V41A-0389
The Iceland Deep Drilling Project (IDDP): (I) A New Era in Geothermal Development?
The Iceland Deep Drilling Project (IDDP) announced in September 2007 that an international industrial consortium has signed a new contract to collaborate in exploratory deep drilling in Iceland. The main objective of the IDDP is to investigate whether it is economically feasible to produce energy from geothermal systems at supercritical conditions. This will require drilling to depths of 4 to 5 km in order to reach temperatures of 400 to 600°C. Today, geothermal wells in Iceland typically range up to 2.5 km in depth and produce steam at about 300°C, or less, at a rate sufficient to generate about 4 to 7 megawatts of electricity. It is estimated that producing steam from a well penetrating a reservoir with temperatures >450°C, and at a rate of 0.67 cubic meters a second, could generate 40 to 50 MWe. If IDDP's test of this concept proves successful, it could lead to major improvements in the development of high-temperature geothermal resources worldwide. The consortium collaborating to fund this investigation of supercritical geothermal energy consists of three leading Icelandic power companies, Hitaveita Sudurnesja Ltd., Landsvirkjun, Orkuveita Reykjavikur, together with Orkustofnun (the National Energy Authority) and Alcoa Inc. (an international aluminum company). The three power companies financed a feasibility study for the project that was completed in 2003. Each of the three power companies is committed to drill, at their own cost, a 3.5 to 4.0 km deep well in a geothermal field that they operate. The design of these wells will permit them to be deepened to 4.5 or 5.0 km by the IDDP, and funded by the consortium with additional funds from international scientific agencies. The first deep IDDP well will be drilled in the latter part of 2008 in the Krafla geothermal field near the northern end of the central rift zone of Iceland, within a volcanic caldera that has had recent volcanic activity. Two new wells, ~4 km deep, will then be drilled at the Hengill and the Reykjanes geothermal fields during 2009-2010, and subsequently deepened. In contrast to the fresh water systems at Krafla and Hengill, the Reykjanes geothermal system produces hydrothermally modified seawater on the Reykjanes peninsula, in southern Iceland, where the Mid-Atlantic Ridge comes on land in southern Iceland. Processes at depth at Reykjanes should be similar to those responsible for black smokers on ocean spreading centers. The IDDP has engendered considerable international scientific interest. The US National Science Foundation and the International Continental Scientific Drilling Program will jointly fund the coring and sampling for scientific studies. In preparation for studying the data and samples that will be recovered by deep drilling research is underway on samples from existing wells in the target geothermal fields, and on exposed "fossil" geothermal systems and active mid-ocean ridge systems that have conditions believed to be similar to those that will be encountered in deep drilling by the IDDP. Some of these initial scientific studies by US investigators are reported in the accompanying papers. http://www.iddp.is
V41A-0390
The Iceland Deep Drilling Project (IDDP): (II) Fluid Origin and Evolution in the Reykjanes Geothermal System - A Stable Isotope Study of Hydrothermal Epidote
The Reykjanes geothermal system, located on the landward extension of the Mid-Atlantic Ridge in southeast Iceland, provides an on-land proxy to the hydrothermal systems of oceanic spreading centers and is a candidate for future deep drilling into the supercritical zone. In preparation for study of supercritical fluids from this region, an understanding of hydrothermal processes at shallower levels is necessary. Previous studies of elemental composition and salinity have shown that Reykjanes geothermal fluids are likely hydrothermally modified seawater. However, hydrogen isotope properties of these fluids indicate a significant component of meteoric water, with δDFLUID values as low as -23‰. Here we constrain the origin of hydrothermal solutions by analysis of hydrogen and oxygen isotope compositions of geothermal epidote from drilling wells within the Reykjanes system at depths between 1 and 3 km. δDEPIDOTE values range from -64 to - 70‰ in well RN-10 between 1.0 and 2.1 km depths, from -63 to -78‰ in well RN-17 at .95 to 3.0 km depth, and between -61‰ and -63‰ in well RN-9 between 1.0 and 1.3 km depth. Published δDEPIDOTE values from well RN-8 at 1.6 km depth are -48‰. At the same depths, δ18OEPIDOTE range from 1.8 to -0.4‰ in well RN-10, from 2.3 to -0.1‰ in well RN-17, and from 0.2 to -3.0‰ in well RN-9. δD values of epidote progressively increase moving away from the geothermal upflow zone at well RN-10, whereas δ18O values decrease. For comparative analysis, the Nesjavellir and Krafla geothermal systems, which are dominated by meteoric water and have a δDFLUID of approximately -79‰ and -89‰ respectively, have a δDEPIDOTE of -115‰ and -125‰. However, δDEPIDOTE from the mixed meteoric-seawater Svartsengi geothermal system is -68‰; comparable to δDEPIDOTE from well RN-10. Stable isotope compositions of geothermal fluids are computed based upon the measured isotope composition of Reykjanes epidotes and temperatures approximated from the boiling point curve with depth, and are compared to the published temperature dependent isotope fractionation curves of epidote. Calculated δD and δ18O of geothermal fluids are less than 0‰, suggesting that fluids of meteoric origin are an important component of the hydrothermal solutions. Additionally, variations between wells suggest a heterogeneous evolution of fluid flow or fluid source within the system. These results, in conjunction with the hydrogen and oxygen isotope composition and elemental chemistry of modern geothermal fluids, allow evaluation of the relative influence that fluid source, mixing, rock-fluid interaction and boiling have had on the geochemical evolution of the Reykjanes geothermal system.
V41A-0391
The Iceland Deep Drilling Project (IDDP): (III) Hydrothermal Fluid Geobarometry
The IDDP wells will penetrate high pressure geothermal reservoirs where an understanding of the pressure effects on mineral equilibria is essential. The chemical compositions of fluids from active hydrothermal systems have long been applied to estimating reservoir temperature in subaerial geothermal systems at temperatures less than 300 °C and pressures along the H2O liquid/vapor P-T curve, where the pressures are low and the pressure effects on mineral equilibria are small. At pressures of hundreds of bars beneath mid-ocean ridge black smoker springs, the effect of pressure on mineral solubilities is substantial, and can be exploited to estimate pressure and temperature from fluid composition. In practice we compute mineral saturation indices, log(Q/K), for a given fluid for a wide range of P-T combinations, then plot log(Q/K) for alteration minerals against pressure at a series of temperatures so as to identify a possible "knot" in P-T-log(Q/K) space where a group of probable alteration minerals equilibrated with the fluid. We find that saturation index surfaces distinctly converge to zero in a narrow range of pressure and temperature. As an example, we estimate that for an East Pacific Rise 21 °N NGS fluid with a vent T=273 °C and vent P=260 bar, the reservoir conditions are likely T=370-420 °C and P=480-530 bar. To explore what aspect of the fluid chemistry causes the strong pressure effect on mineral solubilities, we computed the effect of pressure change on the activities of aqueous H+, Na+, K+, Ca2+, and other significant species in the 21 °N NGS fluid. At 420 °C, pH changes from 8 to 5 as pressure changes from 200 to 700 bar, an effect resulting from dissociation of HCl with increasing pressure. Similarly, chloride complex dissociations yield approximately 10-fold increases in Ca2+, Na+, and K+ concentrations with a 200 to 700 bar pressure increase. In another series of calculations, we synthesized a seawater-like fluid that was equilibrated at 400 °C and 500 bar with clinopyroxene, chlorite, epidote, feldspars, and quartz, then treated the fluid as an "unknown" for estimating P-T. Even for small departures from equilibrium P-T (e.g. +/- 25 °C), the mineral saturation surfaces change markedly, thereby supporting the conclusion that pressure effects on fluid composition are large enough to enable meaningful pressure and temperature estimations in deep hydrothermal systems.
V41A-0392
Iceland Deep Drilling Project (IDDP): (IV) Fluid Inclusion Microthermometry of the Geitafell Hydrothermal System – a Possible Analog of the Active Krafla System
The Miocene Geitafell volcanic complex in southeast Iceland hosts an extinct high temperature hydrothermal system that provides an excellent opportunity for study of the interior of an analog to the Krafla and Hengill active systems, which will be penetrated by IDDP drilling. The Geitafell volcano formed on the central Icelandic rift zone at approximately 5-6 Ma. Glacial erosion has exposed the deep interior of the volcano, revealing a complex of tholeitic lavas, hyaloclastites and rhyolites, cut by 12 intrusive phases and a sequence of seven related vein sets with distinct vein fillings and alteration haloes. Mineralogical studies by Fridleifsson (1983) show that when Geitafell was active, it hosted a supercritical hydrothermal system with fluids exceeding 400°°C at pressures up to 300 bar. We have begun fluid inclusion microthermometry studies of this system with the goal to define the specific relationship of the vein sequence to vein temperatures and alteration haloes, and thereby improve the understanding of supercritical hydrothermal systems . We have sampled veins in a basaltic lava from Fridleifsson's vein sets 2 and 3, and a quartz-filled amygdale tied to vein set 2. Vein set 2 is bordered by a narrow (5-10mm) dark alteration halo of chlorite and albite; set 3 veins have cm-scale epidote-rich envelopes. Fluid inclusions were not visible in the quartz and epidote of vein set 3, but quartz in vein set 2 contains abundant fluid inclusions 5 to 15 micrometers in size with vapor bubbles ranging from 10 to 60 vol%. In the amygdale, fluid inclusions are 5 to 30 micronmeters in size with vapor bubbles ranging from 25 to 60 vol%. The average freezing point depression for vein set 2 and amygdale inclusions is 0.1°°C, indicating a salinity of 0.2 wt% NaCl equivalent--largely fresh water. Fluid inclusions homogenize to liquid or to vapor at temperatures ranging from approximately 300 to 394°°C. Most liquid-dominated inclusions homogenize between 300 and 380°°C. The coexisting vapor rich and liquid rich inclusions and the homogenization behavior indicate a boiling hydrothermal system at a temperature of at least 380°°C.
V41A-0393
Monitoring of Acoustic Emissions Within Geothermal Areas in Iceland: A new Tool for Geothermal Exploration.
With increased emphasis on geothermal development new exploration methods are needed in order to improve general understanding of geothermal reservoirs, characterize their extent and assess the potential for sustainable power production. Monitoring of acoustic emissions within geothermal areas may provide a new tool to evaluate the spatial extent of geothermal fields and model rock-fluid interactions. Three-dimensional seismic data have been used to assess the spatial and temporal distribution of noise within several high-temperature geothermal fields in Iceland. Seismic noise in the 4-6 Hz range within the Svartsengi field can be attributed to steam hydraulics and pressure oscillations within the geothermal reservoirs. Seismic noise surveys compliment electrical resistivity soundings and TEM-surveys by providing information pertinent to the current geothermal activity and extent of steam fields within the uppermost crust of the geothermal reservoir. Information related to acoustic emissions can thus help define targets for future wells.
V41A-0394
Detection of Surface Temperature Anomalies in the Coso Geothermal Field Using Thermal Infrared Remote Sensing
We use thermal infrared (TIR) data from the spaceborne ASTER instrument to detect surface temperature anomalies in the Coso geothermal field in eastern California. The identification of such anomalies in a known geothermal area serves as an incentive to search for similar markers to areas of unknown geothermal potential. We carried out field measurements concurrently with the collection of ASTER images. The field data included reflectance, subsurface and surface temperatures, and radiosonde atmospheric profiles. We apply techniques specifically targeted to correct for thermal artifacts caused by topography, albedo, and thermal inertia. This approach has the potential to reduce data noise and to reveal thermal anomalies which are not distinguishable in the uncorrected imagery. The combination of remote sensing and field data can be used to evaluate the performance of TIR remote sensing as a cost-effective geothermal exploration tool.
V41A-0395
Integration of 3D MT Resistivity Imaging With Borehole Petrology, Temperature and Resistivity Log Data to Characterize the Geothermal Resource at Glass Mountain, California
The integration of resistivity images from magnetotelluric (MT) surveys with supporting geophysics, geology and borehole data shows that the resistivity pattern to depths of at least 3000 m in the Glass Mountain geothermal resource area is primarily controlled by interface conduction in temperature-dependent hydrothermal clays. Over 200 MT stations, 350 TDEM stations and 500 gravity stations are integrated into the analysis along with temperature and petrology data from 26 boreholes from 500 to 3000 m and a resistivity well log from 340 to 2800 m depth. These data cover the Glass Mountain geothermal area within the 7 by 12 km ring fracture at the summit of Medicine Lake Volcano and extend down its flanks. The integration of the geophysical data illustrates the relative effectiveness of 1D, 2D and 3D MT inversions and highlights limitations of some conventional joint analyses such as the use of TDEM to correct MT static distortion. The most effective conceptual integration is a comparative analysis of the 3D MT resistivity imaging with respect to detailed borehole petrology, resistivity and temperature logs. The 3D MT inversion images and well data illustrate the petrophysical origin of two prominent resistivity transitions in the Glass Mountain geothermal resource area. Near surface, unaltered volcanics have relatively high resistivity, over 200 ohm-m. At depths from 100 m to 700 m, there is a transition from the resistive unaltered volcanics to a 2 to 10 ohm-m zone correlated with low resistivity zeolite and smectite hydrothermal clay alteration found at temperature lower than 200°C. Where temperature exceeds 200°C, smectite clay becomes unstable and alters to more resistive illite, accounting for a transition to 10 to 100 ohm-m resistivity at 500 to 1400 m depth. The correlation of resistivity with temperature-sensitive clay alteration provides a basis for interpreting subsurface temperature throughout the volume imaged by the 3D MT inversion to 3000 m depth in the Glass Mountain area, as confirmed by data from the 26 boreholes.
V41A-0396
Towards an Automatic, Real-time Detection of Subsurface Cracks in Geothermal Fields Using Shear-wave Splitting
We have developed, borrowed and consolidated a number of algorithms that can in principle reduce production costs in geothermal plants by simplifying the monitoring of the field's subsurface crack system, during exploration and into production. The data gatherer is an array of seismic sensors, and the data consists of shear-wave splitting parameters, obtained from natural or induced local seismic events. The operation starts with a portable seismic array of 20-25 three-component geophones telemetering to a computerized portable station that will display in real time the natural and induced seismicity, detect crack geometry and intensity of fracturing as the seismic data streams into the array. The display will progressively show an emerging cloud of seismic events, followed by images of the crack geometry and distribution, as newly data becomes available and the inversion of the measured SWS parameters stabilizes. The computer contains data from previously detected crack systems at the site and so before-and-after-injection comparisons can be readily done. As the data accumulate, tomographic images of the surrounding rock volume slowly become available. Changes in fluid motion, in crack orientation, in temperature will result in identifiable changes in the tomographic computer display. Since a real-time shear wave splitting monitoring system that performs as described here is unprecedented, it presents a number of important challenges - as well as opportunities - to advance geothermal science and technology. Some of these challenges and opportunities will be discussed.
V41A-0397
Electrical Surveys for Geothermal Reservoir Characterization
A geothermal reservoir simulator was used to model the natural state of the Beowawe geothermal field in north- central Nevada, and to compute the subsurface distributions of temperature, salinity, and pore-fluid resistivity. Subsequently, DC, MT and SP postprocessor software was used to compute the expected response corresponding to available survey data. The measured apparent resistivity distribution from a dipole-dipole DC resistivity survey is in good agreement with the computed values. The computed self-potential distribution reproduces the main features of an available SP survey. Although the computed MT apparent resistivity sounding curves reproduce the shapes of the measured MT sounding curves, an overall scale factor exists between the measured and computed MT responses. Possible reasons are static shifts in the coarsely sampled MT stations, and resistivity anisotropy due to the stratigraphy. Taken as a whole, the results of present work indicate that a suite of carefully designed electrical surveys (DC, MT, and SP) may be utilized to infer subsurface geothermal reservoir characteristics.
V41A-0398
Tracking of Volcano Fumarole Field Variations Using Real Time, High Temporal Resolution Data From A Permanent Thermal Camera
In June 2006, we installed an A 40 Forward Looking InfraRed (FLIR) thermal camera at Vulcano's La Fossa Crater (Aeolian Islands, Italy) for monitoring the fumarole activity. This was installed on the inner southern flank of the crater at a distance of about 400 m from the fumarole field (target pixel size of ~ 50 cm). Our aim was the collection of identical geometry and resolution thermal images that would have improved our ability to track temporal and spatial thermal trends of the fumarole field. In January 2007, a permanent weather station, recording air temperature, pressure, relative humidity and rainfall rate, was installed in the same site of the camera. An electronic micro-controller board was developed to interface the station with the thermal camera allowing the automatic and real-time atmospheric corrections within the camera software. The whole system is remotely controlled through wireless transmission from INGV Catania Section, where in real-time temperature and atmospheric data are transmitted, stored and automatically analyzed. Here, we present the first year of data showing the temperature distribution frequency at La Fossa's fumarole field. Analysis were carried out on the raw images and only on data collected between 7:00 pm and 7:00 am (GMT) to prevent the maximum heat release from the ground. Additionally, to exclude seasonal and weather effects, we fixed a preliminary temperature threshold of 70oC. Hot pixels above the threshold were plotted versus temperature to obtain daily temperature distribution frequencies. Additionally, the average of daily maximum temperatures for each of the main fumaroles (control fumaroles) versus time was plotted. Finally, to better imagine the hottest spots, their location and, through periodic comparison, their migration (fumarole field spatial variations), we used 3D diagrams.
V41A-0399
ASTER Observations of 2000-2007 Thermal Features at Pavlof Volcano and Mt. Hague (Emmons Lake Volcanic Center), Alaska
Emmons Lake Volcanic Center (ELVC) is a 15 km by 30 km area of nested calderas, stratovolcanoes, lava domes, hyaloclastite rings, and cinder cones aligned along the arc axis. Pavlof Volcano is the most active volcano along the ELVC, with more than 40 historic eruptions since 1790. The most recent eruption of Pavlof Volcano began in August 2007 after almost 11 years of quiescence. Mount Hague is a prominent intracaldera vent with no known historical eruptions that lies approximately 7 kilometers to the southwest of Pavlof. The southern crater of Mount Hague commonly fluctuates between a crater-filling lake to a dry crater floor with vigorously steaming fumaroles. Mount Hague has another fumarole field on the southeast flank at nearly the same elevation as the crater floor. To better document the behavior of persistent thermal features at these remote volcanoes, we have compiled temperature and dimension data using a seven-year long time series of satellite data. Over 25 daytime and 40 nighttime clear thermal infrared (TIR) images (90 m resolution) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) have recorded variations in the thermal activity at both volcanic vents since July 2000. All cloud-free ASTER TIR observations document persistent low- temperature features at both Pavlof Volcano and Mount Hague during this period. The size and temperature of each thermal feature varies throughout the study period. The data show that the 2518 m summit of Pavlof Volcano is occasionally snow-free in early summer whereas neighboring peaks at lower elevations are still snow-clad. FLIR data acquired near the summit of Pavlof in 2004 show that the majority of warm ground was at 20°C to 40°C. These warm areas commonly persist snow-free into the winter. Temperature variations observed at Mt Hague crater usually correlate to the size of the ephemeral crater lake. As the lake grows, the pixel-integrated ASTER TIR temperature increases. Measurements using higher resolution (15 m) daytime ASTER visible-near infrared (VNIR) images show that the crater lake size varies between 0 to 4.5 hectares each year. Combined field and satellite observations from the last seven years suggest that the changes to the lake size can occur within a few weeks each summer. When the lake is absent, the fumarole temperatures in the crater parallel the fumarole temperatures observed on the southeast flank of Mount Hague. Periods of vigorous steaming from the Hague crater may coincide with periods of little or no water filling the crater. Although the final data processing is ongoing, preliminary results show no correlation between the thermal activity at Pavlof Volcano with the activity at Mount Hague.
V41A-0400
STRUCTURAL CONTROLS ON THE HYDROTHERMAL SYSTEM OF VILLARRICA: EVIDENCE FROM SELF-POTENTIAL MEASUREMENTS
Geological studies at Volcan Villarrica have investigated the volcanic history of this part of the Andes southern volcanic zone but have revealed little information about the hydrothermal and magmatic circulation system. Hydrothermal circulation, and the extent over which it is active on volcanoes, has connotations to hazard mitigation as areas within the hydrothermal cell are often less competent and more prone to failure. A self- potential survey was conducted over a period of three months on two sub-parallel transects from the summit of the volcano. Initial results suggest fluid circulation is occurring. The survey detected a strong amplitude dipolar anomaly reaching a value of -2.7 volt, the minimum in the self potential data indicating the transitional zone from a hydrothermal to hydrological regime of fluid circulation. This anomaly is believed to be a result of a combination of rapid fluid disruption, electro-kinetic, and thermoelectric effects within and surrounding the magmatic conduit system. Heat supplied from the active lava lake and its supply system is the likely driving mechanism for the shallow hydrothermal cell. The location of the dipolar anomaly is coincident with relict caldera from Villarrica II, upon which the modern day Volcan Villarrica is formed. The collocation of the self potential anomaly and the relict caldera suggest that this structural feature acts as a boundary for the hydrothermal cell. The temporal stability of the self potential signal, coupled with the low surface recharge of the system indicates that the hydrothermal system is maintained by water vapour being exsolved from the degassing magma, with only a minor and short lived perturbation resulting form the infiltration of surface waters. The seasonal stability of the self potential field, coupled with stability of the field to infiltration of meteoric waters suggests that any perturbations to the self potential field that are a result of precipitation are short lived. Thus self potential provides a low cost and relatively simple volcanic monitoring tool.
V41A-0401
3-D Thermal Modelling of the Western Area of Mt. Amiata Geothermal Field, Italy.
Mount Amiata, a quiescent quaternary volcano located in Tuscany, central Italy, hosts a high enthalpy water- dominated geothermal field. We focus our modelling on an adjacent area, west of the geothermal field, where thermal and gravity surveys highlighted a probable continuity of the geothermal features at depth. The model domain extends over an area 15 by 12 km. The model thickness is 5 km, corresponding to the average depth to the K-horizon, a regional seismic reflector underlying the area. Deep geothermal wells existing in the field nearby allow a temperature control down to about 4 km. The model is composed by three main layers, according to the generalized stratigraphy of the area. The 3-D numerical modelling was performed using the code SHEMAT 7.1, considering various boundary conditions, inner geometries and hydraulic permeabilities. The model was realized by means of unsteady forward simulations, under the assumptions of impervious and isothermal top and bottom boundaries, lateral adiabatic faces and variable internal physical properties. Several sets of simulations were carried out, with different bottom boundary temperatures and different hydraulic permeability values for the two deeper layers. The results indicate that the present temperature and pressure distribution with depth in the Mount Amiata field requires deep reservoir rocks with permeability locally much higher than the overlying cover units, to allow fluid convection and favour the upwards migration of over- pressurized fluids, which may break through the overburden, feeding the currently exploited geothermal field.