Geochemical and Geophysical Applications to ASR

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Geochemical and Geophysical Applications to ASR

• Concerns and Data Gaps

Sam B. Upchurch Thomas L. Dobecki SDII Global
Corporation Tampa, Florida April 2003
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Introduction

• ASR is an exciting and effective means of
  managing water for storage and later use
• There are several issues that, in our opinion,
  have not been adequately addressed
• These deal with
• Characterization of the injectate bubble,
• Monitoring designs, and
• Geochemical reactions operative in the aquifer

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Historic Concerns

• Potentials for drift of injectate away from
  control of ASR system
• Increasing concentrations of gross alpha
  (polonium-210), arsenic, and other constituents
  in injectate
• Potential plugging and loss of storage capacity
• Microbial activity

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Geologic Controls
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Example

• Connected fractures and caverns are usually
  coated with colloidal and microcrystalline iron
  sulfide, ferric hydroxide, and clay
• Dissolution releases arsenic, polonium, and other
  constituents

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Needs

• Predict porosity type and distribution
• Predict plume movement
• Monitor for accurate physical behavior of plume
• Avoid or correct for adverse chemical conditions

Solutions involve early understanding of geologic
controls and a well-designed monitoring plan
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Injectate Bubble Characterization

• The configuration of the mass of injectate in the
  aquifer has been the subject of much debate
• Unfortunately, little has been done to resolve
  the shapes of injectate masses (geometries are
  probably site specific)
• The shape of the injectate mass (the bubble)
  has significant implications as to fluid behavior
  (chemistry and amount recovered) and monitoring
  (detection, safety)

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The Ideal Bubble

• The ideal bubble is more or less a flattened
  sphere
• The concept requires that several conditions
  exist in the injection zone

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The Ideal Bubble (cont.)

• Assumes more-or-less isotropic materials
• Permeability
• KH KV rough sphere
• KH lt KV squashed sphere
• Injectate fills intergranular porosity, so
  waterrock interface surface area is
• Very high and
• Chemical reactions should progress moderately
  because of high grain surface areas
• Residual fluids are probable

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Monitoring an Ideal Bubble

• Monitoring is simple
• Leads to radial plan
• If ideal bubble is present, extent is the only
  issue

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Ideal Bubble Movement

• Ground-water movement can cause bubble to shift
  down gradient

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Ideal Bubble Movement

• Radial design may miss
• Extent and/or
• Orientation of plume

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Bubble Buoyancy

• Buoyancy issues cause bubble to migrate out of
  injection zone
• Monitoring designs should account for such events

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The Ganglion Model

• Injectate moves along bedding planes, caverns,
  fractures
• System is anisotropic
• KH gtgt KV,
• KH1 gtgt KHH2

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Ganglion Model

• Surface area in contact with injectate is
  relatively low
• Chemical reactions inhibited unless colloids
  present

• Monitoring difficult to predict
• Need to guide monitoring plan

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Glangion Movement

• Compounds monitoring difficulty
• May exaggerate extent of plume

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Data Gaps and Concerns

• Traditional monitoring may limit understanding
  and detection of injectate
• Prior knowledge of isotropy and porosity
  distribution important to monitoring design
• Porosity distribution important to controlling
  reaction rates and access to constituents of
  concern

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Suggested Approaches

• Accurate photolineament studies with deep
  geophysical ground-truthing (seismic profiling)
• Video and geophysical borehole logs to
  characterize fractures, porosity types, and
  fracture fill (if possible)
• Modeling (Monte Carlo simulations of fractures,
  flow modeling, geochemical modeling) of
  worst-case scenarios for transport prior to
  monitoring design

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Suggested Approaches (cont.)

• Cross-hole geophysics (seismic, electrical
  tomography) for block-of-rock characterization
• Surface geophysics (transient electromagnetic
  sounding, controlled source audio magnetotelluric
  profiling, etc.) to develop a flexible monitoring
  program that can move with the bubble