Interpretation of Prematurely Terminated Air‐Pressurized Slug Tests

Abstract

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. If the maximum declining (or new equilibrium) water level is achieved for a constant applied air pressure, the slug‐test solution of Cooper et al. (1967) can be used to interpret the water‐level recovery data and estimate the formation properties. In low‐permeability terranes, the time required to achieve the equilibrium water level during the pressurized part of the test may be too long for practical purposes, and it may be necessary to terminate the applied air pressure prior to establishing a new equilibrium. To analyze data from such tests, a solution to the boundary‐value problem for the declining and recovering water level during an air‐pressurized slug test is developed for an arbitrary time‐dependent air pressure applied to the well. For the special case of applying a constant air pressure and then reducing it instantaneously to atmospheric pressure at a prescribed time, the general solution reduces to the superposition of the solution of Cooper et al. (1967) at two displaced times. Type curves are generated to estimate formation transmissivity and storativity from the recovering water level associated with prematurely terminated air‐pressurized slug tests. The application of the type curves is illustrated in tests conducted in wells completed in the Minnelusa and Madison aquifers near Rapid City and Spearfish, South Dakota.

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

“…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 references cited here provide detailed descriptions of the analytical methods used and their underlying assumptions.…”

“…Their method includes a specialized application of the Cooper, Bredehoeft, and Papadopulos type-curve solution Shapiro and Greene, 1995). The method, modified for partially penetrating conditions, assumes radial flow and a confined aquifer of homogeneous and isotropic material.…”

“…Airpressurized slug tests were conducted from March 8 through April 8, 1999. Analytical methods used to estimate hydraulic conductivity were the Bouwer and Rice (Bouwer, 1989) method; the Cooper, Bredehoeft, and Papadopulos (1967) method; the Shapiro and Greene Shapiro and Greene, 1995) method; and the van der Kamp (1976) method.…”

Hydrogeologic characterization of the Minnelusa and Madison aquifers near Spearfish, South Dakota

“…The method used to conduct and interpret the airpressurized slug tests in this report are presented in Greene and Shapiro (1995) and Shapiro and Greene (1995). Air-pressurized slug tests are conducted by pressurizing the air in the casing above the column of water in the well, monitoring the declining water level, and then instantly releasing the air pressure and monitoring the rising water level until the original static level is achieved.…”

“…Air-pressurized slug tests are conducted by pressurizing the air in the casing above the column of water in the well, monitoring the declining water level, and then instantly releasing the air pressure and monitoring the rising water level until the original static level is achieved. The recovery data are analyzed graphically using a family of type curves developed by Shapiro and Greene (1995) to determine transmissivity and storativity.…”