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Confidential Institute of Petroleum Engineering Herriot-Watt University Well Test Analysis

Prepared by the IPE-WT teaching team 1

WELL TESTING TUTORIALS

Exercise 1: Data preparation

1. INTRODUCTION

This document describes the procedures that should be followed when entering well test

data into PanSystem. Manual entry of Well and Reservoir data is always required. Manual

entry of Time-related Pressure and Rate Data is only required when the user does not have

Gauge Data in ASCII files. For a Black Oil Fluid Type Well, once the data are set-up, the user

will:

Plot "raw" data

Analyze the test with Log-Log, specialized and Type-Curve plots

Simulate the test response to validate it.

A number of steps need to be followed as described below.

When you open Pansystem you will see a framework as displayed below which includes

different display and navigation menus (i.e. Navigation pane, Pansystem view buttons,

Pansystem ribbon , Tool bar, Graphic area, and Status bar. These are shown in figure below.

1. Navigation Pane

2. Pansystem view buttons

3. Pansystem Ribbon

4. Tool bar

5. Graphic area

6. Status bar



2. DATA PREPARATION

2.1 Well/Fluid/Layer Data Entry

First, from the Pansystem View button window on the bottom left side of the Pansystem

framework select the Data preparation option and then, select the Well, Reservoir & Fluid

Description option from the corresponding Pansystem ribbon.

From the options displayed under this ribbon click on Analytical Model to gain access to

the data entry dialog for Well, Fluid and Reservoir data. The Reservoir Description dialog

should now be displayed.

The Reservoir Description dialog is split into three main sections and these will be reviewed

in turn.

It should be noted that the system has been set up to allow consistent data entry for all data

types. This means that within the various dialogs illustrated throughout this example there are

many fields which may not be required if the users objective is to analyze the Pressure

Transient data. The mandatory parameters, which must be entered, are highlighted in red.

These fields must be completed to allow the system to compute the required essential results

such as Permeability, Wellbore Storage, etc. Note that PanSystem always checks for missing

data.

2.1.1 Fluid Control



In the Fluid Type part of the Reservoir Description dialog, ensure that the selection is set

to Oil only because a Single-Phase Oil Producer will be studied here. The Multi-Phase

checkbox options must be left unchecked.

2.1.2 Well Control

The Well Control section of the dialog allows the user to define the Number of the Wells in

the system and to select which Well he/she wants to edit.

For the purpose of Analyzing Welltest data of a single Well, the default selection can be

used:

Well1

P - Well 1; Active

To access Well-specific data entry press the Well Parameters button, which will take you to

the Well Parameters sub-dialog:



In this example, only two items must be initialized for the Analysis of a single Well test:

Well Radius: Enter 0.31 ft

Wellbore Storage Model: Leave this at the default "Classic" model. The user will be

able to select a different Model during Analysis if the data suggests he/she should.

The other fields are required for Advanced Simulation, which is not covered in this

example.

Select OK to close the sub-dialog.

2.1.2.1 Principal Well Orientation

The Principal Well Orientation should be set to Vertical (= Vertical or Slant Well). This

selection will define subsequent options for Analysis of the data such as the Type-Curves that

are presented in Type-Curve Matching.

2.1.3 Layer Control

The Layer Control section of the Reservoir Description dialog allows access to input

reservoir data. For this exercise the default setting should be retained at:

Layer 1

Layer 1; Active



Select the Layer Parameters button to access the Layer Parameters sub-dialog:



Enter the following values as shown in the above illustration:

Formation Thickness (30 ft)

Porosity (0.10 decimal fraction)

These are highlighted in red because they are mandatory.

The Layer Pressure field can either be left at zero or an estimated value can be entered; it

should be noted that this value is not used in Analysis of data and is actually one of the

derived parameters.

The Water Saturation, Gas Saturation and Rock Compressibility fields are used in the

calculation of Total Compressibility (Ct), and can be left at zero if the user intends to enter a

value for Ct in the Fluid Parameters section (see the following section for details). The Total

Compressibility field can not be edited on this sub-dialog.

The bottom section of the Layer Parameters dialog allows the user to select a Reservoir

Flow Model, which later is used for Analysis of data. This can be easily changed when

Analyzing data and is often unknown at this stage of data entry. The default model of Radial

Homogeneous Model, is a good starting point for the Analysis.

The Model Parameters button provides access to the parameters characterizing the

selected Reservoir Flow Model. In the case of Radial Homogeneous these are the Skin and

Permeability. Since the objective of the Analysis is to derive these parameters there is no

need to initialize them at this stage. Select OK to return to the Reservoir Description dialog.

2.1.5 Fluid Parameters

Now select the Layer Fluid Parameters button located on the bottom right hand side of the

main Well, Reservoir & Fluid description dialogue to access the (Oil) Fluid Parameters sub-

dialog shown below:



Enter the following values:

Bo (1.2)

(0.84)

Ct (3E-6)

Only the mandatory (red) parameters should be entered for subsequent calculations to be

performed in PanSystem.

It is possible to use Correlations available in PanSystem to calculate these values; in this

case, the input data fields in the upper part of the Fluid Parameter sub-dialog need to be

populated with data and the Use Correlations checkbox option must also be checked. The

user can select the required Correlation, and press the Calculate button to have the necessary

computed values. The Water Saturation, Gas Saturation and Rock Compressibility values

must also be entered in the Layer Parameters sub-dialog, if the user requires them to be used

in the computation of Total Compressibility.

Once the mandatory Oil Fluid Parameters data have been entered, select OK to return to

the Reservoir Description dialog. Select OK again to return to the opening PanSystem screen.

All the non Time-based data have now been entered.



Question: What is the relationship between the total compressibility and rock/fluid

compressibilities? Can you sort the reservoir fluids compressibilities in descending order?

2.2. Gauge Data

2.2.1 Importing Gauge Data Files

From the Pansystem View button window on the bottom left hand side of the Pansystem

framework select the Import/Export Data option. This will activate a new Pansystem ribbon,

which allows the user to import and export the gauge data in different formats. In this

exercise we are using an ASCII file, which is the most widely used format in the petroleum

industry. Under the Import Data section of the Pansystem ribbon select the ASCII text

format, . This will bring on a dialogue to select the corresponding data file.

Accept the default to add the imported data file to the existing Pansystem file, which has

been automatically created by Pansyetem and includes the previously imported reservoir fluid

and layer properties.

For this example, select the pressure gauge file i.e. PRESSURE2011.TXT from the pop-

up dialogue and then click open button at the bottom right hand-side of the displayed

dialogue.



When the dialog is first opened, only files with the default extension *.DAT are displayed.

To import PRESSURE2011.TXT, the user will have to select the All Files (*.*) option from

the Files of Type option to see all files including the desired *.txt files.

2.2.2 Defining the Data Columns

The next dialog that is generated allows the user to specify what data is allocated to each

Column in the Gauge Data file. The user will see the following Data File dialog:



The user is presented with a view of the data file with PanSystem making a first guess at

what the Columns are. The Column Names and Gauge Type (Pressure, Rate, etc.) displayed,

at this stage, will depend on what was the last set-up when using this option.

In the case of PRESSURE2011.TXT, the user can see the structure which is:

Time in Column #1, with format Hours

Pressure in Column #2 (Pisa)

The data file was supplied with the comment lines. In the example, the

Number of Lines in Header field contains the number 2 (means two first lines are

comments and need to be ignored by PanSystem). Select each column separately to

make sure that each one is in the right format. As it was mentioned before Pansystem

makes a guess on what the column are. Therefore you may not be required to change

anything.

Select the Import button and load the PRESSURE2011 file. A warning message will

appear that if the user wants to save the template. At this stage we dont want to save this.



Therefore, select no from the available options. The following pop-up window appears

confirming that the 334 data points have successfully been imported.

2.2.3 Selecting and Plotting Data

Once the file has been correctly imported, the data are ready to be Plotted.

From the Navigation Pane on the left-hand side of the Pansystem framework select

PRESSURE2011: Pressure #1 option, which is listed under the Data Files/ Column Lists tree.

Double click on the listed pressure. Now the following Data Edit Plot appears in Pansystem

Graphic Area:



QUESTION: Can you guess how many rate-changes do we have? Can you find the

Drawdown or the build-up flow periods?

Note: You can zoom in or out any part of this plot using the available buttons available in

the toolbar.

You can use Zoom a box button, , to have an enlarged view on any particular part of

the data point. After selecting this button, hold the left click button of the mouse cursor and

draw a rectangle around any part of the plot. You can use Zoom Back button, , to restore

the original view. Feel free to play with the rest of the buttons to get used to the functionality

of each button. Use the undo button, , to restore any changes you have made.

Note: It is suggested that after each stage you save your work. To do so, select the

Weatherford Logo that is available on the top left hand side of the Pansystem and save your work by selecting it from the menu that appears after pressing this button. 2.3 Flow Periods

2.3.1 Defining Flow Periods

The user should identify the duration of flow periods and their associated rates before

being able to analyse any well test gauge data. The simple example below shows the concept:



Having imported the Gauge Data files, and selecting the proper gauge file as discussed in

the previous sections, the user can now define the Flow Periods on the gauge file,

PRESSURE2011.TXT. In PanSystem, there are different graphical methods that can be

employed for this purpose. These options are listed in the Rate Changes Ribbon of the gauge

plot area. In this exercise three of them will be discussed to define different rate changes

occurring in this example.

2.3.2 Rate Change Using Exact Coordinates



Use the Mark Exact Point tool icon (illustrated above) for this purpose. The user should

identify the first Rate Change (i.e. start of first Flowing Period) and Mark where he/she think

the Flow Period began. This does not necessarily have to correspond to a reported (measured)

Data Point. To do this, you would need to use the zoom in capability as described above.

By clicking any point, the Rate Change dialog appears which displays the co-ordinates of

the exact position that was marked. As this is the start of the test, the Rate for this Rate

Change should be zero. Selecting OK from the dialog, a Rate Change Marker is displayed on

the Data Plot.

Use the numbers shown in red on the Figure below (e.g. use pressure=5000 psi, rate=0

bbl/day and time =0) to provide the required information if yours are different from the

values shown here.

2.3.3. Rate Change Using Intersecting Lines:



This is the second method; start by clicking two points before and two after the Flow Rate

Change, and then select the corresponding tool icon shown above. The intersection of the two

lines is taken as the Rate Change.

If the values displayed on the pop-up window are different from what is shown on the

graph below, perhaps the points have not been selected accurately. You can continue with

your numbers however for matter of consistency with this tutorial you may want to change

the information with those shown here, i.e. time= 17.1hr, pressure=4055.848psi and rate=500

bbl/day. It should be noted that for a real data set this information may not be available.

Therefore, you should always make effort to select the right data points.

Note: The point selection/de-selection is simply done by clicking the left button of your

mouse curser when the mouse pointer is placed on the point. This will make the point

brighter than the others.

For the third rate change (end of build-up) we use another method.

2.3.4 Rate Change Using Nearest Point:

Selecting this tool icon and clicking on the plot, marks a Flow Rate Change on the Data

Point nearest to the cursor position. Zoom-In on the end of the data plot and click the cursor

near the last Data Point. Enter the Flow Rate and the other data needed in the dialog, i.e.

rate=0 bbl/day, time 37.1 hr, pressure =4879.77 psi.



Note:



To edit a Rate Change point via the Rate Change dialog, click on its Marker in the

Ruler Bar with the right mouse button, or use the left button whilst simultaneously

holding down the Ctrl key. To drag the Marker and re-position it manually, just click

on it with the left mouse button and drag.

You can Save your data using the Weatherford Logo and then save, or Save as... options.

You also can edit the rate change points by selecting Rate Changes icon.



Now you are ready to switch to a specialized plot. From the Pansystem View area select

Analysis option. From the Pansystem ribbon select Workflow and then Test Overview plot.

The user needs to select a period to be plotted in specialized plots. This can be accessed by

clicking on the ruler bar to highlight one flow period. Here you can click on the last period to

select the main build-up or choose the previous flow period to choose the drawdown period

for analysis.

Now you are ready to switch to a specialized plot. Select the drawdown period and

under the Plot Type ribbon click on the Log-Log button, to plot the data on a Log-

Log plot. You should be able to see the following.



After this stage, the user should save the PanSystem file in his/her directory and choose

the following name for it: CompleteDD_CompleteBU2011. This file includes all

information you need for analysis. We will use this file later on.

As mentioned above, the user can save his/her PanSystem file at any time by selecting

Save/Save as options from the menu that appears after pressing the Weatherford logo.

You can open that file later by clicking on the file. PanSystem will automatically recognize

the file.

3. ANALYSIS

Question: Before starting the analysis, can you list what are the main well test analysis

assumptions?

At this stage we have successfully imported all the data necessary for the interpretation and

analysis. Although we can analyze the whole data set, however for the sake of simplicity and

teaching purposes, we have divided the complete Draw Down periods into several different



stages. We will sequentially add the additional information to the test response and finally we

will have the whole data set.

The necessary *.Panx files corresponding to these different stages have been prepared and

are available in the tutorial directory. A *.Panx file is a recognizable PanSystem file in

which all data needed have already been provided and is ready for analysis. Each Pan file

represents a part of the whole test. As we move through the files, the longer and more

complex response time will be investigated. The available files are as follows:

1. sDD2011.PanxA simple drawdown: Duration: 0.1 hr. 2. sDD_WBS2011.PanxA simple drawdown + Wellbore storage : duration 0.1hr. 3. sDD_WBS_S2011.Panx A simple drawdown+ Wellbore storage +Skin : duration

0.1 hr.

4. sDD_WBS_S_B12011.PanxA simple drawdown + Skin +Wellbore storage + boundary 1, duration 4 hr.

5. CompleteDD_CompleteBU2011.Panx Complete drawdown and complete build-up (this is the file you have already saved in your directory in the previous section).

Drawdown period: A drawdown + skin +Wellbore storage +

boundary 1+boundary 2: duration 17.1 hr.

Build-up periodthe same period as complete drawdown.

After successful completion of above steps you are ready to analysis the data. However you

are required to read the following section beforehand.

4. How to Recognize Different Flow-Regimes?

Flow regime identification is a crucial step in well test interpretation and model recognition.

Conventionally the flow regimes are defined as follow

1. ETR

2. MTR

3. LTR

They are identified by searching for signature of similar observed responses from a library

of available drawdown type curves. It is usually done based on LOG-LOG plot of pressure

derivative data. In Pansystem a set of lines with different slopes are used to distinguish each

flow regime.

1. ETR:



a. WBS (unit-slope trend in early time)

b. Linear

c. Bilinear

d. Spherical

e. Hemi-spherical

f. Radial ( zero slope trend in early time)

g. etc

2. MTR

a. Channel linear*

b. Radial (Primary zero-slope line in middle time)

c. Semi radial (secondary-zero slope line in middle time)

d. Dual porosity

e. Dual permeability

f. Fault*

g. etc

3. LTR

a. SS

b. PSS (unit-slope trend at late time)

c. Fault*

d. Channel linear*

The popular Flow Regime Identification tool is used to differentiate the eight common

subsurface flow regimes on Log-Log plots for their application in determining and

understanding downhole and reservoir conditions.

The figure below summarizes the flow regime identification on a Log-Log plot

based on the Pressure Derivative trends.



ETR MTR LTR

WELL TESTING TUTORIALSExercise 1: Data preparation1. INTRODUCTION2. DATA PREPARATION2.1 Well/Fluid/Layer Data Entry2.1.1 Fluid Control2.1.2 Well Control2.1.2.1 Principal Well Orientation2.1.3 Layer Control2.1.5 Fluid Parameters2.2. Gauge Data2.2.1 Importing Gauge Data Files2.2.2 Defining the Data Columns2.2.3 Selecting and Plotting Data

2.3 Flow Periods2.3.1 Defining Flow Periods2.3.2 Rate Change Using Exact Coordinates/2.3.3. Rate Change Using Intersecting Lines:/2.3.4 Rate Change Using Nearest Point:/

After this stage, the user should save the PanSystem file in his/her directory and choose the following name for it: CompleteDD_CompleteBU2011. This file includes all information you need for analysis. We will use this file later on.3. ANALYSISQuestion: Before starting the analysis, can you list what are the main well test analysis assumptions?

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Documents

reservoir data

data entry dialog

rate data

gauge data

data types

welltest data

missing data

consistent data entry