Halldór Ármannsson

Environmental aspects of geothermal energy utilization

Geothermal energy is a clean and sustainable energy source, but its development still has some impact on the environment. The positive and negative aspects of this environmental impact have to be considered prior to any decision to develop a geothermal field, as well as possible mitigation measures. The main environmental effects of geothermal development are related to surface disturbances, the physical effects of fluid withdrawal, heat effects and discharge of chemicals. All these factors will affect the biological environment as well. As with all industrial activities, there are also some social and economic effects. In Iceland an enforcement program was launched in the early 1990s to study the environmental impact of developing geothermal resources. Work began on tackling the environmental issues relative to the high-temperature geothermal fields under development in Iceland. Research was conducted on microearthquake activity in geothermal areas and a methodology developed for mapping steam caps. The foundations were laid of networks for monitoring land elevation and gravity changes. Baseline values were defined for the concentrations of mercury and sulfur gases. Groundwater monitoring studies were enforced. Atmospheric dispersion and reaction of geothermally-emitted sulfur gases and mercury were studied. Aerial thermographic survey methods were refined and tested and their capacity to detect and map changes in surface manifestations with time was demonstrated. To further the use of geothermal energy worldwide the International Energy Association set up a Geothermal Implement Agreement (GIA) in 1997; its environmental Annex has been actively implemented, with several projects still under way.

Fluid/mineral equilibrium calculations for geothermal fluids and chemical geothermometry

Abstract Aquifer temperatures of 13 geothermal wells in Iceland whose measured reservoir temperatures range from 47 to 325°C have been estimated from the chemical composition of the discharged fluid by considering simultaneously temperature dependent equilibria between many mineral phases and the solution. This approach to chemical geothermometry was initially proposed by Reed and Spycher [(1984) Geochim. cosmochim. Acta48, 1479–1492]. Its advantage over individual solute geothermometers such as the silica and the Na—K and Na—K—Ca geothermometers is that it allows a distinction to be made between equilibrated and non-equilibrated waters. However, care should be taken in interpreting the results of multi-mineral/solute equilibria as the results depend on both the thermodynamic data base used for mineral solubilities and the activities of end-member minerals in solid solutions. When using old analytical data attention has to be paid to analytical methods, especially in the case of important constituents present at low concentrations in the fluid, such as aluminium, for which analytical results obtained by two methods yielded very different equilibrium temperatures. The results for selected wells in Iceland, presented here, indicate that the geothermometry results are with few exceptions within 20°C of measured aquifer temperatures, and within 10°C for about half the wells considered. The method responds rapidly to changes such as cooling or mixing.

Geothermal environmental impact

Abstract Geothermal utilization can cause surface disturbances, physical effects due to fluid withdrawal, noise, thermal effects and emission of chemicals as well as affect the communities concerned socially and economically. The environmental impact can be minimized by multiple use of the energy source and the reinjection of spent fluids. The emission of greenhouse gases to the atmosphere can be substantially reduced by substituting geothermal energy for fossil fuels as an industrial energy source wherever possible.

Gas changes in the Krafla geothermal system, Iceland

Abstract A massive influx of gas was encountered in the Krafla geothermal system, Iceland, following the start of magmatic activity in the area in 1975. The gas was of magmatic origin, but its composition had been modified to predominantly carbon dioxide and a small amount of hydrogen sulphide. The gas concentrations of Krafla borehole fluids have been monitored since, and the pattern has been similar for wells in the affected Leirbotnar field, i.e. a maximum in 1977/1978, a secondary maximum in 1980 and a steady decline since. The more southerly Suđurhliđar and Hvitholar fields were not affected. Fumaroles were sampled extensively in 1978/1979 and 1984/1985. A similar decline was observed in the affected area, but a geographical trend that had been noticed for the borehole fluids was much clearer in this case. The decline is smallest in the northeastern part of the field, but more pronounced to the south and west. It is suggested that magmatic gas has not entered the geothermal system after 1980 and that the excess gas observed now comes from a supply located in the northeastern part of the field near the explosive crater, Viti.

Environmental Impact of the Utilization of Geothermal Areas

Turkey is one of the fastest growing power markets in the world and is facing an ever-increasing demand for power in the coming decades. Geothermal is one of its important renewable energy sources; Turkey is rated the 7th country in the world in terms of geothermal potential. The countrys installed capacity is 992 MWt for direct use and 20.4 MWe for power production. These are expected to almost triple in the next ten years and more than quadruple in the next twenty years. Geothermal energy is generally accepted as being an environmentally benign energy source. Geothermal development over the last forty years in Turkey has shown that it is not completely free of impacts on the environment. Environmental impacts are projected to limit the use of this needed energy resource. Geothermal waters of Turkey are highly mineralized with elevated levels of arsenic (As), boron (B), cadmium (Cd), and lead (Pb), resulting in scaling and corrosion. Because they are not reinjected, geothermal discharges also result in an observed contamination of soil and waterways. Reinjection is recommended to be installed as a standard procedure to avoid these adverse impacts.

Groundwater in the Lake Myvatn area, northern Iceland: Chemistry, origin and interaction

Lake Myvatn, northern Iceland is unique in that almost all the inflow is supplied through the groundwater by artesian springs. Hardly any surface water is encountered in the area which is covered by young and porous lava fields and transected by faults. The inflow of water and its chemical composition is, therefore, very stable. Geothermal and volcanic activities affect the groundwater system in the Lake Myvatn area and greatly influence the lakes chemistry and thus the biological conditions especially by providing continuous and ample sources of silica and sulphate. Groundwater studies have been intensified in the area during the last years for further developing the Námafjall geothermal field in the area and the Krafla geothermal field about 10 km from Námafjall. Groundwater chemistry was monitored regularly for 2 years at 22 sampling sites and for determining selected indicator constituents in the samples. Concurrently, several tracer tests were performed in the area, the rate of groundwater flow measured, a reservoir model of the groundwater system established. These studies enabled us to divide cold groundwater and geothermal effluent in the Lake Myvatn area into six distinct groups, based on stable isotope ratios, chemical composition and geographical position. The groundwater has separate origins in the local high ground north of Lake Myvatn and the highlands far to the south, possibly as far south as the glacier Vatnajökull. The waters are to a different extent affected by geothermal activity, and effects of volcanic activity were noted during the Krafla fires in 1975–1984. Although these have diminished, they have not completely disappeared. The effluent from Krafla seems to travel to the east of Lake Myvatn and traces of it have not been found to enter the lake. The Námafjall effluent on the other hand travels along fissures to the lake. Attempts made to simulate the evolution of the geothermal water of Krafla and by theoretically titrating local groundwater with rock at elevated temperatures and adding volcanic gas seem promising and result in a composition close to the natural one.

Sulfur gas emissions from geothermal power plants in Iceland

Abstract Sulfur gas (H 2 S and SO 2 ) emissions from geothermal fields in Iceland have been studied as part of a project, aimed at enhancing environmental research concerning effects of geothermal development. Short-term measurements of the gases have been carried out in several high-temperature geothermal fields in Iceland. In four exploited fields, baseline values for the concentration of sulfur gases have been obtained by long-term measurements. The data strongly reflect the dependence of gas concentrations on climatic factors, especially precipitation. Interpretation of the data by air distribution modeling, and by simple experiment, indicate minor, or at least very slow conversion of H 2 S to SO 2 at atmospheric conditions in Iceland.

Surface exploration of the Theistareykir high-temperature geothermal area, Iceland, with special reference to the application of geochemical methods

Abstract The surface exploration of the Theistareykir high-temperature geothermal area in northeast Iceland is reported. The results of stable isotope and Cl determinations are used to characterise the origin of the fluid, gas geothermometers to indicate underground flow temperatures, and major gas ratios. Rn, and Hg concentrations to infer permeability, boiling conditions, upflow locations, and flow directions. These results are used in conjunction with geological and geophysical studies to construct a model of the geothermal system, whose main features are upflow zones under the northeast and southwest parts of the geothermally active surface area, with a cooler zone between, which could result from poorer permeability and additional cooler inflow. A suggestion is made as to the siting of the first exploratory well in the Tjarnaras area close to the southwesterly upflow area.

Gas geothermometry in selected icelandic geothermal fields with comparative examples from Kenya

Abstract Using data from selected geothermal fields in Iceland, several gas geothermometers are applied to calculate reservoir temperatures. Results for well fluids are compared to estimated inflow temperatures. The effects of gases from other sources, e.g. magmatic fluid entering reservoirs, condensation/boiling, loss of components and mixing of different fluids during upflow, are discussed. Those geothermometers that give results reasonably close to the inflow temperatures, and are not constrained by the need to know thermodynamic parameters, are used to estimate subsurface temperatures from fumarole steam composition. It is suggested that geothermometers based on H 2 and H 2 S concentrations are relatively effective. The CO 2 , H 2 S and H 2 geothermometers are also evaluated by thermodynamic simulation using plausible mineral buffers. The CO 2 geothermometer generally gives slightly low temperatures for values in the range 100–200°C. The calibration of the existing H 2 S and H 2 geothermometers needs improvement when reservoir temperatures are higher than 220°C. The mineral buffer controlling H 2 S in reservoirs seems to be pyrite + magnetite + epidote + prehnite changing into pyrite + pyrrhotite + epidote + prehnite with increasing temperature.

Chemical monitoring of Icelandic geothermal fields during production

Abstract The long-term exploitation of a geothermal field will, in most cases, cause pressure drop or drawdown in the system, creating a potential for cold-water inflow. The system may suffer subsequent cooling or changes in production characteristics. Chemical changes in geothermal fluids are often precursors of cooling, and chemical monitoring may thus give warning in time for preventive action. Monitoring programs have therefore been developed for different types of geothermal fields. The effectiveness of many of these has been demonstrated in both high-temperature and low-temperature geothermal exploitation.