groundwater profiling for selective extraction: steve walden and debra cerda
DESCRIPTION
TAGD October 2013 Quarterly MeetingTRANSCRIPT
Selective Extraction Case Study:
Lee County WSC
Presented byDebra Cerda and
Steve Walden
Questions
• What have I been missing in my well?– Variable flow– Variable quality
• What is selective extraction?• How can it be applied to
solve water quality issues?
• Visual• Depth-dependent flow• Depth-dependent quality• Ambient mixing
Miniaturized Down-hole Diagnostics
• Represents normal working conditions
• Use the good water, leave the bad in the ground
Miniaturized Down-hole Diagnostics
Straddle Packer / Pump Assemblies for Zone Isolation Testing
Dynamic Flow and Chemistry Profiling
Flow
Chemistry
Packer
Pump
Vs.
Comparisons of Technology for Groundwater Profiling
As & NO3 ?
As & NO3?
As & NO3 ?
As & NO3 ?
Production Well XYZZone Test #1
Zone Test #2
Zone Test #3
Packer
Pump
1,000 GPMAs = 9 - 12 PPB
NO3 = 49 – 53 PPM Zone Test #4
Disadvantages of Packer Testing
• Time – can take weeks
• Effort and impact
• Cost-prohibitive
• Data quality – suction on a well zone not indicative of normal operation conditions
High Tech, Low Cost Technology
• U.S. Geological Survey Developed Tracer-Pulse Profiling Method
• BESST Inc. holds exclusive U.S. license
Tracer system deployed down hole with existing pump in place
What data can be collected?
Dynamic profiling breaks down flow and quality into slices along the length of production zones
Miniaturized Tools
• Apply easily attainable z-axis data for
three-dimensional view
• Minimally invasive downhole diagnostics
• To date, BESST has profiled over 400
wells for cost savings of ~$300 M
– Reduced or avoided treatment
5 PPB As 10 PPB As 50 PPB As
100 GPM ZOI300 GPM ZOI
700 GPM ZOI
Dynamic Flow and Water Quality Profiling
• Fairly easy to implement– Existing pump or test equivalent
close to normal operations– In-line flowmeter– Sample tap– Water discharge and disposal
option– Access pipe if limited annular
space
Access Pipes
Dye Injection Scheme
Q1
Q2
Q3
Q4
Q5
T1
T2
T3
T4
?
?
?
?
Incremental Flow Contribution
Incremental Flow Contribution
Incremental Flow Contribution
Cumulative Flow Contribution
Cumulative Flow Contribution
Cumulative Flow Contribution
Cumulative Flow Contribution
Cumulative Flow Contribution
Profiling is a visual, volumetric and chemical mass accounting system
Dynamic Flow Profile Under Steady State
Draw-Down
Fluorometer
Flow From Well To Fluorometer
Flow From Fluorometer To Waste
1,900 GPM
406080
100120140160180200220240260280300320340360380400
Dye Injection Shot Points
Ft. Below Ground Surface
Water Sampling Spool
Dye Injection Spool
Explanation of Dye Injection Process For Dynamic Flow Profiling In Production Wells
Cumulative Flow Slices (CFS)
Flow Equation
The basic equation used for calculating flow between two points is:
Q = vA where v = (d2-d1)/(t2-t1)
Q: flowA: cross sectional area of well
A = π(r12-r2
2) if above intake
A = πr12 if below intake
v: velocity
d2: injection depth #2d1: injection depth #1t2: return time of d2
t1: return time of d1
r1: inner radius of well casingr2: outer radius of pump column
Recent Gulf Coast Aquifer Brackish Well Flow Profile
Dynamic Groundwater Sampling Under Steady
State Draw-Down
406080
100120140160180200220240260280300320340360380400
Groundwater Sampling Points
Ft. Below Ground Surface
Ca1
Ca2
Ca3
Ca4
Ca5
Ca6
Ca7
Ca8
Ca9
Ca10
Ca11
Ca12
Ca13
Ca14
Ca15
Ca16
Ca17
Cumulative
Concentration
Explanation of Basic Mass Balance Calculations
Slices of Water Quality
Contaminant Concentration Calculation
Average Cumulative Contaminant Concentration Calculation can be defined as:
Ca1= (Q1C1 – Q2C2)/Q1- Q2
Incremental Average Contaminant Concentration between two imaginary flow planes within the well can be expressed as:
Ca1- Ca2
Case Study: Groundwater in Lee County, Texas
Lee County Water Supply Corporation (LCWSC): • Serves 3536 connections and over
10K customers• Recipient of numerous industry
awards, including TCEQ Superior rating
• Experienced water quality issues from Country Corners well site, primarily: color, turbidity, and iron
• In 2012, contracted BESST Inc. to locate zones of poor water quality
8” Liner
1452’Top of Liner
1554’
1734’
1840’
1646’
1664’
1672’
1636’
1723’
Color
Lithology
Hard Shale & Rocks
Broken Rocks & Fine SandShale & Rocks
Coarse Light Gray Sand & Rocks
Hard Shale
Hard Sand & Shale Streaks
Hard Shale & Rocks
1400-1500
1554-1600
1600-1636
1646-1664
1672-1723
1734-1755
1755-1820
below 1820
0 20 40 60 80 100 120
0
110
0
NC
26
60
20
100
Dynamic Chemical Mass Balance Profile
Color Units
Sam
plin
g In
terv
al (ft
. bgs
)
High Color correlates with Shale formations
High Color correlates with Shale formations
Lower Color section correlates with Coarse Light Gray Sand & Rocks
~20% of flow
~60% of flow
~80% combined
23
Change Pumping Rate
Change Pump Intake Location and/or Diameter
Packers, Sleeves and Engineered Suctions
Lower or Raise Pump (Intake)
Attach Suction Pipe To Bottom of Pump
Higher Pumping Rate Vertically Shifts Flow Contribution Downward Inside Well – Away From Pump IntakeLower Pumping Rate Vertically Shifts Flow Contribution Upward Inside Well – Towards Pump Intake
Change Well Diameter and/or Length DiameterInstall Liner
Backfill Bottom of Well
How Do We Hydraulically Manipulate Groundwater Production Wells?
Well RehabilitationRemove mineral encrustations and biofilm on Well Screen
Well Reconstruction / Re-Engineering
Selective Extraction at Work: Block off zones of poor water quality
8” Pump Column
1452’Top of Liner
1554’
1734’
460’
1840’
1646’
1664’
1672’
1636’
13.25” Inner Casing
Pump
Intake
8” Liner
1723’
Grout deepest screen
Sleeve off shallow screen
Potential Solutions:
Before modification (avg) After modification0
0.1
0.2
0.3
0.4
0.5
0.6
0.501
0.05
Total Iron (mg/L)
Total Iron (mg/L)
Less than detect = 100% reduction
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Feedback from LCWSC
“Sometimes you have to look at the whole picture, and take a chance on new science or methods. Sticking our head in the dirt and never trying anything new will not benefit us as a water provider” -- Wade Dane, LCWSC Assistant General Manager
Questions?
Debra Cerda-BESST Inc. Director of Technical Sales and Licensing, Texas
[email protected] cell
---------------------------Steven Walden