Aquifer and well test analysis and simulation: Summary

The CG programs: a summary of what they do

Note that these programs were originally written in about 1988, they run under DOS, not Windows, and have become antiquated.

A simulation fitted to drawdown and recovery in an aquifer test. (Well C was being pumped, the aquifer test data were recorded in piezometer D.) The CG programs can handle many stages in well or aquifer tests; variations in pumping rates including a zero rate (recovery).

Introduction

• Aquifer types: Confined, unconfined, leaky;
• Boundaries: discharge boundary, recharge boundary, partial boundary, parallel boundaries (strip aquifer), no boundary;
• Types of tests: Step tests, constant rate, recovery, slug tests;
• Single piezometers, multiple piezometers;
• Analysis of aquifer test and well test data having breaks or variations in discharge rates
• Output to VDU monitor (graphs and listings), printer, data file;
• Output suitable for spreadsheet

Simulated data from a steady-rate well discharge test. The blue (Isotropic) curve is the simple case with no boundaries. The purple (Discharge) curve is for a simple discharge (water-tight) boundary. The yellow (Recharge) curve is for a simple recharge (constant-head) boundary.

The data for all the graphs (charts) on this page were:

• entered into the CG programs from actual well/aquifer tests,
• edited or otherwise organized within the CG programs,
• produced using the CG programs in analysis of field data,
• or were produced as simulations by the CG programs.

The graphs on this page are examples of uses to which the programs can be put; they are not neccessarily conected with the adjacent text.

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Publication

A data fit produced by CG. Here the well discharge test included a stepped rate test, followed by a period of recovery, followed by a one-day steady-rate test, followed by recovery. The CG programs can analyze a data set like this as easily as for a simple, single-rate test. The displacement between the final recovery and simulated recovery is most likely due to entrapped air in the fractured rock aquifer.

Here the data of the preceding graph are plotted against the logarithm of time.

There are many ways in which the programs might be used. Some examples are:

• Well test analysis;
  • Data entry using the editor,
  • save data file to disk,
  • data validation by graphing on screen,
  • correction, if required, back in the editor; save again,
  • well test analysis on a graphics screen, various graph types,
  • compensation for well storage effects,
  • projections using the Well Equation program,
  • s versus Q or Q/s verses Q output for graphing on spreadsheet.
• Aquifer test analysis
  • Data entry and validation steps as above,
  • aquifer test analysis; there are many options available, some are:
    • Evaluation of transmissivity,
    • Evaluation of storativity,
    • Theisfit (simultaneous evaluation of T and S),
    • Evaluation of leakage,
    • Leakyfit (simultaneous evaluation of T, S, and L),
    • Evaluation of boundary conditions (single boundary or strip),
    • Simultaneous consideration of data from several wells,
    • DeGlee analysis.
• Slug test analysis
  • Data entry and validation steps as above,
  • slug test analysis with a graph on the VDU screen.
• Output of type curves to VDU screen, plotter, or third party software
  Type curves, for output or analysis, can consider T, S, Leakage, confined or unconfined aquifers, aquifer thickness, boundaries, partial boundaries, strip aquifers, well storage effects, etc.
• Education
  The programs can provide students with dynamic demonstrations of the responses of many types of aquifer and boundary configurations. A number of tutorials are provided to this end. Other possibilities are numerous.

This distance drawdown graph has been produced by the stand-alone program CGSim.exe. It is based on a semi-bounded strip aquifer with T=38 inside the strip and T outside the strip (T2) equal to 260. S=0.005 and the strip width is 30m. All units here are based on metres and days.

The CG programs can, and have, been used for educational purposes. For example, as part of a short course in hydrogeology for graduates.

CGSim

Notes on CGSim

Purpose
To produce type curves:

An aquifer test simulation showing the slight differences to be expected depending on the location of pumped well and piezometer within a strip aquifer.

The example data file, CLRPU1DD.CTD, fits well with a strip aquifer with T=1160, S=0.0039, and strip width=365m. As it's set up, the .CFG file starts the program using the Theis solution, change to the strip solution to get a good fit. Then experiment.

One of the minor functions of the CG programs. This sort of graph can be produced from what I've called a 'well characteristics file'. It compares well losses to total drawdown for a series of increasing discharge rates in a particular well.

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Another example of a graph produced from a 'well characteristics file': discharge rate (Q) plotted against specific capacity (Q/s).

Another example of a graph produced from a 'well characteristics file': discharge rate plotted against drawdown (s).

An example of a semibounded strip simulation fitted to data from an actual well test. (As the data were from a pumped well a bit of data manipulation was required.)

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An aquifer test analysis based on water levels recorded in a piezometer during a stepped rate discharge test.

A simulation and field data after evaluation of the well equation.

A simulation demonstrating how a time-drawdown data falls on a straight line on a log-log graph after boundary effects have come fully into play.

The same drawdown data as in the above graph, but here plotted against the square root of time.

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The CG programs can simulate well storage effects while evaluating the well equation in a well test. This graph shows a simulation based on the evaluated well equation with and without well storage effects, compared to the recorded data.

Best fit DeGlee analysis for well Waik6. T=27m2/day, L=334m.

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Index