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Slug Tests

Slug Tests. 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

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Slug Tests

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  1. Slug Tests Chapter 16 Kruseman and Ridder (1970) Stephanie Fulton March 25, 2014

  2. 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

  3. Types of Slug Tests • Curve-Fitting methods (conventional methods) • Confined, fully penetrating wells: Cooper’s Method • Unconfined, partially or fully penetrating wells: Bouwerand 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 oscillation test • Prior knowledge of storativity needed

  4. 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)

  5. 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:

  6. 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)

  7. 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)

  8. 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 rcshortens 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, rc2/2rw2S and the skin factor

  9. 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

  10. Uffink’s Method (cont.) • This oscillation response is given by Van der Kamp (1976) and Uffink (1984) as:

  11. 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)

  12. Uffink’s Method (cont.)

  13. Uffink’s Method (cont.) • The nomogram in Figure 16.4 (below) provides the relation between B and rc2/ω04KD for different values of αas calculated by Uffink: Figure 16.4

  14. Uffink’sMethod: 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

  15. 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

  16. Bouwer-Rice’s Method • Combining Eqs. 16.16 and 16.17, integrating, and solving for K:

  17. 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

  18. Bouwer-Rice’s Method

  19. Bouwer-Rice’s Method: Assumptions and Conditions

  20. Bouwer-Rice’s Method: Remarks

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