grains slide path each other than to crush them, when
rocks fail in compression they fail in shear as result of inter-granular slip.
Resistance to shear is shear strength - due to a combination of cohesion
and friction between rock grains.
dataset A collection of any set of points referenced by a depth value and a data
value that is either imported into the system, created through analysis, or
created manually by the user. It can also be associated with Line Groups
and annotations.
dataset attribute Describes how the dataset appears regarding the type of line, symbol, or
color.
Drillworks Basin A Knowledge Systems software tool that deals with a set of related
geological, petrophysical and drilling data incorporated into a common
pressure evolution framework in basin time scale. The Drillworks Basin
Project comprises these data plus the set of calibrated basin model
parameters providing pore pressure prediction at any point inside the
calibration area.
Drillworks Predict A Knowledge Systems software tool designed to predict pore pressures
and fracture gradients using a variety of types of data. Drillworks Predict is
fully integrated with Drillworks Basinand Geostress and uses the same
database.
Drillworks Witslink A Knowledge Systems software tool that manages the real-time WITS
input and output streams for use with Drillworks Predict.

TERMINOLOGY
PART 4: APPENDIX
Term Description
effective stress A defined stress, which is defined in terms of the total stress and pore
pressure, that makes computations simpler by removing the pore pressure
from the governing equations. Examples, the Terzaghi effective stress,
σ = s – p for models of shear and tensile failure; the Biot effective stress,
σ = s – αp for models that are concerned with volume changes, α is
defined in terms of rock moduli properties.
elastic behavior or model Material behavior or models that are 3-D generalizations of the 1-D
mechanical behavior of a spring. Simple model of a solid in which the
solid’s shape and internal stresses are always the same for the same set of
applied loads. A linear elastic model is one in which all stresses and strains
are linearly related.
equilibrium The fundamental concept in mechanics that the sum of all forces acting on
a body is zero.
failure criteria A combination of effective (Terzaghi) stresses that define the ultimate
strength of a material. Also called Failure Conditions or Yield Conditions.
These are attempts to generalize the strength behavior of rocks measured
in simple laboratory tests to complex 3-D conditions in the real world. The
different criteria with different names (e.g. Mohr-Coulomb, Drucker-Prager,
Stassi d’Alia, Lade) use slightly different ways of generalizing these
conditions.
friction angle (FA) The general Mohr-Coulomb failure criterion is given by:
τ = Co + σ 1 tan φ
where φ is the internal friction angle. Friction angle describes how a rock’s
peak strength increases with additional confining pressure. Friction angle is
related to the Mohr-Coulomb parameter, coefficient of internal friction by
η = tan φ where η is the coefficient of internal friction and φ is the
friction angle.
geological age Time period used in lithology column datasets and can be defined and
represented in PREDICT with names, bitmap pictures, and colors.
hoop stress A term for the tangential wellbore stress in the case of a vertical well. This
stress acts tangentially to the wellbore wall and is higher than the in situ
stresses because of stress concentrations that develop due to the
presence of a wellbore.
Input panels In each Analysis Component window, the left side displays a series of
tabbed Input Panels. Parameters, datasets, conditions and/or methods are
determined by user input and choices.

TERMINOLOGY
PART 4: APPENDIX
Term Description
lithology column dataset A feature that models the stratigraphical column for a well. It includes
lithology patterns and colors, as well as geological ages and formation
names.
menu bar The bar at the top of the program that shows the selection of menus for
Drillworks Predict, i.e., Project, View, Analyze and Help.
Mohr’s circle A geometric construction that represents stress states at rock failure in, for
example, a triaxial laboratory test. For Mohr circles the Mohr-Coulomb
strength parameters (Cohesion and Friction Angle) can be determined
Mohr-Coulomb A failure condition method that assumes rock strength is measured by the
maximum shear stress (one-half the difference between the maximum and
minimum principal stresses) and increases linearly with the average of the
maximum and minimum principal stresses
normal stress Stress component that acts perpendicular to a surface.
OBG The abbreviation that represents the overburden gradient.
plastic behavior or model Material behavior where a rock deforms at a constant stress level and does
not return to its original shape as one the stress is reduced.
Plotting Area In each Analysis Component window, the right side displays graphic results
of the analysis.
Poisson’s ratio An elastic property which describes lateral expansion of a body. It affects
the stresses or strains in a material in directions other than the direction of
loading.
pop-up menu The menu that appears on screen when you right-click over the track or
plotting area.
project The project function allows you to organize your well data within the
Drillworks Predict database. Three types of projects are frequently used:
Pre-drilling well planning projects
Drilling well monitoring projects
Teaching/demonstration projects.
realtime analysis Allows you to make analyses using data that streams while drilling.
Datasets in Drillworks Predict are updated dynamically (realtime) as data
comes in.
scale A system of ordered marks at fixed intervals used as a reference standard

in measurement. It is displayed on the tracks and sometimes on Plotting
areas, both vertically and horizontally.
Shear Failure Gradient Minimum mud weight required to prevent shear failure
(SFG)

TERMINOLOGY
PART 4: APPENDIX
Term Description
shear stress Stress component that acts parallel to a surface. The maximum shear
stress equals one-half of the difference between the maximum and
mimimum principal stresses.
Stassi-d’Alia Failure Condition method that assumes rock strength is measured by the
root mean square of differences between the three principal stresses (the
octahedral shear stress). The strength increases with the square-root of
the mean effective stress.
stress The generalization of the forces acting on individual particles to the internal
forces acting throughout a continuous body.
stress invariants Specific values or combinations of stress components that do not change
when the coordinate system changes, e.g. principal stresses, octahedral
shear stress.
stress ratio Defined by the abbreviation ko is the ratio of the horizontal to the vertical
effective stress.Sometimes called the matrix stress ratio.
tectonics Loading condition in which lateral loads are actively applied to a sediment
(in contrast to the ‘normal’ condition where lateral loads develop passively
because of constraints against lateral deformations). Tectonics can be
caused by globally continental drift forces or locally by salt bodies or down-
slope movements.
toolbar A “shortcut” bar that contains buttons to open certain dialog boxes in order
for you to perform a selected function.
total stress The fundamental stress that controls equilibrium
track An area on Drillworks Predict’s screen that displays datasets, annotations,

lithology columns and/or Line Groups and consists of a track name, width,
horizontal scale type, and vertical scale.
triaxial strain Rock mechanics test in which a cylindrical rock sample is tested where the
radial stress (confining pressure), axial stress, and pore pressure is
controlled independently.
TS Abbreviation for Tensile Strength
UCS Abbreviation for Unconfined Compressive Strength
uniaxial strain Terminology for condition in which strains occur only in one direction
(typically vertical).

TERMINOLOGY
PART 4: APPENDIX
Term Description
views Cases investigated in the Advanced Wellbore Stability Analysis Mode of

Drillworks Geostress can be named and saved for future retrieval as Views.
Drillworks Predict Track Views display a customized screen that can show
a maximum of eight tracks. Also used to display a 3D representation of the
well path trajectory in Well Path View. Datasets can be compared in the
Cross Plot View.
workhardening or Material behavior where increasing stresses are needed to deform a rock
strainhardening behavior but the rock does not return to its original shape once the stress is reduced.
or model
Back to Geostress Analysis Overview on page 3

TERMINOLOGY
PART 4: APPENDIX


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Drillworks Geostress

Knowledge Systems ©2005

PART 1: GETTING STARTED ................................................................1

Purpose and Scope............................................................................. 1

PART 2: NAVIGATING THE TUTORIAL ...............................................3

Geostress Analysis Overview ....................................................... 3

Basic Wellbore Stability Analysis ..................................................... 3

Advanced Wellbore Stability Analysis ............................................. 4

PART 3: THE TUTORIAL .......................................................................7

Basic Wellbore Stability Analysis ............................................... 7

Shear Failure Gradient Analysis....................................................... 7

Creating and Editing Rock Strengths in Lithology Columns ........ 23

Advanced Wellbore Stability Analysis .................................... 33

The Component Windows............................................................... 33

Wellbore Orientation Component................................................... 33

Tutorial Knowledge Systems iii

The Basic Input Panel ................................................................................... 34

Failure Criteria Component ............................................................ 39

Stress Distribution Component ...................................................... 43

Safe Operating Mud Weight Component ....................................... 48

Strength Analysis Component........................................................ 53

iv Knowledge Systems Copyright©2005

Mud Weight Option .................................................................................. 55

PART 4: APPENDIX .............................................................................59

Tutorial Knowledge Systems v

PART 1: GETTING STARTED

PART 1: GETTING STARTED

Purpose and Scope

Tutorial Knowledge Systems 1

PART 1: GETTING STARTED

Represents something important, a warning or precaution that

Is a helpful tip you can use.

Geostress Analysis Overview on page 3

2 Knowledge Systems Copyright©2005

PART 2: NAVIGATING THE TUTORIAL

PART 2: NAVIGATING THE TUTORIAL

Geostress Analysis Overview

Basic Wellbore Stability Analysis

To import the Geostress Tutorial project

Tutorial Knowledge Systems 3

PART 2: NAVIGATING THE TUTORIAL

Shear Failure Gradient

Specifying Rock Strength Parameters

Advanced Wellbore Stability Analysis

4 Knowledge Systems Copyright©2005

PART 2: NAVIGATING THE TUTORIAL

Tutorial Knowledge Systems 5

PART 2: NAVIGATING THE TUTORIAL

6 Knowledge Systems Copyright©2005

PART 3: THE TUTORIAL

PART 3: THE TUTORIAL

Basic Wellbore Stability Analysis

The following analyses are available and discussed in this section:

Shear Failure Gradient Analysis

To perform a shear failure gradient analysis.

Tutorial Knowledge Systems 7

PART 3: THE TUTORIAL

2 Choose the Use Mohr-Coulomb failure condition option.

4 In the Well Name list box, select ANALOGUE.