Evaluating the Volume of Porous Medium Investigated During Slug Tests

Abstract

This paper presents a methodology for quantifying the volume of porous medium investigated during a slug test in an unbounded porous medium, in the presence of a linear constant‐head or no‐flow boundary, and in the presence of a radial no‐flow boundary. For the unbounded case, type curves are generated for different values of the wellbore storage coefficient, which relate the distance travelled by a given pressure perturbation (1, 5, and 10% of the initial drawdown in the well), to dimensionless time. This distance is found to increase linearly on a log‐log plot until it reaches a maximum which is a function of the wellbore storage coefficient. The appropriate choice of dimensionless groups allows the different curves for each level of perturbation to be collapsed into one curve. Functional relationships offer an alternative to using the type curves graphically. For bounded systems, type curves relate the distance to the boundary to the time of 1 and 5% deviation from the unbounded response. Although these curves cannot be collapsed, the presented range of wellbore storage coefficients covers most practical situations. Developed relationships allow the estimation of the maximum distance travelled by the pressure perturbations in the unbounded case, and the maximum distance at which a linear constant‐head or no‐flow boundary, or a radial no‐flow boundary, still produces a given deviation in the pressure response measured at the well. An application shows that substantial error may result if the distance to a boundary is evaluated while neglecting storage in the well. Finally, application of the methodology developed for a linear no‐flow boundary to a real data set yields a realistic distance to the boundary and a far better match between simulated and measured data than if an unbounded system is considered. The type curves and relationships presented here should be applicable to slug test design and analysis.

Results of Detailed Hydrologic Characterization Tests?Fiscal and Calendar Year 2005

“…The effects of linear boundaries on slug-test response have been examined previously by Karasaki et al (1988) and Guyonnet et al (1993). These effects are largely dependent on the nature of the boundary (i.e., no-flow or constant-head), proximity to the test well, and the storage characteristics of the aquifer and well.…”

“…These effects are largely dependent on the nature of the boundary (i.e., no-flow or constant-head), proximity to the test well, and the storage characteristics of the aquifer and well. As a generalization, Guyonnet et al (1993) state that no-flow boundaries cause the slug-test response to deviate from and delay recovery, while constant-head boundaries cause the slug test to recover faster than that predicted for a corresponding unbounded system response. Karasaki et al (1988) accounts for the presence of linear boundaries within the slug-test response by employing imagewell theory.…”

Slug tests in a confined aquifer: experimental results in a large soil tank and numerical modeling

“…Slug tests involve a very small volume of water (e.g., Schneebeli 1996;Guyonnet et al 1993) and they are deemed to provide approximate k values within an aquifer. The k values derived from several slug tests are part of the data to be used to assess the aquifer local homogeneity.…”

Slug Test Characterization Results for Multi-Test/Depth Intervals Conducted During the Drilling of CERCLA Operable Unit OU ZP-1 Wells 299-W11-43, 299-W15-50, and 299-W18-16

“…It is difficult to assess the representative scale or radius of investigation that the slug test characterization results represent. However based on theoretical relationships presented in Guyonnet et al (1993), slug test results are likely more representative of formation conditions within ~3 m of test site. This scale-of-investigation estimate, however, is highly uncertain and provided only for qualitative discussion purposes.…”