Volume 7 geothermal energy 7 04 – geochemical aspects of geothermal utilization

Volume 7 geothermal energy 7 04 – geochemical aspects of geothermal utilizationVolume 7 geothermal energy 7 04 – geochemical aspects of geothermal utilizationVolume 7 geothermal energy 7 04 – geochemical aspects of geothermal utilizationVolume 7 geothermal energy 7 04 – geochemical aspects of geothermal utilizationVolume 7 geothermal energy 7 04 – geochemical aspects of geothermal utilization

7.04 Geochemical Aspects of Geothermal Utilization H Ármannsson, Iceland GeoSurvey (ISOR), Reykjavik, Iceland © 2012 Elsevier Ltd All rights reserved 7.04.1 7.04.2 7.04.3 7.04.4 7.04.5 7.04.6 7.04.7 7.04.8 7.04.9 7.04.10 7.04.11 References Introduction Collection of Liquid and Gas Samples Characterization of Solids Analysis of Fluids Classification of Water Alteration Tracing the Origin and Flow of Geothermal Fluids Speciation and Reaction Path Calculations Geothermometry Applications during Production Case History Exploration of a Geothermal Area Theistareykir, NE Iceland 97 97 99 102 103 105 110 130 136 143 157 165 7.04.1 Introduction Geochemistry is used at all stages of geothermal utilization, from preliminary exploration to production of geothermal energy The major goals of geochemical exploration are to obtain the subsurface composition of the fluids in the system and use this to obtain information on temperature, origin, and flow direction, which help in locating the subsurface reservoir Equilibrium speciation is obtained using speciation programs and simulation of processes such as boiling and cooling to get more informa­ tion in order to predict potential deposition and corrosion Environmental effects are foreseen and the general information is used as a contribution to the model of the geothermal system Prediction and analysis of scaling and corrosion become more important at later stages, although studies on changes in characteristics of geothermal systems such as temperature and origin still remain important Geochemistry is also an important tool in environmental management and monitoring Geochemical work generally consists of • collection of samples • chemical analysis of samples • interpretation of analytical results In this chapter sampling and chemical analysis will be discussed before going on to interpretation of the results first in exploration and then during production Case histories will be used to illustrate the methods 7.04.2 Collection of Liquid and Gas Samples General The collection of samples for chemical analysis is the first step in a long process, which eventually yields results that provide building blocks in the model of a geothermal system It is imperative that this step be properly carried out because all subsequent steps depend on it There are several hidden dangers inherent in the collection of geothermal samples The terrain may be treacherous and dangerous chemicals need to be handled Thus, there is an obvious need for well-trained personnel with insight into possible errors and interferences in order to carry out this task The most common mistakes made during sampling involve the use of improper containers, improper cleaning, and a lack of or improper treatment for the preservation of samples Containers For lightness, ruggedness, and tolerance of bumps in the field, plastic bottles are the best Most plastics are, however, relatively permeable and let atmospheric air easily through, possibly setting off oxidation reactions, and liquids may easily evaporate through them causing concentration of constituents and possible oversaturation Many plastics are also rife with possible adsorption sites for sample constituents and may thus decrease their concentrations Glass is fragile and relatively heavy, but can fairly easily be made airtight Thus, glass containers are preferable for the preservation of constituents affected by atmospheric air Constituents that are sensitive to light are collected into amber bottles If containers have not been specifically precleaned and prepared for a certain task, they should be rinsed at least three times with the sample fluid prior to collection Comprehensive Renewable Energy, Volume doi:10.1016/B978-0-08-087872-0.00709-5 97 98 Geochemical Aspects of Geothermal Utilization Sample preservation Some constituents will not survive intact from sample collection to analysis without special precautions Common reasons for concentration changes are interaction with suspended matter, adsorption on the walls of the containers, biological activity, redox reactions, polymerization, and precipitation Different preservation methods are needed for the various processes and therefore the total sample will comprise several subsamples Preservation methods may be physical or chemical and the more common ones are listed in Table It is desirable that samples be kept relatively cool apart from the inconvenience of handling boiling hot water and steam Fluid that is well above ambient temperature is therefore cooled to ambient temperature using a cooling device, usually a cooling coil immersed in cold water, during collection Steam samples collected into NaOH in double-port bottles may bypass the cooling device and the bottle itself be cooled in cold water Collection The collection of samples of nonboiling water can be divided into two categories: samples from natural springs and samples from hot water wells When collecting samples from hot springs it is desirable that the water be free-flowing from the sample spot If not, a sampling pump is needed Water temperature and discharge as well as wellhead pressure if available are reported The collection of representative samples from high-temperature drill holes is done either by using the separator on the wellhead separating the whole discharge or with a small Webre separator Natural steam discharge may occur in many different forms, such as gentle discharge from a large area of hot ground or major discharge from large fumaroles The most useful information is often obtained from steam discharged from powerful fumaroles It has been shown that the most representative samples are collected from the flow of a two-phase well at about 1.5 m distance from the T-joint at the well top The various subsamples collected are described in detail in Table 2, but the total procedure for collection from high-temperature wells is shown in Figure Samples are collected into plastic bottles unless otherwise specified The vents on the Webre separator are opened and the fluid is allowed to flow from the borehole through the separator Care is taken that the pressure in the separator does not deviate much from that of the wellhead For the collection of the vapor phase, the water level inside the separator is kept low until preferably a mixture of water and steam issues through the water vent A blue cone should form at the steam vent showing that dry steam is being issued To check the efficiency of the separation, a small sample of condensed steam may be drawn and the concentration of a nonvolatile component such as Na or Cl determined, compared with the concentration of the same component in the liquid phase, and the percentage of carryover calculated If t < 70 °C, it may be desirable to determine the dissolved oxygen concentration of the water to estimate its corrosion potential This determination is carried out during sampling as described below When sampling fumaroles, care has to be taken that a discrete, directed outflow is chosen and diffuse ones avoided at all costs A good guide to the suitability of an outflow for sampling is sulfur deposits A funnel is placed atop the outflow and care taken that no atmospheric air is drawn in The funnel is connected to a titanium or a silica rubber tube, which is directed to a lower point where the sample is collected When sampling springs care has to be taken to obtain a sample as near to the outflow as possible An indicator such as ink may be used if it is difficult to find Normally the water sample will be drawn with a pump into an evacuation flask The filtering apparatus is fitted between the sample and the pump when appropriate If a gas sample is required, two evacuated flasks, one with taps on both ends below and a double-port gas bottle containing 40% NaOH above, are Table Preservation methods for geothermal samples Type Method Purpose Used for Physical Filtration Freezing Airtight container On-site analysis Base addition Acidification Precipitation Prevent interaction with suspended matter Prevent biological activity Prevent interaction with atmospheric air Anions, cations Nutrients Volatiles Prevent reactions of reactive constituents Reactive constituents Absorption of acid gases Prevent adsorption on walls of containers Prevent a constituent from reaction to change the concentration of another Prevent biological activity, using HgCl or formaldehyde CO2, H2S in steam, δ34S in H2S in vapor Cations Sulfide to preserve sulfate Chemical Sterilization Dilution Redox Ion exchange Extraction Prevent polymerization and precipitation To change oxidation state of a volatile constituent to make it less volatile Concentrate and further prevent adsorption on walls of container of trace constituents Concentrate and further prevent adsorption on walls of container of trace constituents δ34S and δ18O in SO4, prevents biological oxidation of sulfide Silica Hg Trace cations Trace cations Geochemical Aspects of Geothermal Utilization Table 99 Treatment and subsamples from geothermal sampling Phase Treatment Specification To determine Vapor None; amber glass bottle 0.5 ml 0.2 M ZnAc2 added to sample in 100 ml volumetric glass flask to precipitate sulfide None 0.8 ml conc HNO3 (Suprapur) added to 200 ml sample Added to 50 ml 40% NaOH in evacuated double-port bottle Ru Rp δ2H, δ18O SO4 Ru Ra Gas sample, Ai Ru Rd (1:10 to 1:1) Ru Fu Fp, Fpi Anions Cations CO2, H2S in NaOH, residual gases in gas phase, δ34S in H2S in vapor Mg, SiO2 if 100 ppm pH, CO2, H2S (if not in field) Anions SO4, δ34S and δ18O in SO4 Fui, Fuc, Fut δ2H, δ18O, 13C, 3H Fa Cations Liquid None Dilution; 10–50 ml of sample added to 90–50 ml of distilled, deionized water None; amber glass bottle with ground glass stopper Filtration (0.45) Filtration; ml 0.2 M ZnAc2 added to sample in 100 ml volumetric glass flask and ≥10 to ≥500 ml bottle containing ≥25 mg SO4 to precipitate sulfide Filtration; one 60 ml and two 1000 ml amber glass bottles, with ground glass stoppers Filtration; 0.8 ml conc HNO3 (Suprapur) added to 200 ml sample SAMPLING VAPOR PHASE SAMPLING LIQUID PHASE Pressure gauge Webre separator Evacuated double-port bottle Borehole 40% NaOH Thermometer pocket Water level during collection of liquid phase Ru 250 ml amber airtight bottle 10 ml sample pipetled into a volumetric flask Filled to the mark with distilled water Ru (200 ml) Rd triplicate in plastic bottle Water vent Water level during collection of vapor phase Steam vent Filtering equipment 0.8 ml HNO3 Plastic bottle Ra 200 ml Rp Plastic bottle Rp 0.5 ml 0.2 M ZnAc2 into 50 ml volumetric flask + 0.8 ml HNO3 Plastic bottle Run Amber glass bottle Rui 60 ml Cooling > 10 ml 0.2 M ZnAc2 + ml 0.2 M ZnAc2 into 100 ml volumetric flask Fa Fu Fp Fp Fui Amber glass amber glass (200 ml) (500 ml) (>500 ml) (100 ml) bottles bottle Plastic bottle (1000 ml) (60 ml) Figure Overview of collection of a sample from a two-phase geothermal well for chemical analysis arranged in series The taps are opened slowly, first on the two-ended flask, and care taken that water does not enter the double-port bottle (Figure 2) Sampling techniques are described in more detail by Ármannsson and Ólafsson [1] Summary For proper sampling clean containers of appropriate material are needed Care has to be taken that appropriate preservation techniques for particular constituents are applied Thus, each sample will be composed of several sample fractions ready for analysis Volatile and urgent constituents are analyzed in a field laboratory or upon sampling 7.04.3 Characterization of Solids Solid samples are characterized during drilling either cuttings or core samples Similar methods are employed to characterize samples of deposits and corrosion products formed during production The latter are either collected from their formation sites or coupons of similar material as the pipes are inserted into the flow for a known period of time and the material formed characterized by weighing and analysis The most common techniques of solid characterization are described below The interpretation of the analysis of the fluids is in fact dependent on knowledge of the alteration minerals present 100 (a) Geochemical Aspects of Geothermal Utilization (b) Sampling raw water for volatiles, Mg, and diluted portion Sampling gas 250 ml into brown airtight flask 40% NaOH Fill to mark with distilled water Evacuated flasks Three plastic bottles containing Rd portion in triplicate Ru 200 ml Pipet 10 ml sample into volumetric flask Filter flask Pump (c) Stainless steel cooling coil Sampling filtered portions (incl for isotopes) Plastic funnel Stick Gas flow Sampling spring + 0.8 ml HNO3 Filtering equipment >10 ml 0.2 M ZnAc2 +2 ml 0.2 M ZnAc2 into 100 ml volumetric flask Hot spring Fui Fa Fu Fp Amber glass amber glass (200 ml) (500 ml) (>500 ml) bottles bottle Plastic bottle (1000 ml) (60 ml) Fp (100 ml) Figure Collection of sample from a spring ‘Microscopy’ is the technical field of using microscopes to view samples or objects There are three well-known branches of microscopy: optical, electron, and scanning probe microscopy ‘Optical and electron microscopy’ involve the diffraction, reflection, or refraction of an electromagnetic radiation/electron beam interacting with the subject of study and the subsequent collection of this scattered radiation in order to build up an image This process may be carried out by wide-field irradiation of the sample (e.g., standard light microscopy and transmission electron microscopy, TEM) or by scanning of a fine beam over the sample (e.g., confocal laser scanning microscopy and scanning electron microscopy (SEM)) In SEM an incident beam of electrons strikes the sample and both photon and electron signals are emitted The signals most commonly used are the secondary electrons, the backscattered electrons, and X-rays Electron signals are collected by a secondary detector or a backscatter detector, converted to a voltage, and amplified Amplified voltage is applied to the grid of a cathode ray tube (CRT) and causes the intensity of the spot of light to change The image consists of thousands of spots of varying intensity on the face of the CRT and corresponds to the topography of the sample Scanning probe microscopy involves the interaction of a scanning probe with the surface or object of interest X-ray methods Emission, absorption, scattering, fluorescence, and diffraction of magnetic radiation are measured and an idea of deceleration of high-energy electrons or electronic transition of electrons in inner orbitals of atoms obtained The possible wavelength range is 10−5–102 Å, but in conventional X-ray spectroscopy it is 0.1–25 Å A metal target is bombarded with a beam of high-energy electrons and the substance exposed to a primary X-ray beam to obtain a secondary beam of X-ray fluorescence (XRF) A radioactive source whose decay process results in X-ray emission, for example, a synchrotron radiation source, is deployed X-ray diffraction (XRD) An X-ray tube with suitable filters is deployed to obtain a pattern by automatic scanning The source is commonly an X-ray tube with suitable filters A powdered sample is mounted on a goniometer or a rotatable table that permits variation in the angle θ between the crystal and the collimated beam In some instances the sample holder may be rotated in order to increase the randomness of the orientation of the crystals The diffraction pattern is obtained by automatic scanning Specific interpretation is empirical based on massive existing libraries A computer search is extremely useful Each mineral has its characteristic spectral pattern so that if a crystalline mineral is present it can be characterized individually This method is inter alia very important in recognizing alteration minerals in borehole cuttings Geochemical Aspects of Geothermal Utilization 101 XRF Absorption of X-rays sends excited atoms to their ground state by transition of electrons from higher energy levels Excited ions are sent to their ground states via series of electronic transitions characterized by X-ray emission (fluorescence) of same wavelength (λf) as excitation Absorption removes electrons completely, but emissions give rise to transition of electrons from a higher energy level within the atom An X-ray tube with high enough voltage for λ0 to be shorter than the absorption edge of the element is deployed Three types of X-ray sources are used: • X-ray tube A highly evacuated tube with a W filament cathode and a massive anode The target material may be various metals The filament is heated and the electrons accelerated, thus controlling the X-ray intensity The voltage determines the energy or the wavelength This is an inefficient source • Radioisotopes A given isotope is used for a range of elements giving a simple spectra This has proved to be a powerful source • Secondary fluorescent sources The fluorescence spectrum of an element is excited by an X-ray tube The successful application of XRF depends on the fact that they are powerful for all but the lightest elements; for nine elements in granitic rocks and sediments, precision < 0.1% has been obtained It is easily deployed for materials collected on filters and natural water samples collected on ion exchange resins The main advantages to using XRF are that the spectra are simple, spectral line interference is unlikely, the technique is nondestructive, it is independent of sample size, and it can be applied with speed to multielement analysis with accuracy and precision The main disadvantages are that it is not very sensitive, yet expensive and not applicable to lighter elements This method has inter alia been used with great success to characterize scales formed in boreholes Microprobe X-ray emission is stimulated on the surface of a sample by a narrow, focused beam of electrons The resulting X-ray emission is detected and analyzed with either a wavelength or an energy-dispersive spectrometer A wealth of both qualitative and quantitative information on the physical and chemical nature of the surfaces is obtained This method has been deployed to characterize scales formed and in cores obtained from boreholes Energy-dispersive X-ray spectroscopy (EDS) is one of the variants of XRF It relies on the investigation of a sample through interactions between electromagnetic radiation and matter, analyzing X-rays emitted by the matter in response to being hit with charged particles Capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing X-rays that are characteristic of an element’s atomic structure to be identified uniquely from one another To stimulate the emission of characteristic X-rays from a specimen, a high-energy beam of charged particles such as electrons or protons or a beam of X-rays is focused onto the sample being studied The incident beam may excite an electron in an inner shell, ejecting it from the shell while creating an electron hole where the electron was An electron from an outer, higher energy shell then fills the hole, and the difference in energy between the higher energy shell and the lower energy shell may be released in the form of an X-ray The number and energy of the X-rays emitted from a specimen can be measured by an energy-dispersive spectrometer, allowing the elemental composition of the specimen to be measured There are four primary components of the EDS setup: the beam source, the X-ray detector, the pulse processor, and the analyzer A number of free-standing EDS systems exist However, EDS systems are most commonly found on scanning electron microscopes (SEM-EDS) and electron microprobes SEMs are equipped with a cathode and magnetic lenses to create and focus a beam of electrons, and since the 1960s they have been equipped with elemental analysis capabilities A detector is used to convert X-ray energy into voltage signals; this information is sent to a pulse processor, which measures the signals and passes them onto an analyzer for data display and analysis This method has been used for most types of geological samples and proves useful when a total analysis is required Differential Thermal Analysis (DTA) The sample is heated up and characteristic changes observed The method is useful in studies of alteration Little sample preparation is needed and it is found to be sensitive to sulfides and carbonates and subtle differences in the thermal characteristics of clays Infrared spectrometry (IR) A major advantage is that a small sample is needed The method has been found to be useful for identifying clay, zeolite, and feldspar minerals It can be developed as a quantitative tool too Fluid inclusion geothermometry Fluid inclusions are heated or cooled under a microscope and homogenization temperatures on double polished crystals are obtained To obtain the original system salinity, a freezing stage is included Wet chemical analysis H2O is determined by heating and CO2 by ascarite absorption and gravimetry or coulometry If silica is included in the analysis, solution (a) is prepared by fusion with sodium hydroxide and Si determined by UV/Vis spectro­ photometry, for example, ammonium molybdate α-complex, atomic absorption spectrophotometry (AAS), or in inductively coupled plasma (ICP) by mass spectrometry (MS) or atomic emission spectrometry (AES), and Al by UV/Vis spectrophotometry, for example, alizarin red, AAS, or ICP (MS or AES) If silica is not included in the analysis, solution (b) is prepared after removal of SiO2 by fuming HF Ti is determined by spectrophotometry, for example, Tiron, or ICP (MS or AES); P by UV/Vis spectro­ photometry or ICP (MS or AES); and other metals by AAS or ICP (MS or AES) This method has proved its worth in studies of scales and in total rock analysis Coulometry Carbon in cuttings is determined by automated coulometry Combination of techniques Neither full chemical analysis nor crystal characterization gives the full picture in studies of solids and the most powerful method is based on combining the two, for example, • The crystalline phases are determined by XRD and the amorphous phases by SEM • Total elemental analysis is obtained by EDS or wet chemical methods 102 Geochemical Aspects of Geothermal Utilization • The total composition of the phases is then calculated, for example, if zinc, lead, and copper sulfides have been found to be significant but iron sulfides and silicates are observed as well as amorphous silica the zinc, lead, and copper are assumed to combine with sulfide only, the rest of the sulfide to combine with Fe, then the rest of the Fe to combine with silicate (Fe:Si 3:4), and the rest of the silica is assumed to be amorphous silica 7.04.4 Analysis of Fluids Main laboratory The choice of an analytical technique depends on several factors, that is, the availability of instruments, potential servicing facilities for different types of instruments, the presence of trained personnel, and the speed, reliability, and cost of the different methods Field laboratory In a field laboratory facilities for the determination of volatile constituents (pH, CO2, H2S, NH3, and O2), urgent constituents (e.g., SiO2), constituents used for separation efficiency checks (Na or Cl), and apparatus for specific tests if required (e.g., analytical balance, drying oven) and a supply of deionized water are needed Gas analysis The most important techniques for gas analysis are titrimetry, gas chromatography, MS, and radiometry CO2 and H2S are determined titrimetrically in a solution of a strong alkali (NaOH or KOH), by an alkalinity titration with HCl, but by either iodometry or with mercuric acetate using dithizone as an indicator Gases that are not absorbed by the strong alkali (N2, H2, CH4 (higher hydrocarbons if present), O2, Ar, and He) are determined by gas chromatography Gas chromatographs are usually designed for their specific function The University of Iceland/Iceland GeoSurvey instrument is a Perkin-Elmer Arnel 4019 Analyzer designed for the analysis of geothermal gases Its most important features are three carrier flow sources, dual and single thermal conductivity detectors, four valves, five analytical columns, and three auxiliary carrier gas sources It combines into three analytical channels and employs N2 and He as carrier gases Its special capability are the separations of H2 and He and of O2 and Ar Trace noble gases (Ne, Kr, and Xe) are determined by MS and radioactive gases (e.g., Rn) by radiometry CO2 flux measurements The closed chamber method [2, 3], using a closed chamber CO2 flux meter equipped with a single-path, dual-wavelength, nondispersive infrared gas analyzer, is deployed Flux measurements are usually made using a chamber with known total internal volume and basal area The flux measurement is based on the rate of CO2 increase in the chamber If jCO2 through the soil is moderate, the CO2 concentration increase is generally linear for several minutes, allowing for relatively precise flux determinations Determination of volatile constituents in water It is recommended that analysis for oxygen and hydrogen sulfide be carried out in the field Oxygen is determined colorimetrically using ampoules from CHEMetrics, Inc., containing Rhodazine D for concentrations 0–100 ppb, but Indigo carmine for higher concentrations, but may also be determined by a Winkler iodometric titration Hydrogen sulfide is determined titrimetrically using mercuric acetate and dithizone [1] Mercury can behave as a volatile constituent Even though it is usually present as Hg2+ it is easily reduced to elemental Hg, which is extremely volatile Therefore, it is recommended that an oxidizing agent such as KMnO4 be added upon collection to samples for mercury analysis, which is carried out by reduction, gold amalgamation of elemental mercury, heating, and flameless AAS [4] Cation analysis AAS (flame for major cations, carbon furnace for minor cations), flame emission spectrometry (FES) (major cations), ion chromatography (IC, major cations), and ICP with atomic emission spectrometry (ICP/AES) or mass spectrometry (ICP/MS) (major and minor cations, respectively) are all widely used techniques for cation analysis Specific applications include fluorometry for Al3+, spectrophotometry for field determinations of Fe2+ and the determination of ammonia in saline water, and ion-selective electrode for the determination of ammonia in dilute water Anion analysis IC is the most convenient technique for chloride, bromide, and sulfate Sulfide has to be removed from the sample upon collection by precipitation with zinc acetate before sulfate determination Fluoride can also be determined by IC if care is taken to separate its peak from the chloride peak, but it is more conveniently determined using an ion-selective electrode Boron and silica can both be determined easily by spectrophotometry and ICP It is also fairly common to determine sulfate by colorimetry (CO) and turbidometry (TU) In Table the results for the three methods used by laboratories taking part in a comparative exercise are compared and for the two samples the best results are obtained by IC Isotope analysis Stable isotope ratios are determined by MS in comparison with a standard, but radioactive isotopes by radio­ metry The most common stable isotopes determined during geothermal work are 2H, 18O, 13C, and 34S but the most common radioactive isotopes 3H and 14C used for dating, and 222Rn Due to interferences such as that of water vapor in MS, the compounds containing the IC, CO, and TU isotopes to be determined are converted to constituents that not interfere Thus, H2O is converted to H2 for 2H analysis and CO2 for 18O analysis H2S and SO4 are converted to SO2 for 34S analysis and SO4 to CO2 for 18O determination The reduction of H2O to H2 has been problematic Originally hot uranium was used [6] but that is too dangerous Zn metal [7] has been widely used, but the general experience shows that for unexplained reasons the only reagent that seems to work is zinc shot from British drug houses (BDH) Equilibration using a Pt catalyst [8] has given some useful results but only works for some samples Those that give erroneous results generally contain H2S More recent developments involve the use of hot Cr for the reduction [9, 10] Oxygen is generally equilibrated with carbon dioxide according to the method of Epstein and Mayeda [11] Hydrogen sulfide is converted to SO2 by precipitation as Ag2S followed by oxidation with Cu2O or V2O5 [12] BaSO4 is precipitated either directly from high-sulfate solutions or following ion exchange from low-sulfate solutions and then reduced with graphite to Geochemical Aspects of Geothermal Utilization 103 Table Comparison of results for different methods of sulfate determination in the IAEA laboratory comparison 2001 Sample no Method Number of labs IC CO TU Reference IC CO TU Reference 16 11 17 11 Mean (mg l−1) RSD (%) 22.3 24.2 26.9 23.2 31.5 32.5 30.4 31.8 10.0 27.0 38.2 6.4 8.8 24.2 By Alvis-Isidro R, Urbino GA, and Pang Z (2002) Results of the 2001 IAEA inter-laboratory comparison IAEA Report, 57pp [5] Table Methods used for selected constituents by laboratories in IAEA interlaboratory comparison 2003 Method Cl SO4 SiO2 Co Tm IC TU AA ICP/MS ICP/AES FE 23 16 14 9 K Mg 2 24 21 Co, colorimetric; Tm, titrimetry; IC, ion chromatography; TU, turbidometry; AA, atomic absorption; ICP/MS, inductively coupled plasma/mass spectrometry; ICP/ AES, ICP/atomic emission spectrometry; FE, flame emission After Urbino GA and Pang Z (2004) 2003 Inter-laboratory comparison of geother­ mal water chemistry IAEA Report, 42pp [14] obtain CO which then is converted to CO2 used for 18O determination [13] The reduced sulfide is precipitated as Ag2S and converted to SO2 using the above procedure The radioactive isotopes are determined by liquid scintillation counting Quality control The precision of methods can be checked by repeated analysis of the same sample or by duplicates or triplicates of several samples To obtain an idea of the accuracy of the determinations several approaches are possible, that is, the use of standard additions to sample to obtain % recovery, carrying out determinations of the same constituent by different methods, using standards or reference samples that are run with each batch of samples determined, checks on ionic balance, that is, whether the sum of anions determined is close to the sum of cations determined, or a check on mass balance, that is, whether the sum of constituent concentrations matches that of the result of the determination of total dissolved solids One of the most useful checks is an interlaboratory comparison in which samples whose composition is known are sent to a number of laboratories that use different methods for the determination of each sample Thus, each laboratory can measure itself against others in the same field Examples are the interlaboratory comparisons for the determination of major constituents of geothermal fluids organized by the International Atomic Energy Agency [5], from which the results presented in Table are obtained It is interesting to find out which methods were used by the various laboratories that took part in the 2003 exercise [14] presented in Table Summary Analysis for most anions is usually best performed in the home laboratory, but cations and most trace constituents may be advantageously analyzed in a commercial laboratory applying ICP techniques A survey of 30 laboratories taking part in an IAEA laboratory comparison exercise showed that AAS, spectrophotometry, and titrimetry were the techniques most widely employed 7.04.5 Classification of Water Subsurface waters It has proved difficult to obtain a generic classification of subsurface waters The waters that have been studied in detail are mostly those that are of economic interest as potable water Water also tends to flow away from its point of origin and also 104 Geochemical Aspects of Geothermal Utilization undergo water–rock interaction during its travels, making it increasingly difficult to decipher its origins White’s [15] classification is followed here Meteoric water: circulates in the atmosphere, coexisting with near-surface, uncemented sediments, can circulate in subsurface rocks and dissolve constituents, for example, evaporites Ocean water: partly evaporated products of meteoric water Evolved connate water: forms in young marine sediments It is initially 10–50% oceanic or pore water mixed with combined water Upon increased burial depth more interaction takes place at modest temperatures, and compaction leads to lower pressure environments Variable salinity is observed and may be due to filtration, evaporation, or dissolution of evaporites Metamorphic water: contained in or driven from rocks undergoing metamorphic dehydration reactions Being overpressured at depth, it may escape in response to lithostatic load Magmatic water: derived from oceanic and evolved connate waters subducted along with oceanic crust into the mantle At deep crustal level it is mostly due to rocks undergoing metamorphism Juvenile water: classified as water that has never circulated in the atmosphere If it exists it must be extremely rare Juvenile 3He and CO2 of mantle origin exist and thus suggest that juvenile H2O may exist too, but it has not yet been identified conclusively Geothermal waters In most cases geothermal waters are either meteoric or ocean waters Giggenbach [244] has, however, shown that so-called andesitic waters that are found in subduction zones encompass at least partly evolved connate water which mixes with magmatic steam and water Ellis and Mahon [16] classified geothermal water into four categories based on major ions: Alkali chloride water: pH 4–11, least common in young rocks, for example, Iceland These are mostly sodium and potassium chloride waters although in brines Ca concentration is often significant Acid sulfate water: These waters arise from the oxidation H2S → SO4 near the surface and most of its constituents are dissolved from surface rock Thus, such water is generally not useful for prediction of subsurface properties The sulfate in acid sulfate waters occurring in andesitic systems [244] is, on the other hand, considered to be derived directly from magmatic SO2 Acid sulfate-chloride water: Such water may be a mixture of alkali chloride water and acid sulfate water or it can arise from the oxidation H2S → SO4 in alkali chloride water or dissolution of S from rock followed by oxidation Sulfate-chloride waters need not be very acid and may then reflect subsurface equilibria and be used for prediction of subsurface properties Bicarbonate water: Bicarbonate water may derive from CO2-rich steam condensing or mixing with water; it is quite common in old geothermal waters or on the peripheries of geothermal areas in outflows They are commonly at equilibrium and may be used to predict subsurface properties A good way of distinguishing the differences between the different types of geothermal water is the use of the chloride– sulfate–bicarbonate ternary diagram described by Giggenbach [243] An example from Uganda is seen in Figure 3, where the geothermal water from one area, Kibiro, is a typical alkali chloride water, the water from another, Buranga, is a relatively alkaline Legend Title Cl 10 Katwe, cold water, dilute Katwe, cold water, saline Katwe, cold water, brackish Katwe, hot spring water Buranga, cold water, dilute Buranga, hot spring water Kibiro, cold water, dilute Kibiro, cold water, brackish Kibiro, hot spring water 50 50 Wa ter s 25 75 Mature waters Pe nic Vo HCO3 25 SO4 ter wa 75 ral lca he rip Cl s 10 SO4 25 Steam-heated waters 50 75 HCO3 100 Figure A ternary Cl–SO4–HCO3 diagram showing the characteristics of waters from different Ugandan geothermal systems Geochemical Aspects of Geothermal Utilization 105 chloride–sulfate–bicarbonate water, but the geothermal water from the third one, Katwe, is a sulfate water The cold groundwater in the areas is scattered The dissolved constituents of geothermal water may originate in the original meteoric or oceanic water, but more likely they are the result of water–rock interaction and possibly modification by magmatic gas They are divided into ‘rock-forming constituents’, for example, Si, Al, Na, K, Ca, Mg, Fe, and Mn, and ‘incompatible or conservative constituents’, for example, Cl, B, and Br Summary Subsurface waters are divided into six categories but have mostly at one time or another circulated in the atmosphere In areas of spreading the origin of geothermal waters is almost exclusively meteoric or oceanic but in subduction areas components of evolved connate and magmatic water are found Geothermal water has been divided into four groups according to their major ion composition, that is, alkali chloride, acid sulfate, acid sulfate-chloride, and bicarbonate waters 7.04.6 Alteration Products of geothermal alteration are controlled by temperature, pressure, chemical composition of water (e.g., CO2, H2S), original composition of rock, reaction time, rate of water and steam flow, permeability, and type of permeability, and these products in turn control the chemical composition of the fluid Some of the effects are that the silica concentration depends on the solubility of quartz/chalcedony; temperature-dependent equilibria of Al-silicates control Na/K, Na/Rb ratios; pH is controlled by salinity and Al-silicate equilibria involving hydrogen and alkali ions, while Ca2+ and HCO3 − concentrations depend on pH and CO2 concentra­ tion; F− and SO4 − concentrations are related to that of Ca2+, limited by solubility of fluorite and anhydrite and temperature; and salinity-dependent silicate equilibria control a very low Mg2+ concentration The results of alteration studies show that the chemical composition of geothermal fluids originates in controlled reactions dependent on temperature, pressure, and rock composition Therefore, it is possible to deduce the properties of subsurface water from the chemical composition of water which has been collected at the Earth’s surface In studies of hydrothermal alteration a distinction is made between the ‘intensity’ of alteration, which is a measure of how completely a rock has reacted to produce new minerals, and alteration ‘rank’, which depends upon the identity of the new minerals and is based on their significance in terms of subsurface conditions, for example, when considering permeability and temperature [250] Basic chemical reaction processes Processes taking place on the surface of the Earth are usually referred to as weathering, those taking place in the top layers of the crust (0–4 km) as alteration, but those taking place at greater depth as metamorphism The basic progress of chemical weathering can be described as primary minerals + O2 + H2O → secondary minerals The reactions involve acid dissolution, iron oxidation, and hydration, and the higher the temperature the greater is the rate of reaction and where the runoff is large the transport of chemical components is fast Ca and Mg are dissolved from the rock and will combine with CO3 − as the runoff mixes with seawater and contributes to the deposition of CaCO3 and thus depletion of CO2 from seawater, which in turn favors the dissolution of CO2 from atmospheric air The main solid products are noncrystalline clay minerals and hydrated iron oxides Soil formation is an essential consequence of the process High-temperature geothermal areas are commonly characterized by acid sulfate alteration manifested by clay, yellow sulfur, gray FeS2, and red hematite Hydrogen sulfide is oxidized to sulfuric acid in the following process: H2 S ỵ O2 S þ H2 O ½1Š H2 S þ 2O2 ↔ H2 SO4 ½2Š The H2SO4 dissolves primary minerals and leaches elements such as Na and K, whereas other elements, for example, Ti, Al, and Fe, will be bound in secondary minerals The approximate order of mineral formation is smectite, kaolinite, amorphous silica, and anatase (+S, FeS2, and CaSO4) The process of alteration is represented by primary mineral + groundwater → dissolved solid → secondary mineral The secondary minerals replace primary minerals or form amygdales The nature of the primary mineral, the extent of the contact surface of rock and water, and temperature control the ‘intensity’ (a measure of how completely a rock has reacted to produce new minerals (0–100%)) and ‘rank’ (which depends upon the identity of new minerals based upon their significance in terms of subsurface conditions) of alteration The volume of rock is increased The most common secondary minerals formed are quartz, chalcedony, calcite, zeolites, celadonite, apophyllite, chlorite, and epidote The alteration minerals are classified according to the anion but if necessary by structure as is the case with silicates The most important types are as follows: • Carbonates: calcite, aragonite, siderite • Sulfates: anhydrite, alunite, soda alunite, barite • Sulfides: pyrite, pyrrhotite, marcasite, sphalerite, galena, chalcopyrite • Oxides: hematite, magnetite, leucoxene, diaspore • Silicates: Ortho, ring: sphene, garnet, epidote; sheet: illite, biotite, pyrophyllite, kaolin, montmorillonite, prehnite; framework: adularia, albite, quartz, cristobalite, mordenite, laumontite, wairakite Information on alteration is used in studies of the thermal stability of the field Mineral temperatures are compared to measure and obtain the thermal history of the system Such information can also be applied to infer the subsurface permeability and thus may be 106 Geochemical Aspects of Geothermal Utilization useful in deciding the casing depth of wells during drilling Furthermore, it can give early indications of the nature of the fluid composition in the geothermal system such as whether it is CO2 rich, H2S rich, acid, single or two phase, whether there is boiling in formation or inside the well, and also of the depth of recharge and/or discharge zones A hot, impermeable zone tends to have alteration of high rank but low intensity, whereas the alteration in a cold, permeable zone is of low rank but high intensity Browne (1984) has thus divided the alteration observed in basalts and rhyolites in wells in Olkaria, Kenya, according to rank as shown in Table 5, which is used as a general guide to permeability in geothermal systems One of the most important processes of alteration is replacement of primary rock minerals by alteration minerals The rate of replacement is variable and depends upon permeability Sometimes incomplete replacement takes place Such reactions are preserved in cores and are visible under the microscope They are easily distinguished in volcanic reservoir rocks but with more difficulty in sedimentary or low-grade metamorphic rocks as many of the latter’s primary minerals are also stable in geothermal environments It is important to note that minerals control composition but not the salinity of water Thus, the ratios of elements may be controlled by alteration in fluids at different salinities with temperature as the controlling parameter and this is the basis for many geothermometers Hydrothermal alteration involves changes in density, porosity, permeability, magnetic strength (usually decreased), and resistivity (reduced) inflicted on the host rock Events which may be related or unrelated to alteration, for example, faulting and formation of joints, may affect the alteration process In the event of replacement it can proceed isochemically, but constituents may still be added or removed The data in Table on the behavior of major elements are compiled from Browne (1984) for typical behavior and Franzson et al [17] on their behavior in Icelandic systems The factors that control alteration are temperature which affects the stability of OH groups and bound water, for example, in clays, zeolites, prehnite, and amphibole; pressure which controls the depth at which boiling occurs; reservoir rock type because its texture controls permeability; the reservoir permeability; fluid composition with pH and relative constituent concentrations being most important; and finally the duration of the activity which is related to the kinetics of the reactions Effect of temperature on clays In the kaolin group, acidic waters interact to produce kaolin and at 250 °C pyrophyllite will be formed from dickite In the chlorite group, for example, at Reykjanes, Iceland, smectite is observed at < 200 °C, it is interlayered with chlorite at 200–270 °C, but at >270 °C it has gone over to chlorite (nonswelling) In many geothermal systems, montmorillonite, illite, and interlayered montmorillonite/illite are observed at Table Table Alteration in Olkaria (Kenya) basalts and rhyolites Rank Minerals 10 No hydrothermal alteration minerals Traces of calcite, montmorillonite, pyrite, quartz Fresh primary feldspars, partially altered ferromagnesium minerals Fresh primary feldspars, completely altered ferromagnesium minerals Partially altered primary feldspars, completely altered ferromagnesium minerals Completely altered primary feldspars, trace of hydrothermal albite Host rock altered, lots of hydrothermal albite Lots of hydrothermal albite, less adularia Adularia, less albite Adularia only feldspar Adularia all over host rock and porphyritic alteration Behavior of major constituents during alteration [250] Oxide Typical Icelandic Hydrothermal minerals SiO2 TiO2 Al2O3 FeO, Fe2O3 MnO MgO CaO Na2O K2O CO2 S, SO3 H2O P2O5 Cl F Added Unchanged Added/removed Added/removed Unchanged Removed Added/removed Added/removed Added Added Added Added Unchanged/removed Removed Added/unchanged Added Unchanged/(removed) Added Added Added Added Unchanged (added/removed) Added/removed Added/removed Added Added Added Unchanged Quartz, cristobalite, silicates Sphene, leucoxene Silicates, oxides Chlorite, pyrite, pyrrhotite, siderite, epidote, hematite MnO Chlorite, biotite Calcite, wairakite, epidote, prehnite, anhydrite Albite Adularia, illite, alunite, biotite Calcite, siderite Anhydrite, alunite, pyrite, pyrrhotite, barite Clay, epidote, prehnite, zeolites, diaspore, pyrophyllite, amphibole Apatite Fluorite 156 Geochemical Aspects of Geothermal Utilization 500 Monomer silica (SiO2, mg l−1) 400 pH = 3.0 300 200 pH = 7.3 100 pH = 5.3 0 500 1000 1500 2000 Time (min) 2500 3000 Figure 46 Monomer decrease of silica at different pH values in brine collected at 19.4 bar g pressure Monomer silica (SiO2, mg l−1) 500 400 t = 90 (�c) 300 t = 65 (�c) 200 100 t = 25 (�c) 0 1000 2000 3000 Time (min) Figure 47 Monomer decrease of silica at different temperatures in brine collected at 19.4 bar g pressure Table 33 Materials tested in corrosion tests on steam from well Asal-3, Djibouti Material Typical use Stainless steel (304,316,405,2205,904L, 254SMO) 12CrMo stainless steel, welded and unwelded 13%CrMo stainless steel 17-4PH steel, welded and unwelded CrMoNiV steel CrMoV steel CrMoNi steel Carbon steel Mild steel Ti alloy Turbine blade, condenser lining Turbine blade Turbine blade Turbine blade Turbine shaft Turbine rotor Turbine casing Pipe, casing Condenser lining Geochemical Aspects of Geothermal Utilization Fuji, 13% Cr stainless steel DIN × 20 Cr 13 (uncondensed steam) B5 801 Virkir-Orkint CrNiMo steel 30 CrNiMo (DIN 17200) (uncondensed steam) A5 Fuji CrMoNiV steel DIN 30 CrMoNiV 11 (uncondensed steam) Fuji stainless steel 405 (uncondensed steam) C5 A2 Fuji CrMoNiV steel DIN 30 CrMoNiV 11 (condensed steam) C2 Fuji stainless steel 405 (condensed steam) G2 Fuji stainless steel 304L (condensed steam) B2 157 Fuji, 13% Cr stainless steel DIN × 20 Cr 13 (condensed steam) Figure 48 Some coupons after being placed in uncondensed (left) and condensed (right) steam flows Table 34 Weight change, visual observations, and results of chemical analysis of coupons placed in uncondensed steam flow Material Weight change (%) Visual signs CrMoV Ti alloy CrNiMo Mild CrMoV CrMoV-coated CHEMIFLAKE EV70 +0.05 +0.31 +0.22 +0.43 –0.06 –0.44 Many small pits Uncorroded Few small pits Small even corrosion Slight pitting Cracked coat, base metal corroded Table 35 steam flow Fe (%) Al (%) Si (%) S (%) 43.0 22.2 13.3 44.5 28.9 2.2 9.5 1.3 1.2 0.2 43.1 34.5 81.1 39.1 26.2 0.9 0.8 0.7 2.3 0.6 Weight change, visual observations, and results of chemical analysis of coupons placed in condensed Material Weight change (%) CrMoV St 405 Mild CrMoV welded –4.61 +0.19 –2.04 –2.79 Visual signs Even corrosion Uncorroded Small even corrosion Even with small pitting, pronounced in heat-affected zone Fe (%) Al (%) Si (%) S (%) 45.5 88.0 56.6 61.9 0.2 0.5 7.6 0.1 0.1 1.5 0.2 0.2 27.3 4.5 33.0 36.2 Three sets of coupons were inserted, one for the client, one for the contractor, and one for the vendor The contractor dealt with the contractor and client’s specimens; however, the third set was sent to the vendor They were photographed, dried, weighed, and characterized Examples of test coupons are seen in Figure 48 Results for those placed in uncondensed steam are presented in Table 34 and those placed in condensed steam in Table 35 These results suggest that there is more danger of corrosion in the condensed steam flow and the annual corrosion rate was estimated from the tests with the results in Table 36 Thus the stainless steel samples appear uncorroded, but CrMoV considerably, yet evenly corroded The welded steel appeared unsatisfactory as there was some pitting, but the mild steel was less and evenly corroded These results lead to a decision by the client and the vendor as to which materials to use for each part of the installation 7.04.11 Case History Exploration of a Geothermal Area Theistareykir, NE Iceland In this case history the main emphasis is on the geochemical part but other methods of investigation will be briefly reviewed to show how the combination leads to a model of the area Theistareykir is a high-temperature geothermal area in NE Iceland (Figure 49) For centuries it hosted the main sulfur mine in Iceland, providing the Danish king with raw material for gun powder Early records tell of prospecting for sulfur; Bemmelen and 158 Geochemical Aspects of Geothermal Utilization Table 36 Corrosion rate of various materials in condensed steam flow from well Assal-3, Djibouti 24° Steel type Corrosion rate (mm yr−1) DIN CrMoNiV 11 Carbon steel JIS SS41 (Fuji) Mild steel (No 37) 30 CrNiMo CrMoV 10325MGB Carbon steel JIS SS41 (MHI) 0.28 0.28 0.29 0.22 0.34 0.15 22° 18° ÖxarfjÖdur 20° 14° 66° Theistareykir 65° 64° REYKJAVIK Tertiary flood basalts (>3.1 m.y.) Postglacial shield volcano or single crater Plio-Pleistocene flood basalts (3.1–0.7 m.y.) Active zones of tilting and voicanism ( 50 °C Low-temperature steam < 50 °C Borehole (with name) 66°C/100m Temp at water level Figure 50 A geothermal map of the Theistareykir geothermal system Ưxarfjưrður in the north The area is covered in lava, all of which except for one being erupted in the last stages of the Ice Age or shortly afterward The youngest lava is about 2700 years old Surface manifestations have been estimated to cover about 11 km2 [229] as is shown on the geothermal map (Figure 50) [234], but recent time-domain electromagnetic (TEM) and magneto-telluric (MT) soundings suggest that the extent of the actual geothermal area be up to 45 km2 [235, 236] (Figure 51) Ármannsson et al [228] divided the active surface area into five subareas (Figure 52), three of which (A, C, and D) appeared promising for drilling Gas geothermometers gave the temperature ranges shown in Table 37 Darling and Ármannsson [55] concluded from isotope values for fumarole steam that, in area D (Tjarnarás), the steam had been condensed to a fraction of 0.15–0.25 of the original steam at temperatures in the range 130–200 °C, and that gas geothermometer temperatures were probably too high Their interpretation of isotope values for area C (Theistareykjagrundir) was that the steam was mostly secondary steam and that the geothermometer temperatures were probably too low They concluded, however, that the steam rising from area A (Ketilfjall) was undisturbed and that the geothermometer temperatures were close to true values Ármannsson et al [228] proposed a deep inflow to the area from the southeast with area C closest to the source Thus area C was considered promising, even though the gas geothermometer values seemed rather low A relatively large, cool, shallow flow was predicted through Bóndólsskarð (Figure 52), preventing primary steam from rising to the surface in area B Areas C and D are more accessible than area A, and therefore the suggestion was that the first drill holes be situated in these two subareas The dissolved solids content of the steam was very low, suggesting that the reservoir fluid was dilute Low radon concentrations were interpreted to suggest good permeability especially in area D Monitoring and heat loss The area was visited again in 1991 at the beginning of a monitoring program in which some unexploited high-temperature areas were to be monitored to establish the extent of natural changes in geothermal areas as opposed to changes due to production [231] Changes in surface manifestations were mapped and steam samples collected from three fumaroles, one from each of areas A, C, and D At that time considerable changes in surface manifestations were observed, mainly cooling in area D (Figure 52) There was information from local people that following earthquakes in 1958 the surface activity in the area had increased drastically but had been declining since The gas geothermometer temperature for the fumarole from area D (G-6, 160 Geochemical Aspects of Geothermal Utilization 405 410 415 420 7310 7310 7305 7305 7300 7300 7295 7295 1.8 3.2 5.8 10 18 32 58 100 178 316 562 1000 3182 10000 Vi nàm (Ωm) Figure 51 Resistivity at 500 m bsl at Theistareykir (top left) and Gjástykki (bottom right) [235] High-resistivity cores are surrounded by low resistivity Figures 52 and 53) had decreased drastically, but little change or a slight increase was recorded for gas geothermometer temperatures for fumarole steam from areas A (G-3, Figures 52 and 53) and C (G-1, Figures 52 and 53; Table 37) It is possible that the secondary effects suggested by Darling and Ármannsson [55], condensation and formation of secondary steam, were less pronounced this time The area has been visited a few more times, but it has remained relatively unchanged after 1991 Using information from Hafstad ([237], personal communication) about the Lón estuary in Ưxarfjưrður, 20 km to the north of the Theistareykir area, Ármannsson [232] calculated the heat loss from the Theistareykir area (Table 38) This estuary is believed to receive solely subsurface water from the Theistareykir area The values are minimum but they suggest a total output of 300 MW Therefore, a powerful geothermal system with a temperature of about 280 °C recharged with dilute, probably relatively old, water from far south and with an isotope signature of δD = –100‰ and δ18O = –12‰ was predicted prior to drilling Drilling results Prior to deep drilling, four shallow ‘cold water’ wells, ThR-1–ThR-4 (Figure 52), were drilled to obtain drilling fluid Well ThR-2, which is 102 m deep, just reached the groundwater table, and the temperature of the water proved close to boiling In ThR-3, the groundwater table is also close to 100 m depth The temperature was 66 °C there, but 90 °C at 140 m depth The groundwater table was at about 100 m depth in wells ThR-1 and ThR-4, the former is 128 m deep and the temperature of the water was 26–28 °C, but the latter is 150 m deep, with water temperature 26–35 °C [238] Water from these two wells was used as drilling fluid for the deep geothermal wells Well ThG-1 was drilled in area C (Theistareykjagrundir; Figure 52) in autumn 2002 to a depth of 1953 m, with a casing 614 m deep The major inflows are at 620–640 m depth and 1620–1640 m depth Other inflows are observed at 710, 860–880, 1050, 1230–1240, and 1350 m depths and possibly at 1780–1800 and 1900–1910 m depths An overpressured aquifer was observed at 212 m depth [239] The well started discharging in late October 2002 The results of chemical analysis suggest that in November 2002 the fluid was still contaminated by drilling fluid and thus the results from July 2003 (Table 39) are used for the purpose of interpretation The measured enthalpy at the surface was 2180 kJ kg−1 and the total flow from the well 16–17 kg s−1 The calculated steam fraction at a depth of 280 °C was 0.611 Geochemical Aspects of Geothermal Utilization 161 Figure 52 Theistareykir Division into five subareas [228] Geothermal and cold water boreholes in and north of the geothermal area are shown as well as three fumaroles sampled during monitoring 1991–2000 Table 37 Gas geothermometer temperatures in A, C, and D (°C) Subarea 1980s (°C) Fumarole 1991 (°C) A C D 272–315 232–271 274–309 G-3 G-1 G-6 289 284 263 162 Geochemical Aspects of Geothermal Utilization Hot (>90 °C) 1983–1984, 1991,and 1995–1997 Mt.KETILFJALL Cold (50–55 l s−1) from 657 m depth It was finished with a slotted liner Pumping tests suggested very high permeability Extremely strong flows are inferred from 260 m depth and considerably below this There is a possibility that this constitutes a large cave or some such feature whose temperature has been estimated at a little over 200 °C, and that this large flow might cause cooling of the rock over some distance from the cave, possibly sufficient to cause partial condensation of steam rising to the surface in the vicinity It is suggested that this may be the mechanism responsible for the condensation of steam in area D suggested by Darling and Ármannsson [55] Using information from wells ThG-1 and ThG-2 a model of the flow in the system was constructed (Figure 54) showing the large relatively cool flow in area D, the intermediate aquifers at 600–800 m depth, and the deep hot aquifer at about 1600–1800 m depth Well ThG-3 was drilled in area A in 2006 to a depth of 2659 m and the maximum temperature recorded was 380 °C Its flow oscillated with enthalpy varying from about 1600 to 2600 kJ kg−1 but has approached the higher value with time and eventually settled as a high-enthalpy well giving 10–12 kg s−1 of high-temperature steam The total dissolved solids in the fluid are low and so is the gas concentration Wells ThG-4 and ThG-5 were both drilled directionally from the same well pad as well ThG-1 ThG-4 is to the SE beneath Mt Bæjarfjall, but well ThG-5 is toward well ThG-2 Well ThG-4 is a high-enthalpy well with a steam flow of 30 kg s−1 of high-temperature steam, but well ThG-5 is a low-enthalpy well similar to well ThG-2 with a large liquid water flow The concentration of dissolved solids and gas is low in these two wells and the results for the wells drilled after ThG-2 not conflict with the model suggested in Figure 55 Finally, well ThG-5 was redrilled under a sharper angle in 2008 (ThG-5b) and well ThG-6 was drilled directionally from the well pad of well ThG-3 to the west These wells started discharging in early November In late October the maximum temperature in Geochemical Aspects of Geothermal Utilization C Theistareykjagrundir ThG-1 G-1 D E Steam rest Theistareykja­ hraun Tjarnarás ThG-2 G-6 Open fractures cool water ~200 °C Ketilfjall °C Water-dominated aquifer ~28 Primary uncondensed steam 1000 Bónd­ hólsskarð Primary uncondensed steam Depth (m) Residual steam Condensed steam A G-3 Secondary steam B Primary uncondensed steam 164 Vapor-dominated aquifer ~300 °C W E 2000 Distance (km) Figure 54 The most important aspects of fluid flow in the Theistareykir geothermal system based on surface exploration and results of drilling wells ThG-1 and ThG-2 E D C Theistareykja­ grundir ThG1 G-1 Tjarnarás Theistareykjahraun ThG-2 G-6 Depth(m) Residual steam Open fractures 200 °C Condensed steam G-3 A Ketilfjall Secondary steam B Bónd­ hóls­ skarð °C Powerful upflow E Primary uncondensed steam 1000 Primary steam Primary uncondensed steam Liquid phase 250–28 Vapor 300 °C W 2000 Distance (km) Figure 55 A conceptual model of the Theistareykir geothermal system [241] ThG-5b was 300 °C but in ThG-6 312 °C In early December the enthalpy of ThG-5b flow was 1485 kJ kg−1 and the amount of high-temperature steam 20.8 kg s−1, but the enthalpy of the ThG-6 flow was 2663 kJ kg−1 and high-temperature steam 13.2 kg s−1 The strata observed in the wells show thick palagonite strata (tuff, breccias, and pillow lavas) in the top part The number of intrusions increases with depth At a depth of about 1150–1300 m a change occurs and lava layers with intermediate layers become prominent The alteration pattern suggests a steadily increasing temperature with depth Geochemical Aspects of Geothermal Utilization 165 The results of temperature and pressure logging show wells ThG-2 and ThG-5 to be cooler than the others, presumably reflecting cooling from the surface of the fissure system shown in Figure 55 A conceptual model (Figure 55) has been presented on the lines of Figure 54 showing a strong upflow in area C, a weaker one in area A, and a possible one in area E but a possible downflow in area D The possible potential of the system has been estimated using the so-called Monte Carlo method and the most probable values are 348 MWe (90% probability 191–622 MWe) for 30 years, 209 MWe (90% probability 115–373 MWe) for 50 years, and 104 MWe (90% probability 57–187 MWe) for 100 years [241] Main findings The results of surface exploration in the Theistareykir area suggested that it encompassed three distinct subareas (A, C, and D, Figure 52) suitable for drilling, drawing fluid from a single base reservoir with a temperature of at least 280 °C The fluid originates far to the south of the area and is probably more than 100 years old Results for stable isotopes in fumarole steam suggested that in area D, there was condensation of fumarole steam during its passage from the reservoir to the surface, but that in area C the fumarole steam was in some cases secondary steam During drilling of wells ThG-1 and ThG-2 large inflows of relatively shallow cool water, which can explain condensation and secondary steam formation in areas C and D, were encountered Good permeability was predicted for area D from the results of surface exploration Thus the preliminary results of drilling not contradict those of surface exploration The results for wells ThG-1 to ThG-6 confirm these results and show area C to be powerful probably above the main upflow, although a smaller upflow is predicted for area A References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] Ármannsson H and Ólafsson M (2006) Collection of geothermal fluids for chemical analysis ÍSOR Report, ÍSOR-2006/016, 17pp Reykjavic, Iceland: ISOR Chiodini G, Cioni R, Guidi M, et al (1998) Soil CO2 flux measurements in volcanic and geothermal areas Applied Geochemistry 13: 543–552 Parkinson KJ (1981) An improved method for measuring soil respiration in the field Journal of Applied Ecology 18: 221–228 Ólafsson J (1974) Determination of nanogram quantities of mercury in sea water Analytica Chimica Acta 68: 207–211 Alvis-Isidro R, Urbino GA, and Pang Z (2002) Results of the 2001 IAEA inter-laboratory comparison IAEA Report, 57pp Vienna, Austria: IAEA Friedman I (1953) Deuterium content of water and other substances Geochimica et Cosmochimica Acta 4: 89–103 Coleman ML, Shepherd TJ, Durham JJ, et al (1982) Reduction of water with zinc for hydrogen isotope analysis Analytical Chemistry 54: 993–995 Horita J (1988) Hydrogen isotope analysis of natural waters using an H2-water equilibrium method: A special implication to brines Chemical Geology (Isotope Geoscience Section) 72: 89–94 Donnelly T, Waldron S, Tait A, et al (2001) Hydrogen isotope analysis of natural abundance and deuterium-enriched waters by reduction over chromium on-line to a dynamic dual inlet isotope-ratio mass spectrometer Rapid Communications in Mass Spectrometry 15: 1297–1303 Schoeller DA, Colligan AS, Shriver T, et al (2000) Use of an automated chromium reduction system for hydrogen isotope ratio analysis of physiological fluids applied to doubly labeled water analysis Journal of Mass Spectrometry 35: 1128–1132 Epstein S and Mayeda T (1953) Variation of 18O content of waters from natural sources Geochimica et Cosmochimica Acta 4: 213–224 Yanagisawa F and Sakai H (1983) Thermal decomposition of barium sulphate vanadium pentoxide silica glass mixture for preparation of sulfur dioxide in sulfur isotope ratio measurements Analytical Chemistry 55: 985–987 Nehring NI, Bowen PA, and Truesdell AH (1977) Techniques for the conversion to carbon dioxide of oxygen from dissolved sulphates in thermal waters Geothermics 5: 63–66 Urbino GA and Pang Z (2004) 2003 Inter-laboratory comparison of geothermal water chemistry IAEA Report, 42pp Vienna, Austria: IAEA White DE (1986) Subsurface waters of different origins In: Ólafsson J and Ólafsson M (eds.) Fifth International Symposium on Water-Rock Interaction Extended Abstracts, pp 629–632 Reykjavík: International Association of Geochemistry and Cosmochemistry, National Energy Authority Ellis AJ and Mahon WAJ (1977) Chemistry and Geothermal Systems, 392pp New York: Academic Press Franzson H, Zierenberg R, and Schiffman P (2008) Chemical transport in geothermal systems in Iceland: Evidence from hydrothermal alteration Journal of Volcanology and Geothermal Research 173: 217–229 Kristmannsdóttir H (1978) Alteration of basaltic rocks by hydrothermal activity at 100–300° In: Mortland M and Farmer VC (eds.) International Clay Conference, pp 359–367 Amsterdam: Elsevier Scientific Publishing Company Franzson H (2007) Temperature and salinity changes in three high temperature systems at Reykjanes peninsula, SW-Iceland Evidence from fluid inclusion data In: Bullen TD and Wang Y (eds.) Water–Rock Interaction, pp 947–951 London: Taylor & Francis Group Arnórsson S, Gunnarsson I, and Stefánsson A, et al (2002) Major element chemistry of surface- and ground waters in basaltic terrain N-Iceland I: Primary mineral saturation Geochimica et Cosmochimica Acta 66: 4015 Johnson JW, Oelkers EH, and Helgeson HC (1992) SUPCRT92 – A software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from bar to 5000 bar and °C to 1000 °C Computational Geoscience 18: 899–947 Arnórsson S (1995) Geothermal systems in Iceland: Structure and conceptual models–I High-temperature areas Geothermics 24: 561–602 Kristmannsdóttir H and Tómasson J (1978) Zeolite zones in geothermal areas in Iceland In: Sand LB and Mumpton FA (eds.) Natural Zeolites, pp 227–284 Oxford: Pergamon Press Ltd Saemundsson K and Gunnlaugsson E (2002) Icelandic Rocks and Minerals, 233pp Reykjavík: Mál og menning Franzson H, Gunnlaugsson E, Árnason K, et al (2010) The Hengill geothermal system, conceptual model and thermal evolution In: Horne R (ed.) Proceedings of the World Geothermal Congress 2010, 9pp Bali, Indonesia, 25–29 April 2010 Reykjavic, Iceland: IGA Franzson H, Thordarson S, Björnsson G, et al (2002) Reykjanes high-temperature field, SW-Iceland, geology and hydrothermal alteration of well RN-10 In: Kruger P and Raney Jr HJ (eds.)Proceedings of the 27th Workshop on Geothermal Reservoir Engineering, 8pp Stanford University, California, SGP-TR-171 Craig H (1961) Isotopic variation as in meteoric water Science 153: 10702–10703 Ólafsson J (1991) The basis of life in Lake Mývatn (in Icelandic) In: Gardarsson A and Einarsson Á (eds.) Náttúra Mývatns, pp 140–165 Reykjavík: Hid íslenska Náttúrufrỉdifélag De Zeeuw E and Gíslason G (1988) The effect of volcanic activity on the groundwater system in the Námafjall geothermal area, NE Iceland National Energy Authority OS-88042/JHD-07, 39pp Ármannsson H and Ólafsson M (2002) Chemical studies of water from wells, springs and fissures in Búrfellshraun lava and vicinity (in Icelandic) National Energy Authority OS-2002/076, 35pp Einarsson Á (1982) The palaeolimnology of Lake Mývatn, Northern Iceland: Plant and animal microfossils in the sediment Freshwater Biology 12: 63–82 166 Geochemical Aspects of Geothermal Utilization [32] Sæmundsson K (1991) The geology of the Krafla system In: Gardarsson A and Einarsson Á (eds.) The Natural History of Mývatn (in Icelandic), pp 24–95 Reykjavík: Hid íslenska náttúrufrỉdifélag [33] Thórarinsson S (1951) Laxárgljúfur and Laxárhraun A tephro-chronological study Geografiska Annaler Stockholm H 1–2, 1–89 [34] Thórarinsson S (1979) The postglacial history of the Mývatn area Oikos 32: 17–28 [35] Jónasson PM (ed.) (1979) Ecology of eutrophic, subarctic Lake Mývatn and the River Laxá Oikos 32: 308pp [36] Líndal B (1959) Diatomite production from bottom deposits in Lake Mývatn (in Icelandic) Tímarit Verkfrỉdingafélags Íslands 44: 19–29 [37] Einarsson Á, Stefánsdóttir G, Jóhannesson H, et al (2004) The ecology of Lake Mývatn and the River Laxá: Variation in space and time Aquatic Ecology 38: 317–348 [38] Ĩlafsdóttir R and Gudmundsson HJ (2002) Holocene land degradation and climatic change in Northeastern Iceland The Holocene 12: 159–167 [39] Käyhkö J, Alho P, Hendriks JPM, and Rossi MJ (2002) Geomorphology of the Ódádahraun Semi-desert, NE Iceland: A landsat TM-based land cover mapping Jökull 51: 1–16 [40] Árnason B (1976) Groundwater systems in Iceland traced by deuterium Vísindafélag Íslendinga 42: 236pp [41] Gíslason GM (1994) River management in cold regions: A case study of the River Laxá, North Iceland In: Calow P and Petts GE (eds.) The Rivers Handbook Hydrological and Ecological Principles, vol 2, pp 464–483 Oxford: Blackwell Scientific Publications [42] Ólafsson J (1979) The chemistry of Lake Mývatn and River Laxá Oikos 32: 82–112 [43] Wetzel RG (2001) Limnology Lake and River Ecosystems, 3rd edn London: Academic Press [44] Thorbergsdóttir IM and Gíslason SR (2004) Internal loading of nutrients and certain metals in the shallow eutrophic Lake Mývatn, Iceland Aquatic Ecology 38: 177–189 [45] Sæmundsson K (1969) Drilling at Námafjall (in Icelandic), 55pp Jarðhitadeild: National Energy Authority [46] Sæmundsson K, Arnórsson S, Ragnars K, et al (1975) Krafla A report on the results of exploratory drilling 1974 (in Icelandic) National Energy Authority OS JHD7506, 47pp [47] Ármannsson H (2003) The disposal of effluent from the Krafla and Bjarnarflag power plants (in Icelandic) National Energy Authority OS-2003/032, 32pp [48] VST – Virkir hf (1975) Kröfluveita Pre-feasibility report on pipelines for the Krafla Power Station (in Icelandic) National Energy Authority, 48pp [49] Arnórsson S and Gunnlaugsson E (1976) The catchment of the stream Hlídardalslỉkur and effluent from the Krafla Power Station (in Icelandic) National Energy Authority OS JHD 7602,13pp [50] Ingimarsson J, Elíasson J, and Sigurdsson STh (1976) Discharge from the Krafla Power Plant National Energy Authority OSSFS-7602, 30pp [51] Jóhannesson B (1977) On groundwater currents in a strip of land extending from Dyngjufjưll Mountains in the south to Ưxarfjưrdur Bay in the north (in Icelandic) Tímarit Verkfrỉðingafélags Íslands 62: 33–38 [52] Jóhannesson B (1980) On groundwater in the catchment area of Lake Mývatn (in Icelandic) Tímarit Verkfrỉðingafélags Íslands 65: 74–77 [53] Thóroddsson ThF and Sigbjarnarson G (1983) The diatomite plant by Lake Mývatn Groundwater studies (in Icelandic) National Energy Authority OS-83118/VOD-10, 41pp [54] Verkfræðistofan Vatnaskil (1999) Lake Mývatn Groundwater model of Lake Mývatn catchment area (in Icelandic) Report, 82pp Reykjavík: Verkfrædistofan Vatnaskil [55] Darling WG and Ármannsson H (1989) Stable isotopic aspects of fluid flow in the Krafla, Námafjall and Theistareykir geothermal systems in northeast Iceland Chemical Geology 76: 197–213 [56] Hjartarsson A, Sigurðsson Ó, Guðmundsson Á, et al (2004) A computer simulation of the Námafjall geothermal system and forecast about its future state upon production of 90 MW electricity from Bjarnarflag (in Icelandic) ÍSOR-2004/009, 119pp [57] Kristmannsdóttir H, Hauksdóttir S, Axelsson G, et al (1999) A tracer test in the Lake Mývatn area (in Icelandic) National Energy Authority OS-99028, 48pp [58] Kristmannsdóttir H, Axelsson G, Hauksdóttir S, et al (2001) A tracer test with potassium iodide in Bjarnarflag 2000–2001 (in Icelandic) National Energy Authority OS-2001/042, 57pp [59] Elíasson ET, Ármannsson H, Sæmundsson K, et al (1998) The disposal of hot effluent from the Krafla Power Station (in Icelandic) National Energy Authority ETE/HÁ/KS/ KÁ/BS/Krafla, 002, 5pp [60] Ármannsson H, Axelsson G, and Ólafsson M (2009) Reinjection into well KG-26 Tracer test with KI KI 2005-2007 Description and results Landsvirkjun LV-2009/099; ÍSOR-2009/050, 19pp [61] Gadalia A, Braiband G, Touzelet S, and Sanjun B (2010) Tracing tests using organic compounds in a very high temperature geothermal field, Krafla (Iceland) Final Report BRGM/RP-57661-FR, 99pp [62] Kristmannsdóttir H and Ármannsson H (2004) Groundwater in the Lake Mývatn area, North Iceland: Chemistry, origin and interaction Aquatic Ecology 38: 115–128 [63] Jardboranir ríkisins (1951) Chemical Analysis of Hot Springs and Hot Pools Jardboranir ríkisins, 88pp [64] Stefánsson U (1970) A few observations of the chemistry of Lake Mývatn in the summer of 1969 (in Icelandic) Náttúrufræðingurinn 40: 187–196 [65] Ármannsson H, Kristmannsdóttir H, and Ĩlafsson M (1998) Krafla – Námafjall The effect of volcanic activity on groundwater (in Icelandic) National Energy Authority OS-98066, 33pp [66] Ármannsson H, Kristmannsdóttir H, and Ĩlafsson M (2000a) Geothermal influence on groundwater in the Lake Mývatn area, North Iceland In: Iglesias E, Blackwell D, Hunt T, et al (eds.) Proceedings of the World Geothermal Congress 2000, pp 515–520 International Geothermal Association, Pisa, Italy [67] Ármannsson H and Ólafsson M (2004) Monitoring the effect of disposal of effluent from the Krafla Power Plant and the Bjarnarflag Power Plant (in Icelandic) Landsvirkjun LV-2004/052, ÍSOR ÍSOR-2004/005, 14pp [68] The Ministry of the Environment (1999) Regulation No 76/1999 on Protection against Water Pollution In: Law and Ministerial Gazette of Iceland, Series B, 785–810, 2231–2253 [69] Ármannsson H and Ólafsson M (2010) Monitoring the effect of disposal of effluent from the Krafla and Bjarnarflag Power Plants (in Icelandic) Landsvirkjun LV-2010/055, ÍSOR ÍSOR-2010/018, 17pp [70] Darling WG (1998) Hydrothermal hydrocarbon gases: Genesis and geothermometry Applied Geochemistry 13: 815–824 [71] Darling WG (1998) Hydrothermal hydrocarbon gases: Application in the East African Rift System Applied Geochemistry 13: 825–840 [72] Darling WG, Griesshaber E, Andrews JN, et al (1995) The origin of hydrothermal and other geysers in the Kenya Rift Valley Geochimica et Cosmochimica Acta 59: 2501–2512 [73] VGK and VBL (1993) Nesjavellir Power Plant Hydrogen sulfide abatement A Report to Reykjavík Heating Company (in Icelandic), 112pp VGK, VBL Engineering [74] Delgado H, Piedad-Sànchez N, Galvian L, et al (1998) CO2 flux measurements at Popocatépetl volcano: II Magnitude of emissions and significance (abstract) EOS Transactions of the American Geophysical Union 79(45): 926 [75] Favara R, Giammanco S, Inguaggiatio S, and Pecoraino G (2001) Preliminary estimate of CO2 output from Pantelleria Island volcano (Sicily, Italy): Evidence of active mantle degassing Applied Geochemistry 16: 883–894 [76] Baubron J-C, Mathieu R, and Miele G (1991) Measurement of gas flows from soils in volcanic areas: The accumulation method (abstract) In: Tedesco D (ed.) Proceedings of the International Conference on Active Volcanoes and Risk Mitigation Osservatorio, Vesuviano, 27 August–1 September 1991 [77] Etiope G, Beneduce P, Calcara M, et al (1999) Structural pattern and CO2-CH4 degassing of Ustica Island, Southern Tyrrhenian basin Journal of Volcanology and Geothermal Research 88: 291–304 [78] Werner C and Brantley S (2003) CO2 emissions from the Yellowstone volcanic system Geochemistry Geophysics Geosystems 4(7): 1061 [79] Sorey ML, Evans WC, Kennedy BM, et al (1998) Carbon dioxide and helium emissions from a reservoir of magmatic gas beneath Mammoth Mountain, California Journal of Geophysical Research 103(15): 303–315, 323 [80] Evans WC, Sorey ML, Cook AC, et al (2002) Tracing and quantifying magmatic carbon discharge in cold groundwaters: Lessons learned from Mammoth Mountain, USA Journal of Volcanology and Geothermal Research 114: 291–312 [81] Gerlach TM, Doukas MP, McGee KA, and Kessler R (2001) Soil efflux and total emission rates of magmatic CO2 at the Horseshoe Lake tree kill, Mammoth Mountain, California, 1995–1999 Chemical Geology 177: 101–116 Geochemical Aspects of Geothermal Utilization 167 [82] Wardell LJ and Kyle PR (1998) Volcanic carbon dioxide emission rates: White Island, New Zealand and Mt Erebus, Antarctica (abstract) EOS Transactions, AGU 79(45) (Fall Meeting supplement): 927 [83] Cruz JV, Couthinho RM, Carvalho MR, et al (1999) Chemistry of waters from Furnas volcano, São Miguel, Azores: Fluxes of volcanic carbon dioxide and leached material Journal of Volcanology and Geothermal Research 92: 151–167 [84] Gerlach TM (1991) Etna’s greenhouse pump Nature 315: 352–353 [85] Marty B and Tolstikhin IN (1998) CO2 fluxes from mid-ocean ridges, arcs and plumes Chemical Geology 145: 233–248 [86] Fridriksson T, Kristjánsson BR, Ármannsson H, et al (2006) CO2 emissions and heat flow through soil, fumaroles, and steam heated mud pools at the Reykjanes geothermal area, SW Iceland Applied Geochemistry 21: 1551–1569 [87] Mörner NA and Etiope G (2002) Carbon degassing from the lithosphere Global and Planetary Change 33: 185–203 [88] Kerrick DM (2001) Present and past non-anthropogenic CO2 degassing from the solid earth Reviews in Geophysics 39: 564–585 [89] Ármannsson H, Gíslason G, and Hauksson T (1982) Magmatic gases aid the mapping of the flow pattern in a geothermal system Geochimica et Cosmochimica Acta 46: 167–177 [90] Ármannsson H (2002) Green accounting applied to geothermal energy Gaseous emissions compared with those from other energy sources (in Icelandic) In: Gunnarsdóttir MJ (ed.) Samorka’s Conference on Matters Relating to Distribution System Undertakings, 9pp Akureyri, 30–31 May 2002 Samorka, Reykjavic [91] Ármannsson H, Fridriksson Th, and Kristjánsson BR (2005) CO2 emissions from geothermal power plants and natural geothermal activity in Iceland Geothermics 34: 286–296 [92] Bachu S, Gunter WD, and Perkins EH (1994) Aquifer disposal of CO2: Hydrodynamic and mineral trapping Energy Conversion and Management 35: 269–279 [93] Benson SM and Cole DR (2008) CO2 sequestration in deep sedimentary formations Elements 4: 325–331 [94] Holloway S (2001) Storage of fossil fuel-derived carbon dioxide beneath the surface of the earth Annual Review of Energy and the Environment 26: 145–166 [95] Metz B, Davidson O, de Coninck H, et al (eds.) (2005) IPCC Special Report on Carbon Dioxide Capture and Storage New York: Cambridge University Press [96] Oelkers EH and Cole DR (2008) Carbon dioxide sequestration A solution to a global problem Elements 4: 305–310 [97] Kharaka YK, Cole DR, Hovorka SD, et al (2006) Gas-water-rock interactions in Frio Formation following CO2 injection: Implications for the storage of greenhouse gases in sedimentary basins Geology 34: 577–580 [98] Hawkins DG (2004) No exit: Thinking about leakage from geologic carbon storage sites Energy 29: 1571–1578 [99] Rochelle CA, Czernichowski-Lauriol I, and Milodowski AE (2004) The impact of chemical reactions on CO2 storage in geological formations: A brief review Geologicat Society of London, Special Publications 233: 87–106 [100] Gíslason SR, Wolff-Boenisch D, Stefánsson A, et al (2010) Mineral sequestration of carbon dioxide in basalt: A pre-injection overview of the CarbFix project International Journal of Greenhouse Gas Control 4: 537–545 [101] Gíslason SR and Arnórsson S (1990) Saturation state of natural waters in Iceland relative to primary and secondary minerals in basalts In: Spencer RJ and Chou I.-M (eds.) Fluid–Mineral Interactions: A Tribute to Hans Eugster, pp 373–393 Geochemical Society Special Publication No San Antonio, Texas [102] Gíslason SR, Veblen DR, and Livi KJT (1993) Experimental meteoric water–basalt interactions: Characterization and interpretation of alteration products Geochimica et Cosmochimica Acta 57: 1459–1471 [103] Gíslason SR and Eugster HP (1987) Meteoric water–basalt interactions II A field study in N.E Iceland Geochimica et Cosmochimica Acta 51: 2841–2855 [104] Gíslason SR and Eugster HP (1987) Meteoric water–basalt interactions I A laboratory study Geochimica et Cosmochimica Acta 51: 2827–2840 [105] Gysi AP and Stefánsson A (2008) Numerical modelling of CO2–water–basalt interaction Mineralogical Magazine 72: 55–59 [106] Matter JM, Takahashi T, and Goldberg D (2007) Experimental evaluation of in situ CO2-water-rock reactions during CO2 injection in basaltic rocks Implications for geological CO2 sequestration Geochemistry, Geophysics, Geosystems 8, doi: 10.1029/2006GC001427 [107] Oelkers EH and Gíslason SR (2001) The mechanism, rates, and consequences of basaltic glass dissolution I An experimental study of the dissolution rates of basaltic glass as a function of aqueous Al, Si, and oxalic acid concentration at 258 °C and pH = and 11 Geochimica et Cosmochimica Acta 65: 3671–3681 [108] Kelemen P and Matter JM (2008) In situ carbonation of peridotite for CO2 storage Proceedings of the National Academy of Sciences of the United States of America 105: 17295–17300 [109] McGrail BP, Schaef HT, Ho AM, et al (2006) Potential for carbon dioxide sequestration in flood basalts Journal of Geophysical Research 111: B12201 [110] O’Connor WK, Rush GE, and Dahlin DC (2003) Laboratory studies on the carbonation potential of basalt: Applications to geological sequestration of CO2 in the Columbia River Basalt Group In: AAPG Annual Meeting Expanded Abstracts, Salt Lake City, Utah, USA, vol 12, pp 129–130 Tulsa, OK: AAPG [111] Oelkers EH, Gislason SR, and Matter J (2008) Mineral carbonation of CO2 Elements 4: 331–335 [112] Ĩlafsson M, Friðleifsson G.Ĩ, Eiríksson J, et al (1993) On the origin of organic gas in Öxarfjörður, NE-Iceland National Energy Authority Report OS-93015/JHD-05, 76pp [113] Schoell M (1980) The hydrogen and carbon isotopic composition of methane from natural gases of various origins Geochimica et Cosmochimica Acta 44: 649–661 [114] Jakobsson SP and Friðleifsson GÓ (1989) Asphalt in amygdales in Skyndidalur, Lón (in Icelandic with English abstract) Náttúrufræðingurinn 59: 169–188 [115] Saemundsson K (1980) Outline of the geology of Iceland Jökull 29: 7–28 [116] Des Marais DJ, Stallard ML, Nehring NL, and Truesdell AH (1988) Chemical Geology 71: 159–167 [117] Ármannsson H, Benjamínsson J, and Jeffrey A (1989) Gas changes in the Krafla geothermal system, Iceland Chemical Geology 76: 175–196 [118] Sano Y, Urabe A, Wakita H, et al (1985) Chemical and isotopic compositions of gases in geothermal fluids in Iceland Geochemical Journal 19: 135–148 [119] Gunter BD and Musgrave BC (1971) New evidence on the origin of methane in hydrothermal gases Geochimica et Cosmochimica Acta 35: 113–118 [120] Arnórsson S and Gíslason SR (1994) CO2 from magmatic sources in Iceland Mineralogical Magazine 58A: 27–28 [121] Óskarsson N (1996) Carbon dioxide from large volcanic eruptions Short term effects (in Icelandic) In: Bragason A et al (eds.) Biological Society of Iceland The Carbon Budget of Iceland Conference, Program and Abstracts, p 17 Reykjavík, Iceland, 22–23 November 1996 [122] Ármannsson H, Fridriksson T, Wiese F, et al (2007) CO2 budget of the Krafla geothermal system, NE-Iceland In: Bullen TD and Wang, Y (eds.) Water–Rock Interaction, pp 189–192 London: Taylor & Francis Group [123] Einarsson P (1978) S-wave shadows in the Krafla caldera in NE Iceland, evidence for a magma chamber in the crust Bulletin of Volcanology 43: 1–9 [124] Björnsson A (1985) Dynamics of crustal rifting in NE Iceland Journal of Geophysical Research 90(B12): 10151–10162 [125] Mortensen AK, Gudmundsson Á, Steingrímsson B, et al (2009) Overview of research of the geothermal system and a review of the conceptual model (in Icelandic) Landsvirkjun LV-2009, 111, 206pp + maps [126] Ármannsson H, Guðmundsson Á, and Steingrímsson BS (1987) Exploration and development of the Krafla geothermal area Jökull 37: 13–30 [127] Ármannsson H (2001) Reaction of groundwater with rock from the Krafla area, N-E Iceland and volcanic gas In: Cidu R (ed.) Water-Rock Interaction, pp 779–782 The Netherlands: Balkema, Swets & Zeitlinger, Lisse [128] Sinclair AJ (1974) Selection of threshold in geochemical data using probability graphs Journal of Geochemical Exploration 3: 129–149 [129] Ingri N, Kakolowicz W, Sillén LG, and Warnqvist B (1967) High-speed computers as a supplement to graphical methods-V: Haltafall, a general program for calculating the composition of equilibrium mixtures Talanta 14: 1261–1286 [130] Eriksson G (1979) An algorithm for the computation of aqueous multi-component, multi-phase equilibria Analytica Chimica Acta 112: 375–383 [131] Morel F and Morgan J (1972) A numerical method for computing equilibria in aqueous chemical systems Environmental Science and Technology 6: 58–67 [132] Westall JC, Zachary JL, and Morel FFM (1976) MINEQL, a Computer Program for the Calculation of Chemical Equilibrium Composition of Aqueous Systems Technical Note 18, R.M Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA [133] Truesdell AH and Jones BF (1974) WATEQ, a computer program for calculating chemical equilibria of natural waters U.S Geological Survey Journal of Research 2: 233–248 168 Geochemical Aspects of Geothermal Utilization [134] Kharaka YK, Gunter WD, Aggarwal PK, et al (1988) SOLMINEQ88, a computer program for geochemical modelling of water-rock interactions U.S Geological Survey Water Resources Investigations Report 88–4227 [135] Kharaka YK and Barnes I (1973) SOLMINEQ: Solution-mineral equilibrium computations U.S Geological Survey Computer Contributions Report PB–215–899 [136] Wolery TJ (1979) Calculation of chemical equilibrium between aqueous solutions and minerals: The EQ3/6 software package Lawrence Livermore National Laboratory Report UCRL–52658 [137] Wolery TJ (1983) EQ3NR, a computer program for geochemical aqueous speciation-solubility calculations: User’s guide and documentation Lawrence Livermore National laboratory Report UCRL–53414 [138] Wolery TJ (1992) EQ3/EQ6, a software package for geochemical modelling of aqueous systems, package overview and installation guide (version 7.0) Lawrence Livermore National Laboratory Report UCRL-MA-110662 (1) [139] Wolery TJ (1992) EQ3NR, a computer program for geochemical aqueous speciation-solubility calculations: Theoretical manual, user’s guide and related documentation (version 7.0) Lawrence Livermore National laboratory Report UCRL-MA-110662 (3) [140] Reed MH (1977) Calculations of Hydrothermal Metasomatism and Ore Deposition in Submarine Volcanic Rocks with Special Reference to the West Shasta District PhD Dissertation, University of California, Berkeley [141] Reed MH (1982) Calculation of multi-component chemical equilibria and reaction processes in systems involving minerals, gases and an aqueous phase Geochimica et Cosmochimica Acta 46: 513–528 [142] Reed MH, Spycher NF, and Palandri JL (2010) SOLVEQ-XPT: A Program for Computing Aqueous-Mineral-Gas Equilibria, 41pp Eugene, OR: University of Oregon [143] Arnórsson S, Sigurðsson E, and Svavarsson H (1982) The chemistry of geothermal waters in Iceland I Calculation of aqueous speciation from °C to 350 °C Geochimica et Cosmochimica Acta 46: 1513–1532 [144] Bjarnason JÖ (1994) The Speciation Program WATCH, Version 2.1, 7pp Reykjavík: National Energy Authority [145] Helgeson HC, Brown TH, Nigrini A, and Jones TA (1970) Calculation of mass transfer in geochemical processes involving aqueous solutions Geochimica et Cosmochimica Acta 34: 569–592 [146] Reed MH, Spycher NF, and Palandri JL (2010) CHIM-XPT: A Computer Program for Computing Reaction Processes in Aqueous-Mineral-Gas Systems and MINTAB Guide, 73pp Eugene, OR: University of Oregon [147] Gunnlaugsson E and Einarsson Á (1989) Magnesium silicate scaling in mixture of geothermal water and deaerated fresh water in a district heating system Geothermics 18: 113–120 [148] Kristmannsdóttir H, Ĩlafsson M, and Thórhallsson S (1989) Magnesium silicate scaling in district heating systems in Iceland Geothermics 18: 191–198 [149] Kristmannsdóttir H, Ildefonse Ph, Bertaux J, and Flank AM (1998) Crystal-chemistry of Mg-Si and Al-Si scales in geothermal waters, Iceland In: Ármannsson H (ed.) Geochemistry of the Earth’s Surface, pp 519–522 Rotterdam: Balkema [150] Liping B (1991) Chemical modelling programs for predicting calcite scaling, applied to low temperature geothermal waters in Iceland United Nations Geothermal Training Programme, Reykjavík, Iceland Report 3, 1991, 45pp [151] Reed MH and Spycher NF (1984) Calculation of pH and mineral equilibria in hydrothermal water with application to geothermometry and studies of boiling and dilution Geochimica et Cosmochimica Acta 48: 1479–1490 [152] Kristmannsdóttir H, Axelsson G, Sæmundsson K, et al (1998) The Rangæingar Heating Company Monitoring of geothermal production 1997–1998 and the status of water provision (in Icelandic) National Energy Authority Report OS-98077, 89pp [153] Kristmannsdóttir H, Axelsson G, Sæmundsson K, et al (2002) The Rangæingar Heating Company Monitoring of geothermal production in the company’s production areas in Laugaland in Holt and Kaldárholt 2001 (in Icelandic) National Energy Authority Report OS-2002/009, 20pp [154] Swanteson J and Kristmannsdóttir H (1978) The chemical composition of altered rock in Krafla (in Icelandic) Report OSJHD-7822 Reykjavík: National Energy Authority [155] Gerlach TM (1980) Evaluation of volcanic gas analyses from Surtsey volcano, Iceland 1964–1967 Journal of Volcanology and Geothermal Research 8: 191–198 [156] Ármannsson H (1993) Námafjall geothermal system Geo-chemical investigations (in Icelandic) National Energy Authority Report OS-93053/JHD-29 B, 30pp [157] Reed MH and Spycher NF (1989) SOLTHERM: Data base of Equilibrium Constants for Aqueous-Mineral-Gas Equilibria Eugene, OR: Department of Geological Sciences, University of Oregon [158] Guðmundsson Á (1993) Alteration heat of the Námafjall geothermal system (in Icelandic) National Energy Authority Report OS-93065/JHD 31B, 21pp [159] Guðmundsson Á, Steingrímsson B, Sigursteinsson D, et al (1983) Krafla, Well KJ-13 Redrilling in July and August 1983 (in Icelandic) National Energy Authority Report OS-83077/JHD 23B, 29pp [160] Kristmannsdóttir H, Guðmundsson Á, Kjartansdóttir M, and Friðleifsson GÓ (1976) Krafla Well KG-8, drilling, inflows, pressure testing, permeability testing, lithology and alteration (in Icelandic) National Energy Authority Report OS JHD 7713 [161] Torssander P (1986) Origin of volcanic sulfur in Iceland A sulfur isotope study Doctoral thesis, Stockholm: Department of Geology, University of Stockholm No 269, 164pp [162] Tole MP, Ármannsson H, Pang Z, and Arnórsson S (1993) Fluid/mineral equilibrium calculations for geothermal fluids and chemical geothermometry Geothermics 22: 17–37 [163] Fournier RO and Rowe JJ (1966) Estimation of underground temperatures from the silica content of water from hot springs and wet steam wells American Journal of Science 264: 685–697 [164] Arnórsson S (1975) Application of the silica geothermometer in low-temperature hydrothermal areas in Iceland American Journal of Science 275: 763–784 [165] Fournier RO (1977) Chemical geothermometers and mixing models for geothermal systems Geothermics 5: 41–50 [166] Truesdell AH and Fournier RO (1975) Calculation of deep reservoir temperatures from chemistry of boiling hot springs of mixed origin In: The 2nd United Nations Symposium on the Development and Use of Geothermal Resources, Abstract Volume III, p 25 San Francisco, 20–29 May 1975 Washington, DC: Government Printing Office [167] Arnórsson S (1985) The use of mixing models and chemical geothermometers for estimating underground temperatures in geothermal systems Journal of Volcanology and Geothermal Research 23: 299–335 [168] Fournier RO and Potter RW II (1982) An equation correlating the solubility of quartz in water from 25° to 900 °C at pressures up to 10,000 bars Geochimica et Cosmochimica Acta 46: 1969–1974 [169] Fournier RO and Potter RWII (1982) A revised and expanded silica (quartz) geothermometer Geothermal Resources Council Bulletin 11(10): 3–12 [170] Gíslason SR, Heaney PJ, Oelkers EH, and Schott J (1997) Kinetic and thermodynamic properties of moganite, a novel silica polymorph Geochimica et Cosmochimica Acta 61: 1193–1204 [171] Fournier RO (1981) Application of water geochemistry to geothermal exploration and reservoir engineering In: Rybach L and Muffler LJP (eds.) Geothermal Systems: Principles and Case Histories, pp 109–143 New York: John Wiley [172] Ragnarsdóttir KV and Walther JW (1983) Pressure sensitive ‘silica geothermometer’ determined from quartz solubility experiments at 250 °C Geochimica et Cosmochimica Acta 47: 941–946 [173] Fournier RO and Truesdell AH (1973) An empirical Na-K-Ca geothermometer for natural waters Geochimica et Cosmochimica Acta 37: 515–525 [174] Fournier RO and Potter RW II (1979) Magnesium correction to the Na-K-Ca chemical geothermometer Geochimica et Cosmochimica Acta 43: 1543–1550 [175] Giggenbach WF (1988) Geothermal solute equilibria Derivation of Na-K-Mg-Ca-geoindicators Geochimica et Cosmochimica Acta 52: 2749–2765 [176] D’Amore F and Truesdell AH (1985) Calculation of geothermal reservoir temperatures and steam fraction from gas compositions 1985 International Symposium on Geothermal Energy Geothermal Resources Council Transactions 9: 305–310 [177] Bertrami R, Cioni R, Corazza E, et al (1985) Carbon monoxide in geothermal gases Reservoir temperature calculations at Larderello (Italy) Geothermal Resources Council Transactions 9: 299–303 [178] Arnórsson S and Gunnlaugsson E (1985) New gas geothermometers for geothermal exploration – Calibration and application Geochimica et Cosmochimica Acta 49: 1307–1325 Geochemical Aspects of Geothermal Utilization 169 [179] Arnórsson S (1987) Gas chemistry of the Krísuvík geothermal field, Iceland, with special reference to evaluation of steam condensation in upflow zones Jưkull 37: 32–47 [180] Arnórsson S, Fridriksson T, and Gunnarsson I (1998) Gas chemistry of the Krafla geothermal field, Iceland In: Arehart GB and Hulston JR (eds.) Water-Rock Interaction, pp 613–616 Rotterdam: Balkema [181] D’Amore F and Panichi C (1980) Evaluation of deep temperature of hydrothermal systems by a new gas geothermometer Geochimica et Cosmochimica Acta 44: 549–556 [182] Tonani F (1980) Some remarks on the application of geochemical techniques in geothermal exploration In: Strub AS and Ungemach P (eds.) Proceedings of the 2nd International Seminar on the Results of E.C Geothermal Energy Research, Strasbourg, France, pp 428–443 Strasbourg: EC [183] Zhao P and Ármannsson H (1996) Gas geothermometry in selected Icelandic geothermal fields with comparative examples from Kenya Geothermics 25: 307–347 [184] Giggenbach WF (1980) Geothermal gas equilibria Geochimica et Cosmochimica Acta 44: 2021–2032 [185] Karingithi CW, Arnórsson S, and Grưnvold K (2010) Processes controlling aquifer fluid compositions in the Olkaria geothermal system, Kenya Journal of Volcanology and Geothermal Research 196: 57–76 [186] Kristmannsdóttir H and Ármannsson H (1996) Chemical monitoring of Icelandic geothermal fields during production Geothermics 25: 349–364 [187] Björnsson S and Benediktsson S (1968) An account of enthalpy and flow measurements in steam boreholes (in Icelandic) National Energy Authority, 15pp [188] Macambac RV, Salazar ATN, Villa RR, et al (1998) Field-wide application of chemical tracers for mass flow measurements in Philippine geothermal fields In: Proceedings of the 19th Annual PNOC EDC Geothermal Conference, Makati City, Philippines, pp.153–159 Manila, Philippines [189] Hirtz P and Lovikin J (1995) Tracer dilution measurements for two-phase geothermal production: Comparative testing and operating experience In: Barbier E, Frye G, Iglesias E, and Pálmason G (eds.) World Geothermal Congress, pp 1881–1886 Florence, Italy Auckland, New Zealand: IGA [190] Agamata-Lu CS (1998) Chemical tracer applications at the Broadlands-Ohaaki and Wairakei geothermal fields In: Proceedings of the 19th Annual PNOC EDC Geothermal Conference, Makati City, Philippines, pp.137–151 Manila, Philippines [191] Magadadaro MC (1998) Sodium benzoate analysis for on-line brine flow measurements In: Proceedings of the 19th Annual PNOC EDC Geothermal Conference, Makati City, Philippines, pp 169–176 Manila, Philippines [192] Adams MC (1995) Vapor, liquid and two-phase tracers for geothermal systems In: Barbier E, Frye G, Iglesias E, and Pálmason G (eds.) World Geothermal Congress, pp 1875–1880 Florence, Italy Auckland, New Zealand: IGA [193] Ármannsson H (1989) Predicting calcite deposition in Krafla boreholes Geothermics 18: 25–32 [194] Wangyal P (1992) Calcite deposition related to temperature and boiling in some Icelandic geothermal wells Geothermal Training Programme Report 1992-11, United Nations University, 33pp [195] Gunnarsson I, Arnórsson S, and Jakobsson S (2005) Precipitation of poorly crystalline antigorite under hydrothermal conditions Geochimica et Cosmochimica Acta 69: 2813–2828 [196] Truesdell AH, Haizlip JR, Ármannsson H, and D’Amore F (1989) Origin and transport of chloride in superheated geothermal steam Geothermics 18: 295–304 [197] D’Amore F, Truesdell AH, and Haizlip JR (1990) Production of HCl by mineral reaction in high temperature geothermal systems In: Tsang CF (ed.) Proceedings of the 15th Workshop on Geothermal Reservoir Engineering, pp 23–25 Stanford University, Stanford, CA [198] Allegrini G and Benvenuti G (1970) Corrosion characteristics and geothermal power plant protection U.N symposium on the development and utilization of geothermal resources Geothermics 2(Part 1): 865–881 [199] Thórhallsson S, Pálsson B, Fridleifsson GĨ, et al (2008) Description of ENEL corrosion resistant wellheads IDDP Drilling Technology Report, 6pp [200] Bell D (1989) Description of an operational desuperheating and chloride scrub system Geothermal Resources Council Transactions 13: 303–307 [201] Hirtz P, Buck C, and Kunzman R (1991) Current techniques in acid-chloride corrosion control and monitoring at the Geysers In: Degens G and Neuman SP (eds.) Proceedings of the 16th Workshop on Geothermal Reservoir Engineering, pp 83–95 Stanford University, Stanford, CA [202] Hirtz PN, Broaddus ML, and Gallup DL (2002) Dry steam scrubbing for impurity removal from superheated geothermal steam Geothermal Resources Council Transactions 26: 751–754 [203] Izquierdo G, Arellano VM, Aragón A, et al (2000) Fluid acidity and hydrothermal alteration at the Los Humeros geothermal reservoir Puebla, Mexico In: Iglesias E et al (eds.) Proceedings of the World Geothermal Congress 2000, pp 1301–1305 Kyushu-Tohoku, Japan Pisa, Italy: IGA [204] Moya P, Nietzen F, and Sanchez E (2005) Development of the neutralization system for production wells at the Miravalles geothermal field In: Proceedings of the World Geothermal Congress 2005, 10pp Antalya, Turkey Reykjavic, Iceland: IGA [205] Villa RR, Siega FL, Martinez-Oliver MM, et al (2000) A demonstration of the feasibility of acid well utilization: The Philippines’ well MG-9D experience In: Zaide-Delfin, MC (ed.) Proceedings of the 20th Annual PNOC EDC Geothermal Conference, pp 25–32 Philippines [206] Sugiaman F, Sunio E, Molling P, and Stimac J (2004) Geochemical response to production of the Tiwi geothermal field, Philippines Geothermics 33: 57–86 [207] Moore JN, Christenson B, Browne PRL, and Lutz SJ (2002) The mineralogic consequences and behaviour of descending acid-sulfate waters: An example from the Karaha-Telaga Boda geothermal system, Indonesia In: Kruger P and Raney Jr HJ (eds.): Proceedings of the 27th Workshop on Geothermal Reservoir Engineering, pp 257–265 Stanford University, Stanford, CA [208] Reyes AG (1990) Petrology of Philippine geothermal systems and the application of alteration mineralogy to their assessment Journal of Volcanology and Geothermal Research 43: 279–309 [209] Reyes AG (1991) Mineralogy, distribution and origin of acid alteration in Philippine geothermal systems In: Matsuhisa Y, Masahiro A, and Hedenquist J (eds.) High temperature Acid Fluids and Associated Alteration and Mineralization, Geological Survey of Japan Report, vol 277, pp 59–65 Tsukuba, Japan: Geological Survey of Japan [210] Angcoy EC, Abarquez AL, Andrino RP, et al (2008) Mechanisms of erosion-corrosion in well 311D, South Sambaloran, Leyte geothermal production field In: Proceedings of the 29th Annual PNOC EDC Geothermal Conference, pp 159–164 Markati City, Philippines [211] Kiyota Y, Matsuda K, and Shimada K (1996) Characterization of acid water in the Otake-Hatchobaru geothermal field In: Proceedings of the 17th Annual PNOC EDC Geothermal Conference, pp 131–135 Makati City, Philippines [212] Bowyer D, Bignall G, and Hunt T (2008) Formation and neutralization of corrosive fluids in the shallow injection aquifer, Rotokawa geothermal field, New Zealand Tauhara North No Trust, GNS, Mighty River Power wwww.geothermal.org/Powerpoint08/Tuesday/GeochemistryI/BowyerTue08.ppt (accessed December 2010) [213] Hauksson T (1979) Well KG-12 (in Icelandic) National Energy Authority Well Letter No 11, 5pp [214] Hauksson T and Benjamínsson J (2005) Krafla and Bjarnarflag Borehole production and the chemical composition of water and steam in boreholes and production equipment in 2004 (in Icelandic) Landsvirkjun Report, Krafla Power Station, 78pp [215] Hauksson T and Gudmundsson A (2008) Krafla Acid wells Landsvirkjun Report, 17pp [216] Ármannsson H and Gíslason G (1992) The occurrence of acidic fluids in the Leirbotnar field, Krafla, Iceland In: Kharaka YK and Maest AS (eds.) Water-Rock Interaction, pp 1257–1260 Rotterdam: Balkema [217] Sanchez Rivera E, Sequeira HG, and Vallejos Ruiz O (2000) Commercial production of acid wells at the Miravalles geothermal field, Costa Rica In: Proceedings of the World Geothermal Congress 2000, pp 1629–1633 Kyushu-Tohoku, Japan [218] Virkir-Orkint (1990) Djibouti Geothermal scaling and corrosion study Final Report Electricité de Djibouti, Virkir-Orkint, Reykjavík, 270pp [219] James R (1962) Steam-water critical flow through pipes Proceedings of the Institution of Mechanical Engineers, London 176: 741–745 [220] Turekian KK (1969) The oceans, streams and atmosphere In: Wedepohl KH (ed.) Handbook of Geochemistry, vol 1, ch 10, pp 297–323 Berlin: Springer-Verlag [221] Gallup DL (1989) Iron silicate formation and inhibition at the Salton Sea geothermal field Geothermics 18: 97–103 [222] Swedlund PJ and Webster JG (1999) Adsorption and polymerisation of silicic acid on ferrihydrite, and its effect on arsenic adsorption Water Resources 33: 3413–3422 [223] Jost (1980) US Patent 4,224,151 [224] Gallup DL (1993) The use of reducing agents for control of ferric silicate scale deposition Geothermics 22: 39–48 170 [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263] [264] [265] [266] [267] [268] [269] [270] Geochemical Aspects of Geothermal Utilization Bemmelen RW and Rutten MG (1955) Table mountains of Northern Iceland, 217pp + 52 plates and maps Leiden: E.J Brill Kjartansson H (1972) Clay formations in Dalasýsla and Thingeyjarsýsla districts (in Icelandic) National Energy Authority JKD, 83pp Grưnvold K and Karlsdóttir R (1975) Theistareykir An interim report on the surface exploration of the geothermal area (in Icelandic) National Energy Authority JHD-7501, 37pp Ármannsson H, Gíslason G, and Torfason H (1986) Surface exploration of the Theistareykir high-temperature geothermal area, Iceland, with special reference to the application of geochemical methods Applied Geochemistry 1: 47–64 Gíslason G, Johnsen GV, Ármannsson H, et al (1984) Theistareykir Surface exploration of the high-temperature geothermal area (in Icelandic) National Energy Authority OS-84089/JHD-16, 134pp + maps Layugan DB (1981) Geo-electrical soundings and its application in the Theistareykir high-temperature area United Nations University Geothermal Training Programme Report 1981–5, 101pp Ármannsson H, Kristmannsdóttir H, Torfason H, and Ólafsson M (2000b) Natural changes in unexploited high-temperature geothermal areas in Iceland In: Iglesias E, Blackwell D, Hunt T, et al (eds.) Proceedings of the World Geothermal Congress 2000, Kyushu-Tohuku, Japan, pp 521–526 International Geothermal Association, Pisa, Italy Ármannsson H (2001) Theistareykir A review of research, exploration and its cost (In Icelandic) National Energy Authority OS-2001/035, 24pp Gautason B, Ármannsson H, Árnason K, et al (2000) Thoughts on the next steps in the exploration of the Theistareykir geothermal area (in Icelandic) National Energy Authority BG-HÁ-KÁ-KS-ĨGF-STh-2000/04, 11pp Sỉmundsson K (2007) The geology of Theistareykir (in Icelandic) Iceland GeoSurvey Report, ÍSOR-07270, 23pp Karlsdóttir R, Eysteinsson H, Magnússon ITh, et al (2006) TEM soundings at Theistareykir and Gjástykki 2004–2006 (in Icelandic) Iceland GeoSurvey Report ÍSOR-2006/028, 88pp Yu G, He LF, He ZX, et al (2008) Iceland Theistareykir 2-D MT survey Data acquisition report KMS Technologies – KJT Enterprises Inc and VGK-Hưnnun Hafstad TH (1989) Ưxarfjưrdur Groundwater investigations 1987–1988 A contribution to a special project on fish farming (in Icelandic) National Energy Authority OS-89039/ VOD-08 B, 25pp Hafstad TH (2000) Theistareykir: The drilling of a fresh water well (in Icelandic) National Energy Authority ThH-00/14, 6pp Gudmundsson Á, Gautason B, Thordarson S, et al (2002) Exploration drilling at Theistareykir Well Th.G-1 3rd stage: Drilling of production part to 1953 m depth (in Icelandic) National Energy Authority OS-2002/079, 59pp Arnórsson S, Gunnlaugsson E, and Svavarsson H (1983) The chemistry of geothermal waters in Iceland III Chemical geothermometry in geothermal investigations Geochimica et Cosmochimica Acta 47: 567–577 Guðmundsson Á, Gautason B, Axelsson G, et al (2008) A conceptual model of the geothermal system at Theistareykir and a volumetric estimate of the geothermal potential (in Icelandic) Iceland GeoSurvey, VGK-Hönnun and Vatnaskil Engineering Office, Report, 57pp Arnórsson S (1989) Deposition of calcium carbonate minerals from geothermal waters – Theoretical considerations Geothermics 18: 33–40 Giggenbach WF (1991a) Chemical techniques in geothermal exploration In: D’Amore F (coordinator) Applications of Geochemistry in Geothermal Reservoir Development, pp 119–142 Rome: UNITAR/UNDP Publication Giggenbach WF (1991b) Isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and their origin Earth and Planetary Science Letters 113: 495–510 Hardardóttir V, Ármannsson H, and Thórhallsson S (2005) Characterization of sulfide-rich scales in brines at Reykjanes In: Horne R and Okenden E (eds.) Proceedings of the World Geothermal Congress 2005, 8pp Antalya, Turkey, 24–29 April 2005 Reykjavic, Iceland: IGA Hardardóttir V, Brown KL, Fridriksson Th, et al (2009) Metals in deep liquid of the Reykjanes geothermal system, southwest Iceland: Implications for the composition of seafloor black smoker fluids Geology 37: 1103–1106 Seward TM and Kerrick DM (1996) Hydrothermal CO2 emission from the Taupo Volcanic Zone, New Zealand Earth Planetary Science Letters 139: 105–113 Khalilabad MR, Axelsson G, and Gíslason SR (2008) Aquifer characterization with tracer test technique; permanent CO2 sequestration into basalt SW Iceland Mineralogical Magazine 72: 121–125 Reed MH and Spycher NF (1989) SOLVEQ: A Computer Program for Computing Aqueous-Mineral-Gas Equilibria A Manual, 37pp Eugene, OR: Department of Geological Sciences, University of Oregon Browne PRL (1984) Lectures on Geology and Petrology UNU Geothermal Training Programme, Iceland Report 1984-2, 92 pp Browne PRL and Ellis AJ (1970) The Ohaaki-Broadlands hydrothermal area, New Zealand: Minerology and related geochemistry American Journal of Science 269: 97–131 Rist S (1979a) Water level fluctuations and ice cover of Lake Mývatn Oikos, 32: 67–81 Xu T, Apps JA, Pruess K, and Yamamoto H (2007) Numerical modelling of injection and mineral trapping of CO2 with H2S and SO2 in a sandstone formation Chemical Geology 242: 319–346 Rist S (1979b) The hydrology of River Laxá Oikos 32: 271–280 Sigbjarnarson G, Tómasson H, Eliasson J, and Arnörsson S (1974) A report on the risk of pollution from a power plant situated either at Krafla or Hverarónd (in Icelandic) OS JHD 7427, OS ROD 7421, 16pp Reykjavik, Iceland: Orkustofnun Sveinbjưrnsdóttir ÁE, Johnsen SJ, and Arnórssen S (1995) The use of stable isotopes of oxygen and hydrogen in geothermal studies in Iceland In: Barbier E, Frye G, Iglesias E, and Pálmason G (eds.) Proceedings of the World Geothermal Congress, pp 1043–1048 Florence, Italy Auckland, New Zealand: International Geothermal Association International Geothermal Association (2002) Geothermal power generating plant CO2 emission survey A Report, International Geothermal Association, Pisa, Italy, 7pp Sheppard D and Mroczek E (2004) Greenhouse gas emissions from the exploitation geothermal systems IGA Quarterly 55: 11–13 Parkhurst DL, Thorstenson DC, and Plummer LN (1980) Phreeqe – A computer program for geochemical calculations US Geological Survey Water-Resources Investigations Report 80–96 Böðvarsson G (1960) Exploration and exploitation of natural heat in Iceland Bulletin Volcanology Series 23: 241–250 Haas JL, Jr (1976) Physical properties of the coexisting phases and thermochemical properties of the H2O component in boiling NaCl solutions USGS Bulletin 1421-A: 73 pp Pacˇes T (1975) A systematic deviation from the Na-K-Ca geothermometer below 75 °C and above 10-4 atm PCO2 Geochimica et Cosmochimica Acta 29: 541–544 Nehring N and D’Amore F (1984) Gas chemistry and thermometry of the Cerro Prieto, Mexico, geothermal field Geothermics 13: 75–89 Björnsson G and Böðvarsson G (1987) A multi-feedzone wellbore simulator Geothermal Resources Council Transaction 11: 503–507 Gíslason G and Arnórsson S (1976) Interim report on changes in flow and chemical composition in Boreholes and in Krafla Report OS-JHD-7640, 13pp (in Icelandic) Reykjavik, Iceland: Orkustofnun Gudmundsson A (2001) An expansion of the Krafla power plant from 30 to 60 MWe geothermal consideration GRC-Transactions 25: 741–746 Giroud N, Ármannsson H, and Ólafsson M (2008) Well KJ-35 in Krafla Chemical composition of liquid and steam in Autumn 2007 ÍSOR 08055, 10pp Reykjavik, Iceland: Exposition ´I SOR Ármannsson H (1979) Dithizone extraction and flame atomic absorption spectrometry for the determination of cadmium, zinc, lead, copper, nickel, cobalt and silver in sea water and biological tissues Analytica Chimica Acta 110: 21–28 Ármannsson H and Ovenden PJ (1980) The use of dithizone extraction and atomic absorption spectrometry for the determination of silver and bismuth in rocks and sediments and a demountable hollow cathode lamp for the determination of bismuth and indium Journal of Environmental Analytical Chemistry 8: 127–136 Gunnarsson G (2001) The cleaning of residual gas from geothermal plants (in Icelandic) In: Samorka GMJ (eds.) Orkuỵing (Energy Symposium) pp 281285 Abstracts Reykjavik, Iceland, 11–13 October ... 0.2 ≤ 0.3 ≤ 0 .7 ≤ 0.4 0. 5–3 5–2 0 0.0 1–0 .1 0. 2–1 0. 3–5 0 .7 1.5 0. 4–5 3–9 2 0–6 0 0. 1–0 .3 1–3 5–1 5 1. 5–4 .5 5–1 5 9–4 5 6 0–3 00 0. 3–1 .5 3–1 5 15 75 4. 5–2 2.5 15 75 >45 >300 >1.5 >15 >75 >22.5 >75 I, negligible... (δ18O = –8 0.4 to –8 0 .7) , II (δ2H = –8 3.0 to –8 6.9), and III (δ2H = – 87. 7 to –8 8.9) are local water groups, whereas the water found in groups IV (δ2H = –9 1.5 to –9 4.8) and V (δ2H = –9 0.9 to –9 3.5%)... Trace 0.0123 0.0152 0.01 47 0.0132 0.2 97 –3 1.9 –1 38 0.229 –2 9.6 0.384 –2 9.0 –1 54 0.3 57 –2 9.0 0.455 –2 2.5 δ13 CCH4 (‰) δ DCH4 (‰) 0.0080 0.426 –2 8.6 –2 22 0.0034 0.0002 0.021 –2 6.6 0.0035 0.0058 Sep.,