Groundwater Profiling for Selective Extraction: Steve Walden and Debra Cerda
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This document discusses selective extraction, a technique to improve water quality from groundwater wells. It summarizes a case study where selective extraction was used on a well in Lee County, Texas. Dynamic profiling identified zones of high contaminant levels, such as color and iron. Solutions included sleeving off shallow screens and grouting the deepest screen to block poor quality zones. This improved water quality, reducing total iron levels by over 95%. The water provider was initially skeptical but saw benefits from applying new diagnostic methods rather than traditional approaches.
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Groundwater Profiling for Selective Extraction: Steve Walden and Debra Cerda
- 1. Selective Extraction Case Study: Lee County WSC Presented by Debra Cerda and Steve Walden
- 2. 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?
- 3. Miniaturized Down-hole Diagnostics • Visual • Depth-dependent flow • Depth-dependent quality • Ambient mixing
- 4. Miniaturized Down-hole Diagnostics • Represents normal working conditions • Use the good water, leave the bad in the ground
- 5. Comparisons of Technology for Groundwater Profiling Dynamic Flow and Chemistry Profiling Straddle Packer / Pump Assemblies for Zone Isolation Testing Flow Packer Pump Vs. Chemistry
- 6. Production Well XYZ Zone Test #1 1,000 GPM As = 9 - 12 PPB NO3 = 49 – 53 PPM Zone Test #2 Zone Test #3 Zone Test #4 Packer As & NO3 ? As & NO3? Pump Disadvantages of Packer Testing • Time – can take weeks • Effort and impact • Cost-prohibitive As & NO3 ? As & NO3 ? • Data quality – suction on a well zone not indicative of normal operation conditions
- 7. 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
- 8. What data can be collected? Dynamic profiling breaks down flow and quality into slices along the length of production zones
- 9. 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
- 10. 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
- 11. Access Pipes
- 14. T1 ? Profiling is a visual, volumetric and chemical mass accounting system Incremental Flow Contribution Q1 Cumulative Flow Contribution T3 ? Q2 Cumulative Flow Contribution Incremental Flow Contribution T2 ? Cumulative Flow Contribution Q4 Q3 Cumulative Flow Contribution Q5 Cumulative Flow Contribution T4? Incremental Flow Contribution
- 15. Water Sampling Spool Flow From Well To Fluorometer Dye Injection Spool Fluorometer Flow From Fluorometer To Waste Explanation of Dye Injection Process For Dynamic Flow Profiling In Production Wells Cumulative Flow Slices (CFS) Dynamic Flow Profile Under Steady State Draw-Down Dye Injection Shot Points 1,900 GPM Ft. Below Ground Surface 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400
- 16. Flow Equation The basic equation used for calculating flow between two points is: Q = vA where v = (d2-d1)/(t2-t1) Q: flow A: cross sectional area of well A = π(r12-r22) if above intake A = πr12 if below intake v: velocity d2: injection depth #2 d1: injection depth #1 t2: return time of d2 t1: return time of d1 r1: inner radius of well casing r2: outer radius of pump column
- 17. Recent Gulf Coast Aquifer Brackish Well Flow Profile
- 19. Slices of Water Quality Dynamic Groundwater Sampling Under Steady State Draw-Down Groundwater Sampling Points Ft. Below Ground Surface 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 Cumulative Concentration Ca1 Ca2 Ca3 Ca4 Ca5 Ca6 Ca7 Ca8 Ca9 Ca10 Ca11 Ca12 Ca13 Ca14 Ca15 Ca16 Ca17 Explanation of Basic Mass Balance Calculations
- 20. 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
- 21. 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
- 22. Dynamic Flow Profile: Keyes Well 7 Color Dynamic Chemical Mass Balance Profile 1452’ Top of Liner Lithology 0 1400-1500 Hard Shale & Rocks 1554’ 110 1554-1600 Broken Rocks & Fine Sand High Color correlates with Shale formations Shale & Rocks 1636’ 1646’ Coarse Light Gray Sand & Rocks 1664’ 1672’ Sampling Interval (ft. bgs) 1600-1636 0 1646-1664 NC ~20% of flow Lower Color section correlates with Coarse Light Gray Sand & Rocks ~80% combined 26 1672-1723 ~60% of flow 1723’ 60 1734-1755 1734’ Hard Shale Hard Sand & Shale Streaks Hard Shale & Rocks 1840’ 8” Liner High Color correlates with Shale formations 20 1755-1820 100 below 1820 0 20 40 60 Color Units 80 100 120
- 23. Well Reconstruction / Re-Engineering How Do We Hydraulically Manipulate Groundwater Production Wells? Change Pumping Rate Higher Pumping Rate Vertically Shifts Flow Contribution Downward Inside Well – Away From Pump Intake Lower Pumping Rate Vertically Shifts Flow Contribution Upward Inside Well – Towards Pump Intake Change Pump Intake Location and/or Diameter Lower or Raise Pump (Intake) Attach Suction Pipe To Bottom of Pump Packers, Sleeves and Engineered Suctions Change Well Diameter and/or Length Diameter Install Liner Backfill Bottom of Well Well Rehabilitation Remove mineral encrustations and biofilm on Well Screen 23
- 24. Dynamic Flow Profile: Keyes Well 7 Selective Extraction at Work: Block off zones of poor water quality 13.25” Inner Casing 8” Pump Column 460’ Pump Intake 1452’ Top of Liner Potential Solutions: 1554’ Sleeve off shallow screen 1636’ 1646’ 1664’ 1672’ 1723’ 1734’ Grout deepest screen 1840’ 8” Liner
- 25. Total Iron (mg/L) 0.6 0.501 0.5 Less than detect = 100% reduction 0.4 0.3 Total Iron (mg/L) 0.2 0.1 < 0.05 0 Before modification (avg) After modification
- 28. 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
- 29. Questions? Debra Cerda-BESST Inc. Director of Technical Sales and Licensing, Texas dcerda@besstinc.com 512-785-6813 cell --------------------------Steven Walden stevenwalden@sbcglobal.net 512-971-7151
Hinweis der Redaktion
- Examples given are non-exclusiveWhy should we capture data as close to normal working conditions as possible?We want to gather the most accurate data against the problem statement. If a well is producing 12 mg/L arsenic, we want to diagnose the well as it is producing that result. If we change the operating conditions, in any way, we will alter the results of the diagnostics and ultimately have less confidence in mitigating actions we can pursue since the data will have less fidelity to the situation that was producing the 12 mg/L arsenic in the first place.
- Examples given are non-exclusiveWhy should we capture data as close to normal working conditions as possible?We want to gather the most accurate data against the problem statement. If a well is producing 12 mg/L arsenic, we want to diagnose the well as it is producing that result. If we change the operating conditions, in any way, we will alter the results of the diagnostics and ultimately have less confidence in mitigating actions we can pursue since the data will have less fidelity to the situation that was producing the 12 mg/L arsenic in the first place.
- BESST founder and CTO co-inventor of that technology; just received extension and expansion of license
- We can perform diagnostics for any testable water parameter and optimize production output to meet stated project goals. Minimally or non-invasive downhole diagnostics.Savings survey.
- The dye tracer pulse technology was developed and patented by USGS and is licensed exclusively to BESST, Inc. During a dynamic profile test, fluorescent rhodamine red dye is injected into the well at a series of depths and tracked as it travels to the surface to determine the velocity of the water in the well. A portion of the wellhead discharge is rerouted through the fluorometer with a hose running off a sample tap. This portion of the flow mimics the dynamic dye concentration of the entire flow. The dye fluoresces when hit with a laser; the fluorometer induces and measures this fluorescence to detect concentrations of dye in the water passing through it.The dye is circulated through a pump which, when triggered, pushes it through hundreds of feet of spooled up nylon tubing. The dye-filled tubing is lowered into the well with a check valve and nozzle at the end. The valve ensures that dye is only released through the nozzle when the pump pressurizes the line and that water does not push itself up into the tubing. The nozzle guides the dye into a horizontal spray in four directions, 90° apart.The dye is injected in pulses, or discreet durations of injection. The injection time can be altered by changing the injection time set on the injection control box and by loosening or tightening the valve at the end of the tubing. The pulses are tracked by the fluorometer as they are pumped to the surface; each dye injection pulse returns as a distinct rise and fall in the numerical reading on the fluorometer. The duration between the beginning of an injection and the peak value of its appearance in the fluorometer is deemed a return time. Differences between return times are used to calculate the vertical velocity of water traveling from one point to another within the well.The basic equation used for calculating flow between two points is:
- Most likely artifact of constituent
- Very likely background TDS