[en] This paper reports that the maximum amount of subsidence at Wairakei Field due to fluid withdrawal reached 11.6 m during 1989. The maximum subsidence rate has decreased from 450 mm/y during the 1970s, to 350 mm/y during the late 1980s. Although the subsidence has caused a pond to form along a 1 km length of the Wairakei Stream passing through the center of subsidence, there has been remarkably little damage to structures around the borefield due to associated horizontal strains. Modelling of the subsidence suggests it originates from a compaction zone of about 150 m depth. This coincides with a pumice breccia unit sandwiched between lacustrine mudstone units. The rate of compaction appears to be controlled by the rate of steam pressure decline near the top of the reservoir. Modelled compressibilities of 10 kbar^-1 are consistent with measurement on pumice breccias. Hydrothermal alteration near the original outflow zone of the field may have contributed to the location of the high compressibility zone

[en] A method was developed to enhance geothermal steam production from two-phase wells at THE Geysers Geothermal Field. The beneficial result was increased geothermal production that was easily and economically delivered to the power plant

[en] In summary, assuming that conventional criteria are fulfilled for a plant location at a geothermal field, then the following aspects should receive primary consideration: (a) Is the process energy intensive? (b) Is energy price a significant fraction of the product price? (c) Can it be adapted to geothermal steam? (d) What are the necessary process modifications? (e) What do they cost? (f)What is the cost of the steam when the steam supply system has been optimized in conjunction with the plant heat exchanger system? (g) Do the increased transport costs of raw materials to the site, and the product to market, do more than outweigh the advantages of low energy costs? The paper describes and illustrates ways to optimize these systems and illustrates what is the best potential system based on the temperature and amount of geothermal energy available

[en] The paper presents some new concepts of hydrogen production in Iceland for domestic use and export. A brief overview of the Icelandic energy consumption and available resources is given. The cost of producing hydrogen by electrolysis is calculated for various alternatives such as plant size, load factors and electricity cost. Comparison is made between the total cost of liquid hydrogen delivered to Europe from Iceland and from Northern America, showing that liquid hydrogen delivered to Europe from Iceland would be 9% less expensive. This assumes conventional technology. New technologies are suggested in the paper and different scenarios for geothermally assisted hydrogen production and liquefaction are discussed. It is estimated that the use of geothermal steam would lead to 19% lower hydrogen gas production costs. By analysing the Icelandic fishing fleet, a very large consumer of imported fuel, it is argued that a transition of fuel technology from oil to hydrogen may be a feasible future option for Iceland and a testing ground for changing fuel technology. (Author)

[en] A model is presented for evaluation of the most important factors influencing the siting of industrial plants using significant amounts of geothermal steam and electric power. A comparison is made of the operating conditions at the geothermal field and by transporting the steam for 10-30 km via a pipeline to a harbor site. Results based on the evaluation of up to 40 separate plants, are analyzed in view of optimum operating conditions

[en] During the last decade various steam consuming industrial processes have been studied at IceTec. The prerequisite for the studies was the potential and available cheap steam from high temperature geothermal wells. Steam prices in the early eighties were estimated in the range of 1.5 - 3.0 USD/t steam, based on transport distance and well productivity, giving geothermal steam an advantage of 10 - 12 USD/t steam, compared to steam fired boilers. Additionally at that time, changes were seen in the industry such as feedstock shortages, higher energy cost and more stringent pollution requirements. Different processes have been studied, having steam consumption from 4-110 ton steam per ton product. Most of these processes are based on hydrothermal technology, either leaching and/or precipitation. The steam consuming process steps are digestion, evaporation, hydrolysis, drying, distillation etc. Based on prices at the time of study, the savings were estimated to be up to one fifth of the production cost. Geothermal steam is a very localized energy source, which consequently restricts the sitting of new industrial plants. Despite apparent cost benefits, the direct use of geothermal steam in industry, is growing very slowly

[en] The authors present the results of the modeling of a 3-D differential attenuation structure (Q) beneath the Northwest Geysers geothermal field. A set of 480 high-quality microearthquakes distributed evenly throughout the field and with a minimum of 10 P-wave arrivals was selected for the study. They constructed spectral ratios by dividing each spectrum with a reference spectrum from each observing station. The reference spectrum was derived from the average spectrum of all events that were recorded at that station to correct for the strong site dependence of the observed spectra. They then estimated the differential attenuation operator from the slopes of the spectral ratios. The velocity models and the raypaths for all events are known from a previous velocity inversion study. The inversion for the differential attenuation structure was carried out using a modified progressive inversion method. The observed Q structure correlates well with mapped geologic units. High Q and lower velocities correlate with Franciscan melange, while lower attenuation and higher velocities correspond to metagraywacke units. High P-wave Q also underlies the southern region between 2 and 3 km depth where low V_p/V_s values suggest undersaturation of the reservoir rocks. Most of the steam entries also occur within this region and probably delineate the steam reservoir. These anomalies may be explained by high rock temperatures and the presence of steam and other gases

[en] This paper gives a short description of Kisilidjan hf. (The Icelandic Diatomite Plant, Ltd.), a description of the production, the use of geothermal steam in the plant, steam supply, steam use, steam price, experience associated with the use of steam, and some conclusions

[en] Many areas of the world exist where high temperature isotherms supported by heat flow from the core of the earth occur very close to the surface of the earth. Commercial exploitation of these sources of energy has only recently become practical and is limited to those areas where a natural system of fracture acts to collect heat from a large volume of rock and sufficient natural water is available to act as a heat transfer agent. Recent studies have indicated many more areas of geothermal heat are available than had been identified previously. The nuclear application envisages the creation of a chimney and associated fracture system with a nuclear explosion, introduction of water into the chimney-fracture system, and removal of superheated steam for the generation of electrical power. Three phenomena are considered: utilization of the heat content of the rock in the chimney and fracture zone; heat flow from the surrounding medium to the fracture zone or chimney by conductivity; and interconnection of a preexisting network of fracture by the highly permeable chimney and fracture zone. A 1-Mt example is examined showing that over 10⁹ kWh are available in the chimney, and over 10¹⁰ kWh in the central portion of the fracture zone. Using the current commercial value of 2 mills/kWh for such steam, the above heat has a worth of over S30,000,000. In addition, heat flow into the fracture zone would represent over $1 million per year additional value. Interconnection of fractures drawing heat from far removed volumes would be very site-dependent and difficult to estimate, and have not been included. Use of an array would permit circulation between chimneys with the resultant utilization of the heat energy contained in the intervening volume. Ground shock associated with such an application would probably require development of a 30 to 50 year supply before the power plant is constructed. Radiological safety problems would be confined to operation of the power plant. (author)

[en] This book is designed as an instructional manual of essential nuclear and complementary methodologies for a multidisciplinary approach to geothermal exploration development and monitoring. It provides comprehensive procedures for carrying out isotope and geochemical investigations of geothermal systems. It focuses on the three stages of geothermal studies of geothermal fluids, i.e. sampling, analysis and data interpretation. Specific chapters of the book provide some background information on the generally adopted strategy and on the behaviour of chemical and isotopic components in the geothermal environment; deal with the nature of surface thermal manifestations and sampling techniques; present analytical data handling and presentation; and concentrate on data interpretation