Geothermal Utilization Research Articles

Thermal performance analysis of a deep coaxial borehole heat exchanger with a horizontal well based on a novel semi-analytical model

This study introduces a novel semi-analytical model for deep coaxial borehole heat exchanger with a horizontal well(H-DBHE), which incorporates the effects of formation stratification and transient heat conduction within the pipe walls. Initially, the model's validity was checked through a comparison with the results derived from the published numerical models. This semi-analytical approach significantly reduces computational time while ensuring calculation accuracy. Subsequently, the study quantitatively examined the influence of the operation parameters, structural characteristics and the thermal capacity within the borehole on the dynamic heat extraction of H-DBHE. The numerical results demonstrate that the thermal capacity within the borehole significantly influences the heat extraction performance during intermittent operations of H-DBHE. Based on this finding, the study further investigated the effects of intermittent operation and heating time on the heat recovery performance of the system. Additionally, the study compared the long-term operational performance and thermal attenuation between H-DBHE and deep coaxial borehole heat exchanger (DBHE) over a ten-year simulation period. This research introduces a novel semi-analytical model for H-DBHE, which is of significant theoretical guidance for accurately predicting the heat extraction performance of H-DBHE and scientifically designing geothermal utilization systems.

Thermodynamic Performance Characterization of a Small-Scale Organic Rankine Cycle with 5 kW Net Power Output

Abstract Indonesia’s current energy landscape predominantly depends on fossil fuels and non-renewable energy sources, thereby exacerbating the issue of global warming. On the other side, geothermal utilization in the country still needs to be expanded to reduce the dependency on fossil fuels, particularly through organic Rankine cycle (ORC) systems. As an example, Ulumbu Geothermal Power Plant in Flores Island currently uses a back pressure turbine, which releases expanded steam directly into the atmosphere at 98.7°C and 0.98 bar. This paper presents a thermodynamic analysis of a small-scale Organic Rankine Cycle with 5kW Net power output based on the waste heat data of the Ulumbu Geothermal Power Plant. The study includes selecting the working fluid based on Ozone Depletion Potential (ODP) and Global Warming Potential (GWP) values, thermal efficiency, refrigerant, and steam mass flow rate calculation. Among 20 refrigerants available in Indonesia, R245fa shows promise, offering a Rankine system efficiency of 10-11%, zero ODP, a GWP of 850, and the lowest refrigerant mass flow rate. These parameters inform useful initial parameters for designing a small-scale ORC system producing 5 kW of net power, promoting cleaner and sustainable energy solutions for communities.

Kajian potensi pengembangan teknologi hidrogen sebagai sumber EBT melalui skema CDM dalam mendukung pencapaian NDC Indonesia

Background: In realizing the mitigation of global climate change, Indonesia is committed to participating in formulating policies for the use of environmentally friendly clean energy. One of the policy formulations produced is an effort to reduce emissions by implementing New and Renewable Energy (EBT). Findings: One of the potential uses of EBT that can be developed is hydrogen. Hydrogen technology is a potential fuel-producing technology because it can produce clean and sustainable energy sources without emissions. This article aims to review the prospects and challenges of the potential use of hydrogen-producing technology in Indonesia. Methods: To achieve this goal, the systematic literature review method is used in examining primary and secondary data sources from previous studies. The results of the literature study were then analyzed qualitatively (descriptively). Conclusion: The results of the study show that as a potential fuel, hydrogen is the most abundant element in the earth and can be produced based on the energy source used. In addition to its clean combustion features, the appeal of hydrogen as an environmentally friendly EBT comes from its greater level of effectiveness than gasoline. Based on the results of the comparative analysis, the opportunity for hydrogen production using geothermal energy in Indonesia is considered high because geothermal resources are widespread in several regions of Indonesia. The results of the study also revealed that the cost for small-scale geothermal utilization is 1.08 USD/kgH2 using a power plant. However, of all the resources considered in this article, Steam Methane Reforming (SMR) and coal gasification are the cheapest techniques related to operational technical factors and costs of 1.2 - 2.2 USD / kg.H2. With the CDM mechanism, Indonesia can use hydrogen EBT to achieve national emission reduction targets. This article ends with a form of proposal that can help implement CDM in Indonesia towards achieving national emission reduction targets or Nationally Determined Contribution (NDC).

Design and performance optimization of a novel CAES system integrated with coaxial casing geothermal utilization

At present, the heat storage sub-system in the adiabatic compressed air energy storage system generally has low heat storage density and limited heat storage temperature, resulting in mediocre power generation efficiency of the system. To address these issues, this paper proposes a novel approach for coupling the energy storage system with geothermal energy utilization. This study innovatively uses coaxial casing wells to extract geothermal energy and to preheat compressed air in front of the expander. Detailed numerical investigations and dynamic thermodynamic analysis are carried out to evaluate system performance. Sensitivity and optimization are analyzed to identify the operational and design parameters of the proposed system. In addition, an economic analysis is conducted to estimate the investment and payback of the energy storage system. The results show that geothermal energy utilization can directly and significantly enhance the electric, heating and cooling energy output of compressed air energy storage system. During one 24-hours operation cycle, the electricity output is 104.45GJ, the heating supply output is 81.59 GJ, and the cooling supply output is 16.69 GJ. The RTE and energy efficiency are 64.26 % and 122.68 %, respectively. Economic analysis shows that the static payback period is 12.17 years, and the net present value can reach 3.46 million USD. It can be concluded that geothermal energy plays a greater role in energy storage systems than geothermal power production alone. The compressed air energy storage system combined with geothermal energy addresses current issues and leads to improved system performance.

Evaluation of development potential of pumped hydroelectric storage and geothermal utilization system in abandoned coal mine

Evaluation of development potential of pumped hydroelectric storage and geothermal utilization system in abandoned coal mine

Analysis and optimization of a medium-depth ground source heat pump heating systems with heat storage and borehole heat exchangers

The medium-depth ground source heat pump (MD-GSHP) heating technology is considered a clean energy solution with the potential to mitigate air pollution issues attributed to winter heating in northern China. However, it currently suffers from problems such as a mismatch between heat supply and demand and a lack of optimal operation. To overcome these limitations, this study focuses on a 3000 m2 residential building in Xi’an and implements two configurations: coupling MD-GSHP heating systems with heat storage tank and shallow borehole heat exchanger (BHE). Additionally, an optimization strategy based on the improved particle swarm algorithm is proposed, integrating chaos optimization and dynamic parameters. Finally, noteworthy outcomes were revealed by optimizing the MD-GSHP heating systems under different objective functions. In system coupled with shallow BHE, the variation trend of flow in the medium-depth BHE was similar to that of heating load when the heating cost was taken as the objective function. After the optimization, heating cost reduced by 10.02%, while system coefficient of performance (COP) and medium-depth geothermal utilization coefficient increased by 10.43% and 2.00%, respectively. For system coupled with heat storage tank, the optimized flow exhibited a generally decreasing-increasing-decreasing trend, with the peak preceding the heating load curve. This resulted in a 12.82% reduction in heating cost, along with increases of 10.35% and 1.96% in system COP and the medium-depth geothermal utilization coefficient, respectively. Comprehensive consideration of heating cost and system COP suggested a favorable weight of 2.8 for continuous system operation. In conclusion, when prioritizing heating cost, the system coupled with heat storage tank yields greater economic benefits compared to the system coupled with shallow BHE. The findings of this study can provide a guidance for the applications of the MD-GSHP heating technology.

The Authority of the District/City Government Related to The Utilization of Geothermal Energy According to Article 156 of Law Number 11 of 2006 Concerning the Government of Aceh

Objective: This research examines the Authority of Regency /City Governments related to Geothermal Energy Utilization based on Law No. 11/2006 on the Government of Aceh. Geothermal utilization can help the government program for clean energy utilization, considering that geothermal is a form of renewable energy that produces few greenhouse gas emissions and can maintain national energy stability and security. Based on the provisions of Article 156 of Law No. 11/2006 on the Government of Aceh which regulates the management of natural resources, district/city governments have the authority to manage natural resources in Aceh both on land and at sea, including geothermal energy. However, this authority has not been exercised by the district/city in the utilization of geothermal energy in Aceh. This article aims to determine and analyze the authority of the district/city government in utilizing geothermal energy based on Article 156 of the LoGA the Government of Aceh. This article aims to discuss and analyze the authority of the Regency / City Government in the utilization of geothermal energy sources based on Article 156 of Law No. 11/2006 concerning the Government of Aceh.
 
 Methodology: This research uses a juridical sociological approach which aims to obtain field data as primary data in analyzing the law and looking more deeply at the effectiveness of law in society. This research is supported by primary data and secondary data. Primary data was obtained by conducting field research in several districts (Central Aceh District and Aceh Besar District). While secondary data is obtained by searching the literature and regulations related to the focus of the research, data collection techniques are carried out through structured interviews with the parties involved in this study.
 
 Result and Conlusion: The authority contained in Article 156 of the LoGA has not been exercised by the district/city government in utilizing geothermal energy in Aceh, this is due to regulations issued by the central government regarding the utilization of geothermal energy in the region. Thus, it is necessary to regulate in the form of Qanun Aceh and District/ City Qanun in utilizing geothermal energy in Aceh.

A potential for climate benign direct air CO2 capture with CO2-driven geothermal utilization and storage (DACCUS)

To reduce the overaccumulation of carbon dioxide (CO2) in the atmosphere, direct air CO2 capture (DACC) technologies must (a) satisfy the process requirements for heat and electricity with energy that has few if any CO2 emissions, and (b) physically isolate the CO2 from the atmosphere after its extraction from the air. To isolate the CO2 from the atmosphere at meaningful scale, the CO2 will likely need to be geologically stored in deep saline aquifers. Here we propose to leverage geologic CO2 storage (GCS) in sedimentary basin geothermal resources to produce geothermal heat and electricity for the process energy requirements of solid sorbent DACC. This sedimentary basin CO2-driven geothermal utilization (SB-CO2DGU, also known as CO2 Plume Geothermal) circulates some of the emplaced CO2 to extract geothermal heat in a closed loop between the subsurface reservoir and surface geothermal facility. The proposed integration of DACC and CO2-driven geothermal Utilization and Storage (DACCUS) adds CO2 from the air to this closed loop system that produces renewable energy for use in the DACC process. The strategy first primes the GCS reservoir with CO2 from large point sources, and then integrates CO2 from DACC facility to form the DACCUS system. We focus on the process integration of DACCUS and present a case study of its potential deployment and scaling in the Gulf Coast of the United States. We combine data from prior analyses for a novel investigation of two DACCUS configurations: (1) a DACCUS heat system uses the geothermal heat to regenerate the solid sorbent in the DACC process, and (2) a DACCUS heat and power system uses the electricity generated from the produced geothermal heat for the DACC process. In general, deeper CO2 storage reservoirs (>3.5 km) with higher geothermal temperature gradients (>35 °C km−1), may provide sufficient production wellhead temperatures (>100 °C), and satisfy the electric load in 93% of the combinations of reservoir characteristics we examined.

Threats to human health and ecosystem caused by coal-fired winter heating in China since 2010

Coal-fired winter heating (CWH) results in serious air pollution, but limited studies have investigated its threats to health and ecosystem. The environmental impact and social cost of CWH in China at the province level was quantified via a “bottom-up” life cycle assessment approach. The ecosystem damage and social cost of CWH maintained high values over the last decade, although exhibited a downward trend. Approximately 688 Mt CO2 eq of greenhouse gas emitted from CWH activity in 2019, accounting for 4.9% of China's total emission. Shandong and Liaoning Provinces dominated the nationwide environmental and economic burdens of CWH. Heavy metals atmospherically emitted from CWH exerted significant carcinogenic impacts and showed a correlation with regional cancer incidence (e.g., respiratory, reproductive, urinary, neurological, and blood-lymphatic systems), indicating the potential multi-system damage of CWH. Energy-saving buildings, geothermal utilization, efficient heavy metal end-point control technology, and improving emission factors quality are highly recommended.

Experimental and Numerical Study of the Thermal Properties of Dry Green Swales to Be Used as Part of Geothermal Energy Systems

Low-enthalpy geothermal systems are a promising source for renewable and clean energy for heating, cooling, and air conditioning residential buildings, contributing to the reduction in greenhouse gas emissions in line with the United Nations’ Sustainable Development Goals. Previous research emerged around the geothermal utilization of Sustainable Drainage Systems (SuDS) as multifunctional surfaces for stormwater control and energy saving, developing the water–energy nexus. However, these studies did not comprehensively considered the energy aspects for SuDS design, using non-standardized tests to measure the main thermal parameters. This research aims to address this gap by proposing a novel hybrid engineering procedure to study the thermal properties of SuDS layers and materials through experimental tests combined with steady-state and transient numerical simulations, using green swales operating under dry and wet conditions as a first case study for SuDS techniques. Novel materials incorporated into dry swales (expanded clay and construction and demolition waste) were tested. The results validated this new methodology, reporting an increase of 87% under dry conditions, and 51% under wet scenarios in the thermal insulation performance in comparison to standard materials. A better thermal performance of the systems can be achieved by approaching SuDS design from a holistic viewpoint that integrates energy aspects.

Company Fair Valuation Considering Esg Factor (Case Study: Pt Pertamina Geothermal Energy, Tbk)

The increments of environmental, social, and governance-based investments have been seen recently by institutions or retail investors. The growth has increased rapidly since 2012. Some research gives a positive correlation between the ESG factor represented by ESG rating and company performance. PT Pertamina Geothermal Energy, Tbk. (PGEO), IPO on 24th February 2023 has outstanding ESG performance. It was audited by Sustainable Fitch and got the highest second rank, 77 out of 100 points. Not only is it exceptional ESG performance, but it also has excellent business performance. PGEO started its journey of geothermal utilization in 1974, upon discovering 70 geothermal areas in Indonesia as a sub-business of PT Pertamina EP. PGEO was established in 2006 to continue the efforts to produce clean and environmentally friendly energy, and as of now, it has contributed 82% of the installed geothermal energy capacity in Indonesia. It has the world’s most extensive geothermal installed capacity by December 2021 and promises to expand even more significantly in its prospectus. Investors should consider their value rather than positive sentiment as an investment decision. Then, this study determines whether the PGEO price is undervalued or overvalued considering their project expansion and ESG factor. This study utilizes secondary data from prospectuses, financial statements, annual reports, sustainability reports, company-published documents, and data from IDX.co.id and stockbit.com. The data was gathered and processed to understand the need to expand, analyze its financial performance, and value the company. The author considers company ESG performance to develop financial projections. To fulfill company promises in expansion and stay sustained by adding more production, injection, and startup wells, it needs 1.588.612.527 USD using ESG-based financing. The historical financial performance of PGEO is quite good, but the investor should be careful about its liquidity since the current liability is more significant than its current asset. Based on the calculation of absolute valuation using discounted cash flow, the value of each share of PGEO is Rp12.686,00, which is undervalued, and its IPO price is Rp875,00. Based on relative valuation using PER to its peers and average industry, PGEO’s price is overvalued. The PGEO price that pars with the industry average is Rp490,00. The author can determine the fundamental value of PGEO.

Legal Developments On The Use Of Protected Forest Areas For Geothermal Power

The latest developments related to indirect Geothermal utilization in conservation areas in connection with the issuance of Law Number 11 of 2020 concerning Job Creation, which includes the forestry sector and its amendments through Government Regulation in Lieu of Law Number 2 of 2022 concerning Job Creation. The creation of the facilities provided by the Government can positively impact the ease of Geothermal utilization. The research method used is a normative juridical method. The method of data analysis in this study was carried out qualitatively by elaborating and analyzing various secondary data and legal materials obtained in order to answer each of the problem formulations. Conservation forest areas in the Sumatra region have many animals that must be preserved. Geothermal utilization is required to follow specific standards and norms by not damaging the landscape area of forest areas.

The Geothermal Development Policy on Environmental in Indonesia and the USA

Geothermal utilization is generally used as clean green energy because of its contribution to gradually eliminating high carbon energy. However, in practice, geothermal damage to the environment, even regulation of its utilization does not guarantee environmental justice. This research study aims to determine environmentally just geothermal regulations to eliminate negative environmental impacts and public rejection of geothermal utilization. This study uses normative legal research. The results of this study indicate that geothermal potential can replace high-carbon energy even though it still has a damaging impact on the environment. Community rejection occurs in various areas where geothermal exploitation occurs in conservation forest areas. Geothermal energy regulation in Indonesia is no more pro-ecological than in the USA. Based on the analysis of the legal gap between the theory of ecological justice and the legal triangle and energy policy, it is found that the principles of geothermal regulation must prioritize ecology, not mere exploitation. The findings of this study are strengthening the principles of geothermal regulation based on ecological justice. Standardization of handling and monitoring of environmental impacts must be carried out in an integrated manner based on area category to avoid the widening of the ecological impact of geothermal utilization which results in rejection of the next project.

Evaluation method of underground water storage space and thermal reservoir model in abandoned mine

A large number of mines are closed or abandoned every year in China. Geothermal utilization is one of the important ways to efficiently reuse underground resources in abandoned mines. How to calculate the volume and distribution of underground water storage space is the key to accurately evaluate the sustainable geothermal production in abandoned mines. In this paper, according to the multi-scale characteristics of the underground space in abandoned mine, the flow and heat transfer equations in the multi-scale space are sorted out systematically, and the calculation methods of different secondary space volumes are derived in detail. Taking Jiahe abandoned mine as the background, the volume and distribution of underground secondary space are calculated, and three heat storage evaluation models considering different water storage spaces are established by using COMSOL. The simulation results show that there are great differences among different models, and the results of the equivalent porous media model considering the multi-scale space are most consistent with the reality. Sensitivity analyses of key parameters model results indicated that the heat production is closely related to not only the recharge flow rate but also the recharge temperature and operating time. Furthermore, the energy saving and emission reduction benefits of geothermal utilization in abandoned mines are calculated, the results show that geothermal utilization of abandoned mines can effectively reduce energy consumption and CO2 emissions, and it has great economic benefits.

Present status and sustainable utilization of hydrothermal geothermal resources in Tianjin, China: a critical review

<abstract> <p>Tianjin, as one of the pioneering and most prominent cities in China, has a long history of harnessing geothermal energy. The geothermal resource available in Tianjin is primarily characterized as a low- to medium-temperature hydrothermal geothermal resource. This manuscript introduces the ongoing status and potential of geothermal utilization in China, with a particular focus on the characteristics and utilization status of geothermal resources in Tianjin, China. Moreover, the relevant strategies and challenges for cost-efficient sustainable utilization of Tianjin geothermal resources are identified. The formation parameters of heat storage characteristics of Tianjin geothermal resources are also discussed. In addition, the key paths, guidelines and challenges on how to solve the obstacles related to the geothermal resources development in Tianjin are also suggested. The summarized results indicate that the geothermal reservoirs exploited in Tianjin vary greatly, which include sandstone of Neogene Minghuazhen formation, Guantao formation, Ordovician and Cambrian and carbonate of Proterozoic Wumishan formation. Most of the exploitative geothermal resources (146 geothermal wells) in Tianjin have mainly been produced from the Wumishan formation of the Jixian system and the Guantao formation of the Neogene system. The current production capacity has been doubled, and a two-stage cascade utilization system has been established, incorporating geothermal power generation and geothermal heating. The geothermal utilization share in Tianjin is estimated to be 81.66% for heating, 16.6% for domestic hot water and 1.35% for bathing. In conclusion, notwithstanding the diversity of geothermal resources in Tianjin, it is difficult to guarantee the sustainable development and utilization of geothermal resources in Tianjin due to the unreasonable layout of geothermal wells, imbalance of production and reinjection. Hence, the integration of distributed temperature sensing and distributed strain sensing monitoring demonstrates significant promise and effectiveness in tracking water circulation and detecting flow localization problems as dynamic monitoring processes and smart thermal response tests should be recommended and established as a substantial feature required in the future utilization and development of geothermal resources in Tianjin.</p> </abstract>

Sensitivity Analysis Using One-Factor-at-a-Time and Response Surface Method in Liquid-Dominated Geothermal Reservoir

In addition to extensive information that has been obtained from pre-feasibility, exploration, and drilling phase, we can improve our knowledge of reservoir behavior related to thermal extraction using sensitivity analysis. Such analysis is commonly applied to address technical uncertainty and risks in economic evaluation. The purpose of this study is to determine the parameters that have the most influence on thermal power generation using two different approaches named one-factor-at-a-time or OFAT and response surface method or RSM. Moreover, RSM analysis allowed us to make a predictive model for thermal power extracted in liquid-dominated geothermal reservoir. Literature study is conducted to understand various properties commonly encountered in a liquid-dominated geothermal reservoir including porosity, conductivity, reservoir temperature, and permeability. This information is then used to construct reservoir model in CMG STARS simulator with a single producer and injector. Two different sampling method, named OFAT and Box-Behnken are used to construct dataset, each contains different combination of levels of reservoir porosity, conductivity, temperature, permeability, and re-injection temperature. A total of 31 models using OFAT method with 7-level for each parameter are simulated to understand individual effect of each parameter. Meanwhile, 47 models are constructed using RSM method with 3-level for each parameter to evaluate the effect of interaction between parameters on thermal generation potential as well as constructing predictive model. Sensitivity analysis using both OFAT and RSM agree that the reservoir temperature is the most significant characteristic of geothermal reservoir to affect its thermal power potential. Meanwhile, re-injection temperature that initially expected to strongly effect the lifetime and sustainability of a liquid-dominated geothermal utilization is insignificant. This finding suggest that optimization re-injection temperature is solely for the purpose of maintaining sustainability of geothermal reservoir or cater the concern of environmental issue on wastewater management, and not for maximizing the thermal extraction.

Techno-Economic Assessment of Geothermal Resources in the Variscan Basement of the Northern Upper Rhine Graben

Deep geothermal energy represents an essential component of the future energy supply because the resources greatly exceed the demand, and the base load capability can compensate for temporal fluctuations in wind and solar power. By far, the largest amount of heat is contained in the crystalline basement, accessible almost everywhere through deep drilling. An interdisciplinary approach for a techno-economic resource assessment was applied to provide stakeholders with a more reliable basis for decision-making in the Northern Upper Rhine Graben. This approach incorporated data from various sources such as boreholes, outcrops, geophysical surveys, geomechanical models, and operating geothermal power plants. Emphasis was placed on resources tied to large-scale fault zones, exhibiting preferential hydraulic properties. Uncertainties in the calculations were quantified using Monte Carlo simulations. The resource base in the basement of the Northern Upper Rhine Graben is about 830 PWhth, of which about 8.2–16.1 PWhth could potentially be extracted with current technologies in enhanced geothermal systems. A comprehensive sensitivity analysis was carried out, examining the economic influence of nine parameters. Considering the reference power plant and the energy prices before the Ukraine war began in February 2022, the geothermal reserves are about 65% of the resources. However, given the massive recent increase in heat and electricity prices, a higher percentage is also possible. Finally, a socio-economic-environmental assessment shows that in the Northern Upper Rhine Graben, geothermal resources largely coincide with favorable conditions at the surface, making the region a preferred target for geothermal utilization.

Numerical simulation of thermo–hydraulic coupling processes in fractured karst geothermal reservoirs

Fractured karst geothermal reservoir is a kind of typical geothermal reservoirs with the advantages of abundant storage water and easy reinjection of tail water during the period of geothermal utilization. Such geothermal system is also one of the geothermal reservoirs with the greatest potential for the development and utilization of geothermal energy in China. However, its geological structures are diverse (e.g. pore, fracture and vug), exhibiting complex characteristics of multiple scales, strong heterogeneity and various flow regimes. Therefore, the fluid-heat transfer processes and geothermal production performance of fractured karst geothermal reservoirs are not clarified. In this paper, a numerical model considering thermo–hydraulic coupling processes based on the discrete fracture–vug network approach is put forward, according to the characteristics of fractured–vuggy geothermal reservoirs. In addition, the accuracy of the numerical model is verified. The results obtained from this research are as follows. First, the numerical model considering the thermo–hydraulic coupling process is put forward, in which the Darcy's law is used to describe the flow zone of porous medium, the Navier–Stokes equation is used to illustrate the free flow zone of vugs, and the Beavers–Joseph–Saffman boundary condition is used to couple the fluid flow between these two zones. Second, the connectivity of fracture network is the key parameter to control and evaluate the flow and heat transfer effects in fractured vuggy geothermal reservoirs. The existence of vugs plays an important role in the fluid flow and heat transfer in geothermal reservoirs. Third, the thermo–hydraulic coupling model based on the discrete fracture–vug network can effectively describe the fluid flow and heat transfer processes in fractured vuggy geothermal reservoirs. The connectivity of fracture networks controls the thermo–hydraulic coupling processes in fractured vuggy geothermal reservoirs. Fourth, the existence of vugs seriously impacts the thermo–hydraulic coupling processes in geothermal reservoirs. For instance, on the one hand, it increases the number of high-speed flow channels spanning across the system and even makes the system get connected. On the other hand, it increases the speed of local flow channels inside the system. In conclusion, this proposed method is of great significance for studying the development characteristics and optimizing their geothermal production performance of fractured vuggy geothermal reservoirs.

Vertical ground heat exchanger parameter characterization through a compound design of experiments

Vertical ground heat exchangers (VGHE) are the most extended elements in geothermal utilization systems. For design and optimization purposes, the precise determination of several thermal properties is of utmost importance. While soil properties can be accurately obtained from simple mathematical models and short identification procedures, the grout characterization and additional uncertainties are usually identified from time-consuming and complex models. In order to optimize and simplify this process, without loss of accuracy, the present work proposes the use of design of experiments (DoEs) for that estimation. Thus, a multi-physic 3D model that replicates the geothermal heat exchanger (GHE) environment has been employed to develop a fractional factorial design of experiments, obtaining a set of output errors by comparison with experimental data. A response surface methodology (RSM) has been used to conduct second-order linear regression fittings, that approximate the error functions to obtain the parameter values through the minima of such surfaces. Overall mean errors lower than 0.01 °C are obtained, which provide excellent agreement in modelling the experimental test. Finally, an additional full-scale experiment has been simulated in order to validate the numerical DoE approach. Consequently, the proposed methodology has been demonstrated to accurately predict the grout thermal parameters.

Geological and environmental implications of the utilisation of geothermal energy in the Lahendong working area, Indonesia

This study presents the characteristics of the Lahendong geothermal working area (GWA) in terms of the geological, geophysical, geochemical, and environmental implications. The investigated area is located in the Sulawesi North Arm, where the volcanic arc extends from Sangihe Island to Minahasa with two major strike-slip faults. NE–SW (northeast-southwest) trending faults control the thermal surface manifestation. The geothermal field is grouped into two hydrochemical systems: acid-sulphate-chloride (acid reservoir) and chloride (closer to neutral) types. The environmental implication analysis shows that the North Sulawesi province is experiencing water shortages due to excessive mining activities, inadequate wastewater management, and periods of drought. Although geothermal wastewater is being re-injected, the possibility of water contamination by hazardous materials from geothermal power plant activity is still evident. This study reviews the actual geothermal utilisation in the form of the 120 MWe power plant, the 500 kWe binary power plant, while the heat from geothermal energy is used for palm sugar production. Furthermore, the article also analyses the potential of the rational use of geothermal resources in this area. As a result of the high salinity and silica concentration of the brine, the geothermal wastewater should be treated before further utilisation and it potentially benefits both local communities and geothermal companies.