16. Slug tests - UGA Hydrology
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Transcript 16. Slug tests - UGA Hydrology
Chapter 16
Kruseman and Ridder (1970)
Stephanie Fulton
March 25, 2014
Background
Small volume of water—or alternatively a closed cylinder—
is either added to or removed from the well
Measure the rise and subsequent fall of water level
Determine aquifer transmissivity (T or KD) or hydraulic
conductivity (K)
If T is high (i.e., >250 m2/d), an automatic recording device
is needed
No pumping, no piezometers
Cheaper and faster than conventional pump tests
But they are NO substitute for pump tests!!!
Only measures T/K in immediate vicinity of well
Can be fairly accurate
Types of Slug Tests
Curve-Fitting methods (conventional methods)
Confined, fully penetrating wells: Cooper’s Method
Unconfined, partially or fully penetrating wells: Bouwer and
Rice
Oscillation Test (more complex method)
Air compressor used to lower water level, then released and
oscillating water level measured with automatic recorder
All methods assume exponential (i.e., instantaneous)
return to equilibrium water level and inertia can be
neglected
Inertia effects come in to play for slug tests in highly
permeable aquifers or in deep wells
Prior knowledge of storativity needed
oscillation test
Cooper’s Method (1967)
Confined aquifer,
unsteady-state flow
Instantaneous
removal/injection of
volume of water (V) into
well of finite radius (rc)
causes an instantaneous
change of hydraulic
head:
(16.1)
Cooper’s Method (cont.)
Subsequently, head gradually returns to initial head
Cooper et al. (1967) solution for the rise/fall in well
head with time for a fully penetrating large-diameter
well in a confined aquifer:
Cooper’s Method (cont.)
Annex 16.1 lists values for
the function F(α,β) for
different values of α and β
given by Cooper et al.
(1967) and Papadopulos
(1970)
These values can be
presented as a family of
curves (Figure 16.2)
Cooper’s Method: Assumptions
Aquifer is confined with an apparently infinite extent
Homogeneous, isotropic, uniform thickness
Horizontal piezometric surface
Well head changes instantaneously at t0 = 0
Unsteady-state flow
Rate of flow to/from well = rate at which V changes as head
rises/falls
Water column inertia and non-linear well losses are negligible
Fully penetrating well
Well storage cannot be neglected (finite well diameter)
Remarks
May be difficult to find a unique match of the data to one of
the family of curves
If α < 10-5, an error of two orders of magnitude in α will
result in <30% error in T (Papadopulos et al. 1973)
Often rew (i.e., rew = rwe-skin) is not known
Well radius rc influences the duration of the slug test: a
smaller rc shortens the test
Ramey et al. (1975) introduced a similar set of type curves
based on a function F, which has the form of an inversion
integral expressed in terms of 3 independent dimensionless
parameters: KDt/rw2S, rc2/2rw2S and the skin factor
Uffink’s Method
More complex type of slug test for “oscillation tests”
Well is sealed with inflatable packer and put under
high pressure using an air line
Well water forced through well screen back into the
aquifer thereby lowering head in the well (e.g., ~50 cm)
After a time, pressure is released and well head
response to sudden change is characterized as an
“exponentially damped harmonic oscillation”
Response is typically measured with an automatic
recorder
Uffink’s Method (cont.)
This oscillation response is given by Van der Kamp (1976)
and Uffink (1984) as:
Uffink’s Method (cont.)
Damping constant, γ = ω0B
(16.7)
Angular frequency of oscillation, ω = ω0 1 − B 2
(16.8)
Where
ω0 = “damping free” frequency of head oscillation (Time-1)
B = parameter defined by Eq. 16.13 (dimensionless)
Uffink’s Method (cont.)
Uffink’s Method (cont.)
The nomogram in Figure 16.4 (below) provides the
relation between B and rc2/ω04KD for different values
of α as calculated by Uffink:
Figure 16.4
Uffink’s Method: Assumptions and
Conditions
Assumptions are the same as with Cooper’s Method
(Section 16.1), EXCEPT:
Water column inertia is NOT negligible and
Head change at t > t0 can be described as an
“exponentially damped cyclic fluctuation”
Added condition:
S and skin factor are already known or can be estimated
with fair accuracy
Bouwer-Rice’s Method
Unconfined aquifer, steady-
state flow
Methods for full or partially
penetrating wells
Method is based on Thiem’s
equation for flow into a well
following sudden removal of
slug of water:
The well head’s subsequent
rate of rise:
Figure 16.5
Bouwer-Rice’s Method
Combining Eqs. 16.16 and 16.17, integrating, and solving
for K:
Bouwer-Rice’s Method
Values of Re were experimentally determined using a resistance
network analog for different values of rw, d, b, and D
Derived two empirical equations relating Re to the geometry
and boundary condition of the system
Partially penetrating wells:
A and B are dimensionless parameters which are functions of d/rw
Fully penetrating wells:
C is a dimensionless parameter which is a function of d/rw
Bouwer-Rice’s Method
Bouwer-Rice’s Method:
Assumptions and Conditions
Bouwer-Rice’s Method: Remarks