Low-medium enthalpy geothermal systems on the eastern flank of the Sierra Madre Oriental, México

Efforts focusing on developing geothermal energy in the Kingdom of Saudi Arabia are increasing and drilling operations of geothermal wells are being prepared for. This paper will provide an overview of geothermal energy resources in the Kingdom and an analysis of the potential drilling and well integrity risks that could be faced while developing geothermal resources in the Kingdom with a focus on medium and low-enthalpy geothermal systems. The paper uses drilling data obtained from a massive drilling campaign of geothermal wells and applies the experience gained and lessons learned from this drilling campaign in the prognosis for potential drilling and well integrity risks of drilling geothermal wells in the Kingdom of Saudi Arabia. It will also provide a literature review on the available geothermal resources in the Kingdom of Saudi Arabia, with a focus on medium and low enthalpy geothermal systems, and classify such resources geographically and in terms of economic feasibility and possible geothermal energy utilization and venues of applications. The study demonstrated the availability of vast geothermal energy resources in the Kingdom of Saudi Arabia. Such resources are classified into three main categories. First and most economically feasible to be developed are the high enthalpy geothermal energy resources which are present in radiogenic granites in the Arabian Shield rocks with a total area of 161,467 sq. km. The high heat flow in this system is associated with the radioactive decay of some radioactive minerals (Uranium, Thorium, and Potassium) existing within the granites. Another high enthalpy geothermal system in the Kingdom is the volcanic rocks (Harrats) within the Arabian Shield with a total area of 90,000 sq. Km. Some Harrats were found to be associated with dike intrusion and magma chamber appearing at about 8 km below the Harrat (Lunayyir). Hot springs in the western coast are identified as medium enthalpy geothermal systems and Clastic deposits are classified as low enthalpy geothermal systems available across the country. Main identified drilling risks are lost circulations cement placement. Other important factors affecting the well integrity are mainly casing selection, well design, and pump selection. The study concludes that considering the vast and geographically diversified geothermal resources in the Kingdom and with careful consideration of the drilling and well integrity risks associated with geothermal wells, the Kingdom is set to start an interesting and successful journey in developing its geothermal resources. This paper will be an important reference for developing geothermal resources in the Kingdom of Saudi Arabia in terms of drilling-associated risks and recommended mitigation practices. It will also provide an overview of the horizons for developing geothermal resources in the Kingdom of Saudi Arabia.

Renewable energy is a must in the future. One of them is produced from the geothermal resources. A preliminary study has been done on the geothermal resources in the Rokan Hulu Regency, Riau, Indonesia. In this study, the Google Earth Pro 7.3.1.4507 has been used to map the possibility of the source of groundwater in supplying the hot springs. The 2D geoelctrical resistivity survey with Wenner configuration has been conducted to image the subsurface around the hot springs. The Google earth shows that the water resource of the hot springs is predicted from the highland in southwest part of the study area. The highland is spread from several meters to about 8 km from the hot springs. This area is consisted of the igneous rock with elevation from 100 to 911 meter above mean sea level, whilst the hot spring is located at the elevation of 86 meter above mean sea level. Resistivity values show the possibility path of the groundwater seeping from the rock fractures through the hot rocks of igneous rock to the hot springs. However, the detailed study needs to be conducted to investigate the geothermal resources of the study area.

Relevance. The necessity to develop the technologies in Russia that use non-traditional energy sources. The formation of these technologies will allow providing energy resources to the population without harmful emissions into the environment. Aim. Comprehensive analysis of the operating characteristics of a binary geothermal power plants in various climatic operating conditions. Objects. Thermal diagrams of binary geothermal power plants applicable to installation in different geographic regions and operation from different geothermal sources. Methods. Numerical studies based on mathematical algorithms of binary geothermal plant systems, comparative analysis of the efficiency of binary geothermal plants based on various external parameters. Results and conclusions. Numerical studies have been conducted to determine the efficiency of geothermal power plants with a binary thermal circuit and an air-cooled condenser were conducted during their operation on various sources, for which 15 known geothermal sources located in Russia in different geographical regions were selected. Possible operating parameters of binary geothermal power plants were analyzed based on the known characteristics of the fluid at the well outlet. Since the geothermal power plant has an air-cooled condenser in its thermal circuit, its operating parameters were obtained from the average monthly ambient air temperatures in the calendar year in the region where the analyzed geothermal source is located. Numerical studies showed the impact of thermal source parameters and climatic features on the efficiency of electric energy generation by means of a binary plant. It was revealed that with the possible operation of a binary geothermal plant during a calendar year, the highest average monthly electric power is expectedly achieved in the cold period of time, in this case in January, and is 1752 kW for the Mogoysky hot spring. For the warmest month of the year – July – the binary power plant of the Mechigmen hot spring could have the greatest electric power of 930 kW. The greatest absolute electric efficiency in January reaches 15.22%, depends to a greater extent on the value of the temperature of the heat supply in the cycle and among the binary stations considered in this work, the geothermal power plants in the settlement of Chazhemto could have it.

According to the official definition, approved by the European Geothermal Energy Council (EGEC), geothermal energy is energy accumulated as heat below the surface of solid soil. Geothermal energy is thermal energy generated and stored in the Earth. It is generally defined as the part of geothermal heat that can be directly utilized as heat or converted into other types of energy. Geothermal resources vary by location and depth towards the Earth's core. Their use is possible for different purposes depending on their temperature. This paper presents the harnessing geothermal resources for electricity generation. There are three main types of geothermal power plants: dry steam plants, flash steam plants, and binary cycle plants. Dry steam plants pipe hot steam from underground into turbines, which powers the generator to provide electricity. Flash steam plants pump hot water from underground into a cooler flash tank. The formed steam powers the electricity generator. Binary cycle plants pump hot water from underground through a heat exchanger that heats a second liquid to transform it into steam, which powers the generator. In all mentioned systems the used fluids are recycled. It can be concluded that geothermal power plants work similarly to other power plants, but providing the steam for starting the turbine from the earth's interior. The fact that used fluids return to the ground makes geothermal energy resources renewable.

Tibet boasts many huge geothermal reserves and resource exploitation potential. However, as the geothermal resource is relatively scattered, it is hard to be exploited. The scope of work includes assessments of geothermal and ground water storage capacity, and the amount of exploitable heat and water and the fluid quality are evaluated in separate geothermal districts (fields) on the basis of the former investigation on geothermal wells, springs and geothermal field. Considering the low degree of general survey in Tibet and less information available, the amount of geothermal water in Tibet is calculated by natural heat flux method (SPA). The exploited amount of geothermal fluid (SPA) in Tibet mountainous area is 7.65 × 107 m3/a, and the exploitable geothermal resources (SPA) are 1700.77 × 1013 J/a, equivalent to 51.1 × 104 T of standard coal. A single interception of natural heat flow (SPA) shows that there is a huge potential for the development and utilization of geothermal resources in Tibet mountainous areas. Hot dry rock resources evaluation is conducted as well. Statistics show that this region’s base temperature is greater than 150 °C, and 19 zones are found with surface thermal fluid above boiling point. It is calculated that the thermal reserve 3–5 km below amounts to 145,367.93 × 1015 J, equivalent to 49.68 × 108 tons of standard coal. In south Tibet, the currently developed and utilized geothermal resources are mainly from Yangbajing thermal field. Early exploited amount of shallow geothermal resources amounts to 1512 t/h. Other geothermal active areas are basically unexploited. In middle Tibet, the geothermal active zones are still in natural forms without any exploitation. The total amount of geothermal liquid resources in north Tibet is 8.3 × 104 m3/a. East Tibet area’s geothermal resources are basically unexploited. The total amount of geothermal liquid resources is 3.77 × 105 m3/a. According to the results of geothermal resources evaluation in each area of Tibet, most geothermal active zones are in their natural state and not utilized, and are exploitation zones with high potential, especially in south and east Tibet uplifted zones.

Geothermal studies in China

Jordan, which is considered as part of the ring of fire, is tectonically active and could be considered as potential region for future generation of energy from the available geothermal energy resources.The current article discusses the possibility of utilizing geothermal energy in generating electrical power in Jordan.Jordan encounters geothermal energy resources in two main forms, medium and low energy with variation of temperature ranges from 110-114 o C and 30-65 o C, respectively.The various hot springs and wells have been subjected to a comparison in terms of temperature and flow rate in order to determine the most suitable method for electric power generation.This comparison concluded that electrical power could be generated using geothermal binary power plants and geothermal Stirling engines.

In this study, the Abgarm–Avaj geothermal system in Iran is investigated by analyzing hydrochemistry and stable environmental isotopes of water samples collected from cold and thermal water springs and the Khare-Rud River together with tectonic settings. The findings reveal that the geothermal system is associated with the deep fault zone of Hasanabad and can be categorized into a convection dominated and non-magmatic geothermal system in accordance with the catalog of geothermal play types presented by Moeck (Renew Sustain Energy Rev 37:867–882, 2014). In fact, local rainfall that is occurred over the Kuhe-Bozorg limestone highlands percolates into a high depth along the main active fault of Hasanabad and then heats and emerges finally at the lowest topographic elevation of the fault in the form of thermal springs characterized by temperature ranges from 30 to 52 °C. The water samples from the thermal springs are of a high electrical conductivity value (ranges from 6585 to 11265 µS/cm) with the chloride water type. The lower circulation depth of meteoric water in the geothermal system is estimated to be about 3000 m by considering the possible maximum geothermal gradient of about 46 °C/km. The stable isotopes ratios analysis suggests that thermal water originates predominantly from rainfall occurring over the higher elevations, since the oxygen-18 ratios of the thermal spring waters are depleted than that of the cold spring waters. The equilibrium temperatures of the geothermal system are estimated via using the Na–K (Truesdell, Summary of section III: geochemical techniques in exploration. In: Proceedings of the 2nd U.N. symposium on the development and use of geothermal resources, vol 1. U.S. Government Printing Office, Washington, DC, pp liii–lxxx, 1976) and Na–K (Tonani, Some remarks on the application of geochemical techniques in geothermal exploration. In: Proceedings of advances in European geothermal research, 2nd symposium, Strasbourg, pp 428–443, 1980) geothermometers are 142–148 and 146–153 °C, respectively, which fall within the temperature range suggested by the mineral saturation indices (137–160 °C) and by the warm spring mixing model (135–164 °C) for the thermal spring waters. Furthermore, the results show that geothermal hot water mixes predominantly with shallow cold groundwater during ascending, where the portion of the cold shallow and deep-hot waters is about 70 and 30%, respectively.

Geothermal energy is increasingly recognized for its potential to reduce carbon emissions and U.S. dependence on foreign oil. Energy and environmental analyses are critical to developing a robust set of geothermal energy technologies. This report summarizes what is currently known about the life cycle water requirements of geothermal electric power-generating systems and the water quality of geothermal waters. It is part of a larger effort to compare the life cycle impacts of large-scale geothermal electricity generation with other power generation technologies. The results of the life cycle analysis are summarized in a companion report, Life Cycle Analysis Results of Geothermal Systems in Comparison to Other Power Systems. This report is divided into six chapters. Chapter 1 gives the background of the project and its purpose, which is to inform power plant design and operations. Chapter 2 summarizes the geothermal electricity generation technologies evaluated in this study, which include conventional hydrothermal flash and binary systems, as well as enhanced geothermal systems (EGS) that rely on engineering a productive reservoir where heat exists but water availability or permeability may be limited. Chapter 3 describes the methods and approach to this work and identifies the four power plant scenarios evaluated: a 20-MW EGS plant, a 50-MW EGS plant, a 10-MW binary plant, and a 50-MW flash plant. The two EGS scenarios include hydraulic stimulation activities within the construction stage of the life cycle and assume binary power generation during operations. The EGS and binary scenarios are assumed to be air-cooled power plants, whereas the flash plant is assumed to rely on evaporative cooling. The well field and power plant design for the scenario were based on simulations using DOE's Geothermal Economic Technology Evaluation Model (GETEM). Chapter 4 presents the water requirements for the power plant life cycle for the scenarios evaluated. Geology, reservoir characteristics, and local climate have various effects on elements such as drilling rate, the number of production wells, and production flow rates. Over the life cycle of a geothermal power plant, from construction through 30 years of operation, plant operations is where the vast majority of water consumption occurs. Water consumption refers to the water that is withdrawn from a resource such as a river, lake, or non-geothermal aquifer that is not returned to that resource. For the EGS scenarios, plant operations consume between 0.29 and 0.72 gal/kWh. The binary plant experiences similar operational consumption, at 0.27 gal/kWh. Far less water, just 0.01 gal/kWh, is consumed during operations of the flash plant because geofluid is used for cooling and is not replaced. While the makeup water requirements are far less for a hydrothermal flash plant, the long-term sustainability of the reservoir is less certain due to estimated evaporative losses of 14.5-33% of produced geofluid at operating flash plants. For the hydrothermal flash scenario, the average loss of geofluid due to evaporation, drift, and blowdown is 2.7 gal/kWh. The construction stage requires considerably less water: 0.001 gal/kWh for both the binary and flash plant scenarios and 0.01 gal/kWh for the EGS scenarios. The additional water requirements for the EGS scenarios are caused by a combination of factors, including lower flow rates per well, which increases the total number of wells needed per plant, the assumed well depths, and the hydraulic stimulation required to engineer the reservoir. Water quality results are presented in Chapter 5. The chemical composition of geofluid has important implications for plant operations and the potential environmental impacts of geothermal energy production. An extensive dataset containing more than 53,000 geothermal geochemical data points was compiled and analyzed for general trends and statistics for typical geofluids. Geofluid composition was found to vary significantly both among and within geothermal fields. Seven main chemical constituents were found to account for 95-99% of the dissolved solids in typical geofluids. In order of abundance, they were chloride, sodium, bicarbonate, sulfate, silica, calcium, and potassium. The potential for water and soil contamination from accidents and spills was analyzed by comparing geofluid composition with U.S. drinking water standards. Geofluids were found to present a potential risk to drinking water, if released, due to high concentrations of antimony, arsenic, lead, and mercury. That risk could be mitigated through proper design and engineering controls. The concentration and impact of noncondensible gases (NCG) dissolved in the geofluid was evaluated. The majority of NCG was either nitrogen or carbon dioxide, but a small number of geofluids contain potentially recoverable concentrations of hydrogen or methane.

Chapter 4 - Geothermal systems and resources

Low-enthalpy geothermal energy resources from groundwater in fluvioglacial gravels of buried valleys

Tebing Tinggi, also known as Lemang City, has historically been recognized as a plantation area and was designated by the Dutch government as a “gemeente” (administrative district) in the Padang and Bedagei regions in 1917. While not widely known, Tebing Tinggi also possesses thermal water resources that have been utilized by local residents for at least 100 years. This thermal water has been used for various purposes, including consumption, laundry, and bathing. However, it is crucial to analyze the thermal water to assess its safety for consumption. Further research will enhance the understanding of the water’s properties and any potential changes that may impact public health. In this study, we collected five water samples from Tebing Tinggi: four from thermal water samples and one from a normal water sample for comparison. The samples were analyzed at the Water Quality Laboratory at the Institut Teknologi Bandung to evaluate their quality. Among the 31 parameters tested, most thermal water samples met the standards specified in the Regulation of the Minister of Health of the Republic of Indonesia No. 492/Menkes/Per/IV/2010. Notably, the pH levels of the water were slightly above the standard range, and one thermal sample from Pemandian Umum Bangsal exhibited slightly elevated fluoride content. Total coliform and fecal coliform bacteria levels (indicative of Escherichia coli) were below 1.1 per 100 ml, indicating the absence of coliform bacteria in the thermal water samples. The comparative water sample also fell within the acceptable range for most parameters. The Ground Water Quality Index (GWQI) formula suggests that both the thermal and normal water samples from Tebing Tinggi possess excellent water quality. The thermal water comes from a deeper aquifer, possibly interacting with superheated gases from the shallow magma chamber, whereas the normal water sample comes from a shallower aquifer influenced by Toba tuff material. This geological distinction is evident in the fact that the thermal water and the normal water come from different aquifers. The thermal water in Tebing Tinggi holds potential for balneotherapy due to its therapeutic benefits and could be developed as a tourist attraction or geothermal resource in the future.

Hot water springs are typical surface manifestations of a geothermal system, especially in low enthalpy, amagmatic systems. In many of these systems, numerous cold-water springs are often associated with hot water springs. The smaller number of hot water springs and the wider spatial distribution between them make it difficult to perform a comprehensive study of such a geothermal system. In this case, associated cold water springs can be of particular help in understanding the hydrogeological setting of the geothermal system which is vital information for any future geothermal exploration programs. There are 9 known hot springs in Sri Lanka, however they are spread over a larger area of the eastern lowlands of the country. On the other hand, there are over 225 known cold-water springs distributed among the hot water springs, making Sri Lanka a perfect location for a case study. Most hot water springs are located at a great distance from their recharge zone (~ 50-100 km). With the exception of very few springs, cold water springs have short recharge to discharge distances (< 25 km). Geochemical and isotopic studies of the hot springs and the nearby cold springs show that both kinds are of the same origin and recharge at similar altitudes (> 600m). The electrical resistivity of cold-water springs is comparatively higher than that of rain and fresh surface water, but lower than that of hot water springs. This suggests that these cold spring waters also travel longer through the fault/fracture network through which hot spring waters circulate from recharge zones to discharge zones. These observations of cold-water springs show that they are also part of the geothermal system in Sri Lanka and reveal important information about the fluid flow paths of the geothermal system. The results and observations of the present study highlight the importance of cold-water springs in understanding the hydrogeological setting of a geothermal system. In addition, the new knowledge will be of significant benefit to future geothermal exploration programs, particularly in systems with a smaller number of hot water springs spread over a larger area.

Electricity generation is achieved by means of the medium-temperature geothermal water in the range of 90–140 oC in binary plants with the organic Rankine cycle. So, we investigate a binary geothermal power plant as a case study, from the energy and exergy point of view. Also, exergy destruction rates throughout the plant are quantified and illustrated for comparison purposes. In the plant considered, the brine injection and reinjection temperatures are 140 and 80 oC, with a mass flow rate of 64.87 kg/s, respectively. The energy and exergy efficiencies are calculated as 5.34 and 30.84 %, respectively, based on the heat and exergy input rates to the system at the net power. Furthermore, we examine the effects of some parameters on energy and exergy efficiencies and net power output (e.g., brine injection temperature, brine mass flow rates, turbine inlet temperature and inlet pressure).

Geothermal exploration in mountain regions strongly relies on the successful identification of thermal anomaly in the regions,which can be performed through the extraction of geothermal anomaly information from thermal infrared remote sensing data. However,changes in Land Surface Temperature(LST) in mountain regions are significantly affected by topography in addition to other factors, such as latitude and surface property. This effect strongly weakens the efficient identification of geothermal anomaly over the LST image retrieved from thermal infrared remote sensing data, which consequently limit the application of remote sensing technique to geothermal resource exploration in mountain regions with rough terrain. This study examines the effects of terrain on LST changes in the mountain region of Longchuan in Southern China to establish an efficient approach, which can correct the effects of terrain on the LST changes for the geothermal exploration in the region.LST was retrieved using mono-window algorithm based on Landsat ETM+ remote sensing data. The effects of terrain on LST distribution were then analysed. The statistical analysis showed a parabolic relationship between LST and aspect. Moreover, the southeastfacing slope had the highest average LST and standard deviation, where LST was significantly and positively correlated with slope gradient.To reduce the impact of terrain on LST distribution, the area was divided into sunny slope, shady slope and transitional slope. The LST in the sunny slope was particularly corrected to its horizontal surface equivalent by the linear regression equation between LST and slope gradient. Geothermal anomalies were then extracted from the LST of these three subareas, with the consideration of geologic structure and land cover.Results showed that the spatial variation amplitude of LST evidently decreased because the significant temperature difference among different terrain conditions has become small in subareas. Four possible geothermal anomalies were recognised in which high temperature areas were closely related to faults and showed little variability in land cover. Comparative analysis with known hot springs indicated that they were likely caused by geothermal activities.In conclusion, topography mainly affects LST spatial distribution by controlling incoming solar radiation. The solution of aspect-based partition and gradient correction presented in this article can also effectively reduce topographic effects. It helps improve the recognition accuracy of geothermal anomalies with remote sensing technology. The solution may also provide an enlightening insight into the forecast evaluation of geothermal resources in mountain regions. Moreover, further analyses of the relationship between LST and other factors controlled by terrain are necessary in future research, especially the physical properties of underlying surfaces, such as land use, soil moisture and vegetation.