Geothermal Energy Development Research Articles

A Novel Geothermal Wellbore Model Based on the Drift-Flux Approach

Geothermal energy, being a clean energy source, has immense potential, and accurate wellbore modeling is crucial for optimizing the drilling process and ensuring safety. This paper presents a novel geothermal wellbore model based on the drift-flux approach, tested under three different temperature and pressure well conditions. The proposed model integrates the conservation equations of mass, momentum, and energy, incorporating the gas–liquid two-phase flow drift-flux model and heat transfer model. The key features include handling the heat transfer between the formation and the wellbore, addressing the slip relationship between the gas and liquid phases, and accounting for wellbore friction. The nonlinear equations are discretized using the finite difference method, and the highly nonlinear system is solved using the Newton–Raphson method. The numerical simulation, validation, and comparison with existing models demonstrate the enhanced accuracy of this model. In our tests, the model achieved a high accuracy in calculating the bottom-hole pressure and temperature, with mean relative errors (MREs) significantly lower than those of other models. For example, the MREs for the bottom-hole pressure and temperature of the Rongxi area well in Xiongan, calculated by this model, are 1.491% and 1.323%, respectively. These results offer valuable insights for optimizing drilling parameters and ensuring drilling safety. Comparisons indicate that this approach significantly outperforms others in capturing the complex dynamics of geothermal wellbores, making it a superior tool for geothermal energy development.

Numerical Simulation of Geothermal Energy Development at Mount Meager and Its Impact on In Situ Thermal Stress

The Meager Mountain Geothermal Project stands as one of the pioneering geothermal energy initiatives in its early stages of resource development. Despite its abundant geothermal heat resources, no prior studies have systematically evaluated the potential of implementing coaxial borehole heat exchangers on site. This study addresses this research gap by presenting a comprehensive heat transfer model for an underground closed-loop geothermal system utilizing a single coaxial well. Finite element analysis incorporated fluid and solid heat transfer, as well as solid mechanics. The results obtained facilitated the construction of the temperature and thermal stress profiles induced by the cooling effects resulting from years of heat extraction. After 25 years of operation, the outlet temperature has reached approximately 74 °C, and the maximum radial tensile thermal stress amounts to ~47 MPa. Furthermore, the analysis demonstrates that higher fluid velocities contribute to more perturbed temperature and stress distributions. The study attained maximum thermal and electric power outputs of 208 kW and 17 kW, respectively. This research also underscores the significant impact of geothermal gradient and well length on BHE design, with longer wells yielding more power, especially at higher injection velocities.

Experimental study on mechanical damage and creep characteristics of Gonghe granite under real-time high temperature

It is significant to study the mechanical properties of hot dry rock (HDR) for the development of deep geothermal energy. At present, the creep behavior of granite under real-time high temperature is not fully understood. The creep behavior of granite at 25 ∼ 800°C was investigated by real-time high-temperature uniaxial compression and graded load creep tests, and the thermal damage mechanism of granite was studied by scanning electron microscopy (SEM) experiments. The paper systematically analyzes the evolution of mechanical indexes such as uniaxial compressive strength (UCS), elastic modulus, creep deformation, steady creep rate and long-term strength of granite under thermal-force coupling. The results show that the UCS and elastic modulus of granite increase with increasing temperature in the range of 25 ∼ 200 °C, and decrease with increasing temperature in the range of 200 ∼ 800 °C. The damage speed of granite is the fastest in the temperature range of 400 ∼ 600 °C. The steady creep rate of granite increases with the increase of temperature and stress level. The ratio of long-term strength to UCS decreases with increasing temperature, from 93.6% at 25 °C to 73.2% at 800 °C. The research results provide relevant thermal damage mechanical parameters and theoretical basis for the development of HDR.

Geological conditions for the development of geothermal energy in Azerbaijan

Geological conditions for the development of geothermal energy in Azerbaijan

Investigation on failure characteristics of mode II crack in heat-treated granite specimen subjected to dynamic loading

In order to solve the energy crisis, geothermal energy development has been increasingly valued in recent years. In many geothermal engineering projects, hydraulic fracturing can cause many cracks to appear inside the rock mass during the extraction process of dry hot rock. At present, there have been many studies on mode I cracks and mixed mode I/II cracks. In order to ensure the smooth progress of the project, it is necessary to supplement the research on mode II crack rocks in high-temperature geothermal environments. A series of experiments were conducted using the Split Hopkinson Pressure Bar (SHPB) device and cracked granite specimens treated at different temperatures, the failure modes could be tracked by using a high-speed camera. The dynamic experiment was simulated using software coupling. The Grain Boundary Model (GBM) can well describe the force-thermal coupling damage behavior among various crystal particles. Some analyses were conducted on dynamic fracture toughness, failure mode, strain distribution, thermal damage, and changes in the number of cracks. The research results illustrated that high temperatures lead to a decrease in the mode II fracture toughness of granite, an increase in fracture time, and greater susceptibility to damage. High temperature will increase the maximum strain at the moment of failure. It was also found that the proportion of intra-grain cracks increased with the temperature. After 500 °C, the number of cracks generated during the fracture process is inversely proportional to the temperature.

Study on the integrity assessment of geothermal wellbore under thermal and non-uniform in-situ stresses coupling effects

During the development of geothermal resources, thermal and non-uniform in-situ stresses can lead to wellbore integrity failures in geothermal wells. To evaluate the integrity of casing-cement-formation combination system under coupled thermal and non-uniform in-situ stress, an integrity evaluation mathematical model is established based on thermodynamics, elastodynamics, and the equivalent stress criterion. The performance of cement sheath mechanics and combination system sealing under different temperature conditions is investigated based on the designed experimental apparatus. By integrating numerical simulation and experimental approaches, a method to evaluate the integrity of the wellbore combination system in geothermal wells has been developed and the risk of temperature variations and non-uniform in-situ stresses on the casing, Cementing I and II interfaces has been analysed. Experimental results show significantly reduced mechanical and sealing performance under high temperature conditions. Numerical simulations indicate that the Cementing I and II interfaces, as well as the cement sheath, serve as weak points for potential integrity failure in geothermal wells, with Cementing I interface being particularly susceptible. The developed method can effectively evaluate the wellbore combination system integrity under the coupling effect of thermal stress and non-uniform in-situ stress, which is crucial for ensuring the wellbore integrity and safe development of geothermal energy.

The role of salt basins in the race to net zero: a focus on Australian basins and key research topics

Globally, many salt basins host highly productive fossil fuel resources and provide excellent opportunities for developing economically viable clean energy systems such as (1) energy storage in salt caverns, including hydrogen, helium, natural gas, and other economic gases; (2) permanent sequestration of carbon dioxide; (3) development of geothermal energy; (4) critical mineral exploration and extraction, and (5) natural hydrogen production. Despite the high potential to deploy financially viable clean energy solutions related to the formation and evolution of salt basins, our current knowledge regarding critical aspects of salt basin characterisation in Australia is limited. New research is necessary to develop these sustainable energy systems and achieve net zero emissions; therefore, it is critical to re-evaluate the geology of salt basins. Key research areas to enable these opportunities relate to the precipitation, deposition, and deformation of salt basins. This paper reviews the potential for a range of energy systems within salt basins, outlines emerging research topics, and demonstrates the value of Australian salt basin outcrop analogues for improved subsurface interpretation globally.

Arguments for a Community-Based Approach to Geothermal Energy Development

This paper investigates the theoretical foundation for developing renewable geothermal resources locally. For this reason, we pay attention to the role of communities in geothermal development. We derive it from the integral characteristics of geothermal energy next to the shift in the energy transition policies to focus on managing green resources locally. This study presents arguments for a framework that approaches geothermal resources as an endogenous factor of community development. To analyse it, we create a model that explains the local economic characteristics of geothermal exploitation beyond its geological conditions. It aims to conceptualise a community-based geothermal development standard referring to the endogeneity principle. Geothermal energy is given attention since the characteristics of this resource determine its use locally. This induces the internalisation of labour and technology in the local economic system, a specific condition for local geothermal projects where a community remains a prime beneficiary. We argue that the role of communities in geothermal exploitation is pivotal in the process of green growth for further expansion of geothermal energy use.

Effects of saturated fluids on petrophysical properties of hot dry rock at high temperatures: An experimental study

Hydraulic fracturing is a crucial technology for efficient heat extraction from hot dry rock (HDR). The fracturing process involves the injection of large volumes of cold fluids, which can significantly affect the petrophysical properties of the rock, particularly when temperature differences and fluid-rock interactions are taken into account. However, there is a lack of research on the evolution of HDR petrophysical properties under the influence of different fluids at high temperatures. In this paper, we utilized a high-temperature high-pressure tri-axial loading system, rock spontaneous imbibition instrument, porosity-permeability tester, and thermal conductivity meter, along with comprehensive analysis techniques such as ultrasonic wave velocity monitoring, CT scanning, and nuclear magnetic resonance (NMR), to systematically investigate the effects of distilled water and nano emulsion on the physical and mechanical properties of the HDR at high temperatures. Through comparison with the experimental results of dry samples, comprehensive characteristics of physical parameters for the HDR under the influence of distilled water and nano emulsion are obtained, such as spontaneous imbibition mass and permeability, thermal physical properties, and rock mechanical parameters. The experimental results show that temperature increase promotes the formation of massive thermal damage fractures in the HDR samples, and the fluid weakens the mechanical strength of the HDR. When the effects of temperature and saturated fluids are combined, the hydraulic fracture network in the HDR samples exhibits increased complexity, contrasting with the fracture patterns observed in the heat-treated dry samples. The distilled water has a more pronounced effect on weakening the mechanical strength of the samples than the nano emulsion. Moreover, the analyses of permeability, thermal conductivity, ultrasonic wave velocity, and NMR results are consistent with the results of mechanical experiments. As the temperature rises, the wave velocity of saturated distilled water samples exceeds that of both saturated nano emulsion samples and dry samples, the velocity of the saturated fluid front in the samples increases, and the range of the fluid in the pores expands. Overall, these findings provide valuable experimental evidence and theoretical guidance for better understanding the hydro-thermal-mechanical behaviors of the HDR, which are crucial for the efficient development and utilization of geothermal energy.

Ensuring Accuracy: Critical Validation Techniques in Geochemical Analysis for Sustainable Geothermal Energy Development

Geochemical analysis is a critical tool in geothermal exploration, providing valuable insights into reservoir characteristics. However, obtaining accurate and reliable geochemical data requires rigorous validation techniques. This review examines key factors affecting the accuracy of geochemical data and discusses best practices for ensuring quality. Proper sampling methods, including selection of representative locations, use of appropriate equipment, and adherence to robust protocols for sample collection, filtration, preservation, and storage, are essential for maintaining integrity. Analytical techniques must be carefully selected, with regular calibration and standardization of instruments using certified reference materials. Implementing comprehensive quality assurance and quality control procedures, such as analyzing blanks, duplicates, and spike samples, helps monitor precision and accuracy. Data interpretation should consider the complexities of the geological and hydrological settings, integrating multiple lines of evidence. By following established guidelines and continuously updating methods based on emerging technologies and inter-laboratory comparisons, geothermal teams can optimize the reliability of their geochemical data. Accurate and precise geochemical information, when combined with geological, geophysical, and hydrological data, enables informed decision-making and enhances the success of geothermal projects. As geothermal energy gains importance in the transition to sustainable resources, ensuring the accuracy of geochemical analysis will be crucial for effective exploration and development.

Evaluating the anisotropic thermal–mechanical coupling strength of slate: A discrete element method approach

This study utilizes the discrete element method (DEM) to explore the thermal–mechanical coupling behavior of slate. Initially, a series of triaxial compression tests are conducted on slate specimens with varying orientation angles, temperatures, and confining pressures. Subsequently, the DEM is employed to replicate the mechanical and failure characteristics of the slate under identical laboratory conditions. The DEM constitutive models incorporate the parallel bond model for the rock matrix and the smooth-joint model for foliation. A thermal-degradation function for the parallel bond model is proposed, reasonably capturing the temperature's effect on the strength and failure characteristics of the slate. The simulation results exhibit a series of U-shaped curves in peak strength at different orientation angles, mirroring experimental findings. The study's findings indicate that orientation angles significantly influence the mechanical behavior and failure characteristics of slate. Elevated temperatures have minimal effects on strength anisotropy. Furthermore, applying high confining pressure is observed to mitigate the impact of high temperatures on bond weakening. This proposed method provides a useful tool for tunnel designs and geothermal energy development.

Review of Triassic Sherwood Sandstone Group reservoirs of Ireland and Great Britain and their future role in geoenergy applications

As the world progressively shifts to a low/neutral carbon economy over the course of the twenty-first century, geoscience will continue to play a vital role in the energy sector and beyond. Static and dynamic characterization of the subsurface, a key component of the petroleum industry for decades, will be required to evaluate and unlock a variety of different initiatives including carbon, capture and storage (CCS), hydrogen (or any other gas) storage, thermal energy storage and geothermal energy development. Onshore and offshore Ireland and Great Britain, Lower Triassic sandstones are likely to represent one of the primary geological targets for future geoenergy applications. This paper provides a review of the Triassic Sherwood Sandstone Group depositional system across the British and Irish region of NW Europe including its overall stratigraphic context, palaeogeography, sediment provenance and transport directions, and present-day distribution. In addition to geological outcrop data, there is a wealth of subsurface data available from historical petroleum wells. Looking forward, one important focus of geoscience research will be to extrapolate away from these well-defined control points to predict sandstone facies distribution, diagenetic history and hence overall reservoir quality in new undrilled areas that will be of interest to the geothermal, CCS and gas storage sectors.

Experimental Investigation of the Effect of Fault Reactivation Induced by Water Injection

An understanding of fault reactivation induced by water injection is of great significance for geothermal energy development and utilization. We conducted a series of water injection shear tests on low-permeability granite samples that each contained a single saw-cut fault under locally undrained conditions. Slip characteristics were analyzed by varying the fluid pressurization rate, confining pressure, and stress state of the fault to understand fault reactivation. The experimental results demonstrated that at a high pressurization rate, a higher local fluid pressure was needed to reactivate the fault than had been estimated theoretically, and the required fluid pressure increased with an increase in pressurization rate. The fluid pressurization rate and confining pressure both controlled the slip mode of the fault. The slip mode changed from dynamic slip to quasi-static slip at a high pressurization rate, and the peak slip rate of dynamic slip increased with an increasing pressurization rate. The fault showed significant stick-slip characteristics under a high confining pressure, as fault locking and reactivation phenomena occurred repeatedly. Faults with different initial stress states had little influence on the slip mode after the onset of slip.

Canada’s Geothermal Energy Update in 2023

Geothermal energy exploration, development, and research have been ongoing in Canada for several decades. The country’s cold climate and the push to develop renewable energy sources have driven interest in geothermal energy. Despite this drive, regulatory complexities and competition with other relatively inexpensive energy sources with existing infrastructure have hindered development. As such, interest has grown and waned with changes in the energy economy over several decades, leaving many projects at a standstill. As of January 2023, there are currently no operational geothermal power projects in Canada. Many hot spring pool and spa complexes remain active, and Canada is a leading country in the installation of ground source heat pumps (GSHPs; also called geo-exchange systems). However, in the last decade, the interest in deep geothermal systems has renewed, with many new projects starting up across several provinces and territories. Moreover, projects that had shown limited progress for many years—such as Mount Meager in British Columbia—have begun to renew their development efforts. Research is also expanding within prominent research groups and universities. The areas of focus include both building upon previous studies (such as thermal gradients and the heat flow in sedimentary basins) and researching new methods and resources (such as GSHPs, closed-loop systems, integrated geothermal operations, and hybrid systems, including heat storage). The development is supported by federal, provincial, and territorial governments through grants and the development of regulatory frameworks. Although challenges still remain for Canada to develop its geothermal energy resources, several power, thermal, and co-production projects, ongoing research, funding, and regulatory acts are all moving forward to support geothermal development. This paper aims to study Canada’s geothermal energy update in 2023 regarding the aspects mentioned above.

Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling

Air DTH (Down-The-Hole) hammer percussion drilling (vibration percussion drilling) has proven to be a highly efficient geothermal drilling technique, and percussion fractures near the wellbore benefit geothermal energy development in many ways (such as hydraulic fracturing, perforation, etc.). However, no research has been done on the mechanism of fracture-increasing and permeation-increasing in granite pore walls by air DTH hammer percussion drilling. This article: (1) using an air drilling test device, an air DTH hammer whole bit impact rock fragmentation test was conducted on granite in an atmospheric environment; (2) dyeing experiments, CT scanning, and 3D reconstruction modeling were used to characterize and identify wellbore cracks; (3) research the strength, porosity, and permeability changes of granite wellbore through mechanical and permeability testing experiments; and (4) numerical simulation of impact stress waves using particle flow code (PFC) 6.0 software to demonstrate the rationality of impact experimental results. The results show that the air DTH hammer impact can induce micro-cracks in the wellbore, and the distribution of cracks is regionalized, mainly due to the attenuation of the impact stress wave. The numerical results are consistent with the experimental results. The average strength of granite decreased by 16.5%, the average porosity increased by 9.5%, the average permeability increased by 63.3%, the porosity increased from 0.0025% to 0.03%, and the porosity increased by about 12 times under the air DTH Hammer percussion drilling. The above results provide the theoretical basis and experimental proof for the ability of air DTH hammer drilling to produce wellbore cracks and improve wellbore permeability. The presented experimental results can be a useful reference for building numerical models.

Optimization Simulation of Different Injection and Production Parameters of Enhanced Geothermal Systems

Enhanced Geothermal System (EGS), as a key technology for the extraction and utilization of geothermal energy in deep strata and high temperature rock mass, has a broad application prospect in the field of energy. In order to understand the sustainable utilization capacity of the enhanced geothermal system, explore the influence law of different factors on the heat production capacity of geothermal Wells, and design a reasonable geothermal energy development and utilization program. The influence of different injection and production parameters on thermal recovery performance was studied by numerical simulation, and the main influencing factors were analyzed by orthogonal experiment. The results show that water injection rate has the greatest effect on the injection-production parameters, followed by well spacing and water injection temperature, and fracture opening and fracture number have the least effect. The optimal parameter combination is water injection rate of 10kg/s, well spacing 500m, water injection temperature 40℃, crack opening 0.09mm and crack number 60.

Numerical modeling of temperature-reporting nanoparticle tracer for fractured geothermal reservoir characterization

Information on the temperature distribution of subsurface reservoirs is essential for geothermal energy development. One of the promising tools to detect the reservoir temperature distribution is temperature-reporting nanoparticle tracers whose functionality has been extensively investigated in both theoretical and experimental ways in the last decade. However, most related studies were limited to simplified geometries and ignored the dynamic interplays of fluid flow, heat transfer, transport and reaction of the temperature-reporting nanoparticle tracer. The response behavior and working mechanisms of such nanotracers in a realistic three-dimensional system still have not been fully revealed through a systematic study. In this work, we develop a numerical modeling approach to simulate field implementation of these nanotracers in a fractured geothermal reservoir. This study aims to evaluate whether the injection of multiple temperature-reporting nanoparticle tracers with different thresholds can be used to estimate the temperature distribution and provide information on the thermal and geological heterogeneities. Several scenarios have been investigated for the geothermal reservoir including homogeneous and non-homogeneous cases (e.g., thermal and geological heterogeneities). Our obtained results from the nanotracer breakthrough curves show that the deviation temperatures in peak concentration values provide an upper limit of the lowest temperature and precise highest temperature for the reservoir temperature range. The deviation temperature of the peak arrival time curve accurately estimates the highest temperature along the main streamlines between the wells. The proposed analysis curves based on the nanotracer breakthrough data were visibly affected by geological heterogeneities including their conductivities and orientations as well as thermal heterogeneities in the geothermal reservoir.

Evaluating Geothermal Power Plant Sites with Additive Ratio Assessment: Case Study of Mount Seulawah Agam, Indonesia

Indonesia, a country rich in geothermal resources, has yet to fully exploit its potential, particularly in volcanic regions like Mount Seulawah Agam. This study investigates the application of the Additive Ratio Assessment (ARAS) method for the site selection of Geothermal Power Plants (GPP) in Indonesia. The ARAS method provides a systematic approach to evaluating and prioritizing geothermal development sites by integrating multiple criteria, including geological, environmental, and socio-economic factors. The study collects data from various sources and weights criteria using the Ordinal Priority Approach (OPA), incorporating expert opinions. The findings demonstrate the effectiveness of the ARAS method in identifying optimal locations for GPP development, ensuring sustainability and feasibility. The study also tests the ARAS method in existing GPP locations in Jaboi, Sabang, Indonesia, to investigate alignment with the results and validate the approach. Furthermore, the study presents recommendations for GPP site selection. This research emphasizes the significance of multi-criteria decision-making techniques in facilitating renewable energy projects. It promotes a more systematic and informed approach to geothermal energy development in Indonesia and other geothermal-rich regions.

Origin of high heat flow in the back-arc basins of Sumatra: An opportunity for geothermal energy development

Volcanic arcs such as the Barisan Mountains have been identified as attractive areas for the utilization of geothermal energy, as exemplified by Ulubelu in Lampung and Sarulla in North Sumatra. However, environmental factors in the Barisan Mountains remain a primary obstacle to the exploration and exploitation of geothermal energy. The back-arc basins of Sumatra exhibit the highest heat flow worldwide; however, the heat source in this area remains a controversial issue. This study aims to investigate the origin of the high heat flow in the back-arc basins of Sumatra (North, Central, and South Sumatra basins) based on geothermal data from 384 oil wells and the current literature for geological evaluation. The findings of this study indicate that the back-arc basins of Sumatra experienced severe extensional deformation during the Tertiary Period through a large pull-apart and slab rollback mechanism. This deformation resulted in the thinning of the continental crust in this region (27–32 km) and the formation of multiple normal faults. Consequently, the presence of magma resulting from mantle upwelling implies a high heat flow in the back-arc basins of Sumatra. This condition ranks the back-arc basins of Sumatra among the highest heat flow regions of the world, with heat flows >100 mW/m2. These findings indicate that the back-arc basins of Sumatra have significant opportunities to exploit their geothermal energy potential. This study provides novel insights into the potential of geothermal energy, particularly in the back-arc basins of Sumatra.

Calculation model and influence factors of thermal conductivity of composite cement-based materials for geothermal well

The use of cement-based composites (CBC) with high thermal conductivity for geothermal well cementing is extremely important for the efficient development and use of geothermal energy. Accurate prediction of thermal conductivity can save a lot of experimental costs and time. At present, there is no specific calculation model for the thermal conductivity of CBC. In this study, the microstructure, thermal conductivity model and influencing factors of CBC were investigated by experimental tests, theoretical analysis and numerical simulation. The results showed that the cement-based material could be simplified into a two-layer structure of hydrated and unhydrated layers. Mathematical and numerical models based on the coupled Series model and the Maxwell–Eucken model were established to calculate the thermal conductivity for CBC. The mathematical and numerical models were found to be more accurate by comparison with the conventional models and experimental test results. The cubic packing was more favorable than the spherical packing to improve the thermal conductivity of CBC. The plate material had significant anisotropy. The thermal conductivity of CBC showed a rapid decrease followed by a slow decrease, a decrease followed by a slow increase and finally a rapid decrease, a rapid increase followed by an up and down fluctuation and finally a plateau, respectively, with the increase of filler particle diameter, spacing and curing temperature. Based on these results, the effective methods and future research directions were proposed to maximize the thermal conductivity of geothermal well cementing materials in actual engineering applications. The research findings can provide some technical references for the efficient development of geothermal energy and research on CBC with high thermal conductivity.