Slug TestsChapter 16

Kruseman and Ridder (1970)

Stephanie FultonMarch 25, 2014

BackgroundSmall volume of water—or alternatively a closed

cylinder—is either added to or removed from the wellMeasure the rise and subsequent fall of water levelDetermine aquifer transmissivity (T or KD) or

hydraulic conductivity (K)If T is high (i.e., >250 m2/d), an automatic recording

device is neededNo pumping, no piezometers

Cheaper and faster than conventional pump testsBut they are NO substitute for pump tests!!!Only measures T/K in immediate vicinity of well Can be fairly accurate

Types of Slug TestsCurve-Fitting methods (conventional methods)

Confined, fully penetrating wells: Cooper’s MethodUnconfined, partially or fully penetrating wells: Bouwer

and RiceOscillation 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 neglectedInertia effects come in to play for slug tests in highly

permeable aquifers or in deep wells oscillation testPrior knowledge of storativity needed

Cooper’s Method (1967)Confined aquifer,

unsteady-state flowInstantaneous

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 headCooper 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: AssumptionsAquifer is confined with an apparently infinite extentHomogeneous, isotropic, uniform thicknessHorizontal piezometric surfaceWell head changes instantaneously at t0 = 0Unsteady-state flowRate of flow to/from well = rate at which V changes as

head rises/fallsWater column inertia and non-linear well losses are

negligibleFully penetrating wellWell storage cannot be neglected (finite well diameter)

RemarksMay be difficult to find a unique match of the data to

one of the family of curvesIf 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/rwS, rc

2/2rw2S and the

skin factor

Uffink’s MethodMore complex type of slug test for “oscillation

tests”Well is sealed with inflatable packer and put

under high pressure using an air lineWell 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 (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 rc

2/ω04KD for different values of α as calculated by Uffink:

Figure 16.4

Uffink’s Method: Assumptions and ConditionsAssumptions are the same as with Cooper’s

Method (Section 16.1), EXCEPT:Water column inertia is NOT negligible andHead 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 MethodUnconfined aquifer,

steady-state flowMethods 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 MethodCombining Eqs. 16.16 and 16.17, integrating,

and solving for K:

Bouwer-Rice’s MethodValues 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