NAME
airslug - A Fortran program to generate type curves to interpret the
recovery data from prematurely terminated air-pressurized
slug tests
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 air-
pressurized 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, fluctuations 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 developed by Cooper and
others (1967) can be used to estimate T and S from the rising water-
level data. In low-permeability 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
(recovery) from prematurely terminated air-pressurized slug tests.
The Fortran code AIRSLUG, is used to generate the type curves from
the solution of Shapiro and Greene (1995).
METHOD
In conducting the prematurely terminated air-pressurized slug test,
the column of air in the well is subject to a constant applied air
pressure (pressurized part of test) and then instantaneously reduced
to atmospheric pressure (recovery part of test). The drawdown data
during the recovery part of the test are interpreted with the type
curves generated in this program to estimate transmissivity and
storativity.
HISTORY
Version 1.1 1996/03/12 - First UNIX release
Version 1.0 1996/02/01 - Original release
DATA REQUIREMENTS
The code is completely interactive and requires no data sets. The
program prompts the user for the needed data input. The user will
need to supply input in response to prompts for: (1) DRDELT, which
is the fraction of the maximum water-level change for the applied
air-pressure, (2) an output file name, and (3) the number of type
curves desired. If all nine type curves are selected, the program
generates type curves for all nine values of alpha. If the user
selects one type curve, then the user must enter their own value of
alpha.
OUTPUT OPTIONS
The output is stored in the file named by the user. The user can
then generate plots of the type curves using external software
plotting packages. The values defining the type curves are in 10
columns. The first column contains dimensionless times, at which
the dimensionless drawdowns are evaluated. Columns 2 through 10
contain dimensionless drawdowns for the dimensionless times given in
the first column; each column corresponds to a type curve for a
different value of alpha, alpha = 1.0E-1, 1.0E-2, ... 1.0E-9. The
user of AIRSLUG alternatively can specify that a single type curve
be generated for a specific value of alpha. In this case, the
program will generate values for only one type curve and store them
in a file prescribed by the user. The values defining the type
curve will be stored in 2 columns; the first column contains the
dimensionless time and the second column contains the dimensionless
water levels for the specified value of alpha.
SYSTEM REQUIREMENTS
AIRSLUG is written in Fortran 77 with the following extensions: use
of COMPLEX*16 variables and functions. Generally, the program is
easily installed on most computer systems. The code has been used
on UNIX-based computers and DOS-based 386 or greater computers
having a math coprocessor and 4 mb of memory.
APPLICATIONS
AIRSLUG is used to generate type curves needed to estimate
transmissivity and storativity from water level data collected
during the recovery part of an air-pressurized slug test.
DOCUMENTATION
Greene, E.A., and Shapiro, A.M., 1995, Methods of conducting air-
pressurized slug tests and computation of type curves for
estimating transmissivity and storativity: U.S. Geological Survey
Open-File Report 95-424, 43 p.
Shapiro, A.M., and Greene, E.A., 1995, Interpretation of prematurely
terminated air-pressurized slug tests: Ground Water, v. 33, no.
4, p. 539-546.
RELATED DOCUMENTATION
Cooper, H.H., Jr., Bredehoeft, J.D., and Papadopulos, I.S., 1967,
Response of a finite-diameter well to an instantaneous charge of
water: Water Resources Research, v. 3, no. 1, p. 263-269.
CONTACTS
Operation:
U.S. Geological Survey
Branch of Regional Research
Earl A. Greene
431 National Center
Reston, VA 20192
eagreene@usgs.gov
U.S. Geological Survey
Office of Hydrologic Research
Allen M. Shapiro
431 National Center
Reston, VA 20192
ashapiro@usgs.gov
Distribution:
U.S. Geological Survey
Hydrologic Analysis Software Support Program
437 National Center
Reston, VA 20192
h2osoft@usgs.gov
Official versions of U.S. Geological Survey water-resources analysis
software are available for electronic retrieval via the World Wide
Web (WWW) at:
http://water.usgs.gov/software/
and via anonymous File Transfer Protocol (FTP) from:
water.usgs.gov (path: /pub/software).
The WWW page and anonymous FTP directory from which the AIRSLUG
software can be retrieved are, respectively:
http://water.usgs.gov/software/airslug.html
--and--
/pub/software/ground_water/airslug