Shale reservoirs are recognized for their ability to serve as natural barriers for conventional hydrocarbons and their suitability for CO₂ sequestration, owing to their organic-rich composition and intricate pore structures. This study investigates the shales of the Barakar Formation in the Mand Raigarh Basin, India, to evaluate their potential for CO₂ storage by analyzing factors influencing pore volume and surface area. A comprehensive suite of analytical techniques—XRD analysis, Rock-Eval pyrolysis, and low-pressure gas adsorption using N₂ and CO₂ probes—was employed to assess mineralogy, organic matter content, and pore characteristics. Thermal maturity assessments revealed that the shales are transitioning from immature to marginally mature stages, with kerogen types reflecting a mix of gas-prone and oil-prone organic matter. Mineralogical analysis highlights the predominance of clay minerals, alongside other components influencing shale composition. High-resolution 2D imaging offers a detailed understanding of pore structures, emphasizing the role of organic matter and clay minerals in controlling gas adsorption behaviour. Mesopore development was strongly associated with clay minerals, while organic matter predominantly governed micropore formation. Fractal analysis revealed the complexity of pore morphologies, showing higher irregularity in smaller mesopores than larger ones.  These findings underscore the intricate relationship between mineralogical and organic components in determining the suitability of Barakar Formation shales for CO₂ sequestration. By integrating insights into thermal maturity, organic composition, and pore structure, this study highlights the Barakar Formation shale’s significant potential as a secure and efficient CO₂ storage site, contributing to climate change mitigation, sustainable resource management, and a deeper understanding of shale's role in carbon sequestration. This work contributes to climate change mitigation strategies by leveraging the structural and compositional characteristics of shale formations for carbon management. The results align with global sustainability objectives, transforming shales from traditional energy resources into effective tools for reducing atmospheric CO₂ levels, thereby bridging energy needs with environmental management.

How to cite: Ghosh Dastidar, S., Sarkar, K., Chandra, D., Hazra, B., and Vishal, V.: "Shale Reservoirs as Potential CO₂ Storage Sites: Exploring Mineralogical and Organic Interactions", EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3402, https://doi.org/10.5194/egusphere-egu25-3402, 2025.

This study investigates the usefulness of fractal dimension for assessing fracture network geometry especially, in terms of connectivity in petroleum and geothermal reservoirs. We evaluated connectivity using both static and dynamic approaches and analyzed a set of fractal-fracture models and outcrop maps. The models comprise a deterministic fractal-fracture network and a set of thirty random fractal-fracture networks, all sharing the same fractal dimension. The natural dataset includes a series of nested network maps from an outcrop analog. These maps have been studied for their fractal nature, clustering behavior, and flow properties. For the “static” approach, connectivity of the fracture networks is evaluated by considering three different “nodes” in each of the networks, i.e., cross-cutting (X), abutting (Y), and isolated (I). In considering a “dynamic” approach for evaluating connectivity, the flow response is computed along with the integrated “time-of-flight” (TOF) at different time-steps. The networks are converted into simulation-ready fracture continuum models that were run in a streamline flow simulator, TRACE3D. The TOF plots thus generated provide insights into the connectivity between injection and production wells placed at diagonally opposite corners of the flow domain and are used to evaluate flow pathways and the effects of reservoir heterogeneity. They also implicitly indicate the “percolation connectivity” of a fracture network. This may be confirmed by comparing previously reported values of “percolation connectivity” of the outcrop analogs and the TOF plots. The ultimate goal of this research is to determine whether the fractal dimension can serve as a unique identifier for the connectivity of fracture networks. The results derived from both fractal-fracture models and natural maps indicate otherwise. The findings from this study can improve decision-making across various fields, including hydrogeology, resource management, and environmental engineering, leading to more effective strategies for resource extraction and risk reduction.

How to cite: Roy, A., Sahu, A. K., Biswas, R., and Sahoo, B.: Connectivity and Fractal Dimension of Fracture Networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9983, https://doi.org/10.5194/egusphere-egu25-9983, 2025.

Building high-quality reservoir models that integrate geological and petrophysical properties is a complex task. The primary modeling process involves creating two-dimensional maps of porosity and either absolute or effective reservoir permeability using results from well-log interpretations and laboratory measurements of core samples. Often, the petrophysical relationship between rock porosity and permeability is adjusted, and variograms used for spatial correlation are fine-tuned to reconcile with the measurements. However, such adjustments make it challenging to address significant errors in permeability, which can vary dramatically, spanning several orders of magnitude within a geological formation. In energy security and environmental conservation scenarios—such as enhanced oil recovery (EOR), shale gas production, enhanced geothermal systems, and geological CO₂ storage (GCS)—fluid injection typically results in a permeability drop of 35-86% around the injection well. This reduction can impede the injection process and lead to unnecessary remediation costs. Storage capacity, indicated by porosity, and injection efficiency, governed by permeability, are critical criteria for characterizing GCS sites. Therefore, accurate quantification of permeability is essential. Quantitative permeability modeling holds the key to unlocking the questions about fluid flow direction in hydrocarbon reservoirs, especially in the face of limited measurements from core samples or Well tests. Permeability is strongly influenced by pore-scale heterogeneities, which range from nanometers to micrometers (µm), and the evaluation of these heterogeneities varies depending on the scale considered in Euclidean geometry. This study will present a method based on scale-invariant or fractal geometry to predict reliable permeability and will validate these predictions with core-scale measurements. Additionally, the significance of permeability maps in EOR and GCS studies for forecasting fluid flow directions within a reservoir will be examined through two case studies. Finally, the discussion will include future directions for incorporating ultra-small heterogeneous effects (less than 0.1 µm), which are often overlooked due to observational and mathematical-model limitations.

How to cite: Vadapalli, U.: Permeability modeling for Enhancing Resource Utilization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-210, https://doi.org/10.5194/egusphere-egu25-210, 2025.

The world is striving to achieve net-zero carbon emissions at the earliest possible time. Geothermal energy is one of the renewable energy playing a significant role with its sustainable, consistent and potentially affordable in generating the power and competence in production of green hydrogen. Magnetotellric (MT) method is an excellent way to detect caprock, geothermal fluids and source based on the resistivity models. India’s geothermal resources discloses extensive large number of geothermal provinces with promising energy prospects. However, the present study deals with most promising geothermal province Puga and Chumathag are located in the Indo-Eurasia tectonic collision boundary of NW Himalayan region (altitude ~ 4500m). It is composed of different rock types such as plutonic, basic to ultrabasic, and submarine volcanic rocks (Ophiolites). The Puga valley consists of Precambrian paragneisses, schists, carbonates (Tanglang La) and limestone where as Chumathang region comprises of thick sequence of shallow marine to fluvial deposits of Kuksho formation related to Indus group. A total of 62 MT stations were used in Puga-Chumathang geothermal region to understand the shallow crustal architecture in terms of significant linkage of geothermal fields. The geoelctrical structure derived from the 3D inversion of MT data highlights the different fault structures, lateral extent and upward migration of geothermal fluids at Puga and Chumathang geothermal zones. The study also highlights the presence of secondary magma at a shallow level abducted from Indus Suture zone acts as a possible heat source for these hot springs. 3D MT model along with in observation of negative free air gravity anomaly structural trend signifies the presence of low density material supports the link between both the hot springs. This result greatly helps new pathways in advancing the large-scale plan for geothermal prospecting in India.

How to cite: Pachigolla, V. V. K., Patro, P. K., Azeez, K. K. A., Kadukuntla, C. R., Babu, N., and Mothukuri, S.: Relevance of magnetotelluric method to unlock renewable geothermal energy, A case study from Puga-Chumathang geothermal zone, NW Himalaya, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-405, https://doi.org/10.5194/egusphere-egu25-405, 2025.

Flooded coal mines have the potential to provide low-carbon renewable heating, independent of surface weather and temperature conditions. To develop an open-loop mine water heating system, it is essential to estimate the amount of heat available within the mine. This estimation is necessary to determine the potential size of the system, assess whether it meets surface demand, and evaluate its economic viability.

Various methods can be used for this estimation. Static methods, which do not account for the influence of time or the underground spatial geometry, rely on simplified variables. These include calculating the background heat flow over the mine's area, estimating the heat stored in the rock volume surrounding the mine, assessing the heat in the mine's water volume, and determining a realistic flowrate to calculate the potential heat extraction.

In contrast, dynamic modelling methods provide a more comprehensive approach by accounting for changes in heat availability over time and the mine's structural architecture.

Using the GEMSToolbox, we performed dynamic modelling on a real two-seam coal mine map and a simplified grid model with comparable size and properties. The results from these dynamic models were compared with static methods, revealing significant differences in heat estimates, varying by orders of magnitude from 10¹⁰ MJ to 10³ MJ of heat produced over 40 years.

Dynamic modelling also offers additional benefits, such as tracking heat variation over time, analysing the impact of different injection and abstraction points, and assessing potential interference from nearby geothermal systems. These findings underscore the advantages of dynamic modelling in developing and optimising mine water heating systems.

How to cite: Sweeney, A., van Hunen, J., Mouli-Castillo, J., and Gluyas, J.: Dynamic vs static assessment of the mine water heat energy potential of coal mines, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8295, https://doi.org/10.5194/egusphere-egu25-8295, 2025.

Mine water in disused flooded coal mines is a potentially valuable low carbon heat source. This mine water must be resilient to the impacts of climate change. Changes in temperature and rainfall could affect mine water resources, but the range of impacts and, crucially, whether they are negative or positive – and how they are developed and operated – have not been researched to date. This research is investigating, for the first time, the impacts of climate change on mine water resources. 

To understand these impacts, we work at two mine water heat prospect case study locations in Central Scotland. We selected one on the east coast and one on the west coast to investigate and account for different rainfall patterns. Since May 2023 we have been undertaking field monitoring and subsequent lab analysis to examine seasonal and longer-term changes. In the field, we analyse mine water levels/recharge, chemistry, temperature, and gases (CO₂ and CH₄). In the lab we test for parameters that could be affected by climate change e.g. conductivity, total dissolved solids; a minimum mine water suite e.g. iron; and a standard suite of anions and cations. Additionally, to expand our geographical and temporal coverage, we are collating secondary data from sources including the Mining Remediation Authority, UK Geoenergy Observatories (UKGEOS), and the Scottish Environmental Protection Agency (SEPA).   

Here, we present (a) an assessment of potential impacts of climate change on mine water, (b) early insights into seasonal variation and potential causes and impacts, (c) emerging implications, and (d) future work. 

How to cite: Gillen, C., Burnside, N., McGrane, S., and Roberts, J.: Investigating the potential impacts of climate change on mine water resources: Central Scotland as a case study., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1347, https://doi.org/10.5194/egusphere-egu25-1347, 2025.

In response to growing climate targets and the need for innovative heat management solutions, Durham University, UK, is investigating the reuse of waste heat generated by its high-performance computing (HPC) data centre, which produces up to 1.5 MW of heat. This project explores the potential of repurposing abandoned, flooded mine workings beneath the campus for seasonal thermal energy storage. The system aims to capture surplus heat during the summer and store it within mine water reservoirs for reuse in winter coupled with heat pump technology for building heating, reducing emissions and investigating potential enhancement of campus-wide sustainability.

The Immersion Cooling and Heat Storage (ICHS) projectaddresses critical technical challenges: understanding subsurface water flow dynamics, determining heat injection and retrieval efficiencies, and optimizing borehole configurations between shallower and deeper worked coal seams. Various conceptual designs are evaluated, including dual-depth boreholes for enhanced separation of thermal flow. Initial feasibility assessments highlight opportunities to align this scheme with the university's phased heat network strategy, providing a living laboratory for geothermal research and renewable energy integration.

This presentation will share preliminary findings, insights into borehole site selection, and recommendations for future mine water energy storage schemes. The work contributes to a growing body of research on sustainable heat management in post-industrial landscapes, aligning with broader UK initiatives in Gateshead, Leeds and Edinburgh, as well as Glasgow with the established UKGEOS project.

How to cite: Chapman, S., van Hunen, J., Basden, A., and Gluyas, J.: Data Centre waste heat storage within abandoned flooded mine workings, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9263, https://doi.org/10.5194/egusphere-egu25-9263, 2025.

Abandoned and flooded coal mines have a huge geothermal potential. By circulating mine water and extracting its heat, it can provide a renewable, low-carbon low-enthalpy heat source for domestic and industrial purposes. But capital costs from drilling into those mine workings are significant, and investigating the geothermal potential of a mine system prior to drilling are essential for the success of any mine water geothermal energy (MWGE) system. Numerical modelling provides a quick and low-cost methodology to assess the feasibility of a planned MWGE system, for example to determine optimal mine water abstraction and re-injection sites.

Past coal mining was typically done using two different mining techniques. 1) The room-and-pillar (also referred to as pillar-and-stall) method was used to mine coal through digging tunnels (galleries and roadways), leaving pillars of coal untouched to prevent collapse of the coal seam. 2) The long-wall mining technique used machines to extract the entire coal seam, and allowed collapse in a controlled manner, thereby creating a porous layer of rubble referred to as ‘goaf’. Often both techniques were used within a single mine system. These two techniques result in very different remnant mine geometries, and it is important to address these differences in any MWGE modelling attempt.

We have developed a computationally fast and flexible modelling tool GEMSToolbox to assess the feasibility of mine workings as MWGE system by combining numerical and (semi-)analytical methods. The tool accounts for both room-and-pillar and long-wall mining techniques. In this study, we investigate the geothermal effects of both techniques for mines that are entirely constructed through one technique only, and for mines that combine the two techniques. Both techniques suffer from significant uncertainties in the effective model parameters: e.g. mine galleries may have collapsed since the mine closure, while for goaf, the effective porosity and hydraulic transmissivity are poorly constrained. Furthermore, in mine systems where both techniques were applied, water preferentially flows through the galleries, which potentially makes heat extraction from the goaf areas less efficient. The results of this study are applied to a real-world mine block in the North East of England.

How to cite: van Hunen, J., Wang, Y., Mouli-Castillo, J., and Tu, J.: The impact of different mining techniques on the geothermal potential of abandoned coal mines, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9279, https://doi.org/10.5194/egusphere-egu25-9279, 2025.

Mining activities occur on all inhabited continents, which is why many countries are faced with the question of how exhausted mines can be utilised sustainably. One promising option is their use as energy sources, with flooded structures acting as sub-surface heat exchangers. The large water volumes offer significant potential for heating and cooling. However, the exploitation of abandoned mine is associated with high costs due to preliminary investigations and drilling. In order to minimise the economic risk, a reliable forecast of the mine water temperature is essential to ensure long-term economic viability. As complex thermal-hydraulic simulations require specific expertise, they are difficult to access for many energy suppliers and mine operators. This underlines the need for user-friendly models that allow an initial assessment of the potential without in-depth knowledge of modelling.

Only a few reduced models for predicting mine water temperature exist in the literature. While analytical models impress with extremely short calculation times (Milliseconds for decades), they are not able to take seasonal storage effects into account. Reduced numerical models from the literature can consider these transient effects, but require significantly longer calculation times (Minutes for decades), especially for turbulent flow regimes. This is too time-consuming for a comprehensive parameter study. In order to combine the advantages of both approaches, a new model is required that takes seasonal storage effects into account and works in an acceptable computing time (< 1 minute for decades).

The newly developed model combines two coupled sub-models: The heat transfer in the rock is solved numerically using an implicit finite volume scheme, whereby an irregular grid enables an efficient calculation. The energy transport in the fluid is modelled using an analytical solution. The verification using a reference case shows a high accuracy of the model. At a constant reinjection temperature, the deviation of the outlet temperature after twenty years is 3 % compared to the benchmark (fully numerical axisymmetric CFD simulation). With cyclical heat loads, the maximum deviation occurs for the inlet temperature with 3,5 %. At the same time, the model is around 750 times faster than the benchmark calculations with a run time of 1 s for two decades.

In order to test the model with practical operating modes, it is compared with an existing CFD simulation of the north-west field of the mine in Ehrenfriedersdorf, Germany. The comparison focuses on the temperature development of the mine water at the outlet, assessing how well the model captures seasonal variations and contributes to optimizing operational decisions.

How to cite: Krause, W., Ebel, T., Oppelt, L., Wunderlich, T., Raithel, F., Grab, T., and Fieback, T.: A reduced numerical model for predicting temperature dynamics in flooded mine galleries under seasonal heat loads and storage conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15555, https://doi.org/10.5194/egusphere-egu25-15555, 2025.

The Jharia Coalfield (JCF), the magnificent pocket of coking coal in the southern part of the Dhanbad district of Jharkhand India, has always remained at the peak of attention for the technological challenges that occurred during the mining of coal. The JCF is also the most critically highlighted coalfield as it is the only known depository of prime coking coal in India which is infamous for its extensive coal fires ignited mainly due to its dynamic spontaneous combustion nature. Earlier studies reported significant anomalous temperature variations in the range of 160-200⁰C along subsurface cracks and vents; also the geothermal gradient is locally high in  the basin to be around 40-45⁰C/km. The implementation of geothermal heat extraction technologies to utilise the wasted heat underneath would require a comprehensive understanding and estimation of the techno-economics of various operational and maintenance costs. The economic assessment for a 5 MW geothermal plant revealed an initial investment cost of 12.02 (MM$) and 8.05 (MM$) and NPV to vary between 27.08 (MM$) to 31.04 (MM$)  respectively for the source temperature of 100⁰C and 150⁰C in the burning JCF basin.

How to cite: Dutta, A. J., Mishra, C., Chaturvedi, R., Konwar, D., and Kulkarni, S. D.: Techno-Economic Assessment of Geothermal Energy Resource in the Jharia Coal Field of India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17341, https://doi.org/10.5194/egusphere-egu25-17341, 2025.

As the global energy transition accelerates, innovative solutions such as Mine Water Heat Systems (MWHS) are emerging to address the dual challenges of energy storage and decarbonised heating and cooling. This study focuses on the development of a business model for a heat geobattery system, which utilises abandoned mine workings to store thermal energy for heating, cooling, and thermal storage services, leveraging waste heat from a data centre.

We identify the operational roles, services, and responsibilities of a Mine Water (MW) operator and assess their impact on the heat supply chain. The UK’s regulatory landscape for MWHS is also investigated, highlighting gaps, barriers, and opportunities for regulatory enablement.

Additionally, we aim to build a database of technical risks to quantify the costs of mitigation strategies. This involves identifying critical risks associated with MWHS, including technical failures, environmental impacts, and regulatory non-compliance. Potential liabilities, such as pump and heat exchanger failures, mine gas release, and groundwater disruption, are analysed alongside their consequences, including downtime, environmental harm, and financial penalties. Mitigation strategies, such as regular maintenance, water quality monitoring, emergency response plans, and compliance frameworks, are proposed, with their costs estimated. These measures ensure system reliability, environmental protection, and adherence to regulatory requirements, enabling safe and efficient MWHS operations.

This study underpins the development of an investor-ready business model for the commercialisation of a heat geobattery system. Emphasis is placed on aligning financial incentives with operational feasibility, customer demand, and supply structure. By integrating these findings with the rest of the Galleries2Calories project, this research provides a framework for the seamless adoption of heat geobatteries. The outcomes contribute to understanding how MW operators can enhance the heat supply chain while addressing critical regulatory and environmental considerations.

How to cite: Mouli-Castillo, J., Watson, S., Nandagavi, P., Breunig, H., Swan, L., Smith, S., and Townsend, D.: Towards Investor-Ready Business Models for Mine Water Heat Systems: Regulatory, Technical, and Operational Insights for the Heat Geobattery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17354, https://doi.org/10.5194/egusphere-egu25-17354, 2025.

Underground mines, once vital industrial hubs, hold immense potential for innovative applications, including Mine Thermal Energy Storage (MTES). MTES repurposes partially and fully flooded mine cavities as reservoirs for storing surplus heat or cold, presenting a novel alternative to conventional Aquifer Thermal Energy Storage (ATES). While promising, MTES faces challenges such as scaling, corrosion, energy loss, and interactions between the geological matrix and technical infrastructure.

To address these challenges, TU Bergakademie Freiberg has established a living MTES geo-lab at the historic Reiche Zeche silver mine. Key features of this facility include a 21-cubic-meter water reservoir and over 90 temperature sensors embedded in Freiberg Gneiss. The pilot-scale MTES simulator setup allows for continuously monitoring heat transfer during thermal energy injection and extraction cycles realized by a mobile heat pump system. Early findings are revealing an average background rock temperature of 12 °C, a fast conductive heat transport within the rock as well as a good storage potential with elevated rock temperatures of up to 25 °C in approximately 2 meters from the water body. However, significant heat losses across system boundaries have been observed, with advective heat transport via flowing water identified as the primary contributor.

Parallel laboratory-scale experiments using column flow setups and batch reactors simulate MTES conditions, exposing rock and mine water to temperature cycles ranging from 10°C to 60°C. These experiments demonstrate significant chemical changes, including the precipitation of 90% of dissolved iron. These findings offer valuable insights into the chemical stability and thermal efficiency of MTES systems.

Two complementary methods were employed to quantify effective inflow and energy dissipation caused by mine water movement. First, a dilution test with NaCl was conducted. Second, inflowing water volume was calculated based on reservoir water level reductions. Results indicate that the calculation based on inflowing water volume provided more reliable values, while the formula used in the dilution test requires further refinement.

Additionally, numerical simulations using OpenGeoSys (OGS) software are being developed to assess the influence of fracture networks in the surrounding rock formation on heat storage and recovery performance. Preliminary results indicate that fractures enhance advective heat transport, leading to lower heat recovery ratios during cyclic operation.

How to cite: Arab, A., Binder, M., Oppelt, L., Chen, C., Wiedener, R., Schenker, F., Engelmann, C., Späker, C., Lotter, T., and Scheytt, T.: Storing Thermal Energy in Underground Mines: In Situ Simulations at the Freiberg Living Geo-Lab, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19064, https://doi.org/10.5194/egusphere-egu25-19064, 2025.

Developing geothermal energy utilization technology is critical for achieving a low-carbon, high-efficiency energy system, and carbon neutrality objectives. The deep borehole heat exchanger (DBHE) represents a viable solution for extracting geothermal energy to meet building heating needs, especially in coal mines or oil fields with abundant depleted deep boreholes. In this study, a more comprehensive three-dimensional numerical model was constructed, incorporating segmented design parameters of the DBHE's inner pipe. The model's validity was confirmed through comparison with field experiment monitoring data. Subsequently, a series of long-term simulations were conducted to assess heat extraction performance, elucidating the influence mechanisms and interactive effects of various inner pipe parameters.

Additionally, a thermal-economic analysis was performed from a system-level perspective to quantify and evaluate the impact of inner pipe parameters on the DBHE's heat extraction performance, including assessing the necessity of inner pipe insulation. Results indicate that, under the specified conditions, reducing the thermal conductivity of the inner pipe increases the outlet water temperature while extending the payback period. Furthermore, greater drilling depth and lower circulation flow rate enhance the effectiveness of inner pipe insulation in improving the DBHE's heat extraction capacity, whereas the diameter of the inner pipe exerts a limited effect. These findings provide valuable guidance for the system design of practical DBHE heating projects in areas with depleted deep boreholes, enabling informed selection of inner pipe parameters.

How to cite: Cai, W., Xia, Q., Wang, F., Chen, C., and Meng, B.: Techno-economic performance analysis of deep borehole heat exchanger heating system towards transforming depleted deep boreholes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20061, https://doi.org/10.5194/egusphere-egu25-20061, 2025.