chapter 15: single well tests
DESCRIPTION
Chapter 15: Single Well tests. Presented by: Lauren Cameron. 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 - PowerPoint PPT PresentationTRANSCRIPT
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CHAPTER 15: SINGLE WELL TESTSPresented by: Lauren Cameron
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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!
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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
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IMPORTANT NOTE
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RECOVERY TESTS
Theis’s Recovery Method Birsoy-Summer’s’ recovery method Eden-Hazel’s recovery Method
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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
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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
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PAPADOPULOS-COOPER’S METHOD 2: THE EQUATION
This method uses the following equation to generate a family of type curves:
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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
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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
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RUSHTON-SINGH’S RATIO METHOD 2: EQUATION
The following ratio is used:
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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
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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
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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
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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
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HURR-WORTHINGTON’S METHOD 1: ASSUMPTIONS/USES CONTINUED
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HURR-WORTHINGTON’S METHOD 2: THE EQUATION
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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
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VARIABLE DISCHARGE METHODS
Confined Aquifers Birsoy-Summers’s method Jacob-Lohman’s free-flowing-well method
Leaky aquifers Hantush’s free flowing-well method
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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
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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
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JACOB-LOHMAN’S FREE FLOWING-WELL METHOD 2: EQUATION
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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
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LEAKY AQUIFTERS, HANTUSH’S FREE-FLOWING WELL METHOD 2 : EQUATION
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RECOVERY TESTS
Theis’s Recovery Method Birsoy-Summer’s’ recovery method Eden-Hazel’s recovery Method
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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
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THEIS’S RECOVERY METHOD 2: REMARKS
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BIRSOY-SUMMERS’S RECOVERY METHOD
Data type R esidual 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
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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