Advances in the Past 20 Years: Geochemistry in Geothermal Exploration, Resource Evaluation and Reser

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Advances in the Past 20 Years Geochemistry in
Geothermal Exploration, Resource Evaluation and
Reservoir Management

• Christopher W. Klein
• GeothermEx, Inc.
• Richmond CA, USA
• cwk_at_geothermex.com

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Introduction

• What did we know by the mid-1980s?
• A LOT
• Most theoretical and practical fundamentals of
  geothermal geochemistry, its engineering
  applications and related chemical applications to
  geothermal technology were in place (if not
  widely understood)
• Kudos to
• Ellis, Mahon, White, Fournier, Helgeson,
  Truesdell, Arnórsson, DAmore, Giggenbach and
  others

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Introduction

• Contributions by mid-80s included
• Chemical geothermometry
• Enthalpy Cl models (and analogues)
• Fundamentals of reaction kinetics and
  thermodynamics
• Relationships among geological processes,
  petrology, mineralogy, temperature and fluids
  chemistry
• Stable isotope behaviors
• Phase partitioning
• Scaling mechanisms and how to control them

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Introduction

• Whats new - a post-1980s look at theory,
  technology and applications with emphasis on
• Commercial technology and new developments
• Basic activity categories (sampling, analysis,
  exploration-evaluation, resource management)
• Location (see Transactions for specific
  citations)
• Included applied chemistry (not strictly geo-)
• Not included drilling, power plants,
  environmental monitoring and abatement, minerals
  extraction
• Underlying advances
• Computation hardware and software
• Global Positioning System

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Fluids Sampling - 1

• Basic methods established before mid-80s
• Subsequent refinements
• Standard Practice for Sampling Two-Phase
  Geothermal Fluid for Purposes of Chemical
  Analysis ASTM E1675-95a (1995)
• Active Standard E1675-04e1 (2004)
• ASTM is basically USA technology (TCI)
• Sampling is elsewhere equivalent and differences
  now are inconsequential

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Fluids Sampling - 2

• Nuts and bolts
• General adoption of Teflon stop-cock sealed steam
  and gas sample bottles
• PVC pipe canisters for bottle protection and
  shipping
• Offset (just barely) the headache of shipping
  under IATA Dangerous Goods Regulations

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Fluids Sampling - 3

• Downhole sampling
• High T failure rates were high, sample quality
  often poor
• Current commercial choice Kuster Flow Through
  Sampler (FTS), to 230C
• 300C controlled-piston-displacement tool
  designed, 500C possible (Calidus Eng.UK)

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Analysis an End-Users Viewpoint

• Fluids Chemistry
• High-Performance/Pressure Liquid Chromatography
  (HPLC)
• SO4, tracers
• Lower analysis costs
• Increasing use of AA for SiO2
• Loosens sample storage issues
• 18O in SO4 more services available
• Geothermal Leakage Detection
• Portable, airborne and satellite infrared
  spectroscopes for rock, mineral and soil analyses
  (UNR, elsewhere)
• Portable systems for CO2 flux at ground surface
• Accumlation chamber, infrared gas analyzer
• High-senstivity ICPMS (trace elements in soils)

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Exploration and Resource Evaluation - 1 Cation
and Silica Geothermometry

• Basic forms well-established by mid-1980s
• Mg and Li variants in place by about 1990
• Principal development larger database and
  experience with application
• Effects of cooling
• Roles of chalcedony vs. quartz
• Occasional variants of original defining
  equations continue to be published based on
  selected data sets and/or refined mathematical
  approaches.

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Exploration and Resource Evaluation - 2 Gas
Geothermometry

• Generally newer than the dissolved solids forms
• Numerous contributions continued into late 1990s,
  especially from Iceland, and have continued even
  recently
• liquid phase H2S (2006).

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Exploration and Resource Evaluation - 3 Isotope
Studies

• Most basic development is database growth,
  development and application experience
• He isotopes and magmatic origins
• Reservoir processes and the ratio 3He/4He
• Studies of acidic reservoir fluids
• Increased experience with S, C, Ar, Rn, Ra, Cl,
  B, Sr and K

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Exploration and Resource Evaluation - 4 Fluid
Inclusions

• Microscopic bubbles of water, solutes,
  crystalline solids and gases trapped in minerals
  at time of formation or alteration
• Wellbore Fluid Inclusion Stratigraphy
• Automated sample crushing and analysis using mass
  spectroscopy to map chemistry of trapped
  volatiles (New Mexico Tech)

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Exploration and Resource Evaluation - 5
Dissolved Trace Elements

• Species usually present at lt1 mg/l have not
  played a major role in geothermal RD
• Patterns and T-controlled behaviors rarely more
  useful than more abundant solutes
• Sb, Zn of interest as sources of scale
• Finger-printing studies
• Rare earths and Y in Jordan (Möller)
• Trace elements in Iceland

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Resource Management - 1 Geochemical Reaction
Modeling

• Most chemical reaction modeling codes in place by
  1985 (WATCH, SOLVEQ-CHILLER, EQ3/6, SOLMNEQ,
  TEQUIL, GEOFLUIDS)
• Subsequent improvements
• Code enhancements
• Pitzer method for highly saline solutions
• Kinetics (esp. SiO2)
• MS-Windows interfaces

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Resource Management - 2 Geochemical Reaction
Modeling

• Integration of reaction modeling with numerical
  reservoir simulation
• TOUGHREACT (LBNL), FRACHEM (Euro EGS)
• Case studies
• More directed studies appearing (Coso, Salton
  Sea, Onikobe)
• Very advised use still needed, especially if
  modeling more than silica and calcite or elevated
  salinity and/or T
• differences in thermodynamic equilibrium
  constants, activity coefficients (or
  ion-interaction parameters) and kinetics models
  can result in significant differences in
  predicted mineral precipitation and
  reservoir-porosity evaluation ... differences in
  calculation schemes typically produce less
  difference in model outputs ... (code
  comparisons by André and others, 2006)

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Resource Management - 3 Scaling and Wellbore
Chemistry Modification

• Calcium carbonate inhibition now routine
• Anhydrite scale inhibition appearing (Japan)
• pH-mod for silica scale inhibition now routine
  (Salton Sea, various binary bottoming cycles)
• Silica scale inhibitors still mostly under
  development
• Silica deposition research remains common
  applied and theoretical (New Zealand, Iceland,
  USA, Russia)
• alternation of acid and alkali injection (USA)

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Resource Management - 4 Scaling and Wellbore
Chemistry Modification

• Hydroxide neutralization of acidic production
• Steam (USA, Italy)
• Liquid phase (Costa Rica)

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Resource Management - 5Reservoir Tracers

• Major improvements
• Until mid-80s Na-fluorescein, I-, 3H
• Organic aromatic alcohols (USA)
• toluenesulfonate, 1-naphthalene sulfonate,
  naphthalene disulfonates (1,5-, 2,5-, 2,6- etc.)
• 300340C
• 0.2 ppb
• simultaneous HPLC detection (up to 8 tracers)
• US5000/dose
• expensive analysis (10x fluorescein)

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Resource Management - 6Reservoir Tracers

• Na-fluorescein still of interest (USA)
• Thermal decay constant slow at lt180C, severely
  fast at gt250C (USA)
• Side-by-side tests with aromatic tracer have
  shown amounts lost in excess of thermal
  degradation (Indonesia)
• Analysis by HPLC with laser fluorometer highly
  sensitive (40 ppq) (USA)

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Resource Management - 7Reservoir Tracers

• Vapor Phase Tracers (USA)
• sulfur hexafluoride, hydrofluorocarbons
• hydrochlorofluorocarbons abandoned due to ozone
  depletion
• chain alcohols (ethanol, n-butanol, etc) (Japan,
  USA)
• disadvantages lower T stability, higher
  detection limits (but improving)
• advantages water solubility, easier handling,
  easier sampling, vapor pressure similar to water,
  range of vapor pressures

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Resource Management - 8Tracer Flow (Enthalpy)
Testing

• Measures flow rates of liquid and vapor in a two
  phase flow line (USA, New Zealand)
• e.g. sodium benzoate in liquid
• e.g. SF6 in steam
• Smaller, lighter equipment new developed

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Challenges for Future

• Further refine understanding of geothermometers
  under conditions of cooling
• Silica scale inhibitors
• Test some of the ideas coming out of coupled
  simulation reaction modeling
• e.g. alternate acid base injection for silica
  management (Coso)
• Do the trench work of refining and improving
  thermodynamic databases and understanding how to
  model the highest temperatures and salinities
• Look for further cost reductions in analyses of
  the new tracers
• Better understanding of B behavior (e.g. in
  clays)
• Further refine understanding of chalcedony vs.
  quartz control of SiO2

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Thanks

• To GRC for invitation to deliver this paper
• As a geochemist and member of the industry
• to research scientists
• to private concerns willing to share experience
• to research funding organizations (e.g. USDOE,
  other government)
• To my colleagues at GeothermEx