Seeing into the Earth with Hydrogeophysics : Introduction to Streaming Potential

1. Seeing into the Earth with Hydrogeophysics: Introduction to Streaming Potential Defense Waste Management Programs (6210) Geophysical Research Kristopher L. Kuhlman and BwalyaMalama

2. Groundwater Importance Source: Roy, Summers & Goldstein (2003) Source: economist • Largest unfrozen freshwater source • Growing Southwestern US • Use >> precipitation • Little groundwater recharge

3. Groundwater Depletion Gravity Recovery and Climate Experiment

4. Groundwater Flow and Transport Source: US Geological Survey • Groundwater flow • Is there enough water? • Meeting growing municipal water demand • Water rights / litigation • What is source of water? • Precipitation or infiltration • Old water from storage • Solute transport • Will contaminant migrate? • South Valley contamination • Kirtland AFB jet fuel spill • Can we clean up contamination in our lifetime? • Complexities and heterogeneities critical to transport

5. Wells are Important & Expensive • Wells are primary access points to groundwater • Can’t measure pressure (system state) remotely • Expensive to drill/complete/maintain (often >$100k) • Collect data to maximize usefulness of wells

6. Geophysics to the Rescue m = “Cementation exponent” n = “Saturation exponent” • Allows us to “see into the Earth” • Cheap/easy fields to measure at surface • Electromagnetic fields • X, Y & Z acceleration (seismic) • Gravitational field (microgravity) • Empirical petrophysical relations: • Geophysical properties ↔ Hydraulic properties e.g., Archie’s Law • Easy to formulate, difficult to defend physically

7. Hydrogeophysics • Hydrogeophysics methods “directly” related to presence or movement of water in subsurface • Microgravity change due to extraction of water (mass loss) • Nuclear magnetic resonance (mobility of subsurface water) • Streaming potential due to movement of water in porous medium

8. Spontaneous Potentials Source: wikipedia Source: fulux.com • Potentials arising “naturally” • Electrochemical potentials between • Rock types (Membrane, Nernst, or “shale” potential) • Water salinities (Liquid-junction potential) • Mineralization potential (large) • Due to redox reactions (ore bodies) • Streaming (electrokinetic) potential • voltage arising due to flow of electrolyte through porous medium with surface charge • Electrokineticforces • Electro-phoresis: movement of charged particles in fluid due to applied voltage • Electro-osmosis: flow in channel due to applied voltage (SNL microfluidics)

9. Spontaneous Potentials Voltage Forces Process Voltage Possible coupling

10. SP History • SP Qualitatively used to map “anomalies” • Static ore bodies (membrane/mineralization potentials) • 0.1 to 10 Volts • Transient pumping/recharge (electrokinetic potential) • 0.01 to 1 Volt Source: Bogoslovsky and Ogilvy (1972) Source: Telford et al.,(1990)

11. Static Ion Arrangement Source: wikipedia • Individual quartz grain • Steady-state behavior • Quartz in water (pH 7) • Negative surface charge • Positive ions closest (Stern layer) • Mostly positive ions surrounding (Diffuse layer)

12. Foundation of SP in porous media • Moving electrolyte in a pore throat • Bulk/Diffuse layer flow • Charging a RC system • Current flow proportional to water flow

13. SP Voltage Sensors • High-impedance voltmeter • Non-polarizable single-ended electrodes • Environmental: Pb/PbCl2 • Biomedical: Ag/AgCl • Reference electrode • Sensor development work ongoing in Carlsbad

14. SP Field Test (S. Italy) • Pumping test analysis with SP. Rizzo et al (2004) • Steady-state post-pumping only • Mostly qualitative Recovery Pumping Source: Rizzo, Suski, Revil, Straface & Troisi (2004)

15. SP Field Test (S. Italy) • Data fit using Malama, Revil & Kuhlman (2009) model • Estimated aquifer electrical/flow properties from SP response Source: Malama, Revil & Kuhlman (2009)

16. SP/Flow Mathematical Model • Physics-based model of coupled processes • Conservation equations • If no electro-osmosis: solve for flow problem, insert into electrical problem as source term. Darcy’s law electro-osmosis Darcy’s flux Current flux electro-kinetic Ohm’s law Charge conservation Mass conservation

17. SP Field Test (Boise) • Unconfined test site along Boise River (Boise State Univ.) • Dipole pumping test • Dense network Observation Wells SP electrodes Source: Malama, Kuhlman & Revil (2009) Injection Well Pumping Well

18. SP Field Test (Boise) • Updated SP model for unconfined systems • Matched entire transient dataset (not just recovery) • Estimated unconfined aquifer properties from SP data Source: Malama, Kuhlman & Revil (2009) Source: Jardani, Revil, Barrash, Crespy, Rizzo, Straface, Cardiff, Malama, Miller & Johnson (2009)

19. SP in Granite Tunnel • SNL collaboration with Korean Atomic Energy Research Institute (KAERI) • SP test bed in fractured granite • Double-porosity system Pressure response Voltage response End pumping Begin pumping

20. SP Falling-Head Permeameter Source: Malama & Revil (2013)

21. Sandia SP Permeameter • Malama & Revil (2013) developed a simplified SP solution • Estimates flow/electrical properties • Simple double-exponential form • Good match to late-time permeameter data • SP voltage a viable surrogate for pressure data! • Cheaper / more robust measurements Source: Malama & Revil (2013) Clean quartz sand WIPP sand/silt Head vs. SP

22. Sandia SP Sand Tank • Cylindrical sand tank to test theory / methods / electrodes • Controlled geometry • High instrument density • Can change aquifer material Source: Malama (2013)

23. Sandia SP Sand Tank Source: Malama (2013)

24. SP Lab Test (Carlsbad) Pressure Voltage (SP) • SP voltage signal • Higher signal-to-noise ratio • Easier to measure • Cheaper sensors • Measurable “at a distance” Vadose zone moisture

25. SP Applications Source: Bogoslovsky and Ogilvy (1972) Mostly qualitative applications • Early warning system in dams • Flowing sinkhole detection • Fractures in geothermal systems (electrokinetic + thermoelectric) • Groundwater circulation near volcanoes • Seawater intrusion early warning (liquid junction potential) • Determine hydraulic properties via independent means Source: Revil, Schwaeger, Cathles & Manhardt (1999)

26. Method Benefits / Limitations • Supplement well observations • May replace hydraulic measurements • SP sensors cheaper than pressure transducers • Easier to measure small ΔV than observe small ΔP • Earth models will make other uses quantitative • Non-conductive well casing (PVC, FRP) • Significant cultural noise • Desert soil is highly resistive, reducing surface signal • Deeper electrodes • Oscillatory/repetitive pumping (i.e., stacking) • Higher salinity → lower signal

27. SP Future at Sandia • Sensor development • Sand tank as an SP chemistry test-bed • Upgrade permeameter for intact cores (low-Q high-P systems) • SP in rock salt • Traditional (dilute) theory predicts no signal • Strong signal seen; C(conc) needs to be investigated • Collaborate at Sandia • Electrokineticmicropumps (microfluidics 8620) • Molecular Dynamics modeling (geochemistry 6915) • Electroseismic numerical models (geophysics 6913) • Sandia advancing hydrogeophysical methods • Local applications through NM Small Business Assistance • Research / tool development through LDRD

28. Thank You