Exercise 11: Wellbore Storage and Skin Effects

This tutorial provides an example of the Agarwal (1970) pumping test analysis method for wellbore storage and skin effects.  A 15-day, constant rate (2,592 m3/d) pumping test was performed in a confined aquifer underlain by an impermeable confining unit with a single pumping well and no observation wells. Observations of drawdown versus time were only recorded in the pumping well. AquiferTest Pro will be used to analyze the pumping test results.

For more general information on this solution, please refer to the Section on Wellbore Storage and Skin Effects based on Agarwal (1970).

This exercise is written with the assumption that you have gone through the Quick Start Demo Tutorials, and are familiar with the AquiferTest interface.

NOTE: the Agarwal well skin effects analysis method is only available in the AquiferTest Pro edition.

[1] Launch AquiferTest and from the Welcome page, ensuring that the "Create Pumping Test" box is checked, choose the "Create a new project" button.
If you already have AquiferTest open, create a new project by clicking the (New) button from the toolbar, or select File > New from the main menu.

[2] Complete the fields in the Pumping Test tab, as follows:

In the Project Information frame:

•Project Name: Exercise 11

•Project No.: 11

•Client: ABC

•Location: Your Town

In the Pumping Test frame:

•Name: Agarwal Skin Analysis

•Performed by: Your Name

•Date: filled in automatically

In the Units frame:

•Site Plan: m

•Time: s

•Transmissivity: m2/d

•Dimensions: m

•Discharge: m3/d

•Pressure: Pa

In the Aquifer Properties frame:

•Thickness: 100

•Type: Confined

•Bar. Eff. (BE): leave blank

[3] Define the following well parameters for the blank well record in the Wells table:

•Name: Pumping Well

•Type: Pumping Well

•X [m]:0

•Y [m]:0

•Penetration: Fully

•R[m]:0.25

•L[m]:80

•b[m]: 100

•r[m]: 0.25

•B[m]:0.405

The Pumping Test tab should look similar to the image below:

Next you will assign the discharge record to the pumping well

[4] Click the Discharge tab at the top of the data input window

[5] Make sure that Pumping Well is highlighted

[6] Type a constant discharge rate of 2592 m3/day, as shown below:

Next you will assign water levels to the pumping well.

[7] Select the Water Levels tab

[8] In the Static WL [m] field, type 0

[9] Select File > Import > Import Data..., from the main menu

[10] Browse to the folder "C:\Users\Public\Documents\AquiferTest Pro\Examples\Exercises\Supporting Files\" and select the skineffects.xls file

[11] Click the Open button.

The waterlevel/drawdown data will appear in the data table and will be plotted on the drawdown plot, as shown below:

[12] Click the Analysis tab

[13] From the Data From list, select the Pumping Well (Pumping Well) check box

By selecting the Analysis Graph tab the AquiferTest analysis will show drawdown vs time data on a linear-linear scale, as shown in the image below:

[14] Select the Dimensionless button from the tool bar above the analysis graph

[15] If the drawdown value decreases downward along the Y-axis, reverse the dimensionless water level graph, so that the drawdown increases upward. By expanding the Drawdown Axis item in the Analysis Panel Navigator and selecting checking the Reverse checkbox

Your analysis graph should look similar to the image below:

[16] Under the Analysis Method, select the Agarwal skin solution method

For a classical presentation of the Agarwal wellbore storage and skin effects, the derivative of the type curve and data points should also be shown on the graph.

[17] In the Analysis Navigator Panel, expand the Display item and enable Derivative of the data points and Derivative of the type curve

Next, you will adjust the solution parameters for this analysis:

[18] Click the Analysis Parameters button from the Analysis Graph toolbar.

The Parameter window will appear on your screen. There are 3 parameters that can be adjusted:

•T (Transmissivity): adjusting this value shifts the data points diagonally up+right or down+left

•SD (dimensionless wellbore storage factor): adjusts the data points and curves left or right

•SF (dimensionless skin factor): adjusts the curvature of the type curve.

[19] Change the T, SD, and SF values to 6.5E+1, 2.3E-3 and 1.9E+1, respectively, as shown below:

[20] Click the [X] button in the upper right corner of the window to close the Parameter window

You can also adjust the way the derivative curve is calculated.

[21] Click the Derivative button in the Analysis graph toolbar

[22] From the Derivative Settings dialog, select Bourdet Derviate from the Method combo box.

[23] In the L-Spacing text box, type 0.2

[24] Click the OK button

Now you will adjust the look of the analysis graph.

[25] From the Analysis Navigator Panel, expand the Time Axis item

[26] Make the following changes:

•Minimum: 100,

•Maximum: 1E7,

•Value Format: 0E-0

•Gridlines: Checked

[27] From the Analysis Navigator Panel, expand the Drawdown Axis item

[28] Make the following changes:

•Title: Dimensionless Drawdown sD

•Minimum: 0.1,

•Maximum: 100,

•Value Format: 0E-0

•Gridlines: Checked

The analysis graph should look like the image below:

This concludes the wellbore storage and skin exercise. The next exercise explores the analysis of Lugeon/Packer test data using AquiferTest. You have the choice of exiting AquiferTest or continuing on to the next exercise.

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