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Reinjection into geothermal reservoirs

Description: Reinjection of geothermal wastewater is practiced as a means of disposal and for reservoir pressure support. Various aspects of reinjection are discussed, both in terms of theoretical studies as well as specific field examples. The discussion focuses on the major effects of reinjection, including pressure maintenance and chemical and thermal effects. (ACR)
Date: August 1, 1987
Creator: Bodvarsson, G.S. & Stefansson, V.
Partner: UNT Libraries Government Documents Department

THE NESJAVELLIR HIGH TEMPERATURE GEOTHERMAL FIELD IN ICELAND

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

Analysis of production data from the Krafla geothermal field, Iceland

Description: The analysis of flow rate and enthalpy data from several wells completed in the same two-phase zone of Krafla geothermal reservoir has yielded consistent relative permeability parameters. It is found that k/sub rl/ + k/sub rv/ = 1 over the entire range of two-phase flow conditions from immobile liquid to immobile vapor. The available data provide relative permeability parameters as a function of flowing enthalpy only. The relationship between flowing enthalpy and in-place vapor saturation remains unknown, so that the relative permeability information obtained is of limited value for quantitative modeling of geothermal reservoir performance. Numerical simulation of flow rate and enthalpy transients has yielded excellent matches to production data from well 12. However, there is little information about the reservoir which can be deduced in an unambiguous way, because the field data could be matched with a variety of rather different parameter choices. The only unambiguous piece of information obtained is that the water injected into the well during drilling and completion remains in the vicinity of the wellbore during several weeks of warmup.
Date: December 1, 1983
Creator: Pruess, K.; Bodvarsson, G. S. & Stefansson, V.
Partner: UNT Libraries Government Documents Department

Summary of modeling studies of the Krafla geothermal field, Iceland

Description: A comprehensive modeling study of the Krafla geothermal field in Iceland has been carried out. The study consists of four tasks: the analysis of well test data, modeling of the natural state of the field, the determination of the generating capability of the field, and modeling of well performance. The results of all four tasks are consistent with field observations.
Date: August 1, 1983
Creator: Bodvarsson, G. S.; Pruess, K.; Stefansson, V. & Eliasson, E. T.
Partner: UNT Libraries Government Documents Department

Modeling studies of the natural state of the Krafla geothermal field, Iceland

Description: The modeling of the natural state of the Krafla system has yielded results that closely match all available field data, and agree with a conceptual model developed from geochemical observations. Furthermore, studies of the sensitivity of various parameters give valuable insight into the permeabilities of different reservoir zones, thermal conductivity of the caprock, rates and enthalpies of natural recharge and discharge, and various other important reservoir parameters. The model presented here is two-dimensional, and only considers a part of the old wellfield. In the future, we hope to develop a natural-state model for the entire Krafla system, taking into account the three-dimensional nature of fluid flows.
Date: December 1, 1982
Creator: Bodvarsson, G.S.; Pruess, K.; Stefansson, V. & Eliasson, E.T.
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

Accuracy of reservoir predictions for the Nesjavellir geothermal field, IC

Description: The performance of the 1986 three-dimensional numerical model of the Nesjavellir geothermal field for predicting the deliverabilities and pressure decline of the wells during the period 1987 through 1991 is investigated. The model predicted adequately the flow rate and enthalpy transients of most wells, but overpredicted the pressure decline by 3 to 4 bars.
Date: January 28, 1993
Creator: Bodvarsson, G. S.; Gislason, G.; Gunnlaugsson, E.; Sigurdsson, O.; Stefansson, V. & Steingrimsson
Partner: UNT Libraries Government Documents Department

PRESSURE BUILDUP MONITORING OF THE KRAFLA GEOTHERMAL FIELD, ICELAND

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

Summary of modeling studies of the East Olkaria geothermal field, Kenya

Description: A detailed three-dimensional well-by-well model of the East Olkaria geothermal field in Kenya has been developed. The model matches reasonably well the flow rate and enthalpy data from all wells, as well as the overall pressure decline in the reservoir. The model is used to predict the generating capacity of the field, well decline, enthalpy behavior, the number of make-up wells needed and the effects of injection on well performance and overall reservoir depletion. 26 refs., 10 figs.
Date: March 1, 1985
Creator: Bodvarsson, G.S.; Pruess, K.; Stefansson, V.; Bjornsson, S. & Ojiambo, S.B.
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

Geothermal Field Developments in Iceland

Description: The exploration and research carried out in conjunction with the exploitation of the various geothernal fields has vastly deepened our understanding of the hydrothermal systems in Inceland. They have proved to be more diverse with respect to physical state, chemical composition, hydrological properties, and geological control than previously thought. The purpose of the present paper is to review the present state of knowledge regarding the Icelandic geothermal systems, with emphasis on the production and reservoir engineering aspects.
Date: December 15, 1983
Creator: Palmason, G.; Stefansson, V.; Thorhallsson, S. & Thorsteinsson, T.
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 is discussed.
Date: January 1, 1988
Creator: Bodvarsson, G.S.; Bjornsson, S.; Gunnarsson, A.; Gunnlaugsson, E.; Sigurdsson, O.; Stefansson, V. et al.
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