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Exercise 11: Wellbore Storage and Skin Effects

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

This tutorial provides an example of the Agarwal (1970) pumping test analysis method for wellbore storage and skin effects. For more general information on this solution, please refer to the Section on Wellbore Storage and Skin Effects based on Agarwal (1970).

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.

[1] Launch AquiferTest and 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] A blank project will load with the Pumping Test tab active.

[3] In this step, you will specify the information needed for the project and or/ the test. Not all information is required, however it is helpful in organizing tests and data sets

In the Project Information frame, enter the following

Project Name: Exercise 11

Project No.: 11

Client: ABC

Location: Your Town

In the Units frame fill in the following:

Site Plan: m

Time: s

Transmissivity: m2/d

Dimensions: m

Discharge: m3/d

Pressure: Pa

In the Pumping Test frame, enter the following:

Name: Agarwal Skin Analysis

Performed by: Your Name

Date: filled in automatically

In the Aquifer Properties frame, enter the following:

Thickness: 100

Type: Confined

In the pumping well table, define the following:

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 like 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 "C:\Users\Public\Documents\AquiferTest Pro\Examples\Exercises\Supporting Files\" folder 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 Time-Drawdown 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 decreases downward, reverse the dimensionless water level graph, so that the drawdown increases upward.

[16] Expand the Drawdown Axis item in the Analysis Panel Navigator

[17] Select the Reverse checkbox

Your analysis graph should look similar to the image below:

[18] 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.

[19] 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 parameters for this analysis

[20] 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:

Transmissivity (T) - shifts the data curve up and down

SD - dimensionless wellbore storage factor; adjusts data points and curves left-right

SF - dimensionless skin factor; adjust the shape of the type curves.

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

 

 

[22] 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.

[23] Select Analysis > Derivative... from the main menu

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

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

[26] Click the OK button

Now you will adjust the look of the analysis graph.

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

[28] Change the Minimum to 100

[29] Ensure gridlines are turned on by selecting the Gridlines checkbox.

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

[31] Change the Minimum to 0.1

[32] Ensure gridlines are turned on by selecting the Gridlines checkbox

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.

References

Agarwal, R.G. (1970) An investigation of wellbore storage and skin effects in unsteady liquid flow: I. analytical treatment. Society of Petroleum Engineers Journal 10: 279-289.


 


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