Search Results (83)

At present, research on the long-term stability of multi-cavern coordinated injection–production operations for salt cavern compressed air energy storage (CAES) remains limited. Large-capacity energy storage utilizing multiple interconnected salt caverns has become an inevitable development trend for modern CAES power stations, highlighting the necessity and importance of stability evaluation and design optimization for underground salt cavern storage clusters. Based on the Anning 350 MW CAES demonstration project, this paper takes the abandoned salt caverns of the project as research objects. A three-dimensional geological and cavern model is established using the FLAC3D numerical simulation method, and stability analysis is carried out under static conditions and three long-term gas injection and production scenarios (the pressure conditions are provided by ground-based equipment). The characteristics of the plastic zone, displacement, stress distribution, and volume shrinkage of the caverns are systematically investigated. The results show that under static conditions, the internal pressure significantly controls the development of the plastic zone, and the caverns are generally stable at pressures above 4 MPa. During long-term operation, the plastic zones of each cavern gradually expand, displacements accumulate continuously, and stresses tend to stabilize after an initial accumulation period. After 30 years of operation, no through-going plastic zones appear in any cavern, and all volume shrinkage rates are below 30%. Among the three cases, Case 1 exhibits the best stability, while enhanced monitoring is required for local high-stress regions in Case 3. This study verifies that the salt cavern development for the Anning CAES project is safe and controllable during long-term operation. The layout spacing of caverns is reasonably designed and fully satisfies the stability requirements of salt cavern CAES power stations. The research results can provide a technical guarantee for the construction of the first CAES power station in Yunnan Province and also offer a reliable reference for the design and construction of similar multi-cavity salt cavern CAES projects. Full article

Hydrogen (H₂) is becoming a meaningful way to store energy for long-term use and support thorough decarbonization in systems that use renewable energy. Underground hydrogen storage (UHS) has strategic benefits over above-ground systems because it can hold large volumes, is contained by geology, and is cheap to operate in cycles. This review compares four key geological formations for underground hydrogen storage (UHS): salt caverns, lined rock caverns, depleted hydrocarbon reservoirs, and saline aquifers. Each system is evaluated based on storage mechanisms, efficiency, safety, technological maturity, and economic feasibility. This review also introduces a unified cross-media evaluation framework, a TRL-risk matrix, a technology development roadmap, and novel insights into AI-based monitoring, offering prescriptive guidance for large-scale UHS implementation. Salt caverns have high injectivity, maintain their purity, and undergo 6 to 12 cycles per year at pressures of 60 to 180 bar; however, they are only found in certain places. Lined rock caverns can be built anywhere, but sealing and economic issues make them difficult to use. Depleted hydrocarbon reservoirs with TWh-scale capacity and already built infrastructure. Saline aquifers, on the other hand, have the most potential in the world but need enhanced management of microbiological responses and cushion gas optimization. A synthesis of current studies highlights key research gaps in cyclic geomechanics, hydrogen–rock–microbe interactions, and liner performance for high-pressure storage. The review concludes with techno-economic and safety considerations and identifies future directions for deploying geological UHS as a critical component of a net-zero hydrogen economy. Full article

Against the background of global carbon reduction initiatives and ongoing energy transition, this study addresses the technical challenges of constructing salt cavern storage facilities in bedded salt formations. Typical bedded salt rocks in Southwest China were taken as the research object, and systematic core sampling and multi-dimensional laboratory tests were conducted to investigate their geomechanical and petrophysical properties. The tests included mechanical experiments such as direct shear, uniaxial and triaxial compression, as well as physical property measurements including permeability, porosity, SEM, XRD, and mercury intrusion porosimetry (MIP). The results show that halite exhibits excellent plasticity and tight sealing performance, interlayers have high compressive strength, and mudstone is characterized by significant brittleness. All lithologies possess low permeability and dense internal structures. For this reason, they are well suited for salt cavern energy storage utilization. Furthermore, the research findings provide key basic data and a solid scientific basis. This study supports the construction of salt cavern gas storage and compressed air energy storage (CAES) plants in bedded salt rock areas. Full article

Salt cavern Compressed Air Energy Storage (CAES) is one of the critical technologies for energy storage and an important infrastructure supporting the construction of new power systems and facilitating the achievement of the dual carbon goals. The salt rock resources in China are primarily composed of continental strata salt rocks, characterized by high heterogeneity, well-developed thin-layer interbedding, dissolution resistance among different lithologies, and significant creep variations. These features, to some extent, limit the improvement of wellbore construction accuracy, the reliability of abandoned well sealing, the safety of natural gas storage operations, and enhancements in gas injection–brine displacement efficiency. This study takes the continental bedded salt rock in the Dawenkou Basin as the research object and adopts a method combining theoretical analysis and field engineering verification to improve the systematic construction technology system, covering the whole process of drilling engineering, abandoned well plugging, the design of an injection and brine extraction device, and gas injection and brine drainage. The research results optimize four key technologies, including precise wellbore trajectory control, dual-section milling, and multi-stage redundant plugging of abandoned wells and long-term anti-corrosion completion with laser cladding, and dual-mode adaptive gas injection and brine drainage, and improve the technical system from wellbore construction to salt cavity formation. This study can provide valuable theoretical references and engineering demonstration guidance for underground space development projects in similar salt basins in China. Full article

To support the strategy of building a strong maritime nation, oil and gas resources need to be shifted from inland to coastal areas, and large-scale strategic reserves must be established to meet national security and energy security requirements. Currently, the primary method for offshore gas storage involves onshore steel tanks, which suffer from high costs and limited capacity. The offshore sediment-type salt cavern gas storage is a high-quality alternative solution; however, its long-term stability and economic viability remain to be studied. The feasibility of gas storage in an abandoned cavern of a coastal, low-grade salt mine was simulated using ANSYS Parametric Design Language (APDL) and FLAC3D 7.0, and the cost–benefit comparisons were conducted among abandoned salt caverns, newly constructed single- and double-well salt caverns, and onshore storage tanks. The results show that, without utilizing the sediment storage space, the gas storage capacity is reduced and surrounding rock deformation is increased. On the other hand, the sediment’s supporting effect can mitigate creep deformation and enhance cavern stability. In addition, increasing the operating cycle frequency can significantly reduce volume shrinkage, roof subsidence, and the extent of the plastic zone. Economic analysis shows that the estimated construction cost for repurposing coastal sediment-type salt caverns is approximately 82 million CNY, which is significantly lower than the 450 million CNY required for onshore storage tanks. Compared with newly constructed single- and double-well salt caverns, it offers advantages in cycle time, cost, and revenue. Accordingly, this research can provide theoretical guidance for evaluating abandoned cavern reserves and conducting feasibility studies. Furthermore, it offers technical support for the large-scale, sustainable storage of carbon dioxide, hydrogen, compressed air, and other renew-able energy carriers in abandoned salt caverns. Full article

Compressed CO₂ energy storage (CCES) in deep sedimentary basins offers a promising option to integrate carbon management with long-duration energy storage. However, most existing subsurface energy-storage studies focus on salt caverns or generic porous reservoirs, while the potential of evaporite-bounded carbonate reservoirs remains insufficiently explored. This study presents the first application-oriented numerical assessment of CCES in Southern Ontario. It investigates the feasibility of CCES in the Upper Silurian Salina Group beneath offshore Lake Huron, focusing on a porous A-2 carbonate interval vertically confined by B and A-2 halite caprocks. A fully coupled three-dimensional thermo-hydro-mechanical model is developed in COMSOL Multiphysics 6.3 to simulate two-phase (brine-CO₂) Darcy flow, heat transfer, and poroelastic deformation under a realistic Michigan Basin stress, pressure and geothermal regime. After an initial cushion-gas stage at 8 kg/s that establishes a caprock-parallel supercritical CO₂ wedge beneath the B-salt, 24 h injection-production cycles are imposed for two years, followed by a five-month high-resolution window. Three well completion strategies are compared: full-length, upper-only, and split (upper + lower) perforations. Results indicate that in all simulations the CO₂ plume stabilizes as a persistent gas cap beneath the B-salt, far-field pressures remain close to hydrostatic, and reservoir deformations are very small, pointing to a substantial geomechanical safety margin. Among the three completion strategies, the split completion provides the best compromise: it maintains high and relatively stable CO₂ production while avoiding the stronger lower-zone depressurisation seen in the full-length case and the more limited working volume of the upper-only case. These findings suggest that a Salina A-2 carbonate reservoir bounded by B and A-2 salts can accommodate cyclic CCES under realistic basin conditions, and that appropriately designed split completions offer a practical balance between storage utilisation and operational robustness in this setting. Full article

Underground Gas Storage (UGS) is transitioning from traditional fossil fuel peak-shaving facilities into comprehensive hubs for Terawatt-hour-scale Terawatt-hour (TWh) scale renewable energy storage. The unique physicochemical properties of diverse fluids, such as the negative Joule–Thomson coefficient of hydrogen (−0.03 K/bar), present complex engineering adaptability challenges. Since existing studies primarily focus on single mechanisms or specific geological types, this review integrates a unified engineering framework to evaluate the repurposing potential and retrofitting requirements of existing oil and gas assets. By compiling a property benchmarking matrix for methane, carbon dioxide, and hydrogen, the storage adaptability of various geological formations is summarized. Salt caverns exhibit strong adaptability to highly diffusive and reactive fluids due to their high salinity (exceeding 150 g/L) and mechanical stability, whereas porous media offer massive capacity (more than 10 times) but require overcoming severe biogeochemical obstacles. Based on thermo–hydro–mechanical–chemical–biological (THMCB) coupling mechanisms, an integrity evaluation system for artificial wellbore and natural geological barriers is systematically reviewed. Critical risks, including fatigue failure under high-frequency cyclic loading, material degradation, gas leakage, and indirect Global Warming Potential (GWP), are elucidated. A future evolution route integrating physical, digital, and policy dimensions is outlined. This roadmap emphasizes Hydrogen-Enriched Compressed Natural Gas (HCNG)synergistic storage, dynamic risk control utilizing digital twins and Artificial Intelligence (AI), and standardized Life Cycle Assessment mechanisms (LCA), providing a scientific basis for the sustainable transition of UGS facilities. Full article

Underground gas storage (UGS) in salt caverns is increasingly important for a flexible and secure energy supply and for stabilizing the gas market. However, cavern operations can induce surface ground movements that must be monitored to safeguard infrastructure integrity and environmental compatibility. This research analyzes horizontal (W–E) and vertical ground movements above the cavern field Gronau-Epe in northwestern Germany, using radar interferometry (InSAR), specifically the SBAS (Small Baseline Subset) approach, combined with clustering and multi-criteria analysis. The study was conducted in cooperation between Uniper Energy Storage GmbH, the Research Center for Post Mining at THGA Bochum, and the company EFTAS. Freely available Copernicus Sentinel 1 data were integrated with public soil maps and operational storage information. A multistage workflow quantified deformation patterns, classified coherent deformation zones via clustering, and evaluated geological and technical drivers using multi-criteria analysis to better distinguish operational (primary) from overburden (secondary) influences. Results reveal long term deformation trends closely linked in time and space to injection/withdrawal cycles. Locally confined vertical and horizontal movements near caverns are attributed to salt convergence triggered by cyclic pressure changes, but they are linked to (hydro)geological and pedological factors. The developed approach shows strong monitoring potential in addition to classic mine surveying. Full article

The rapid development of renewable energy requires the support of large-scale energy storage technologies to maintain system balance. Salt cavern compressed air energy storage (CAES) is regarded as one of the key technological pathways for large-scale energy storage. In such systems, the wellbore serves as a critical structure connecting surface facilities and the underground salt cavern, while the cement sheath—formed between the casing and formation during well cementing—acts as the primary barrier ensuring the overall sealing integrity of the wellbore. Through cyclic loading–unloading tests on cement slurries under different temperatures, this study yields the following main conclusions: (1) Increasing temperature aggravates the accumulation of fatigue damage in cement specimens. Taking cumulative plastic strain as an example, it rises from 0.45% to 0.99% as the temperature increases from 25 °C to 115 °C. (2) Elevated temperature promotes greater irreversible energy dissipation under fixed cyclic stress limits. When the temperature rises from 25 °C to 115 °C, the dissipated energy density increases from 0.0033 mJ/m³ to 0.0046 mJ/m³, and its proportion relative to the input energy also increases from 5.52% to 7.13%. (3) Temperature rise leads to notable deterioration of the internal pore structure. At 115 °C, the NMR T₂ distribution peak shifts rightward by 0.49 ms, the total pore volume increases by 150.53 mm³, and the corresponding permeability rises by 1.398 × 10⁻³ μm². (4) Elevated temperature (up to 115 °C) weakens material performance through a dual mechanism: it accelerates dehydration of the cementitious system, reducing interparticle bond strength, while also promoting plastic slip. It is recommended to optimize the cement slurry formulation (e.g., by incorporating thermal stabilizers) to enhance its long-term sealing performance under service conditions. Full article

Both the energy sector transition processes and the industry transformation processes should in the future be based on the use of green hydrogen (GH) obtained using renewable energy sources (RES). It is the symbiosis of RES and GH that will allow for a sustainable energy transformation of the entire economy. The calculated amount of RES in the Kujawsko-Pomorskie Voivodeship (Poland) is 18 TWh—this would provide 4.2 billion m³ (under normal conditions) (0.38 million tons) of GH. The amount of GH produced from RES surpluses in the voivodeship is about 30% of the current production of GH from fossil fuels in Poland. The calculated GH would power 2.64 million cars. The Kujawsko-Pomorskie Voivodeship has numerous salt caverns where GH can be stored. The most important barrier in the context of GH production remains the effective construction of a hydrogen economy chain, which requires a simultaneous costly transformation of the supply and demand sides. In order to implement GH technology, it is necessary to reduce the costs associated with its production, storage and transmission. Full article

During the discharge process of a salt cavern compressed air energy storage (CAES) system, high-speed air flow may entrain salt slag from the cavern floor, posing a threat to pipeline safety. Currently, there is a lack of in-depth research into the transient mechanisms of the entrainment process, particularly the influence of particle shape. This study employs a CFD-DEM coupling approach to conduct, for the first time, a high-fidelity simulation of slag entrainment dynamics during the initial discharge phase of a salt cavern CAES system, with a focus on the motion patterns of three particle shapes: spherical, conical, and square. Results show that: (1) during the initial discharge stage, the flow field rapidly forms vortex structures that migrate toward the wellhead, which is the core mechanism driving particle mobilization; (2) particle shape significantly affects entrainment efficiency through frictional characteristics—spherical particles are most easily entrained (maximum entrainment rate of 0.42 kg/h), while non-spherical particles tend to accumulate below the wellhead; and (3) the entrainment process exhibits strong transient characteristics: the entrainment rate peaks rapidly (approximately 0.82 kg/h) within a short time and then declines sharply, and it is sensitive to particle size, with the most entrainable particle size being around 5 mm. This study reveals the coupling mechanism between transient vortices and multi-shape particle entrainment during discharge, providing a theoretical basis for the design of filtration systems, operational risk prevention, and slag removal strategies in salt cavern CAES power plants. Full article

Underground gas storage (UGS), encompassing hydrogen, natural gas, and compressed air, is a cornerstone of large-scale energy transition strategies, offering seasonal balancing, security of supply, and integration with renewable energy systems. However, the complexity of geological conditions, multiphysics coupling, and operational uncertainties pose significant challenges for UGS design, monitoring, and optimization. Artificial intelligence (AI)—particularly machine learning and deep learning—has emerged as a powerful tool to overcome these challenges. This review systematically examines AI applications in underground storage types such as salt caverns, depleted hydrocarbon reservoirs, abandoned mines, and lined rock caverns using bibliometric and knowledge-graph analysis of 176 publications retrieved from the Web of Science Core Collection. The study revealed a rapid surge in AI-related research on UGS since 2017, with underground hydrogen storage emerging as the most dynamic and rapidly expanding research frontier. The results reveal six dominant research frontiers: (i) AI-assisted geological characterization and property prediction; (ii) physics-informed proxy modeling and multi-physics simulation; (iii) gas–rock–fluid interaction, wettability, and interfacial behavior prediction; (iv) injection-production process optimization; (v) intelligent design and construction of underground storage, especially salt caverns; and (vi) intelligent monitoring, optimization, and risk management. Despite these advances, challenges persist in data scarcity, physical consistency, and generalization. Future efforts should focus on hybrid physics-informed AI, digital twin-enabled operation, and multi-gas comparative frameworks to achieve safe, efficient, and intelligent underground storage systems aligned with global carbon neutrality. Full article

Underground pumped hydro storage (UPHS) in solution-mined salt caverns offers a promising approach to address the intermittency of renewable energy in flat geological regions such as Southern Ontario, Canada. This work presents the first fully coupled thermo-hydro-mechanical (THM) numerical model of a two-cavern UPHS system in Southern Ontario, providing a foundational assessment of long-term cavern stability and brine leakage behavior under cyclic operation. The model captures the key interactions among deformation, leakage, and temperature effects governing cavern stability, evaluating cyclic brine injection–withdrawal at operating temperatures of 10 °C, 15 °C, and 20 °C over a five-year period. Results show that plastic deformation is constrained to localized zones at cavern–shale interfaces, with negligible risk of tensile failure. Creep deformation accelerates with temperature, yielding maximum strains of 2.6–3.2% and cumulative cavern closure of 1.8–2.6%, all within engineering safety thresholds. Leakage predominantly migrates through limestone interlayers, while shale contributes only local discharge pathways. Elevated temperature enhances leakage due to reduced brine viscosity, but cumulative volumes remain very low, confirming the sealing capacity of bedded salt. Overall, lower operating temperatures minimize both convergence and leakage, ensuring greater stability margins, indicating that UPHS operation should preferentially adopt lower brine temperatures to balance storage efficiency with long-term cavern stability. These findings highlight the feasibility of UPHS in Ontario’s salt formations and provide design guidance for balancing storage performance with geomechanical safety. Full article

As industry moves from fossil fuels to green energy, substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns, depleted hydrocarbon fields, and saline aquifers. Among other criteria, these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is, thus, of utmost importance. In this review, the main factors influencing fluid flow are examined. These are the wettability of the caprock formation, the interfacial tension (IFT) between the rock and the gas or liquid phases, and the ability of gases to diffuse through it. To achieve effective sealing, the caprock formation should possess low porosity, a disconnected or highly complicated pore system, low permeability, and remain strongly water-wet regardless of pressure and temperature conditions. In addition, it must exhibit low rock–liquid IFT, while presenting high rock–gas and liquid–gas IFT. Finally, the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals, the evaporites, low-organic-content shales, mudstones, muscovite, clays, and anhydrite have been identified as highly effective caprocks, offering excellent sealing capabilities and preventing hydrogen leakages. Full article

Salt cavern gas storage (SCGS) is a key development direction for future energy storage. However, the stability of the surrounding rock in underground SCGS remains a challenging issue to be resolved. This study uses numerical simulation methods to analyze the stability of the surrounding rock in SCGS at different height-to-diameter ratios and burial depths during both solution mining and long-term operation. The research results show that: SCGS at the same burial depth, as the height-to-diameter ratio increases from 1.2 to 2.2, the maximum displacement of the surrounding rock decreases by 32.3% and the plastic zone area decreases by 54.1%. However, the density of the plastic zone and the volume shrinkage of SCGS rate increase. The optimal cavern shape lies between a height-to-diameter ratio of 1.2 and 1.5. At the same height-to-diameter ratio, the stability of the salt cavern decreases as burial depth increases: the maximum displacement of the surrounding rock, cavern shrinkage rate, and plastic zone area increase by 94.6%, 99.05%, and 78.61%, respectively. Therefore, within a reasonable burial depth range, a shallower burial depth is more favorable for the stability of the surrounding rock. The presence of interlayers reduces cavern displacement, plastic zone, and cavity volume shrinkage, thereby influencing the stability of the surrounding rock. Among them, the interlayer located at the cavern waist reduced the cavern shrinkage rate by 10% and the maximum displacement by 21.9%, exerting the greatest influence on the stability of the surrounding rock. Full article