Monday, July 9, 2012

Catalog of Derivative Plots

Derivative analysis is a powerful diagnostic technique for the interpretation of data from pumping tests. Use of the derivative in pumping test analysis can highlight many flow regime features that otherwise may be hard to discover when inspecting drawdown data alone.

A catalog of derivative plots, showing the theoretical drawdown and derivative signatures on log-log axes for different flow regimes, is a useful reference to the practicing hydrogeologist when performing derivative analysis. For example, Figure 1 shows the drawdown and derivative response for a finite-diameter pumping well with wellbore storage in an infinite nonleaky confined aquifer.

Figure 1. Wellbore storage flow regime, infinite nonleaky confined aquifer.
One observes the wellbore storage flow regime at early time when the drawdown and derivative curves both exhibit unit (1:1) slopes (Figure 1). Radial flow in an infinite-acting aquifer shows up as a plateau on the derivative response.

An extensive catalog of derivative plots is available at the Aquifer Testing 101 section of the AQTESOLV web site to help you with derivative analysis. Use the catalog to become familiar with the derivative plot signatures for various well/aquifer geometries corresponding to different flow regimes.

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