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CHAPTER 15: SINGLE WELL TESTS Presented by: Lauren Cameron.

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Presentation on theme: "CHAPTER 15: SINGLE WELL TESTS Presented by: Lauren Cameron."— Presentation transcript:

1 CHAPTER 15: SINGLE WELL TESTS Presented by: Lauren Cameron

2 WHAT IS A SINGLE WELL TEST?  A single-well test is a test in which no piezometers are used  Water-level changes are measured in the well  Influenced by well losses and bore-storage  Must be considered  Decreases with time and is negligible at t > 25r,2/KD  To determine if early-time drawdown data are dominated by well- bore storage:  Plot log-log of drawdown s vs. pumping time  Early time drawdown = unit–slope straight line = SIGNIFICANT bore storage effect  Recovery test is important to do!

3 METHODS TO ANALYZE SINGLE-WELL TESTS Constant Discharge  Confined aquifers  Papadopulous-Cooper Method  Rushton-Singh’s ratio method  Confined and Leaky aquifers  Jacob’s Straight-Line method  Hurr-Worthington’s method Variable-Discharge  Confined Aquifers  Birsoy-Summers’s method  Jacob-Lohman’s free-flowing-well method  Leaky aquifers  Hantush’s free flowing-well method

4 IMPORTANT NOTE

5 RECOVERY TESTS  Theis’s Recovery Method  Birsoy-Summer’s’ recovery method  Eden-Hazel’s recovery Method

6 CONSTANT DISCHARGE METHODS  Confined aquifers  Papadopulous-Cooper Method  Rushton-Singh’s ratio method  Confined and Leaky aquifers  Jacob’s Straight-Line method  Hurr-Worthington’s method

7 PAPADOPULOS-COOPER’S METHOD 1: ASSUMPTIONS  Curve Fitting Method  Constant Discharge  Fully Penetrating Well  Confined Aquifer  Takes Storage capacity of well into account  Assumptions:  Chapter 3 assumptions, Except that storage cannot be neglected  Added: Flow to the well is in UNSTEADY state  Skin effects are negligible

8 PAPADOPULOS-COOPER’S METHOD 2: THE EQUATION  This method uses the following equation to generate a family of type curves:

9 PAPADOPULOS-COOPER’S METHOD 3: REMARKS  Remarks:  The early-time = water comes from inside well  Points on data curve that coincide with early time part of type curve, do not adequately represent aquifer  If the skin factor or linear well loss coefficient is known  S CAN be calculated via equations 15.2 or 15.3  S is questionable

10 RUSHTON-SINGH’S RATIO METHOD 1: ASSUMPIONS/USES  Confined aquifers  Papadopulos-Cooper type curves = similar  Difficult to match data to (enter Rushton-Sing’s Ratio method)  More sensitive curve-fitting method  Changes in well drawdown with time are examined (ratio)  Assumptions  Papadopulos-Cooper’s Method

11 RUSHTON-SINGH’S RATIO METHOD 2: EQUATION  The following ratio is used:

12 RUSHTON-SINGH’S RATIO METHOD 3: REMARKS  Values of ratio are between 2.5 and 1.0  Upper value = beginning of (constant discharge) test  Type curves are derived from numerical model  Annex 15.2

13 JACOB’S STRAIGHT LINE METHOD 1: USES/ASSUMPTIONS  Confined AND Leaky aquifers  Can also be used to estimate aquifer transmissivity.  Single well tests  Not all assumptions are met so additional assumptions are added

14 JACOB’S STRAIGHT LINE METHOD 2: REMARKS  Drawdown in well reacts strongly to even minor variations in discharge rate  CONSTANT DISCHARGE  No need to correct observed drawdowns for well losses  In theory:  Works for partially penetrating well (LATE TIME DATA ONLY!)  Use the “1 ½ log cycle rule of thumb” to determine is well-bore storage can be neglected

15 HURR-WORTHINGTON’S METHOD 1: ASSUMPTIONS/USES  Confined and Leaky Aquifers  Unsteady-State flow  Small-Diameter well  Chapter 3 assumptions Except  Aquifer is confined or leakey  Storage in the well cannot be neglected  Added conditions  Flow the well is UNSTEADY STATE  Skin effect is neglegable  Storativity is known or can be estimated

16 HURR-WORTHINGTON’S METHOD 1: ASSUMPTIONS/USES CONTINUED

17 HURR-WORTHINGTON’S METHOD 2: THE EQUATION

18 HURR-WORTHINGTON’S METHOD 3: REMARKS  Procedure permits the calculation of (pseudo) transmissivity from a single drawdown observation in the pumped well. The accuracy decreases as Uw decreases  If skin effect losses are not negligible, the observed unsteady- state drawdowns should be corrected before this method is applied

19 VARIABLE DISCHARGE METHODS  Confined Aquifers  Birsoy-Summers’s method  Jacob-Lohman’s free-flowing-well method  Leaky aquifers  Hantush’s free flowing-well method

20 BIRSORY-SUMMERS’S METHOD :  The Birsory-Summers’s method from 12.1.1can be used for variable discharges  Parameters s and r should be replaced by Sw and rew  Same assumptions as Birsory-Summers’s method in 12.1.1

21 JACOB-LOHMAN’S FREE FLOWING- WELL METHOD 1: ASSUMPTIONS  Confined Aquifers  Chapte 3 assumptions  Except:  At the begging of the test, the water level in the free-flowing well is lowered instantaneously. At t>0, the drawdown in the well is constant and its discharge is variable.  Additionally:  Flow in the well is an unsteady state  Uw is < 0.01  Remark: if t value of rew is not known, S cannot be determined by this method

22 JACOB-LOHMAN’S FREE FLOWING- WELL METHOD 2: EQUATION

23 LEAKY AQUIFTERS, HANTUSH’S FREE- FLOWING WELL METHOD 1 : ASSUMPTIONS  Variable discharge  Free-flowing  Leaky aquifer  Assumptions in Chapter 4  Except  At the begging of the test, the water level in the free-flowing well is lowered instantaneously. At t>0, the drawdown in the well is constant and its discharge is variable.  Additionally:  Flow is in unsteady state  Aquitard is incompressible, changes in aquitard storage are neglegable  Remark: if effective well radius is not known, values of S and c cannot be obtained

24 LEAKY AQUIFTERS, HANTUSH’S FREE- FLOWING WELL METHOD 2 : EQUATION

25 RECOVERY TESTS  Theis’s Recovery Method  Birsoy-Summer’s’ recovery method  Eden-Hazel’s recovery Method

26 THEIS’S RECOVERY METHOD 1: ASSUMPTIONS  Theis recovery method, 13.1.1, is also applicable to data from single-well  For  Confined, leaky, or unconfined aquifers

27 THEIS’S RECOVERY METHOD 2: REMARKS

28 BIRSOY-SUMMERS’S RECOVERY METHOD  Data type  Residual drawdown data from the recovery phase of single-well variable-discharge tests conducted in confined aquifers  Birsoy-Summers’s Recovery Method in 13.3.1 can be used  Provided that s’ is replaced by s’w

29 EDEN-HAZEL METHOD : USES/ASSUMPTIONS  For Step-drawdown tests (14.1.2) is applicable to data from the recovery phase of such a test  Assumptions in Chapter 3 (adjusted for recovery test:s)  Except:  Prior the recovery test, the aquifer is pumped stepwise  Additionally  Flow in the well is in unsteady state  u < 0.01  u’ < 0.01


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