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Tutorial 3

Problem: Multiple wells, multiple observation bores, multiple stress periods.

Two production wells are located at coordinates (500m, 500m) and at (750m, 750m) in a confined aquifer 1000-m wide and 1000 m long. The transmissivity and the storativity of the aquifer are 1000 m2/day and 0.0001 respectively. The first well is pumped for 10 days at 1000m3/day, then for 15 days at 800m3/day, five days after the completion of the first pumping period. The second well is pumped at 600m3/day for 20 days. Pumping at the second well started five days after pumping commenced at the first well. Determine the response of the aquifer for 40 days since the beginning of pumping at an observation bore at coordinates (600m, 500m), and another at (700m, 500m).

Solution:

In WIDE, start a new model by selecting the [File | New] menu option.

Add the grid and aquifer property details by selecting the [Edit | Grid/Aquifer Properties...] menu option. In the Properties dialog add the following data for the two tabs [Note: Select the appropriate aquifer type prior to setting the Aquifer Properties. Certain properties are only enabled for specific aquifer types]:

grid coordinates   aquifer properties

This problem requires you to achieve multiple stress periods from Well 1. To achieve this, multiple wells are added at the same location, and the "Pumping Starts at" field is modified to reflect the start of each stress period. This effectively superimposes one well on another, and their combined effect will appear as a single well.

Add the pumping well by right-clicking (ctrl click for MacOS) on the grid and entering the pumping bore details. Note: A pumping well cannot be positioned directly on a node. This will cause a numerical instability when calculating the node's drawdown. By default, WIDE will relocate the well by 0.1[L] north and east.

popup menu
well dialog
popup menu
well dialog

Note, the name field for the two wells that are superimposed (located at 500E, 500N). The 'a' suffix will facilitate in recognising multiple bores in the Grid view. Also, with the mouse, right-click (ctrl-click for MacOS users) on the superimposed well location, will enable the menu option "Send to Back". This will send the current well to the end of the list, thus when you hover over the well location with the mouse, the relevant information will be displayed (see examples below).

popup menu
well dialog

Add two observation bores by selecting "Add Observation Bore..." from the popup menu shown above. Enter the following details.

obs01   obs02

Again from the popup menu, select the "Edit Wells/Bores..." option. In the bottom right of the dialog, there is an option to enter the Investigation Time. Select that field and enter the following data. [Note: This dialog box allows you to Add/Edit/Delete pumping and observation bore details in addition to the Investigation Time]

investigation time


Now select the "Start" button and select the "Drawdown" tab to view the results. The drawdown calculated for Obs01 and Obs02 has resulted to -0.005[L]. This demonstrates that the recovery period has affected the total drawdown. To observe this select the "Observation Bore" tab on the results page, select Obs01 from the pick-list, then select the "Graph" button. Note: you may have to click on the black area to display the graph for the first time.

This graph displays the drawdown that occured over the investigation period (40 days). Between day 0 to 5, the drawdown effects from Well01 is observed. Between day 5 and 10, drawdown is increased further from the pumping contribution of Well02. Day 10 shows the start of recovery as pumping from Well01 is ceased. Recovery continues to Day 15, noting that the rate of recovry is greater than the pumping effects of Well02. On Day 15 pumping starts from Well01(a) and continues through to Day 30. However, the period between Day 15 and Day 25 show the effects of combined pumping from Well01(a) and Well02. Day 25 marks the end of pumping from Well02 and recovery immediately begins. At Day 30, pumping from Well01(a) stops and the system recovers through to Day 40.

time graph