The nestos delta geothermal field and its relation to the associated self potential (sp) field

Prospecting for geothermal reservoirs by geophysical methods has proved to be a challenge in recent years. In the case of Nestos geothermal field, considered to be a blind field (no surface manifestation), the geological and geophysical data were studied and intercorrelated. The geophysical results from SP, gravity, and VES data were compared with basement morphology and tectonics, as well as with the high temperatures measured in the area of main geothermal interest. As a result, the highly conductive subsurface zone and high temperatures observed on the ground surface were closely associated with a specific fracturing system. The latter was successfully mapped by the SP method. The SP method also defined certain fracture zones which, being highly electrically polarized, are hypothesized as future geothermal targets.All existing geophysical data have been re-evaluated, along with the SP data acquired over the geothermal field, and compared with the thermal contour maps and regional tectonics of the area.A deep borehole, drilled earlier in the area of the geothermal field, detected high temperatures in the basement (115°C), but very low flowrate of the geothermal fluids. According to the results of this study, this is due to the fact that the borehole was located outside the area of the main fracture zones of geothermal interest.     

First results of the application of the dipole electrical sounding method in the geothermal area of travale - radicondoli (Tuscany)

A new geoelectric prospecting method has been tested in the Travale - Radicondoli geothermal area. This method is based on the dipolar technique that permits investigation at very great depths with much fewer problems than encountered when using the classical electric prospecting techniques.The following steps were taken in order to operate with relatively low power from a 2 kW generator:

1. (i) the ground was energized with a series of current square waves at a frequency of less than 0.05 Hz in order to avoid the effects of electromagnetic coupling and induced polarization;

2. (ii) the voltage was recorded digitally at the measuring dipole;

3. (iii) the voltage recordings were processed by the spectral analysis method of “maximum likelihood”.

The resulting apparent resistivity diagrams were transformed into Schlumberger diagrams and then interpreted quantitatively.The six soundings are too limited in number to represent a real prospecting but refer to different geological and structural situations typical of a geothermal area. Two electrosoundings were sited for this purpose so as to be directly calibrated by the wells in the local geothermal field. The quantitative analysis of the resistivity diagrams in particular revealed the low resistivity values of the carbonate formation forming the geothermal reservoir, where the hot fluid circulation is particularly strong (15 Ω.m).The dipolar method has proved capable of distinguishing, in the geological situation of Travale area, the various structural features of the geothermal field such as “cover”, “reservoir”. substratum, uplifted structures and tectonic depressions.     

Seismic noise measurements in the Mt. Amiata geothermal area, Italy

A seismic noise study has been carried out on the well-known Mt. Amiata geothermal area; the aim of this work is to understand the correlation between the geothermal system and seismic noise characteristics. The power spectra of the recorded noise show that in the whole geothermal area a low frequency noise (3 Hz) is predominant. The fitting of the results with a pressure variation source model shows contradictory results.     

A study on the optimized control strategies of geothermal heat pump system and absorption chiller‐heater

The world is becoming increasingly interested in renewable energy including geothermal energy. The utilization of geothermal systems is currently low because geothermal systems and existing source systems are used independently, but the supply rate of a geothermal system is increasing. Therefore, suggesting efficient operation plans and evaluations of the energy consumption and efficiency of a geothermal system is needed. This paper reports the results of a field study and survey of the present applications and operation conditions of a geothermal system. In addition, this paper proposes an efficient operation strategy for a geothermal system and compares this operation strategy with an existing operation strategy through simulation. The problems of existing operation condition were found out through a field study, and alternatives were proposed. The improvements were evaluated using the transient systems simulation program. And it would be possible for the reduction of the energy consumption through the comparative analysis of equipment efficiency and energy consumption. The result of analyzing the proposed combination header method through simulations compared with existing operation conditions can increase the use of geothermal systems, but the combined cooling and hot water of a geothermal heat pump and existing thermal source system reduced the efficiency of the heat pump. As a result of simulation on individual load‐sharing method, efficiency of geothermal system is increasing compared with the combination header method. This method was especially made to separate geothermal system's water loop and existing thermal source system's water loop. Copyright © 2013 John Wiley & Sons, Ltd.     

Cold groundwater temperatures and conductive heat flow in the Mt. Amiata geothermal area, Tuscany, Italy

The hydrogeochemical study of the cold springs present in the Mt. Amiata geothermal area, where the Bagnore and Piancastagnaio geothermal fields are situated, has defined the different shallow groundwater systems.The cold groundwater temperature of the volcanic phreatic aquifer is largely correlated with the geothermal heat flow. Through the analysis of the temperature of cold groundwaters, a possible method for geothermal prospection has been developed, supported by the results obtained in the studied area. Through the enthalpic balance of the aquifer and in agreement with available data, a geothermal flow of about 200 mW m^-2 has been calculated.     

Electrical conductivity studies in the Travale geothermal field, Italy

Magnetotelluric and geomagnetic depth soundings have been carried out in the area of the Travale high enthalpy geothermal field (central Tuscany, Italy) in 1980 and 1981 to study the distribution of electrical conductivity in the geothermal anomaly and the crust beneath. Within this project the possible contributions of electromagnetic investigations to geothermal research were to be tested and a geothermal model of the Travale area was to be developed. The time-varying electric and magnetic fields have been recorded in a broad period range from 6–10,000 s, mainly on two profiles, the one parallel, the other perpendicular to the Travale graben. Strong lateral variations of apparent resistivities have been observed. Up to periods of 50–100 s the Travale graben is the dominating 2-D structure, but for longer periods of investigation the three-dimensionality of electrical conductivity structures has to be considered. The apparent resistivities inside the geothermal anomaly are extremely low, reaching not more than 50 ohm · m, even in the lower crust, but they increase to 100–300 ohm · m north of the geothermal field. Total conductance also indicates the geothermal field as a local conductivity anomaly, whereas further to the north the poorly conducting “barrier” has been confirmed. The cause of the high conductivity structures inside the geothermal area is to be seen in a highly fractured basement within this zone, allowing upward movement of hydrothermal fluids.     

Geothermal energy utilization trends from a technological paradigm perspective

The use of geothermal energy and its associated technologies has been increasing worldwide. However, there has been little paradigmatic research conducted in this area. This paper proposes a systematic methodology to research the development trends for the sustainable development of geothermal energy. A novel data analysis system was created to research the geothermal energy utilization trends, and a technological paradigm theory was adopted to explain the technological changes. A diffusion velocity model was used to simulate and forecast the geothermal power generation development in the diffusion phase. Simulation results showed that the development of installed capacity for geothermal generation had a strong inertia force along with the S-curve. Power generation from geothermal power sources reached a peak in 2008 and is estimated to be saturated by 2030. Geothermal energy technologies in hybrid power systems based on other renewable energy sources look to be more promising in the future.     

The geothermal system of Ischia Island (southern Italy): Critical review and sustainability analysis of geothermal resource for electricity generation

In this paper we analyze the main available data related to the geothermal system of Ischia Island, starting from the first geothermal exploration in 1939. Our aim is to define a conceptual model of the geothermal reservoir, according to geological, geochemical, geophysical and stratigraphic data. In recent times, the interest on geothermal exploitation for electricity generation in Italy is rapidly increasing and the Ischia Island is one of the main targets for future geothermal exploitation. Nowadays, one of the main economic resources of the island is the tourism, mainly driven by the famous thermal springs; so, it is crucial to study the possible interaction between geothermal exploitation and thermal spring activities. To this aim, we also analyze the possible disturbance on temperature and pressure in the shallow geothermal reservoir, due to the heat withdrawal for electric production related to small power plant size (1–5 MWe). Such analysis has been performed by using numerical simulations based on a well known thermofluid-dynamical code (TOUGH2^®). Obtained results show that such geothermal exploitation generates a perturbation of temperature and pressure field which, however, is confined in a small volume around the well. At shallow level (0–100 m) the exploitation does not produce any appreciable disturbance, and can be made compatible with thermal spring exploitation. Moreover, such results are crucial both for the evaluation of volcanological processes in the island and for the general assessment of geothermal resource sustainability.     

Exploring public engagement with geothermal energy in southern Italy: A case study

This paper presents the results of an assessment of public views on eventual geothermal energy development in Sicily. The research was carried out under a much wider research project, VIGOR, with the aim to explore the feasibility of geothermal energy utilization in southern Italy. This study has two primary objectives: (1) to explore the views and opinions of local communities regarding the potential of geothermal energy applications; (2) to contribute to the growing literature on public engagement with energy issues. In order to explore public views towards geothermal technologies, we conducted a case study using both qualitative and quantitative methods. Although Italy has enormous geological potential for geothermal energy production, levels of knowledge of this energy source amongst the public are low. The results indicate that the issue is shrouded in uncertainty and that the Sicilian public expresses a diffused lack of trust in decision-making processes. Taken together, these factors are likely to strongly impact eventual further developments in this sector. The results clearly show the need for further societal dialogue supported by a sound communication action strategy as the first stage in a public participation.     

The application of the Na-K-Ca geothermometer to thermal areas of Utah and the imperial valley,California

The sodium (Na), potassium (K), calcium (Ca) geothermometer is discussed as a tool for locating and evaluating areas prospectively valuable for geothermal development. Presented is a regional analysis of the major thermal springs of Utah to demonstrate the use of the Na-K-Ca geothermometer as a rapid and meaningful method of geothermal reconnaissance. Of the thermal areas of Utah, Roosevelt Hot Springs show the greatest geothermal potential where estimated temperatures are nearly 300 °C. This compares favorably with estimated and measured temperatures from proven geothermal fields such as Cerro Prieto in Mexico and the Salton Sea field of California. Also presented are more detailed studies of LaVerkin Ho¹ Springs and Wilson Hot Springs, Utah, and the Mesa anomaly, Imperial Valley, California. These studies examine the accuracy and precision of the Na-K-Ca geothermometer and the physical conditions under which it can be reliably used to predict subsurface temperatures. It is shown that in the saline environment of the Imperial Valley, it should be possible to obtain useful information even though the results might normally be considered suspect due to concentration or dilution of the analyzed samples.     

Flashing point compressibility of geothermal fluids with low CO2 content and its use in estimating reservoir volume

In this study, the bubble point pressure effect or, as it is more commonly known, the flashing point effect of CO₂ on geothermal fluids is shown, and the compressibility of the geothermal fluids containing low concentrations of dissolved CO₂ at the flashing point is formulated for isoenthalpic phase change. The compressibility, termed the isoenthalpic flashing point compressibility, can be calculated with well-known parameters. New, easy-to-use graphs are presented to estimate the compressibility for such systems. Correction for ionic strength of the geothermal brine is also considered. The practical use of the compressibility is illustrated to estimate the fluid content of a geothermal reservoir. A material balance method incorporating the isoenthalpic flashing point compressibility in geothermal modeling is investigated. The material balance method presented in the paper is of primary importance in the evaluation of geothermal reservoirs since both the areal extent and the vertical thickness can not be accurately determined, particularly in the initial development stages of the reservoirs. Applications of the method to geothermal fields are discussed.     

水热型地热资源地球化学勘探技术研究进展

地球化学勘探技术在水热型地热资源勘探中的应用研究具有较长的历史,迄今已形成了一套基于气体与元素指标的勘探技术体系,涵盖了众多技术指标,且已在世界各地诸多地热田勘探研究中获得了广泛应用。结果揭示,在预测地热田发育有利部位、估算深部热储温度以及推断地热水来源等方面,地球化学勘探技术都可发挥其特有的作用,是一种经济有效的地热勘探技术,具有良好的应用前景。但地热地球化学勘探技术也面临其自身的局限性,其应用研究不仅受地热田类型的限制,而且目前主要集中于已知地热田上方的验证性研究,技术本身的多解性也较强。因此,在地热地球化学勘探技术完善与应用研究方面,还有待进一步深化。     

Preliminary evaluation of soufriere geothermal field, St. Lucia (Lesser antilles)

Geological, geochemical and geophysical studies have been carried out in the Soufrière caldera, St. Lucia, Lesser Antilles. The results are in accordance with the data obtained from previously drilled wells. In particular, these studies have also been used to: (i) determine the extent of the heat anomaly; (ii) indicate the levels containing hot geothermal fluids for high enthalpy exploitation; (iii) estimate the nature and extent of the reservoir; (iv) construct a preliminary model of the geothermal system, with a fluid at 220°C and a deeper one at about 350°C, both originating from a concentrated brine. Heat flux is estimated to be 6–7 times the average terrestrial value (250 – 290 mW/m²); (v) determine the most favourable areas for deep drilling.     

Development program of hot dry rock geothermal resource in the Yangbajing Basin of China

Geothermal energy from hot dry rock (HDR), considered an almost inexhaustible source of “green” energy, was first developed and tested in the 1970s, leading to installations in America, Japan, Britain, France and other countries. In the present work, a liquating rock mass at a depth of 5-15 km in the Tibet Yangbajing region in China was subjected to detailed analysis. The temperature distribution of the geothermal field in the region was determined by the finite element method. The results estimate that the HDR geothermal resource of the Yangbajing region is 5.4 × 10⁹ MW a, representing a huge potential source of HDR geothermal energy for China. Based on detailed research into the continental dynamics of the environment forming the HDR geothermal field of Tibet, along with the tectonic characteristics of the southern slope of Tanggula Mountain and the Dangxiong-Yangbajing Basin, and the magnitude and orientation of the in situ stresses in the region, the design of an arrangement for extracting these HDR geothermal resources is proposed: taking the fault zone nearest the high-temperature liquating rock region as the location of an artificial reservoir, a vertical injection well could be drilled at a low point on the downdip side of the fault, and two dipping production wells drilled higher up. In this way, an artificial reservoir 3 × 10¹¹ m³ in volume would be created: 360 times the volume of the HDR geothermal reservoir in Cornwall, UK, which uses hydrofracturing. An investigation of the reservoir features, including seepage analysis of the heat exchange area, project implementation and investment analysis, indicates that a 10⁴ MW capacity power station with a projected operating life of approximately 100 years could be constructed. An analysis of a geothermal extraction system comprising one injection well and two production wells suggest that a power station of 1000 MW installed capacity could be constructed initially to provide electricity production of 8.64 × 10⁹ kWh per year.     

G.E.V.A.: Geothermal electricity venture analysis model

The Monte Carlo technique is a powerful method for quantifying the various risks in geothermal development. G.E.V.A. uses this method to allow users to realistically estimate the range of costs to be expected in geothermal electricity development. Such risk analysis offers a number of distinct advantages over the conventional single estimate approach:

• 1.(1) Risk is made explicit: the uncertainty perceived in the resource estimates are incorporated directly into the cost analysis. Knowledge of both the most likely outcome as well as the range of possibilities helps to create a more rational and informed decision-making process.
• 2.(2) Variability of outcome is measured: the dispersion in the possible outcome is estimated. Other things being equal, lower variability in the estimated cost of power is desirable.
• 3.(3) Promotes better decisions: the simulation approach requires more judgement in estimating the values for the uncertain elements in the investment. Recognizing what is known and not known with regard to the resource, leads to a more careful analysis. The analysis process is documented so that decision makers can build on past experiences.

The simulation program is easy to use and designed for widely available microcomputers. With site specific data on hand, plant costs can be estimated quickly. A comprehensive levelized cost model is used with the ability to distribute uncertain values with triangular probability distributions. The user need know nothing about the nature of the mathematics involved. The most likely value for each uncertain parameter along with the range of possible values are input. Results are given in terms of the levelized cost in mills/kWh for which the geothermal electricity can be produced. A mean value is computed along with range of possibilities and their relative chance. Solution for a two hundred sample run takes only about twenty minutes on an IBM personal computer. Use of a fast structured code, such as C-language, using the 8087 match co-processor could reduce the runtime by an order of magnitude.G.E.V.A. is a useful tool for geothermal assessment. It provides improved insight into the economics of high temperature geothermal resources for investment decisions. As with any such model, the greatest benefits will result when coupled with detailed geological information, skilled analysis and expert opinion.     

A review and analysis of the adequacy of the U.S. legal, institutional and financial framework for geothermal development

The legal and institutional framework within which geothermal energy in the United States must develop had its origin in the early 1970s. The first impetus for the establishment of such a framework was the early successful development of The Geysers geothermal field in northern California. The second impetus came from the oil embargo of 1972 which also raised the demand for the establishment of federal and state financial incentives to encourage more rapid development of geothermal energy.The legal and institutional framework developed by the states and the federal government often differed substantially in format, content, and direction. Too often the legal and institutional framework established left as many questions unanswered as answered, and in some cases, the framework has proven to be more of an obstacle to development than an aid.From an examination of how the states and the federal government have addressed the needs of geothermal development, and how the courts have interpreted some of their decisions, it has become clear that in order to ensure that the legal and institutional framework is adequate to serve the needs of geothermal development, it must address, at a minimum, the following topics:

1. (1) providing developers with access and a priority right to carry out exploration and development activities;

2. (2) carefully characterizing the resources so as to minimize conflicts with other natural resources;

3. (3) establishing ownership; and

4. (4) giving careful consideration to such lease terms as rentals and royalties, renewals, and diligence requirements.

In addition, the framework must address groundwater law and its implications for geothermal development, and how geothermal development will be considered in terms of established utility law.Providing financial incentives to ensure rapid growth of the geothermal industry is another task which the states and the federal government have addressed. Several types of programs can be used. These include grants, loans, guaranteed loans, tax incentives and insurance. Two major conclusions which have emerged from an analysis of the varying programs and types of programs is that no single program can meet the needs of every type of developer, and that to be successful, the program developed must address the financial needs of the developer from exploration through development.     

Seismic reflector imaging by prestack time migration in the Kakkonda geothermal field, Japan

We show that a prestack migration method improves the S/N ratio of seismic reflection profiling in the Kakkonda geothermal field where seismic reflection data are of poor quality. We use non-iterative prestack time migration (PSTM), which does not require multiple iterations to determine the velocity structure for prestack time migration. The optimum constant migration velocity can be determined at each image point from a migration velocity analysis based on primary diffraction patterns. Our results delineate a strong reflector beneath a zone of high seismicity. According to the correspondence between the fracture distribution, the distribution of microearthquakes, and geothermal structure, this reflector is interpreted to be a zone of low-angle fractures saturated with hydrothermal fluids, and to be strongly controlled by the geothermal structure.     

A chloride method for the determination of the enthalpy of steam/water mixtures discharged from geothermal wells

Chloride concentrations and pressures (or temperatures) in two points of a geothermal test line have been used to determine the enthalpy of the steam/water mixture discharged from Nisyros I geothermal well (Greece). The results are in agreement with those obtained by the Russell James method. The chloride method described in this paper is fast, requires cheap, portable equipment and is thus particularly suitable for short-term well testing during drilling or immediately after well completion, especially in steam-rich mixtures.     

Tests of electric and electromagnetic methods in the travale geothermal field

Within the framework of an EEC project involving ten European laboratories, research on the application of several electric and electromagnetic methods to a geothermal field (Travale, Tuscany), has been undertaken by the B.R.G.M. The objective was to refine the conceptual model of the Travale field and, therefore, to describe the morphology of the basement (down to 2 km depth) and of the Rhaetian reservoir covered by impermeable series.The method best suited to this type of prospection appeared to be electrical dipole — dipole profiling, combined with a 2-D interpretation. Contrasts at more than 2 km depth (500 m long dipoles) could be seen and compared to the depths measured in the boreholes. The EM Melos method (Syscal equipment) should be improved (lower frequencies) to increase the depth penetration. It is, however, a good complementary method for the surface layers. An attempt at a computational interpretation of the self potential profiles gave promising results. To make full advantage of the bipole — dipole measurements efforts should be devoted to their computational interpretation.     

Temperature matching method of selecting working fluids for geothermal heat pumps

The fact, that some areas need district heating through heat pumps and at the same time recover residual heat from geothermal water, presents a new working condition: feed water temperature of heat network 80 °C, return water temperature 65 °C; discarded geothermal water temperature 40 °C and its emission standard temperature below 30 °C. But none of known pure refrigerants and mixtures can meet this requirement. The paper introduces a novel approach named temperature-matching method, which provides a direction in selecting high-performance working fluids for further research. It is shown from the results that the mean COPs of binary and ternary mixtures are 4.85 and 4.74 respectively, but that of pure refrigerants is 4.12 under the same ambient condition. This point indicates that temperature matching contributes to energy saving. The novel approach to high-performance working fluids can be conveniently introduced into other working conditions.