Sixth EAGE Global Energy Transition Conference & Exhibition (GET 2025)

This research article enlightens the synthesis and scale-up of calcium carbonate (CaCO3) from waste concrete as calcium-rich material by an inorganic carbonation process. In the laboratory scale condition, productivity was 1 kg/d, the calcium was extracted from waste concrete using hydrochloric (HCl), and the other extracted cations present in the waste concrete such as aluminum, iron or magnesium were precipitated through pH control method. The calcium hydroxide (Ca(OH)2) was synthesized from calcium chloride (CaCl2) by adding sodium hydroxide (NaOH), which induced the spontaneous reaction of CaCO3 without any additional energy consumption. Additionally, carbon dioxide (CO2) was purged into Ca(OH)2 to form CaCO3, to confirm the amount of CO2 capture, the total amount of reaction was measured by analyzing the concentration of CO2 before and after reaction. A process with a CaCO3 productivity of 20 kg/d was designed and manufactured through a laboratory scale. The pilot scale process was operated in the same way as the laboratory scale, and finally, the CO2 reduction amount was calculated through the immobilization ability of CO2 and the power used in the facility, and the power consumption was presented to evaluate the process.

Heating systems are major contributors to CO2 emissions, especially in Northern Europe where they account for up to 30%. To decarbonize this sector, electrification and integration of renewable sources are essential. Medium-deep geothermal heat wells (MDGHWs), at depths of 1,000–3,000 meters, offer a sustainable solution when paired with industrial-scale heat pumps.

MDGHWs enable year-round heating, cooling, and critically, thermal energy storage within local low-temperature heating networks. In winter, they deliver heat; in summer, they recharge via waste heat or excess renewable energy. This stored heat is then reused when needed, improving efficiency and reducing energy waste.

The coaxial MDGHW design optimizes energy extraction from deep thermal wells while mitigating performance issues. Each well delivers heat equivalent to 40 traditional geothermal wells, significantly enhancing thermal exchange and reducing energy losses. The system also allows for the underground storage of waste heat, ensuring thermal stability within networks.

This approach improves heat pump efficiency through lower temperature differentials, extends system lifespan, and reduces maintenance costs. It achieves significantly higher Coefficient of Performance (COP) rates compared to conventional systems while using 97% less land—ideal for dense urban settings. Ultimately, it ensures a resilient, carbon-neutral heating future.

This study presents a numerical analysis of gas storage operations in a full-scale lined rock cavern (LRC) facility located in Skallen, southwestern Sweden. As the energy sector increasingly incorporates renewable sources, LRCs offer a geologically flexible solution for high-capacity, seasonal energy storage. However, thermal challenges—such as freezing near cavern walls or overheating during injection—pose risks to structural integrity and operational efficiency. A thermodynamic model was validated using field data from the initial storage cycle, during which active temperature control was minimally applied in the field. In later cycles, measured temperatures drive the activation of a simulated gas circulation system to estimate circulated volumes and mitigate thermal extremes. Results confirm that circulation markedly limits freezing in the rock mass and dampens injection induced temperature spikes. Despite limitations in measurement resolution and circulation data, the model reproduces observed thermal behavior accurately. This work underscores the role of physics based modeling in optimizing LRC performance and paves the way for its extension to hydrogen storage in low carbon energy systems.

The occurrence of hydrothermal reservoirs is limited, and closed-loop heat exchangers represent an alternative to conventional systems. The HOCLOOP project aims to develop and test a novel CBHE technology. The project deals, among others, with the possibility of using deep salt structures as a geothermal system’s heat source. GTW software was used for calculations of system performance, and CBHE was assumed with a horizontal well using DualPipe technology. The area of the Goleniów was chosen for the analysis because both salt domes and pillows occur there. In addition, the city has a District Heating System based on a coal-fired boiler. Using the HOCLOOP solution would help reduce emissions and transform the fossil-fuel-based system to renewable energy. The results suggest that the system performance is more dependent on the operating parameters than on the geological conditions. The potential for integration into a DHS is a more critical factor in determining the location of a CBHE. The unique feature is that the heat supply from the wells after the initial higher value is flattening out and is estimated to be nearly constant and cover dynamic demands for the future with little maintenance and no need for an external power supply.

Lithium is the element of choice in battery development to support the energy transition. Recent developments in direct lithium extraction from brines (DLE) provide the opportunity to extract lithium in a matter of days from brines associated with geothermal projects or pumped from deep aquifers. This has minimal impact on the surface environment, by contrast to spodumene mining or evaporation in high altitude salars.

This paper will present a new global overview of those basins where lithium content in brines has been established, highlighting areas of particularly high lithium concentration. Key examples will be reviewed in detail, and inferences drawn on lithium sources and the mechanisms of lithium concentration, which may allow overlooked basins with high potential to be identified for further evaluation.

The recent drop in lithium prices emphasizes the need for locating the ‘sweet-spot’ in each of these basins, which is a function of both lithium grade and subsurface geology. An example is provided from the Jurassic Smackover of Arkansas, the likely site of a first commercial DLE plant. Geothermal projects are also emphasized given their potential for synergies and the development of multiple revenue streams, thereby providing hedging against product price fluctuations.

The geological heterogeneity of key CO2 injection targets in the UKCS is exhibited at various scales. However, due to the size and spatial extent of saline aquifers, usually only the regional scale is modelled to investigate the spatial distribution of CO2 over time. Time-lapse seismic is a well-established technology used to monitor CCS operations. This study focuses on the different types of small-scale heterogeneity and translating it onto fine-scale 2D reservoir models. We generate multiple heterogeneity scenarios using available literature, build 2D reservoir models based on them, and flow CO2 across the whole length of the reservoir to simulate progression at the front of the plume. We then utilise Sim2Seis (an ETLP software) to obtain the 4D signal stemming from injection into these heterogeneous reservoirs. As CO2 is highly mobile, we find that its flow pattern may be hard to predict when faced with heterogeneity. The CO2 flow pattern differs based on the proximity to the injection site and inherent heterogeneity of the reservoir. The resulting 4D signal is strong and saturation-driven, and the effect of heterogeneity is visible.

This study explores the optimization of reinjection strategies in Lithuania’s Cambrian geothermal reservoirs, focusing on temperature effects on mineral interactions and long-term reservoir performance. Western Lithuania contains significant geothermal potential, especially in the Cambrian sandstone reservoirs, which reach temperatures up to 96°C at 2000 meters depth. These reservoirs, once used for oil production, are now being reconsidered for geothermal energy, particularly district heating. Using reactive transport modelling (RTM) with TOUGHREACT, the study evaluates the impact of reinjecting saline water at 40°C—a temperature historically aligned with district heating return flows—on mineral dissolution and precipitation.

Simulations reveal that porosity and permeability around the injection well change over time due to geochemical reactions. Near the well, permeability increased by 53%, while it decreased by 83% at 20 meters distance. However, the 40°C reinjection temperature does not significantly impact reservoir quality, making it a viable option for sustained operations. The results suggest that careful reinjection temperature control, combined with horizontal well technologies, can enhance geothermal energy extraction while maintaining reservoir integrity. This research contributes to geothermal field development planning in Lithuania and supports sustainable energy transition efforts.

Underground hydrogen (H2) storage is a key technology for stabilizing Europe’s renewable energy supply, but microbial activity in subsurface environments may lead to H2 loss, gas quality degradation, and infrastructure damage. The CETP-funded HyLife project brings together four European microbiology laboratories and multiple industry partners to quantify microbial risks associated with underground hydrogen storage. Twenty-one brine samples from salt caverns, aquifers, and depleted gas reservoirs across ten countries were characterized so far using developed fully standardized anoxic sampling and analytical workflows, including geochemical analysis, enrichment cultures, qPCR, and 16S rRNA sequencing. Distinct microbial communities were identified at each site, even when brine chemistries were similar. Enrichment experiments revealed rapid H₂ loss within weeks in several porous-rock reservoirs at ≤ 50°C, while most salt-cavern brines showed negligible activity after 12 months. Hydrogen consumption was most commonly linked to methanogenesis. Kinetic parameters derived from these tests are being integrated into 3D reactive-transport models and an open-access database to support techno-economic assessments, mitigation strategies, and evidence-based guidelines for selecting safe and efficient hydrogen storage sites. The project actively engages industry partners and continues to expand its dataset through additional sampling across diverse geological settings.

Among the diverse array of renewable options, geothermal energy emerges as a highly promising resource due to its reliability and efficiency in generating both heat and electricity to meet global demand. This study highlights the geothermal energy supply projections based on Integrated Assessment Models in distinct scenarios from 2030 to 2100. Moreover, point out key geothermal technologies and breakthrough methods that could address projected geothermal energy growth. Emphasis on renewables and technological innovation strongly favors geothermal energy. By evaluating these advancements, the paper elucidates geothermal energy’s possible roles in contributing to sustainable, long-term decarbonization objectives and demand supply.

Underground hydrogen storage (UHS) offers a viable solution for large-scale hydrogen storage, yet understanding the interfacial interactions that govern gas mobility and trapping remains critical. This study investigates the interfacial tension (IFT) behaviour of H2–CO2–brine systems under reservoir-relevant conditions, focusing on the effects of temperature (20–80°C), pressure (10–100 bar), salinity, and gas composition. Using experimental methods, gas-water IFT values were measured in both distilled water and formation brine environments. Results show that IFT trends vary with aqueous composition and gas type: IFT increases with temperature in pure H2-water systems but decreases in brine due to salt-induced weakening of cohesive forces. CO2-containing mixtures exhibit a pronounced pressure-dependent reduction in IFT, linked to greater gas solubility and molecular interactions. Salinity also consistently reduces IFT via the salting-out effect. The study highlights the role of CO2 as a cushion gas, which enhances hydrogen injectivity by lowering IFT and minimizing capillary trapping. Nonlinear IFT responses at high CO2 concentrations further emphasize the complexity of multiphase interactions in porous media. These findings improve the fundamental understanding of interfacial behaviour in subsurface hydrogen storage and inform the design of more effective UHS and CO2 sequestration strategies.