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

25-Sep-07. GeothermEx, Inc.. 2. Introduction. What did we know by the mid-1980s?A LOTMost 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 toEllis, Mahon, White, Fournier, Helgeson, Truesdell, Arn

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

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    1. 25-Sep-07 GeothermEx, Inc. 1 Advances in the Past 20 Years: Geochemistry in Geothermal Exploration, Resource Evaluation and Reservoir Management Christopher W. Klein GeothermEx, Inc. Richmond CA, USA cwk@geothermex.com

    2. 25-Sep-07 GeothermEx, Inc. 2

    3. 25-Sep-07 GeothermEx, Inc. 3 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

    4. 25-Sep-07 GeothermEx, Inc. 4 Introduction What’s 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

    5. 25-Sep-07 GeothermEx, Inc. 5 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

    6. 25-Sep-07 GeothermEx, Inc. 6 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

    7. 25-Sep-07 GeothermEx, Inc. 7 Fluids Sampling - 3 Downhole sampling High T failure rates were high, sample quality often poor Current commercial choice: Kuster Flow Through Sampler (FTS), to 230°C 300°C controlled-piston-displacement tool designed, 500°C possible (Calidus Eng.UK)

    8. 25-Sep-07 GeothermEx, Inc. 8 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)

    9. 25-Sep-07 GeothermEx, Inc. 9 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.

    10. 25-Sep-07 GeothermEx, Inc. 10 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).

    11. 25-Sep-07 GeothermEx, Inc. 11 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

    12. 25-Sep-07 GeothermEx, Inc. 12 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)

    13. 25-Sep-07 GeothermEx, Inc. 13 Exploration and Resource Evaluation - 5 Dissolved Trace Elements Species usually present at <1 mg/l have not played a major role in geothermal R&D 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

    14. 25-Sep-07 GeothermEx, Inc. 14 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

    15. 25-Sep-07 GeothermEx, Inc. 15 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)

    16. 25-Sep-07 GeothermEx, Inc. 16 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)

    17. 25-Sep-07 GeothermEx, Inc. 17 Resource Management - 4 Scaling and Wellbore Chemistry Modification Hydroxide neutralization of acidic production Steam (USA, Italy) Liquid phase (Costa Rica)

    18. 25-Sep-07 GeothermEx, Inc. 18 Resource Management - 5 Reservoir 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.) 300~340°C ~0.2 ppb simultaneous HPLC detection (up to 8 tracers) ~US$5000/dose expensive analysis (10x fluorescein)

    19. 25-Sep-07 GeothermEx, Inc. 19 Resource Management - 6 Reservoir Tracers Na-fluorescein still of interest (USA) Thermal decay constant slow at <180°C, severely fast at >250°C (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)

    20. 25-Sep-07 GeothermEx, Inc. 20 Resource Management - 7 Reservoir 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

    21. 25-Sep-07 GeothermEx, Inc. 21 Resource Management - 8 Tracer 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

    22. 25-Sep-07 GeothermEx, Inc. 22 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

    23. 25-Sep-07 GeothermEx, Inc. 23 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

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