Methods of conducting air-pressurized slug tests and computation of type curves for estimating transmissivity and storativity

Abstract

Air-pressurized slug tests offer an efficient means of estimating the transmissivity (T) and storativity (S) of aquifers. Air-pressurized slug tests are conducted by pressurizing the air in the casing above the column of water in a well, monitoring the declining water level and then releasing the air pressure and monitoring the rising water level. The equipment needed to conduct an airpressurized slug test is easily constructed and assembled at the top of the well. The only equipment in contact with the water is a down-hole sensor to monitor water levels. During the pressurized part of the test, small changes in the applied air pressure result in water-level fluctuations, making it difficult to estimate T and S from the declining water-level data. However, if the applied air pressure is maintained until a new equilibrium-water level is achieved and then the air pressure in the well is released instantaneously, the slug test solution of Cooper and others (1967) can be used to estimate T and S from the rising water-level data. In lowpermeability formations, it may take an extended period of time to achieve the new equilibrium-water level for the applied air pressure. The total time to conduct the test can be reduced, however, if the pressurized part of the test is terminated prior to achieving the new equilibrium-water level. This is referred to as a prematurely terminated air-pressurized slug test. Type curves generated from the solution of Shapiro and Greene (1995) can be used to estimate T and S from the rising water-level data from prematurely terminated air-pressurized slug tests. The Fortran code AIRSLUG, included in this document, is used to generate the type curves from the solution of Shapiro and Greene (1995). A detailed discussion of the equipment and procedures for conducting air-pressurized slug tests is presented along with discussions of data preparation, use of the Fortran code AIRSLUG, and method of matching the data and the type curves to estimate T and S. Field examples are presented to demonstrate the applicability of air-pressurized slug tests in estimating T and S.

Documentation of spreadsheets for the analysis of aquifer-test and slug-test data

“…Greene and Shapiro (1995) extended the method for the analysis of very low permeability material where the introduced slug does not reach equilibrium before being removed. The original assumptions were:…”

“…Transmissivity estimates are affected minimally by the value of storage that is assigned. Greene and Shapiro (1995) state "* * * Air-pressurized slug tests offer a means of estimating formation transmissivity and storativity without extensive downhole equipment and in situations where contact with formation fluids may pose a health concern. An air-pressurized slug test, as discussed in this paper, consists of applying a constant pressure to the column of air in a well, monitoring the declining water level, and then releasing the air pressure and monitoring the recovering water level.…”

Use of air-pressurized slug tests to estimate hydraulic conductivity at selected piezometers completed in the Santa Fe Group aquifer system, Albuquerque area, New Mexico

“…Time-varying water level during (a) air-pressurized slug test, (b) prematurely terminated, air-pressurized slug test, and (c) slug test with oscillation. Delta, A, is the maximum change in water level from applied air pressure; t r is the time at which the pressurized part of the slug test is terminated and recovery starts; H is the initial water level at time, t = 0; and w(tr) is the water level at time t = tr (modified from Greene and Shapiro, 1995). Generally, the Bouwer and Rice (Bouwer, 1989) Shapiro and Greene, 1995) was used to analyze data for the two slug tests that were prematurely terminated; and the van der Kamp (1976) method was used to analyze data for the three slug tests that had oscillatory responses.…”

“…The authors are especially grateful to Rhea Graham and Derrick Lente of the Pueblo of Sandia Environment Department for their assistance, under adverse weather conditions, with the installation of transducers in piezometers. The air-pressurized slug-test method described by Greene and Shapiro (1995) was used to estimate hydraulic-conductivity values of the aquifer material surrounding piezometer screens. This method offers a means of estimating hydraulic conductivity without extensive downhole equipment and without the need to add or remove a column of water.…”

Performance evaluation testing of wells in the gradient control system at a federally operated Confined Disposal Facility using single well aquifer tests, East Chicago, Indiana

“…Monitoring well D40 was chosen as being representative of a background condition within the Calumet aquifer due to its proximity to the CDF, but the well is screened at a shallower depth than the wells on the CDF property. Multiple air slug tests were performed in each monitoring well using an air slug technique (Greene and Shapiro, 1995;fig. 6) during the August-September 2014 and March-May 2015 testing periods.…”