Vasi Passinos

Vasi worked on the characteristics of constant rate pumping tests in the vicinity of simple heterogeneities, like abrupt changes in heterogeneity. The title of her thesis is: Well tests to characterize idealized lateral heterogeneities. Her research was partly supported by the NSF (EAR 9876124).

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Abstract

The hydraulic properties of vertical layers and contacts between different aquifer materials are important to applications ranging from the compartmentalization of reservoirs to the remediation of aquifers. Despite their importance, there are few options for determining the hydraulic characteristics of lateral heterogeneities using field techniques. To address this issue, we have conducted numerical well tests designed to evaluate the possibility of using data from constant-rate pumping tests in the vicinity of idealized lateral heterogeneities. One type of heterogeneity consists of a long vertical strip whose hydraulic conductivity contrasts with the surrounding aquifer. The thickness and hydraulic conductivity of the vertical strip were varied to examine how they affect the drawdown in the vicinity of the layer. The effects of the strip can be recognized on a semi-log plot by two straight-lines with the same slope connected by a sigmoidal curve. A derivative plot shows this behavior particularly well.

The results of numerical well tests indicate that the drawdown response depends on the layer conductance, specifically the ratio of hydraulic conductivity to layer width. Type curves have been generated for this problem and used to analyze field data from a well test conducted in the vicinity of a suspected fault in the Piedmont region of South Carolina.

The possibility of characterizing aquifers that consists of two regions with different properties that are separated by a vertical contact was also investigated. This problem can be solved using an analysis that reduces to the Theis solution for the homogenous case. Results using this analysis suggest that it is possible to estimate the position of a vertical contact by graphically interpreting well test data. Inverse methods using the analytical solution allow both the location of the contact and aquifer properties of both regions to be determined.

Last Updated: August 28, 2007 -- Questions or comments, contact Larry Murdoch.
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