Evaluating the Impact of Highly-Conductive Annular Space on Resolution of Hydraulic Tests and Aquifer Characterization
Abstract
It is common practice for groundwater wells to be drilled/installed with an annular space around the well filled with relatively homogeneous and highly-conductive material (i.e., gravel or clean sand). There are several reasons for this practice, such as increased well production, but this can have other consequences, too. A highly-conductive annular space acts as an artificial hydraulic connection between layers within an aquifer and results in a short-circuiting effect that can impact both groundwater remediation schemes as well as hydraulic testing aimed at resolving aquifer parameters such as hydraulic conductivity and storage coefficients. In this work, we study the latter issue. From standard pumping tests to hydraulic tomography, hydraulic tests stimulate the aquifer and observe the response at one or more locations. For scenarios in which testing is performed over discrete (packed-off) intervals, the annular space may dramatically reduce the sensitivity of the data collected, which reduces the resolution of the results. Thus, a common challenge of site characterization is recognizing and mitigating the effects of the annular space on characterization resolution. Given this issue, we will use numerical models to analyze a number of scenarios that vary (i) the ratio of the mean hydraulic conductivity of the formation to that of the annular space, (ii) the variance of the hydraulic conductivity formation, (iii) and the radius of the annular space. Combined with some background understanding about the structure and variability of an aquifer, our results will provide insight into the value of performing additional tests from discrete intervals compared to other options, such as increasing the number of observation points or recognizing the limitations caused by the annular space and reducing the number of tests to save costs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.H13F1426H
- Keywords:
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- 1829 HYDROLOGY Groundwater hydrology;
- 1847 HYDROLOGY Modeling;
- 1894 HYDROLOGY Instruments and techniques: modeling