Evaluation of the reconnaissance results in geothermal exploration using GIS

Geographical Information System (GIS) is used to determine the spatial association between geophysical and geological evidence and production zones in a well-known geothermal field (Los Azufres, Mexico). Surface observations in Los Azufres were used to delineate areas characterized by high permeability and hot fluid transport from the reservoir: main faults, superficial fracture density, surface manifestations, contacts with the most recent rhyolite domes, and low values in the apparent resistivity surveys. Three knowledge-driven models were constructed based on a conceptual model of the field: a hydrothermal system in rough terrain with secondary permeability. Boolean, Index Overlay and Fuzzy scheme models were proposed and the results obtained show a good correlation with the location of the producing and non-producing wells that have been drilled in the field. The results obtained are useful for well siting (Boolean and Low-Risk Fuzzy models) or for planning further detailed exploration (Index Overlay and High-Risk Fuzzy models).     

Three-dimensional imaging of a geothermal system using temperature and geological models derived from a well-log dataset

The accurate imaging of geothermal systems from the ground surface down to great depths is an interdisciplinary problem common to geothermal resource exploration and development. Rocks can be characterized mainly in terms of their lithology, mineralogy, fracture distribution, permeability, thermal conductivity and porosity, and similarly the geothermal fluid (and its circulation) by its geochemistry, flow pattern, velocity, temperature and pressure. Some of these data are obtained by well logging and from laboratory tests conducted on drillhole cores. In general, the distribution of geothermal wells is not random, and well data are limited in terms of quantity and depth range. Accordingly, a sophisticated spatial modeling technique is indispensable in the three-dimensional imaging of geothermal systems. We describe a versatile 3-D modeling method that can be used to determine the temperature, flow velocity, and distribution of geological units within a geothermal field based on well log data. The model results for the Hohi geothermal area, Japan, provide plausible estimates of temperature, flow velocity, and geology to a depth of 3000 m. Superimposition of the three spatial models we obtained shows that, at Hohi, two geothermal reservoirs are localized near highly fractured fault zones that provide paths for the ascent of thermal fluids from depth.     

Geothermal energy resources and development in Iran

Interest in geothermal energy originated in Iran when James R. McNitt, a United Nations geothermal expert, visited the country in December 1974. In 1975, a contract among the Ministry of Energy, ENEL (Entes Nazionale per L’Energia Elettrica) of Italy and TB (Tehran Berkeley) of Iran was signed for geothermal exploration in the north-western part of Iran. In 1983, the result of investigations defined Sabalan, Damavand, Khoy-Maku and Sahand regions as four prospected geothermal sites in north-western Iran.From 1996 to 1999, a countrywide geothermal energy resource exploration project was carried out by Renewable Energy Organization of Iran (SUNA) and 10 more potential areas were indicated additionally.Geothermal potential site selection using Geographic Information System (GIS) was carried out in Kyushu University in 2007. The results indicated 8.8% of Iran as prospected geothermal areas in 18 fields.Sabalan as a first priority of geothermal potential regions was selected for detailed explorations. Since 1995, surface exploration and feasibility studies have been carried out and five promising areas were defined. Among those prospective areas, Northwest Sabalan geothermal filed was defined for detailed exploration to justify exploration drilling and to estimate the reservoir characteristics and capacity.From 2002 to 2004, three deep exploration wells were drilled for evaluation of subsurface geological conditions, geothermal reservoir assessment and response simulation. Two of the wells were successful and a maximum temperature of 240 °C at a depth of 3197 m was recorded. As a result of the reservoir simulation, a 55-MW power plant is projected to be installed in the Sabalan field as a first in geothermal power generation. To supply the required steam for the geothermal power plant (GPP) 17 deep production and reinjection wells are planned to be drilled this year.     

Use of slim holes with liquid feedzones for geothermal reservoir assessment

Production and injection data from slim holes and large-diameter wells at four geothermal fields (Oguni, Japan; Sumikawa, Japan; Takigami, Japan; Steamboat Hills, U.S.A.) were analyzed in order to establish relationships (1) between injectivity and productivity indices, (2) between productivity/injectivity index and borehole diameter, and (3) between discharge capacity of slim holes and large-diameter wells. The productivity and injectivity indices for boreholes with liquid feedzones are more or less equal. Except for the Oguni boreholes, the productivity and injectivity indices display no correlation with borehole diameter. Thus, the productivity index (or, more importantly, the injectivity index in the absence of discharge data) from a slim hole with a liquid feed can be used to provide a first estimate of the probable discharge capacity of a large-diameter geothermal production well. The large-diameter wells at the Oguni, Sumikawa and Steamboat Hills geothermal fields have a more or less uniform inside diameter, and the discharge capacity of these wells (with liquid feedzones) can be predicted using Pritchett's “scaled maximum discharge rate” in conjunction with discharge data from slim holes. Because of the non-uniform internal diameter for large-diameter Takigami wells, it is not possible to use a simple scaling rule to relate the discharge capacities of slim holes and large-diameter wells at Takigami; therefore, a numerical simulator was used to model the available discharge data from Takigami boreholes. The results of numerical modeling indicate that the flow rate of large-diameter Takigami production wells with liquid feedzones can also be predicted using discharge and injection data from slim holes.     

Prediction of boiling, scaling and formation conditions in geothermal reservoirs using computer programs tequil and geofluids

Predictions of boiling, scaling, and solubility of gases are important to the exploitation of geothermal resources. These chemical phenomena are strong functions of the composition, temperature and pressure of the working fluid and are therefore difficult to predict from prior experience or tabulated data. Thermodynamic models of geothermal brine behavior recently developed by the authors are introduced and used to study various problems involved in geothermal energy production. The models have been extensively tested. Results of comparisons with laboratory measurements indicate that predictions are very close to experimental data for a wide range of conditions. Comparisons with field data also show remarkable agreement. Here the models are also applied to the prediction of breakout and scale formation in geothermal wells. Good agreement is obtained with actual well performance.     

Geothermal development in Thailand

San Kampaeng and Fang geothermal areas are considered areas of interest for the exploitation of geothermal energy. The technologies of exploration and development have been studied by Thai scientists and engineers during the past four years. The first geothermal deep exploration well was drilled, in cooperation with Japan International Cooperation Agency (JICA), in the San Kampaeng geothermal area. In 1985, supplementary work is planned to define the deep structural setting in greater detail before starting to drill the next deep exploration well. In Fang geothermal area some shallow exploitation wells have been drilled to obtain fluid to feed a demonstration binary system of 120 kWe, with the technical cooperation of BRGM and GEOWATT, France. The plant will be installed next fiscal year.     

A generalized non-isothermal tank model for liquid dominated geothermal reservoirs

We present a generalized non-isothermal tank model for predicting the pressure and temperature behaviors of liquid dominated geothermal reservoirs. A geothermal system is represented by a single or multiple tanks. These tanks can represent the reservoir, multiple reservoirs, aquifers or any other component of a geothermal system. The mass and energy balance equations for each tank are solved jointly. One of the main advantages of the model is that only a small number of tanks are used for modeling which avoids over parameterization of a geothermal system and results in faster run times when compared with fully discretized numerical simulators. Synthetic examples are used for studying the effects of heat conduction on reservoir performance, an analysis of the location of injection wells, recovery times of depleted geothermal fields and the benefits of using temperature data for a better characterization of the geothermal system.     

Prediction of downhole circulating and shut-in temperatures

An accurate prediction of downhole circulating temperatures during geothermal well drilling is needed for cement slurry and mud design. At present, API correlations are used to predict bottom-hole circulating temperatures for geothermal wells. Presented in this paper are field data which show that the API predictions overestimate the bottom-hole circulating temperatures for wells with high geothermal gradients. New empirical relationships are suggested to predict downhole circulating temperatures for deep, high temperature wells. Also, an analytical formula for predicting downhole shut-in temperature is presented.     

Temperature–depth relationships based on log data from the Los Azufres geothermal field,Mexico

Equilibrium temperatures based on log data acquired during drilling stops in the Los Azufres geothermal field were used to study the relationship between temperature, depth and conductive heat flow that differentiate production from non-production areas. Temperature and thermal conductivity data from 62 geothermal wells were analyzed, displaying temperature–depth, gradient–depth, and ternary temperature–gradient–depth plots. In the ternary plot, the production wells of Los Azufres are located near the temperature vertex, where normalized temperatures are over 0.50 units, or where the temperature gradient is over 165°C/km. In addition, the temperature data were used to estimate the depth at which 600°C could be reached (5–9 km) and the regional background conductive heat flow (≈ 106 mW/m²). Estimates are also given for the conductive heat flow associated with the conductive cooling of an intrusive body (≈ 295 mW/m²), and the conductive heat flow component in low-permeability blocks inside the reservoir associated with convection in limiting open faults (from 69 to 667 mW/m²). The method applied in this study may be useful to interpret data from new geothermal areas still under exploration by comparing with the results obtained from Los Azufres.     

Geothermal development in Romania

Exploration for geothermal resources began in Romania in the early 1960s, based on a detailed geological exploration program for hydrocarbon resources that had a capacious budget and enabled the identification of eight geothermal areas. Over 200 wells drilled to depths between 800 and 3500 m have indicated the presence of low-enthalpy geothermal resources (40–120 °C). Completion and experimental production from over 100 wells during the past 25 years has led to the evaluation of the exploitable heat resources of the geothermal reservoirs. The proven reserves, with the wells that have already been drilled, amount to about 200,000 TJ for 20 years. The main geothermal systems discovered on Romanian territory are in porous permeable formations such as sandstones and siltstones (Western Plain and the Olt Valley) or in fractured carbonate formations (Oradea, Bors, and north of Bucharest). The total thermal capacity of the existing wells is about 480 MW_t (for a reference temperature of 25 °C). Only 152 MW_t of this potential is currently being exploited, from 96 wells (35 of which are used for health and recreational bathing), producing hot water in the temperature range 45–115 °C. In 2002 the annual energy utilisation from these wells was about 2900 TJ, with a capacity factor of 0.6. More than 80% of the wells are artesian producers, 18 wells require anti-scaling chemical treatment and six are reinjection wells. During the period 1995–2002, 15 exploration-production geothermal wells were drilled and completed, two of which were dry holes. Drilling was financed by the geological exploration fund of the State Budget, to depths varying between 1500 and 3500 m. Progress in the direct utilisation sector of geothermal resources has been extremely slow because of the difficulties encountered during the transition period from a centrally planned to a free-market economy; geothermal production is at present far below the level that could be expected from its assessed potential, with geothermal operations lagging behind in technology. The main obstacle to geothermal development in Romania is the lack of domestic investment capital. In order to stimulate the interest of potential investors from developed countries and to comply with the requirements of the large international banks, an adequate legal and institutional framework has been created, adapted to a market-oriented economy.     

Evaluation of the productivity of geothermal wells by analyzing production measurements and the damage effect

In this work, an analysis of production data for determining the damage effect in geothermal wells is reported. Measurements of some Mexican geothermal wells have been analyzed for evaluating the decrease of their productivity under exploitation conditions. As an innovation of the methodology used in this work, the dimensionless well flow parameters (pressure and mass flow rate), and the inflow performance relationship curves of producing wells were determined by using more representative thermodynamic properties of the geothermal fluid (i.e., characterized as a ternary compound system: H₂O–CO₂–NaCl). Geothermal inflow type‐curves were therefore used for determining the wellbore damage effect. Production measurements of the wells were compiled at different stages of their operative life cycle. From this study, it was found that the wellbore damage effect increases with the exploitation time. These results enable a drop in the fluid flow mechanisms of the wells to be identified. The quantitative knowledge of the wellbore damage effect helped us to define a technical criterion for the decision making of the most appropriate engineering operations to be applied (e.g., cleanings, repairs, stimulations, fracturing, etc.) either to recover or to improve the well productivity. Copyright © 2016 John Wiley & Sons, Ltd.     

GIS based geothermal potential assessment: A case study from Western Anatolia,Turkey

Potential geothermal areas are identified through investigation of spatial relations between geothermal occurrences and their surrounding geological phenomena in western Anatolia, Turkey. The identification is based on only publicly available data. It is expected that the study will guide further preliminary investigations performed for large areas having limited information. Magnetic anomaly, Bouger gravity anomaly, earthquake epicenter and lineament datasets are used for the analysis. The first is used without any modification whereas the rest are utilized to extract three evidence maps; distance to major grabens, Gutenberg–Richter b-value and distance to lineaments, respectively. Predictor maps are produced from these evidence maps as well as from the unprocessed magnetic anomaly map by applying two different binarization procedures. From each binarization procedure a favorability map is produced separately using Index Overlay (IO) and Weights of Evidence (WofE) methods. The findings reveal that weighting predictor maps according to spatial association between evidence maps and training points lead to more accurate prediction in both WofE and IO methods. The potential areas in the final maps are Ayd?n, Denizli, Manisa, Bal?kesir and Kutahya of which first two have been explored and exploited, and thus found to be favorable, while the rest are nearly unexplored.     

冰岛低温地热水供热系统碳酸钙沉积的成因

借助化学模型ＷＡＴＣＨ及ＶＤＡＴＡ程序，研究了冰岛低温地热水供热系统的碳酸钙沉积现象。结果表明，在地热水中允许存在一定的碳酸钙过饱和度，而不发生碳酸钙垢的沉积。饱和指数０．２７为冰岛低温地热水中允许的碳酸钙过饱和度。即地热水中可以含有１．９倍理论量的碳酸钙。研究还发现，深层地热水与地表水的共混是导致本研究工作中Ｈｒｉｓｅｙ５号地热井碳酸钙高度过饱和，进一步引起碳酸钙沉积发生的主要原因     

Geothermal gradients of Alberta in Western Canada

55,246 bottom hole temperature (BHT) values from petroleum exploration well logs of 28,260 wells have been used to estimate geothermal gradients in Alberta. A general decrease in geothermal gradient towards the east is apparent. High gradient areas occur in the Hinton - Edson area of west central Alberta, in the Fort McMurray area of northeast Alberta, in the Steen River area of northwest Alberta, and at the northwest corner of the province. Comparison with gravity, aeromagnetic and relief maps indicates close correspondence between topographic features and geothermal gradients. It is suggested that subsurface temperature distribution in Alberta is strongly influenced by groundwater motion.     

地热井在不同注水和出水条件下热采效率优化研究

基于地热开采概念模型,采用3DEC程序计算分析不同注水和出水的三口地热井对岩体温度场、地热井温度场,及地热井出口水温影响的规律。结果表明：1）中部为注水井或生产井,边缘为生产井或注水井,模型达到稳态时生产井出口水温最低,且几乎相同;2）由于邻近两口生产井抽取水流过程中通过之间的岩体发生热量叠加效应,使其出口水温大幅提升,此时生产井出口水温最高, 同时模型达到稳态所需的时间最长;3）当两口邻近注水井,生产井水流速增大1倍时,其水流传热量增多致其出口水温有所提升,同时模型达到稳态所需的时间最短;4）根据生产井出口水温由高到低,模型优化顺序为两口邻近生产井>两口邻近注水井>两口间隔生产井=两口间隔注水井。     

利用测温资料判别热储流体的运动方向

热储温度数据主要通过钻探过程中温度测井来获取。由于在钻井过程中，钻孔周围的原始热动力条件常受到扰动。因此，地层温度需要通过对测温曲线进行细致地解释来获得。我们以Kaldarholt地热田为例，通过对34口勘探孔测温曲线的解释，分析了地热田的温度场分布特征。据此，建立了Kaldarholt地热田地下热水流动的概念模型，并为地热田开采井KH-36的成功定位起到关键的作用。     

Life cycle assessment of geothermal binary power plants using enhanced low-temperature reservoirs

Geothermal binary power plants that use low-temperature heat sources have gained increasing interest in the recent years due to political efforts to reduce greenhouse gas emissions and the consumption of finite energy resources. The construction of such plants requires large amounts of energy and material. Hence, the question arises if geothermal binary power plants are also environmentally promising from a cradle-to-grave point of view. In this context, a comprehensive Life Cycle Analysis (LCA) on geothermal power production from EGS (enhanced geothermal systems) low-temperature reservoirs is performed. The results of the analysis show that the environmental impacts are very much influenced by the geological conditions that can be obtained at a specific site. At sites with (above-) average geological conditions, geothermal binary power generation can significantly contribute to more sustainable power supply. At sites with less favorable conditions, only certain plant designs can make up for the energy and material input to lock up the geothermal reservoir by the provided energy. The main aspects of environmentally sound plants are enhancement of the reservoir productivity, reliable design of the deep wells and an efficient utilization of the geothermal fluid for net power and district heat production.     

Training in industrial uses of geothermal energy

Specialized training in industrial uses of geothermal energy is available in Iceland. The Geothermal Training Programme of the United Nations University (UNU) has operated in Iceland since 1979 with six months' annual courses for professionals in either Geological Exploration, Borehole Geology, Geophysical Exploration, Borehole Geophysics, Reservoir Engineering, Chemistry of Thermal Fluids, Geothermal Utilization, or Drilling Technology. The trademark of the training is to give university graduates with some practical experience in geothermal work, intensive on-the-job training in their specialization. Industrial applications of geothermal resources is one of the options open to participants in the Geothermal Utilization course. Participants selecting this option have mainly been trained in drying processes and how to adapt the design of conventional steam or hot water/air drying systems to the specific characteristics of the geothermal fluids. One participant studied food drying using low-temperature geothermal energy, and two dealt with heat exchanger selection for geothermal applications and the merits of the combined use of geothermal resources for electricity production and industrial utilization. Of other options directly relevant to industrial applications can be mentioned the selection, installation, and operation of downhole pumps in geothermal wells, the prediction of calcite scaling, and materials selection.     

Estimating temperature distributions in geothermal areas using a neuronet approach

A method is proposed for predicting the distribution of temperatures in geothermal areas using the neuronet approach and, in particular, downhole temperature logs. The method was tested against the results of an analytical model, showing that the errors in neuronet temperature estimates based on well log data derive from: (a) the neuronet “education level” (which depends on the amount and structure of information used for teaching) and (b) the distance of the point at which the estimate is made from the area for which data are available. These conclusions were confirmed when estimating temperatures in eight actual wells, using 50 downhole temperature logs from other wells in the geothermal area. It was found that, for this particular case, neuronet teaching utilizing 30 well logs results in an average forecast error of 20%. As the number of training logs increases (up to 50), the error slightly decreases (down to 16.9%). The effects of the teaching data pattern (conductive-type versus convective-type of temperature profiles) were also studied, and an optimal strategy was developed for the neuronet training, based on the information available.     

Shallow submarine and subaerial, low-enthalpy hydrothermal manifestations in Punta Banda, Baja California, Mexico: Geophysical and geochemical characterization

The low-enthalpy geothermal system at Punta Banda (NW Baja California Peninsula, Mexico) has been studied because it might provide heat to future desalination plants in the city of Ensenada. Utilization of subaerial, intertidal and submarine hot springs is evaluated based on geochemical and geophysical data. The results of the geochemical studies show that the geothermal fluids have a major meteoric water component because seawater is not present at the subaerial springs and hot wells. The highest estimated reservoir temperature (140 °C) calculated using a silica geothermometer corresponds to the Agua Caliente intertidal manifestation, a promising area also identified by geophysics. Geothermometric calculations applied to the computed composition of the thermal end member yield a reservoir temperature of 137 °C. Cl/B ratios indicate that the thermal fluids discharged by the intertidal vents and subaerial springs are similar, but they differ from those of submarine vents. Geoelectrical models depict an anomalous conductive trend from the La Jolla well to the Agua Caliente manifestation, suggesting the presence of a fault that allows upflow of hot water from depth. Lastly, integration of geochemical and geophysical data identified the best site for future exploration drilling at Punta Banda.