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Low-(18)O Silicic Magmas: Why Are They So Rare?

Description: LOW-180 silicic magmas are reported from only a small number of localities (e.g., Yellowstone and Iceland), yet petrologic evidence points to upper crustal assimilation coupled with fractional crystallization (AFC) during magma genesis for nearly all silicic magmas. The rarity of 10W-l `O magmas in intracontinental caldera settings is remarkable given the evidence of intense 10W-l*O meteoric hydrothermal alteration in the subvolcanic remnants of larger caldera systems. In the Platoro caldera complex, regional ignimbrites (150-1000 km3) have plagioclase 6180 values of 6.8 + 0.1%., whereas the Middle Tuff, a small-volume (est. 50-100 km3) post-caldera collapse pyroclastic sequence, has plagioclase 8]80 values between 5.5 and 6.8%o. On average, the plagioclase phenocrysts from the Middle Tuff are depleted by only 0.3%0 relative to those in the regional tuffs. At Yellowstone, small-volume post-caldera collapse intracaldera rhyolites are up to 5.5%o depleted relative to the regional ignimbrites. Two important differences between the Middle Tuff and the Yellowstone 10W-180 rhyolites elucidate the problem. Middle Tuff magmas reached water saturation and erupted explosively, whereas most of the 10W-l 80 Yellowstone rhyolites erupted effusively as domes or flows, and are nearly devoid of hydrous phenocrysts. Comparing the two eruptive types indicates that assimilation of 10W-180 material, combined with fractional crystallization, drives silicic melts to water oversaturation. Water saturated magmas either erupt explosively or quench as subsurface porphyrins bejiire the magmatic 180 can be dramatically lowered. Partial melting of low- 180 subvolcanic rocks by near-anhydrous magmas at Yellowstone produced small- volume, 10W-180 magmas directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.
Date: October 15, 1998
Creator: Balsley, S.D. & Gregory, R.T.
Partner: UNT Libraries Government Documents Department

A summary of modeling studies of the Krafla Geothermal Field,Iceland

Description: A comprehensive modeling study of the Krafla geothermalfield in Iceland has been carried out. The study consists of four tasks:the analysis of well test data, modeling of the natural state of summaryof the the field, the determination of the generating capability of thefield, and modeling of well performance. The results of all four tasksare consistent with field observation.
Date: August 1, 1983
Creator: Bodvarsson, Gudmundur S.; Pruess, Karsten; Stefansson, Valgardur & Eliasson, Einar T.
Partner: UNT Libraries Government Documents Department


Description: The hydrocarbon content of leaf fossils from Iceland has been investigated by gas chromatography-mass spectrometry. The distribution patterns of normal hydrocarbons, branched hydrocarbons, and cyclic hydrocarbons are compared to those of present-day living organisms. The diagenetic pathways of these hydrocarbons are discussed.
Date: October 1, 1970
Creator: Han, Jerry & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department

Subsidence events in the Krafla area: Preliminary report based on tilt and distance measurements

Description: In the inflation-deflation sequence of the Krafla magma chamber since its beginning in 1975, 10 deflation or subsidence events have been identified until July 1978. The tilt and distance measurements relating to these subsidence events are discussed in some detail. All of these subsidence events are associated with horizontal magma flow along the N-S trending fissure zone, which goes through the central part of the suggested Krafla caldera to form a dike 3 to 5 meter wide, 80 km long and 1.0 to 2.5 km high from the bottom to the top. The total volume of magma, which flowed out of the Krafla magma chamber during these 10 events, is estimated as 392 x 10{sup 6} m{sup 3}, whereof 318 x 10{sup 6} m{sup 3} are estimated to have flowed northwards, 72 x 10{sup 6} m{sup 3} southwards and about 2 x 10{sup 6} m{sup 3} came to the surface as basaltic lava.
Date: December 1, 1978
Creator: Tryggvason, Eysteinn
Partner: UNT Libraries Government Documents Department

Seismological evidence for Lateral magma intrusion during the July 1978 deflation of the Krafla volcano in NE-Iceland

Description: The July 1978 deflation of the Krafla volcano in the volcanic rift zone of NE-Iceland was in most respects typical of the many deflation events that have occurred at Krafla since December 1975. Separated by periods of slow inflation, the deflation events are characterized by rapid subsidence in the caldera region, volcanic tremor and extensive rifting in the fault swarm that transects the volcano. Earthquakes increase in the caldera region shortly after deflation starts and propagate along the fault swarm away from the central part of the volcano, sometimes as far as 65 km. The deflation events are interpreted as the result of subsurface magmatic movements, when magma from the Krafla reservoir is injected laterally into the fault swarm to form a dyke. In the July 1978 event magma was injected a total distance of 30 km into the northern fault swarm. The dyke tip propagated with the velocity of 0.4-0.5 m/sec during the first 9 hours, but the velocity decreased as the length of the dyke increased. Combined with surface deformation data, these data can be used to estimate the cross sectional area of the dyke and the driving pressure of the magma. The cross sectional area is variable along the dyke and is largest in the regions of maximum earthquake activity. The average value is about 1200 m{sup 2}. The pressure difference between the magma reservoir and the dyke tip was of the order of 10-40 bars and did not change much during the injection.
Date: July 1, 1978
Creator: Einarsson, Pall & Brandsdottir, Bryndis
Partner: UNT Libraries Government Documents Department

Natural State Model of the Nesjavellir Geothermal Field, Iceland

Description: The Nesjavellir geothermal system in southern Iceland is very complex from both a thermal and hydrologic point of view. There are large pressure and temperature gradients in the wellfield and zones with drastically different pressure potentials. Thus, natural fluid flow is substantial in the system and flow patterns are complex. We have developed a two-dimensional natural state model for the Nesjavellir system that matches reasonably well the observed pressure and temperature distributions. The match with field data has allowed determination of the energy recharge to the system and the permeability distribution. Fluids recharge the system at rate of 0.02 kg/s/m with an enthalpy of 1460 kJ/kg. The permeability in the main reservoir is estimated to be in the range of 1.5 to 2.0 md, which agrees well with injection test results from individual wells. Permeabilities in shallower reservoirs are about an order of magnitude higher. Most of the main reservoir is under twephase conditions, as are shallow aquifers in the southern part of the field. The model results also suggest that the low temperatures in the shallow part of the northern region of the field may be due to the young age of the system; i.e., the system is gradually heating up. If this is the case the estimated age of the system near the wellfield is on the order of a few thousand years.
Date: January 21, 1986
Creator: Bodvarsson, G. S.; Pruess, K.; Stefansson, V.; Steingrimsson, B.; Bjornsson, S.; Gunnarsson, A. et al.
Partner: UNT Libraries Government Documents Department

Multipurpose Use of Geothermal Energy

Description: The conference was organized to review the non-electric, multipurpose uses of geothermal energy in Hungary, Iceland, New Zealand, United States and the USSR. The international viewpoint was presented to provide an interchange of information from countries where non-electric use of geothermal energy has reached practical importance.
Date: October 9, 1974
Creator: Lienau, Paul J. & Lund, John W.
Partner: UNT Libraries Government Documents Department

Cost Effective Surfactant Formulations for Improved Oil Recovery in Carbonate Reservoirs

Description: This report summarizes work during the 30 month time period of this project. This was planned originally for 3-years duration, but due to its financial limitations, DOE halted funding after 2 years. The California Institute of Technology continued working on this project for an additional 6 months based on a no-cost extension granted by DOE. The objective of this project is to improve the performance of aqueous phase formulations that are designed to increase oil recovery from fractured, oil-wet carbonate reservoir rock. This process works by increasing the rate and extent of aqueous phase imbibition into the matrix blocks in the reservoir and thereby displacing crude oil normally not recovered in a conventional waterflood operation. The project had three major components: (1) developing methods for the rapid screening of surfactant formulations towards identifying candidates suitable for more detailed evaluation, (2) more fundamental studies to relate the chemical structure of acid components of an oil and surfactants in aqueous solution as relates to their tendency to wet a carbonate surface by oil or water, and (3) a more applied study where aqueous solutions of different commercial surfactants are examined for their ability to recover a West Texas crude oil from a limestone core via an imbibition process. The first item, regarding rapid screening methods for suitable surfactants has been summarized as a Topical Report. One promising surfactant screening protocol is based on the ability of a surfactant solution to remove aged crude oil that coats a clear calcite crystal (Iceland Spar). Good surfactant candidate solutions remove the most oil the quickest from the surface of these chips, plus change the apparent contact angle of the remaining oil droplets on the surface that thereby indicate increased water-wetting. The other fast surfactant screening method is based on the flotation behavior of powdered calcite ...
Date: September 30, 2007
Creator: Goddard, William A.; Tang, Yongchun; Shuler, Patrick; Blanco, Mario & Wu, Yongfu
Partner: UNT Libraries Government Documents Department

Drilling of a 2000-metre (6562-FT) Borehole for Geothermal Steam in Iceland

Description: Drilling for geothermal heat has been carried out in Iceland since 1928, when hot water was obtained for district heating in Reykjavik. From that time, in particular in the sixties, extensive drilling has resulted in the annual utilization of 54 million tons of water and 2 million tons of steam. Five drilling rigs are used for geothermal drilling, with depth capacity ranging from 400 to 3,600 meters (1,312 to 11,812 feet). Drilling procedures vary extensively and depend on whether a high- or low-temperature field is being drilled, the main difference being the well-casing program and the blowout equipment used.
Date: January 1, 1981
Creator: Ragnars, K. & Benediktsson, S.
Partner: UNT Libraries Government Documents Department

Analysis of Production Data from the Krafla Geothermal Field, Iceland

Description: The Krafla geothermal field in northeastern Iceland consists of several zones, which contain fluids of different composition and thermodynamic state (Stefansson, 1981). In this paper they examine production data from wells which are completed in two-phase zones. Transient changes in flow rate and flowing enthalpy are analyzed to obtain insight into relative (liquid and gas phase) permeabilities, and other reservoir parameters. Numerous studies have shown that predictions of geothermal reservoir behavior are strongly dependent upon the choice of relative permeability functions. There is an extensive literature on gas-oil and oil-water relative permeabilities, but steam-water relative permeabilities which are needed for geothermal reservoir analysis are poorly known. Laboratory experiments by Chen et al. (1978) and Counsil and Ramey (1979) have provided some data which, however, seem to be at variance with relative permeability characteristics deduced from field data by Grant (1977) and Horne and Ramey (1978). The differences may reflect uncertainties in the analysis methods used, or they may reflect ''real'' differences in relative permeability behavior of fractured reservoirs from that of porous medium-type laboratory cores. Recent theoretical work by Menzies (1982) and Gudmundsson et al. (1983) has substantiated the relative permeability characteristics obtained by Horne and Ramey (1978) for Wairakei wells.
Date: December 15, 1983
Creator: Pruess, K.; Bodvarsson, G. S. & Stefansson, V.
Partner: UNT Libraries Government Documents Department

Fractionation of Boron Isotopes in Icelandic Hydrothermal Systems

Description: Boron isotope ratios have been determined in a variety of different geothermal waters from hydrothermal systems across Iceland. Isotope ratios from the high temperature meteoric water recharged systems reflect the isotope ratio of the host rocks without any apparent fractionation. Seawater recharged geothermal systems exhibit more positive {delta}{sup 11}B values than the meteoric water recharged geothermal systems. Water/rock ratios can be assessed from boron isotope ratios in the saline hydrothermal systems. Low temperature hydrothermal systems also exhibit more positive {delta}{sup 11}B than the high temperature systems, indicating fractionation of boron due to adsorption of the lighter isotope onto secondary minerals. Fractionation of boron in carbonate deposits may indicate the level of equilibrium attained within the systems.
Date: January 1, 1995
Creator: Aggarwal, J.K. & Palmer, M.R.
Partner: UNT Libraries Government Documents Department

A field example of free surface testing

Description: Theoretical results on free liquid surface dynamics presented by Bodvarsson (1978, this volume), provide the basis for a technique of reservoir probing and testing which can yield results that are supplementary to conventional well testing data. The Laugarnes geothermal area in Iceland which is one of the sources of the Reykjavik District Heating System is a case where both methods are applicable and appear interestingly, to yield quite different results. A brief account of the free surface results is presented.
Date: January 1, 1978
Creator: Bodvarsson, Gunnar & Zais, Elliot
Partner: UNT Libraries Government Documents Department


Description: The Nesjavellir High Temperature Geothermal Field is located in the Northern part of the Hengill Geothermal Area, which has been estimated to be one of the largest geothermal areas in iceland. Drilling started at Nesjavellir some 20 years ago with five wells. In 1982 a renewed exploration phase began and five additional wells have been drilled during the last three years. The pressure distribution within the geothermal system is very inhomogeneous in both horizontal and vertical directions. Variations in temperature are also considerable. The highest pressure and temperature is found in the southwestern part of the investigated area and both pressure and temperature decreases towards northeast. There seem to be four different zones of pressure potential in the system, which require the existence of both horizontal and vertical barriers in the system. Some parts of the geothermal system are in two-phase condition whereas other parts are in single phase liquid condition. The chemical composition of the fluid seem to be relatively uniform and a common origin of the fluid is assumed. The transmissivity of wells is in the range (1,3-3,5) 10{sup -8} m{sup 3}/Pa {center_dot} s whereas the flowing enthalpy ranges from 1200-2100 kJ/kg. The thermal output of wells are 40-60 MW. The geothermal system at Nesjavellir shows a high degree of three-dimensional variation, but a simple conceptual model described in the paper, seem to be in agreement with all observation made so far in the field.
Date: January 22, 1985
Creator: Stefansson, V.
Partner: UNT Libraries Government Documents Department

Human Resources in Geothermal Development

Description: Some 80 countries are potentially interested in geothermal energy development, and about 50 have quantifiable geothermal utilization at present. Electricity is produced from geothermal in 21 countries (total 38 TWh/a) and direct application is recorded in 35 countries (34 TWh/a). Geothermal electricity production is equally common in industrialized and developing countries, but plays a more important role in the developing countries. Apart from China, direct use is mainly in the industrialized countries and Central and East Europe. There is a surplus of trained geothermal manpower in many industrialized countries. Most of the developing countries as well as Central and East Europe countries still lack trained manpower. The Philippines (PNOC) have demonstrated how a nation can build up a strong geothermal workforce in an exemplary way. Data from Iceland shows how the geothermal manpower needs of a country gradually change from the exploration and field development to monitoring and operations.
Date: January 1, 1995
Creator: Fridleifsson, I.B.
Partner: UNT Libraries Government Documents Department


Description: There have been two major high-temperature geothermal field developments in Iceland in the last decade; Krafla in the north-east, and Svartsengi in the south-west. These and other geothermal developments have recently been reported by Palmason et al. The Krafla field will not be discussed here, but details about the field are available in Stefansson and the power plant in Eliasson et al. Several reservoir engineering studies of the Krafla field have been published. The Svartsengi field is one of several fields on the Reykjanes Peninsula in south-west Iceland. About 15 km west of Svartsengi, on the tip of the Peninsula, the Reykjanes field is now under development, primarily for seawater chemicals production. The recently drilled Eldvorp field is located in line between these two fields, about 5 km west of Svartsengi. There are also several fields to the east of Svartsengi, at 15-20 km distance. The Svartsengi, Eldvorp, and Reykjanes fields exist in the same tectonic-volcanic environment, and are surrounded by similar geohydrological conditions, as discussed by Georgsson; see also Gudmundsson et al. and Franzson. Optimum development of these and other fields on the Reykjanes Peninsula, requires an understanding of their depletion behavior with time; that is, how the reservoir pressure falls with production. While recognizing that no two geothermal fields are alike, we also realize that an understanding of the depletion behavior of Svartsengi, for example, may prove useful in the development of other similar and nearby fields. The main purpose of this paper is to report our depletion analysis of the Svartsengi field using lumped-parameter and water influx modeling: we also report the field's production history.
Date: January 22, 1985
Creator: Gudmundsson, J.S. & Thorhallsson, O.S.
Partner: UNT Libraries Government Documents Department


Description: A break in electrical power generation from the Krafla geothermal plant was planned from beginning of May to early September 1984. Early in June most of the production wells were shutin and their pressure recovery monitored. A regular monitoring of the pressure buildup was carried out on a well to well basis until mid-August, when the wells were put back into production except for wells 12 and 16. They were used to monitor the pressure drawdown due to the start of production. This was abruptly brought to an end by a nearby volcanic eruption in early September. The pressure buildup in the two-phase geothermal reservoir at Krafla is described and the first results presented. The results are compared with parameters determined on the completion of the wells and with predictions from numerical simulations of the reservoir. Finally the status of the Krafla geothermal system is discussed with regard to the comparison.
Date: January 22, 1985
Creator: Sigurdsson, O.; Steingrimsson, B.S. & Stefansson, V.
Partner: UNT Libraries Government Documents Department

Timescales of spherulite crystallization in obsidian inferred from water concentration profiles

Description: We determined the kinetics of spherulite growth in obsidians from Krafla volcano, Iceland. We measured water concentration profiles around spherulites in obsidian by synchrotron Fourier transform infrared spectroscopy. The distribution of OH? groups surrounding spherulites decreases exponentially away from the spherulite-glass border, reflecting expulsion of water during crystallization of an anhydrous paragenesis (plagioclase + SiO2 + clinopyroxene + magnetite). This pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt. We modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary. Numerical models fit the natural data best when a small amount of post-growth diffusion is incorporated in the model. Comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size-dependent growth among a small population of spherulites.
Date: June 25, 2008
Creator: Castro, Jonathan M.; Beck, Pierre; Tuffen, Hugh; Nichols, Alexander R.L.; Dingwell, Donald B. & Martin, Michael C
Partner: UNT Libraries Government Documents Department

Reservoir engineering studies of small low-temperature hydrothermal systems in Iceland

Description: Geothermal energy provides more than one third of the energy consumed in Iceland. Its primary use is for space heating and most of the 28 public hitaveitur (district heating services) in Iceland utilize small low-temperature geothermal fields that have a natural heat output of only a few 100 kW{sub t} to a few MW{sub t}. All of these small reservoirs respond to production by declining pressure and some by declining temperature. During the 1980's the emphasis in geothermal research in Iceland shifted from exploration to reservoir engineering. The reservoir engineering work carried out concurrent with the exploitation of these small fields includes: testing of individual wells, field wide tests, monitoring the response of reservoirs to long-term production and simple modeling.
Date: January 1, 1991
Creator: Axelsson, Gudni
Partner: UNT Libraries Government Documents Department

Carbon dioxide, hydrographic, and chemical data obtained during the R/V Meteor Cruise 18/1 in the North Atlantic Ocean (WOCE Section A1E, September 1991)

Description: The North Atlantic Ocean is characterized by an intense meridional circulation cell carrying near-surface waters of tropical and subtropical origin northward and deep waters of arctic and subarctic origin southward. The related {open_quotes}overturning{close_quotes} is driven by the sinking of water masses at high latitudes. The overturning rate and thus the intensity of the meridional transports of mass, heat, and salt, is an important control parameter for the modeling of the ocean`s role in climate. The Research Vessel (R/V) Meteor Cruise 18/1 was one in a series of cruises in the North Atlantic that started in March 1991 and continued until 1995. This data documentation discusses the procedures and methods used to measure total carbon dioxide (TCO{sub 2}) and total alkalinity (TALK) at hydrographic stations, as well as underway partial pressure of CO{sub 2} (pCO{sub 2}) measured during the RIV Meteor Cruise 18/1 in the North Atlantic Ocean (Section A1E). Conducted as part of the World Ocean Circulation Experiment (WOCE) and the German North Atlantic Overturning Rate Determination expedition, the cruise began in Reykjavik, Iceland, on September 2, 1991, and ended after 24 days at sea in Hamburg, Germany, on September 25, 1991. WOCE Zonal Section AlE began at 60{degrees}N and 42{degrees}30{prime} W (southeast of Greenland) and continued southeast with a closely spaced series of hydrocasts to 52{degrees}20{prime} N and 14{degrees}15{prime} W (Porcupine Shelves). Measurements made along WOCE Section AlE included pressure, temperature, salinity, and oxygen measured by a conductivity, temperature and depth (CTD) sensor; bottle salinity; oxygen; phosphate; nitrate; nitrite; silicate; TCO{sub 2}; TALK; and underway pCO{sub 2}. A total of 61 CTD casts were made, including 59 bottle casts and 2 calibration stations.
Date: July 1, 1996
Creator: Johnson, K.M.; Wallace, D.W.R.; Schneider, B.; Mintrop, L. & Kozyr, A.
Partner: UNT Libraries Government Documents Department

Research on human genetics in Iceland. Progress report

Description: Records of the Icelandic Population are being used to investigate the possible inheritance of disabilities and diseases as well as other characters and the effect of environment on man. The progress report of research covers the period 1977 to 1980. The investigation was begun in 1965 by the Genetical Committee of the University of Iceland and the materials used are demographic records from the year 1840 to present and various medical information. The records are being computerized and linked together to make them effective for use in hereditary studies.
Date: October 31, 1980
Partner: UNT Libraries Government Documents Department

Progress report on research on human genetics in Iceland

Description: Records of the Icelandic population are being used to investigate the possible inheritance of disabilities and diseases as well as other characteristics and the effect of environment on man. The progress report of research covers the period from 1977 to 1980. The investigation was begun in 1965 by the Genetical Committee of the University of Iceland and the materials used are demographic records from the year 1840 to present and various medical information. The records are being computerized and linked together to make them effective for use in hereditary studies.
Date: October 31, 1980
Partner: UNT Libraries Government Documents Department

A summary of modeling studies of the Nesjavellir geothermal field, Iceland

Description: The Nesjavellir geothermal field in Iceland is being developed to provide the capital city of Reykjavik and surrounding areas with hot water for space heating. In the last few years, many wells have been drilled at the site and various geothermal studies have been conducted. The main upflow to the system is underneath the nearby Hengill volcano, and the natural recharge rate and enthalpy are estimated to be 65 kg/s and 1850 kJ/kg, respectively. An extensive vapor zone is believed to be present in the upflow region. Permeabilities and porosities of the system range between 1 and 50 md and 1 and 10 percent, respectively. In this paper, the characteristics of the Nesjavellir field are described and a three-dimensional numerical model of the resource in discussed. 15 refs., 11 figs., 1 tab.
Date: January 1, 1988
Creator: Bodvarsson, G.S.; Bjornsson, S.; Gunnarsson, A.; Gunnlaugsson, E.; Sigurdsson,, O. Stefansson, V. & Steingrimsson, B.
Partner: UNT Libraries Government Documents Department