Geothermal Prospect Research Articles

Application of CSAMT Geophysical Method in Geothermal Exploration of Beijing

Abstract Geothermal resources are abundant in the southeast urban area of Beijing, but the complex geological structure and high geomagnetic interference in the urban area make it difficult to detect the distribution characteristics of geothermal resources by the electromagnetic exploration method from natural sources. This paper presents an integrated physical exploration method combining the controlled source acoustic magneto-telluric (CSAMT) and gravity exploration for middle-deep geothermal exploration in the southeast Beijing urban area. The method is verified by examining the recommended boreholes, which have produced water at temperatures of 62.5°C and 63°C. This is a highly beneficial and socially impactful outcome, and it serves as a valuable reference for future exploration and utilization of geothermal resources in this area. It also has significant implications for future exploration and utilization of geothermal resources not only in the southeastern urban area of Beijing but also in similar urban environments around the world. The methodologies and findings from this research offer a valuable blueprint for future geothermal energy prospecting and development, contributing to the global transition towards cleaner and more sustainable energy alternatives.

Geothermal Resource Assessment and Development Recommendations for the Huangliu Formation in the Central Depression of the Yinggehai Basin

As a renewable resource, geothermal energy plays an increasingly important role in global and regional energy structures. Influenced by regional tectonic activities, multi-stage thermal evolution, and continuous subsidence, the subsurface temperatures in the Yinggehai Basin has been consistently rising, resulting in the formation of multiple geothermal reservoirs. The Neogene Huangliu Formation, with its high geothermal gradients, suitable burial depths, considerable thickness, and wide distribution, provides excellent geological conditions for substantial geothermal resources. However, the thermal storage characteristics and geothermal resources of this formation have not been fully assessed, limiting their effective development. This study systematically collected and analyzed drilling, geological, and geophysical data to examine these reservoirs’ geometric structures, thermal properties, and physical characteristics. Further, we quantitatively evaluated the geothermal resource potential of the Huangliu Formation and its respective reservoirs through volumetric estimation and Monte Carlo simulations, pointing zones with high geothermal prospects and formulating targeted development strategies. The findings indicate: (1) The Yinggehai Basin exhibits an average geothermal gradient of 39.4 ± 4.7 °C/km and an average terrestrial heat flow of 77.4 ± 19.1 mW/m2, demonstrating a favorable geothermal background; (2) The central depression of the Huangliu Formation harbors considerable geothermal resource potential, with an average reservoir temperature of 140.9 °C, and a total geothermal resource quantified at approximately 2.75 × 1020 J, equivalent to 93.95 × 108 tec. Monte Carlo projections estimate the maximum potential resource at about 3.10 × 1020 J, approximately 105.9 ×108 tec. (3) Additionally, the R14 and R23 reservoirs have been identified as possessing the highest potential for geothermal resource development. The study also proposes a comprehensive utilization model that integrates offshore geothermal power generation with multiple applications. These findings provide a method for the evaluation of geothermal resources in the Yinggehai Basin and lay a foundation for the sustainable development of resources.

An assessment of prospects of geothermal energy in India for energy sustanability

The search for indigenous, renewable, environment-friendly, and sustainable energy resources has increased globally during the past few decades. Geothermal energy is one such ubiquitous source of energy, having the potential to become an alternate energy resource with a reduced carbon footprint. In this study, eight crucial characteristic parameters, i.e., heat flow, thermal gradient, Curie point depth, lithology, basement depth, crustal thickness, and seismicity, were integrated into a multi-criteria decision model framework to identify areas that may have the potential for geothermal energy in India. The weights of various parameters estimated using AHP are in the order of heat flow (∼ 0.252), followed by the Curie point depth (∼ 0.195), thermal gradient (∼ 0.173), and crustal thickness. Our analysis indicates that the geothermal province in the Himalayas (including the NW and NE regions), SONATA lineaments, central parts, and some parts of the west coasts and Mahanadi graben may have better prospects of geothermal energy compared to other tectonic provinces. We find that ∼14.86%, and ∼21.98 % of the study region have extremely high to high geothermal potential. About ∼ 27.18 % of the region have medium geothermal prospects, whereas ∼ 11.78 % and 24.20 % of the region have very low to low potential for geothermal energy.

Seismic Node Arrays for Enhanced Understanding and Monitoring of Geothermal Systems

Abstract Harnessing geothermal energy will likely play a critical role in reducing global CO2 emissions. However, exploration, development, and monitoring of geothermal systems remain challenging. Here, we explore how recent low-cost seismic node instrumentation advances might enhance geothermal exploration and monitoring. We show the results from 450 nodes deployed at a geothermal prospect in Cornwall, United Kingdom. First, we demonstrate how the nodes can be used to monitor the spatiotemporal and size distribution of induced seismicity. Second, we use focal mechanisms, shear-wave source polarities, and anisotropy to indicate how the dense passive seismic observations might provide enhanced insight into the stress state of the geothermal systems. All the methods are fully automated, essential for processing the data from many receivers. In our example case study, we find that the injection-site fracture orientations significantly differ from that of the crust above and the regional stress state. These observations agree well with fracture orientations inferred from independent well-log data, exemplifying how the nodes can provide new insight for understanding the geothermal systems. Finally, we discuss the limitations of nodes and the role they might play in hybrid seismic monitoring going forward. Overall, our results emphasize the important role that low-cost, easy-to-deploy dense nodal arrays can play in geothermal exploration and operation.

Dimensionality and Geoelectric Strike Analysis of 2D Magnetotelluric Modeling in Geothermal Area “XYZ”

Abstract Magnetotelluric (MT) method is crucial in geothermal exploration due to its capability to delineate geothermal prospect area by mapping subsurface resistivity distribution. However, in 2D Magnetotelluric modelling, galvanic distortion can distort the regional MT responses, leading to interpretation errors. This study employs phase tensor analysis to eliminate galvanic distortion. Results reveal the dimensionality of each station and three variations of the tipper strike, often referred to as the geoelectric strike. The tipper strike of each station showed varying values, while the tipper strike of all stations indicated N35°E. The tipper strike results required validation against additional geological information, such as faults, fractures, and changes in lithology, significantly influence the conductivity structure of subsurface, which indicated a geological strike of approximately N30°E. This study compares the MT data without rotation, rotation to tipper strike of each station, and tipper strike of all stations to assess effectiveness in eliminating galvanic distortion and improving data quality. The resulting 2D Magnetotelluric cross-section rotated to the tipper strike of all station, exhibits the lowest RMS Error of 2% and roughness of 654.6 among other variations, indicating improve quality. This interpretation identifies a geothermal system in the study area, closely aligning with actual subsurface geological conditions.

Structural Geology Identification based on Derivative Analysis Gravity Data in Tangkuban Perahu Mountain

The earth is composed of structures with different rock types, properties, and characteristics and can be known by applying the laws of physics in the form of geophysical methods such as the gravity method. The gravity method is a passive geophysical method that is widely used for geodynamic and exploration studies in estimating fault structures. The aim of this research is to model the subsurface geological structure based on the results of derivative analysis of gravity data related to geothermal prospects. The data used are GGMplus gravity acceleration data and topography (elevation) from each measurement point, totaling 6889. The data was then subjected to several corrections to produce a complete Bouguer anomaly. Then, the next stage is derivative analysis, which is used to obtain a subsurface geological structure model and geothermal prospects for the Tangkuban Perahu area. Based on the correlation between derivative analysis and two-dimensional modeling results, it can be seen that the Tangkuban Perahu geothermal system is controlled by structures in the form of horsts and grabens formed due to Tangkuban Perahu volcanic activity. The Tangkuban Perahu geothermal reservoir prospect is estimated to be at a depth of around 0.6 km – 2.8 km with a density ranging from 2.15 g/cc to 2.45 g/cc, which is estimated to be basalt breccia.

Discussion on Deep Geothermal Characteristics and Exploration Prospects in the Northern Jiangsu Basin

The Northern Jiangsu Basin (NJB), located at the northeast edge of the Yangtze block, is not only rich in oil and gas resources but also contains abundant geothermal resources. Nevertheless, the distribution of geothermal resources at medium depth in the NJB is still unclear due to its complex geological structure and tectonic–thermal evolution process, which restricts its exploitation and utilization. The characteristics of the geothermal field and distribution of geothermal reservoirs within the NJB are preliminarily analyzed based on available temperature measurements and geothermal exploration data. The prospective areas for the exploration of deep geothermal resources are discussed. The analysis results show that (1) Mesozoic–Paleozoic marine carbonate rocks are appropriate for use as principal geothermal reservoirs for the deep geothermal exploration and development within the NJB; (2) the geothermal field is evidently affected by the base fluctuation, and the high-temperature area is mainly concentrated at the junction of the Jianhu uplift and Dongtai depression; (3) the southeast margin of Jinhu sag, Lianbei sag, the east and west slope zone of Gaoyou sag, the low subuplifts within the depression such as Lingtangqiao–Liubao–Zheduo subuplifts, Xiaohai–Yuhua subuplifts and the west of Wubao low subuplift, have good prospects for deep geothermal exploration.

Integrated coupled assessment of geostorage and geothermal prospects in the oil fields of Upper Assam Basin

This study proposes an integrated approach of assessing CO2 storage potential and geothermal energy prospect based on the data of seventeen depleted wells of Upper Assam Basin which could assist the global objective of net zero transition. The petrophysical properties of Tipam, Barail and Lakadong + Therria Formations from the seventeen wells have been utilised to perform the Monte Carlo simulation for probabilistic estimation of the CO2 storage in the Upper Assam Basin. This preliminary work showed that the mean storage capacity of 18.8 ± 0.7 MT, 19.8 ± 0.9 MT and 4.5 ± 0.8 MT could potentially be stored in the three geological formations of the basin. The corrected bottom hole temperature values for the studied seventeen wells were determined using the well log data and Waples and Harrison method; these values provided a static geothermal gradient for each well, which varies widely from 0.017 to 0.033 °C/m. In order to enable geothermal prospectivity, static formation temperature maps have been generated for the studied wells. The probabilistic assessment of stored heat-in-place and formation temperature maps delimited five prospective sites for the extraction of geothermal energy in the basin. The study also presented a risk assessment for CO2 storage development in the basin. Further, the study illustrated an economic analysis of the implementation of a CO2 storage project and geothermal operations in the basin.

Advances in Thermal Infrared Remote Sensing Technology for Geothermal Resource Detection

This paper discusses thermal infrared (TIR) remote sensing technology applied to the delineation of geothermal resources, a significant renewable energy source. The technical characteristics and current status of TIR remote sensing is discussed and related to the integration of geological structure, geophysical data, and geochemical analyses. Also discussed are surface temperature inversion algorithms used to delineate anomalous ground-surface temperatures. Unlike traditional geophysical and geochemical exploration methods, remote sensing technology exhibits considerable advantages in terms of convenience and coverage extent. The paper addresses the major challenges and issues associated with using TIR remote sensing technology in geothermal prospecting.

Identification of regional rock depth-residual gravity anomaly based on spectrum analysis of geothermal prospect area of Wayratai Lampung

Identification of regional rock depth-residual gravity anomaly based on spectrum analysis of geothermal prospect area of Wayratai Lampung

Assessment of the geothermal potential zone of India utilizing GIS-based multi-criteria decision analysis technique

India, with 80 % energy demand reliant on fossil fuels, is the world's third-largest greenhouse gas emitter, necessitating a shift from fossil fuels to renewable energy. While solar and wind production has grown, geothermal energy remains untapped despite enormous prospects in the country. In this regard, India's first regional-scale geothermal potential (GP) map has been prepared using a GIS based on a multi-criteria decision analysis technique. Five thematic layers (geology, fault, heat flow, thermal spring, and earthquake epicenter) have been used to calculate GP index, which is divided into high, moderate, and low categories. The result shows that most geothermal drilling sites are distributed in the high GP category zone, showing high efficacy. Further, a joint study of the geothermal surface and reservoir temperature with the present study shows that the northern and western parts of India have significant potential for geothermal exploration. Our result also reveals that the projected CO2 emissions are approximately 2.6 gigatons (which is lower than other energy sources) for an output of 10 GW using geothermal energy in the next 75 years. This study can enhance geothermal prospect identification, cutting exploration costs, and site selection, and contributing to multiple UN Sustainable Development Goals.

Joint Diagnostic Approach to Pressure and Tracer Responses from Reservoirs: An Experimental and Theoretical Study to Estimate the Accuracy of Reservoir Models

This study presents a novel perspective for improving the understanding of permeable structures at geothermal prospects by jointly diagnosing the responses of conventional pressure transient and tracer testing. The pressure and tracer responses individually yield apparent porosity–thickness products. The difference between them implies the existence of unknown dead-end features involved in a reservoir model. Laboratory experiments and numerical simulations validate this concept. Potential application to hypothetical exploration demonstrates that the logarithmic ratio of the porosity–thickness products, determined based on pressure and tracer responses, indicates the accuracy of the reservoir model to be successively updated with the progress of the exploration. The reservoir model successfully reproduced the synthetic observations regardless of the accuracy of permeable structure if different porosity–thickness products were allowed to be assumed to individually reproduce pressure and tracer responses. These porosity–thickness products coincided only if the reservoir model correctly captured the permeable structure. This novel perspective will provide strategic guides for successful exploration and development at the prospects of geothermal and, potentially, general geofluid resources.

Differences and Causal Mechanisms in the Lithospheric Thermal Structures in the Cratons in East China: Implications for Their Geothermal Resource Potential

The thermal structure of the lithosphere is key to understanding its thickness, properties, evolution, and geothermal resources. Cratons are known for their low heat flow and deep lithospheric roots. However, present-day cratons in East China have geothermal characteristics that are highly complex, with variable heat flow values, diverging from the typical thermal state of cratons. In this study, we conducted a detailed analysis of the geothermal geological background of the cratons in East China, summarizing the thermal state and tectono-thermal processes of different tectonic units, calculating the temperature at various depths, and discussing differences in temperature and thermal reservoirs at different depths. The observed lithospheric thermal thickness within the North Jiangsu Basin and the Bohai Bay Basin is notably reduced in comparison to that of the Jianghan Basin and the Southern North China Basin. The phenomenon of craton destruction during the Late Mesozoic emerges as a pivotal determinant, enhancing the geothermal resource prospects of both the Bohai Bay Basin and the North Jiangsu Basin. Our findings contribute significantly to the augmentation of theoretical frameworks concerning the origins of heat sources in global cratons. Furthermore, they offer invaluable insights for the methodical exploration, evaluation, advancement, and exploitation of geothermal resources.

Single well geothermal heating systems: Technical and economic assessment of two widely-used configurations

Benefiting from the closed wellbore space, the single well geothermal heating system (SWGHS) could avoid a large number of environmental problems compared to conventional geothermal systems. Combined with heat pump, this technology is attracting growing interest for the development of district heating based on medium-depth geothermal resources. Efforts of the scientific community and of business operators now focus on the technical optimization and commercial viability of the different SWGHS concepts already available. Here, we numerically investigate the heat extraction performance of a butted- and a vertical-well SWGHS possibly operational in a geothermal prospect area in Xi’an, central China. We addressed the performance of the two systems in terms of outlet temperature, heat production rate, heating area, and economic benefits. Sensitivity analysis suggests that large circulation rates and low inlet temperatures have beneficial effects on both thermal efficiency and economic benefits of the project. Our integrated technical and economic analysis suggests that the butted-well SWGHS configuration is particularly suitable for long-run, large-scale applications, compared to the vertical-well design. This work can provide valuable references for the applications of SWGHS, which is of criterial importance for reaching carbon peaking and carbon neutrality goals.

Integrated geophysical methods to constrain subsurface structures of Tulu Moye-Bora-Berecha axial volcanic complex, main Ethiopia rift: Implications for geothermal resources

The Main Ethiopian Rift (MER) is a well-known continental rift whose axial sector is characterized by the occurrence of regularly spaced silicic caldera complexes and central stratovolcanoes, interspersed with large fields of fissural basalts, small mafic scoria cones and numerous young normal faults and fissures. The Tulu Moye-Bora-Berecha volcanic complex is found in the central portion of the MER and includes the Tulu Moye geothermal prospect area. A combination of gravity and magnetic methods was used to better constrain the subsurface volcanic stratigraphy and tectonic structures. Regional and residual anomaly maps were produced from the gravity data and the magnetic data were corrected to produce anomaly and enhanced maps. A complete Bouguer anomaly contour map was produced after the necessary reduction was applied to the gravity data. Due to the geomagnetic field's dipolar nature and since the study area is in the equatorial region (<15°), the reduced-to-equator (RTE) technique was used to minimize external effects and correct the data as if the body had been laid at the magnetic equator. The anomalous source's depth was calculated using a Euler depth solution and spectral analysis approach. Joint 2D forward models on three profiles were developed using GM-SYS of Oasis Montaj software. From the interpretation of the geophysical results, the following conclusions have been reached: (1) the crystalline basement is more raised around Salen ridge and west of it; (2) the main heat source of the geothermal system appears to be a central region of the studied area near Salen ridge and is estimated to be at 4–5 km depth, (3) under Gnaro obsidian dome, the basaltic and silicic volcanic horizon is thin, and the deep-seated regional fault serves as the main conduit for the passage of hot fluid to the surface and (4) the gravity and magnetic anomaly plots, regional-residual maps and enhanced data plots all indicate towards the existence of a major geological feature-a large caldera-comprising of Tulu Moye, Bora and Berecha volcanic centers.

Soil CO2 fluxes measured in the Acoculco Geothermal System, Mexico: Baseline emissions from a long-term prospection programme

The Acoculco Caldera Complex is considered a promissory hidden high-temperature geothermal system in Mexico. To support the geothermal prospection of this anomalous area, a comprehensive programme of soil CO2 flux measurements was performed. A long-term measurement programme was conducted to determine the baseline of natural soil CO2 effluxes. Significant efforts were devoted both to measuring the CO2 fluxes between 2015 and 2022 and interpreting their origin. Eighteen soil gas surveys of CO2 were carried out by using the accumulation chamber method. >1200 diffuse CO2 fluxes were measured in six different areas of the Acoculco Caldera. Two areas (Los Azufres and Alcaparrosa) exhibited cold degassing sites, acid-sulphate springs, and gas bubbling in surface water bodies. The soil CO2 fluxes ranged from 1 to 26,000 g m−2 d−1, whereas lower fluxes <29 g m−2 d−1 were determined as the degassing baseline. A total CO2 output of 492 t d−1 km−1 was estimated using an integrated SGS-GSA approach, where the highest total soil CO2 fluxes were obtained for Alcaparrosa (299 t d−1 km−2) compared with Los Azufres (164 t d−1 km−2), and Surroundings (29 t d−1 km−2). Such results agree well with those values measured in other worldwide volcanic and active geothermal ecosystems. The range of CO2 isotopic composition values from −28.83 ‰ to −3.11 ‰, together with their statistical distribution, suggests multiple CO2 production sources feeding soil degassing. The combined interpretation of flux and isotopic data allowed us to identify two distinct gas sources: endogenous and biogenic. The present study highlights the importance of using soil CO2 monitoring to determine baseline emissions at the early exploration stage of geothermal systems.

Identification of Rock Characteristics Using the Microtremor Inversion Method at Air Putih Geothermal Field, Lebong Regency

Research has been carried out to identify rock characteristics based on Vs values using the microtremor method in the Air Putih geothermal field, Lebong Regency, which aims to determine the geothermal prospect area on rock characteristics using Vs values based on the microtremor method. The data obtained in this study were 20 measurement points obtained from data analysis by obtaining the H/V curve through Geopsy software and HVSR inversion to obtain the Vs value of the inverse. The results of this calculation indicate that at a depth of 0-4 meters the homogeneous Vs value 200 m/s, at a depth of 4 meters the Vs value 200-440 m/s, at a depth of 20 meters the value of Vs 440 -880 m/s and a depth of 20 meters homogeneous Vs value of 880 m/s and for the distribution of Vp values, at a depth of 0-5 meters the Vp values vary between 2000-2900 m/s, at depths of 6-20 meters in general the value of the Vp wave velocity is the same in the range of 3100-3800 m/s and at depth 21-100 meters the Vp value ranges from 3900-5100 m/s. This shows that the greater the depth, the denser the rock.

Use of cold waters geochemistry as a geothermal prospecting tool for hidden hydrothermal systems in Réunion Island

Most untapped high-enthalpy geothermal resources are blind, meaning lacking surface evidence of their existence. The first step in their discovery is to find evidence of hydrothermal activity. Here we apply an approach based on the geochemistry of cold waters, which allowed us to identify evidence of the existence of a hydrothermal system at Piton de la Fournaise volcano (Réunion Island), and constrain its location. This approach uses the concentrations in B, Li, SO4, F, Mo, P, V, As and HCO3 and the isotopic ratios δ13C and δ11B as geochemical markers of hydrothermal activity that can be used even in waters with extremely low ion content (Electrical conductivity <80 µS/cm), and even when their geochemical composition is mainly controlled by other processes. This noninvasive approach is easy to implement and can be applied wherever the presence of a blind geothermal system is suspected.

Influence of subsurface temperature on cryogenic fracturing efficacy of granite rocks from Kazakhstan

Liquid nitrogen (LN2) is a new stimulation technology suitable for geothermal energy extraction that increases porosity, permeability, and overall contact area in candidate subsurface formations. It is considered appropriate for hot dry rock (HDR) reservoirs. Due to the significant temperature difference between hot rock and cryogenic fluid, extensive thermally induced cracking is anticipated upon contact, which is helpful in future water-steam cycling operations. To examine the degree of rock integrity failure in granite samples as a function of exposure mode, different procedures were followed for comparison. In particular, three commercial granite samples from three regions of Kazakhstan: Kapal-Arasan, Zhylgyz, and Zheltau, were heated to various elevated temperatures prior to immersion in LN2 with variations in freezing time (FT) and numbers of freezing-thawing cycles (FTC). Samples were examined by various methods to quantify the impact of the cryogenic fracturing process. Compression, acoustic emission (AE), and permeability tests were performed on granite with different starting temperatures ranging from 200 °C to 500 °C. Permeability enhancement was generally in the range of 50-90 %. Scanning electron microscopy (SEM) was also used to document the microscopic characteristics of thermally-induced cracks and indicated most induced fractures to be microscale features. Results showed reductions in Unconfined Compressive Strength of LN2-treated samples by up to 76 %. The experimental outcomes demonstrate that LN2 cooling of hot granite induces mechanical rock failure and permeability augmentation. Furthermore, the degree of thermo-fracturing increases with temperature difference and time of LN2 treatment in both freezing time and freezing-thawing cycle methods. This is the first systematic study of its kind to test three commercially available granites from Kazakhstan with this combination of examination tools to assess alternate cryo-fracturing methods for geothermal energy prospecting and contact area enhancement.

Three-dimensional magnetotelluric and gravimetric imaging of Mount Lawu geothermal prospect area, Indonesia

Mount Lawu is a stratovolcano located on the border of Central Java and East Java Provinces in Indonesia. At least eleven manifestations indicate its geothermal potential in the form of hot water and fumaroles. This study aims to describe a geothermal system based on an integrated analysis of magnetotelluric (MT) and satellite gravity data. Some additional geochemical and petrological data analyses were also used to explain the existing hydrothermal system in this area. It is inferred from the gravity derivative analysis that fault structures exist in a location with high permeability, which acts as a controlling structure for geothermal manifestations. The 3-D resistivity inversion was carried out using MT full-impedance tensor data, while the 3-D density model was reconstructed based on the residual anomaly computed from the topography-free gravity disturbance. The 3-D resistivity model, from magnetotelluric inversion, shows a clay cap distribution, corresponds to a low resistivity anomaly, centered at the southern part of the mountain peak with a thickness of about 1 kilometer, which narrows to the western region where the hot spring shows an outflow manifestation. The gravity inversion shows several low-density bodies in the same location as the low-resistivity anomaly attributed to a clay cap. Coincident resistivity and density anomalies constrain the horizontal location of the geothermal reservoir. Despite the incapability of the model to resolve the body of the geothermal heat source, it can be inferred from the inversion results that the heat possibly emanates through the thermal conduction passage below the reservoir zone from the source located deeper down than the reconstructed models.