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A published method for calculating excess steam is modified in order to make it applicable to the case of a well producing fluid with a high non-condensable gas content. The method is applied to data from a number of wells from Los Azufres. The results show the expected linear relation between excess steam and the molar fraction of CO{sub 2} in the total discharge. The modified method also provides an estimate for the molar fraction of CO{sub 2} in the liquid phase of the reservoir. It is found that this concentration is relatively homogeneous in the southern section of the field, and seems to be slightly smaller in the deeper zones of the northern section. The calculated values of excess steam agree qualitatively, but not quantitatively, with values of steam quality in the undisturbed reservoir calculated by other authors. The calculation of excess steam tends to overestimate steam quality in cases where steam saturation in the reservoir is low, and has the opposite tendency when the steam quality in the reservoir is high. The first type of deviation is explained in terms of the effects of higher mobility of steam in the two-phase zone induced by pressure drawdown. The second …

Starting from the basic laws of conservation of mass and energy, the differential equations that represent the thermodynamic behavior of a simplified geothermal reservoir are derived. Its application is limited to a reservoir of high permeability as it usually occurs in the central zone of a geothermal field. A very practical method to solve numerically the equations is presented, based on the direct use of the steam tables. The method, based in one general equation, is extended and illustrated with a numerical example to the case of segregated mass extraction, variable influx and heat exchange between rock and fluid. As it is explained, the method can be easily coupled to several influx models already developed somewhere else. The proposed model can become an important tool to solve practical problems, where like in Los Azufres Mexico, the geothermal field can be divided in an inner part where flashing occurs and an exterior field where storage of water plays the main role.

We have refined a method used previously by several authors to estimate water-steam relative permeabilities. Our version provides also reasonable estimates of the corresponding saturations. It relies on production output data obtained by means of short tests. This constitutes a distinct advantage over the previous variants, which require long-term production data, because it allows early accurate assessments of reservoir reserves and producibility. Applying the refined version to data from 5 Cerro Prleto wells we obtained the corresponding relative permeabilities. These results indicate that the relative permeabilities are remarkably homogeneous over a wide area of the field, and over a considerable fraction of the reservoir thickness. They also provide independent evidence that fracture flow is important in Cerro Prieto. Finally, comparison of our results with those found for Wairakei shows that the relative permeabilities of geothermal reservoirs can be sensitively site-dependent.

Turkey is classified among countries which have high geothermal energy potential. Geological and geophysical explorations are continuing in promising areas. However primary emphasis was given to Western Anatolia during the last decade. As a result of these efforts Kizildere field was developed and power plant was put into operation in February 14, 1984. This paper summarizes the power plant, production problems encountered in wells during the last nine months and future field development plans.

We have searched for the production of likesign dilepton events (nu/sub ..mu../ + Ne ..-->.. ..mu../sup -/ + e/sup -/ + ...) in a wideband neutrino beam at Fermilab using the 15-ft bubble chamber. We observe no signal above the background arising from conventional sources. We set 90% confidence level upper limits for the production rates of (nu/sub ..mu../ + Ne ..-->.. ..mu../sup -/ + e/sup -/ + ...)/ (nu/sub ..mu../ + Ne ..-->.. ..mu../sup -/ + ...) < 0.76 x 10/sup -4/ and (nu/sub ..mu../ + Ne ..-->.. ..mu../sup -/ + e/sup -/ + ...)/ (nu/sub ..mu../ + Ne ..-->.. ..mu../sup -/ + e/sup +/ + ...) < 5.3 x 10/sup -2/.

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We have devised a simple method to assess the natural thermodynamic state of two-phase reservoirs. This is usually a complex task. The method is based on inferring sandface flowing pressures and enthalpies from production output (deliverability) curves, and then extrapolating to shutin conditions in the pressure-enthalpy plane. The method was applied to data from 10 wells of the Los Azufres geothermal field. Comparison of the results with measured pressures and temperatures showed that the method is reliable. We present detailed thermodynamic properties of the unperturbed reservoir fluid in the neighborhood of the wells studied, in tabular form. Moreover, we present a match to these results with a very simple model that allows reasonable estimates of natural thermodynamic conditions as functions of height above sea level. The present results have important implications for the assessment of the fluid reserves, which are suggested to be greater than previously thought.

Downhole logging and workover operations on 12-20 year old wells in several high temperature, liquid-dominated geothermal fields in New Zealand has shown that severe corrosion has commonly occurred in the production casing string where this is unprotected by larger diameter casings. To date corrosion products from only one well have been examined in detail. These indicate that corrosion attack commences at the outer casing wall and continues at a rate as great as 0.8mm/year. Rapid corrosion has been attributed to neutral or slightly acid high bicarbonate waters formed by the absorption of steam and gas into shallow aquifers not directly connected to the deeper, high chloride reservoir.

This paper presents a transient pressure analysis method for analyzing the rate decline of a constant pressure well producing in an infinite double-porosity reservoir, without wellbore skin. This analysis method may be used to interpret well test rate data, and to compute the rate behavior of an infinitely acting reservoir that is being produced at constant pressure. The development of the pseudo steady state log-log type curve Is presented along with a hypothetical example of its use. This type curve allows the estimation of the two controlling parameters in double-porosity systems: {lambda} and {omega}. The first parameter, {lambda}, describes the interporosity flow, and the second parameter, {omega} describes the relative fracture storativity. This paper considers the estimation of these two parameters. The estimations of permeabilities and storativities have been described in the past, hence, are not considered. In a double-porosity system, with pseudo steady state interporosity flow, the initial infinite acting rate decline, representing only the fracture system, is followed by a constant rate flow period. The length of this constant rate flow period is controlled by the parameter {omega}. The beginning of this period is controlled by the interporosity flow parameter, {lambda}. Following this constant rate period, the rate …

This temperature-drop model is formulated as an answer to the question, ''How much further up the wellbore will a unit mass of fluid be when its temperature is exactly one-degree cooler than at its current position''. The repeated calculation yields a temperature profile extending upwardly from the bubble point. This approach is based on a paradigm that emphasizes temperature and volume for a system that is dominated by one component. It has only a small overlap with the more popular paradigm for this topic which involves mechanical pressures and energy balances. A set of plots is given which shows the effects on temperature and pressure profiles due to changes of single factors when all other factors are held constant. The factors include common wellbore and reservoir parameters. These latter plots give considerable insight into wellbore processes and the nature of constraints on two-phase flow for an essentially one-component substance.

Reinjection of waste hot water is commonly practiced in most geothermal fields, primarily as a means of disposal. Surface discharge of these waste waters is usually unacceptable due to the resulting thermal and chemical pollution. Although reinjection can help to main reservoir pressure and fluid volume, in some cases a decrease in reservoir productivity has been observed. This is caused by rapid flow of the reinjected water through fractures connecting the injector and producers. As a result, the water is not sufficiently heated by the reservoir rock, and a reduction in enthalpy of the produced fluids is seen. Tracer tests have proven to be valuable to reservoir engineers for the design of a successful reinjection program. By injecting a slug of tracer and studying the discharge of surrounding producing wells, an understanding of the fracture network within a reservoir can be provided. In order to quantify the results of a tracer test, a model that accurately describes the mechanisms of tracer transport is necessary. One such mechanism, dispersion, is like a smearing out of a tracer concentration due to the velocity gradients over the cross section of flow. If a dispersion coefficient can be determined from tracer test data, the …

Miravalles geothermal field lies in the Guanacaste province of Costa Rica in Central America. At the time of the study (late 1982), three wells (named PGM-1, PGM-2 and PGM-3), had been drilled and periodically tested in this field during 1980-82. During several of these tests scaling of the wellbore appeared to be a serious problem. This paper presents a portion of a study conducted to define the nature and causes of the scaling problem. No new data were gathered during this study; it was based on the analysis of already existing data as of late 1982. The main limitations in the data as regards this study were: (1) no bottomhole pressure measurements had been made; (2) no temperature or pressure profile under flowing condition was available from any well; (3) a wellhead separator was available at only one well (PGM-1); and (4) although James' lip pressure measurement facilities were available at all wells, in some of the earlier tests (up to May 1981) no measurement of the liquid flow rate was made. The fact that there was scale deposition in the Miravalles wells was indicated by several observations: (1) unusually rapid decline had been experienced in both flow rate and …

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The Geysers was discovered in 1847, and its therapeutic mineral baths were widely recognized by 1880. It was not until 1921, however, that the first steam well at The Geysers was drilled. Between 1922 and 1925, eight additional wells were drilled and tested as reported by Allen and Day. Development activity ceased until 1955 when Magma Power Company drilled the first ''commercial'' well. This success led to additional drilling in the Thermal Shallow Reservoir and the commissioning of a 12 MW power plant in September 1960, followed by a 14 MW power plant in February, 1963. This completed the commercial development of the Thermal shallow Reservoir.

The Pauzhetka hydrothermal system is located in a volcano-tectonic depression near active volcanic centers. Temperatures at depths of 300-800 m are 180-210 C. The natural discharge of the hydrothermal system includes the discharge of the Pauzhetka springs and a concealed discharge in the bed of the Pauzhetka River (95 kg/s) and the steam discharge in the Kambalny Ridge (15 kg/s). Only the upper part of geothermal reservoir was penetrated by drillholes (up to 1200 m), therefore they have used a mathematical modeling to assess the conditions of water and heat feeding of the hydrothermal system. The hydrothermal system belongs to a linear fracturing zone of NW trend, therefore the two-dimensional model was used in the calculations. It has been defined that (1) the source of heating is a magma chamber located at a shallow depth; (2) the heat and mass transfer in the geothermal reservoir is defined by free and forced hydraulic convection, (3) the conductivity coefficient of a linear fracturing zone is 400-600 m{sup 2}/day, its width is 2 km and length is 10 km, and (4) the water feeding is defined by infiltration in the recharge area. Calculations of temperature and velocity fields agree with real data obtained …

Geophysical data from surface measurements and downhole pressure/temperature data in northern Kyushu centered around Mount Waita are examined. The study area includes the geothermal fields supplying steam for the Hatchobaru and Ohtake power stations, but also extends a considerable distance to the northwest. Evidence from drilling logs, magnetotelluric surveys, lost-circulation horizons, downhole temperature surveys, and thermal and chemical properties of surface hot-spring discharge suggests the presence of a large geothermal reservoir north of the towns of Takenoyu and Hagenoyu.

The stabilities of several tracers were tested under geothermal conditions while injection-backflow tests were conducted at East Mesa. The tracers I and Br were injected continuously while SCN (thiocyanate), B, and disodium fluorescein were each injected as a point source (slug). The tracers were shown to be stable, except where the high concentrations used during slug injection induced adsorption of the slug tracers. However, adsorption of the slug tracers appeared to ''armor'' the formation against adsorption during subsequent tests. Precipitation behavior of calcite and silica as well as Na/K shifts during injection are also discussed.

The purpose of the study is to develop a simplified model to match past performances of a vapor-dominated geothermal reservoir and to predict future production rates and ultimate reserves. The data are fictitious, but are based on real data. A lumped parameter model was developed for the reservoir that is similar to the model developed by Brigham and Neri (1979, 1980) for the Gabbro zone, and a deliverability model was developed to predict the life and future producing rate declines of the reservoir. This report presents the development and results of this geothermal reservoir analysis.

Mokai is a recently-explored geothermal field in New Zealand. After drilling 6 wells, it is clear that there exists an extremely productive reservoir. The future exploration and development options are evaluated to find the most economic path to a developed resource. The basic tradeoff considered is between additional proving effort, and the consequent expense and, more importantly, delay. For fields of the generally very productive type found in New Zealand, comparatively little proving appears justified.

Analysis of an extended flow test of well ST-1 on the flanks of Makushin Volcano indicates an extensive, water-dominated, naturally fractured reservoir. The reservoir appears to be capable of delivering extremely large flows when tapped by full-size production wells. A productivity index in excess of 30,000 lb/hr/psi implies a phenomenal permeability-thickness product, in the range of 500,000 to 1,000,000 md-ft. The flowing bottomhole (1,949-foot) temperature of the fluid is 379 F, which is lower than the measured static temperature at that depth (395 F). This phenomenon, coupled with an observed static temperature gradient reversal from the maximum 399 F observed at 1,500 feet, indicates that the reservoir proper is located some distance from the well. presumably it is at a temperature slightly lower than 379 F and communicates with the wellbore via a high conductivity fracture system. A material balance calculation yields an estimate of reserves that are capable of sustaining all of the present power needs of the island (13 {+-} MW peak) with a geothermal power plant for several hundred years. Theoretically, a single large diameter well at the site of ST-1 could satisfy this requirement.

A large number of studies have been published in the past 10 to 12 years dealing with solute transport in fractured media. The vast majority of this work deals with solute transport in single fractures. Much of this work has been motivated by the need for a repository for storage of nuclear wastes that is safely sequestered from man and the environment. A number of papers deal with dual porosity aquifers, where fractures occur in a rock that also contains primary porosity. Usually, the permeability of the matrix blocks is considered insignificant relative to the permeability of the fracture system. The matrix blocks do not participate in fluid flow through the rock, but can be involved in heat transfer and solute retardation phenomena. Diffusive transfer between fractures and the rock matrix is the mechanism for heat transfer and retardation of solutes. None of the approaches deals with advective transport between fracture and matrix. Solute transport in the fracture is either by advection alone or by advection and dispersion based on a one dimensional solution to the advection-dispersion equation. Research at EG and G is currently oriented at perfecting techniques for simulation of this type of dual permeability fracture system. Simulation …

We present an analysis of the slug test in a well surrounded by an annulus of altered material, which is treated as a skin of finite thickness. By assuming the skin has a thickness, the storage capacity of the altered material is included in the analysis. The problem is solved in the Laplace domain. The solution is found in terms of well-bore storage and the thickness, hydraulic conductivity, and specific storage of the skin. Type curves are generated by numerical inversion of the Laplace transform solution. We find that standard methods of analysis, involving a skin of infinitesimal thickness, are adequate for open-well or drill-stem tests. However, for pressurized tests the response may differ markedly from standard slug-test solutions.