Storage Caverns Research Articles

Safety of Hydrogen Storage Technologies

While hydrogen is regularly discussed as a possible option for storing regenerative energies, its low minimum ignition energy and broad range of explosive concentrations pose safety challenges regarding hydrogen storage, and there are also challenges related to hydrogen production and transport and at the point of use. A risk assessment of the whole hydrogen energy system is necessary to develop hydrogen utilization further. Here, we concentrate on the most important hydrogen storage technologies, especially high-pressure storage, liquid hydrogen in cryogenic tanks, methanol storage, and salt cavern storage. This review aims to study the most recent research results related to these storage techniques by describing typical sensors and explosion protection measures, thus allowing for a risk assessment of hydrogen storage through these technologies.

Effect of a gunite lining on the stability of salt caverns in bedded formations for hydrogen storage

In this paper, a novel methodology to improve the structural behaviour and durability of bedded salt caverns for hydrogen storage is proposed. The suggested technology consists in applying a gunite lining over the whole cavern surface by means of a pneumatic air blowing. This continuous flow projected at high speed onto the cavern surface produces a self-compacted gunite facing. The effect of adding a gunite lining on the structural performance of a bedded salt cavern is analysed. The nonlinear finite element method is then applied to solve the inherent nonlinear solid mechanics problem. It is shown that reinforcing salt caverns with a gunite lining improves the cavern behaviour, specially in the case of caverns located within a horizontal salt stratum confined between other strata. When dealing with these salt formations, the stratum geometry limits the cavern height. In general, wider caverns that exhibit larger displacements are required to achieve a huge storage capacity. Moreover, these caverns can be located at a considerable depth, where the temperature has an important role on the creep deformation process. Therefore, the proposition of stabilization techniques is required to ensure both their structural integrity and the ground subsidence. This technology allows the safe exploitation of salt caverns located at bedded-type stratified horizontal salt formations.

Combined cycle gas turbine (CCGT) plants utilizing methane-hydrogen blends represent a significant element in Australia’s journey toward achieving net-zero emissions

To deliver 570 TWh of dispatchable electricity to the grid in Australia, it is necessary to build up wind and solar photovoltaic power plants generating capacity of 325 GW, and a long-term hydrogen energy storage system comprising 50–150 GW of electrolyzers, 50 TWh of hydrogen storage, and 165 GW of hydrogen power generation. While the addition of other renewable energy producers and energy storage technologies effective on shorter scales are certainly welcome and positively impact the above demand, the inclusion of inter-annual variability and safety negatively impacts these numbers. Fuel cells are currently less advanced compared to electrolyzers and hydrogen storage in salt caverns. Expanding hydrogen power generation will require exploring additional opportunities. Here we advocate for methane-hydrogen Combined Cycle Gas Turbine (CCGT) plants. Their adaptability to effortlessly integrate methane and green hydrogen mixtures positions them as a key player in the evolution toward net zero. This transition will be complete once a fully established wind and solar photovoltaic generation, coupled with an efficient hydrogen energy storage system, is in place. Notably, these CCGT plants consistently yield the lowest Life Cycle Analysis (LCA) carbon dioxide (CO2) emissions during the grid’s progression toward net zero.

Mechanical properties of gypsum mine rock around a strategic petroleum reserve (SPR) cavern under the crude oil seepage condition

AbstractAs China's demand for imported oil continues to grow, large‐scale oil storage facilities have become increasingly important. Currently, China primarily uses underground salt cavern spaces and newly excavated underground water‐sealed caverns for oil storage, which places high demands on the rock formations. China has abundant and widely distributed gypsum mineral resources, and utilizing abandoned gypsum mines for oil storage could not only turn waste into treasure by controlling underground space but also generate significant economic and social value. This article aims to systematically evaluate the mechanical properties of gypsum rock through long‐term immersion tests in crude oil to assess the impact of crude oil immersion on the mechanical performance of gypsum rock and explore the feasibility of using gypsum mines as long‐term stable oil storage caverns. The results show that oil immersion treatment reduces the uniaxial tensile strength of gypsum samples, but has little effect on their compressive strength and long‐term strength. From a mechanical performance perspective, it is feasible to use gypsum mine voids for crude oil storage.

Research on the Stability of Salt Cavern Hydrogen Storage and Natural Gas Storage under Long-Term Storage Conditions

The stability of salt cavern storage during prolonged operation is a crucial indicator of its safety. This study focuses on an operational underground gas storage facility, conducting comparative numerical simulations for the storage of natural gas and hydrogen. We investigated the evolution of stability for natural gas and hydrogen storage under long-term storage conditions. The main conclusions are as follows: (1) A new equation for stress equilibrium and constitutive relations are derived. (2) At the same storage pressure, the effective stress at the same position in the interlayer is greater for hydrogen storage compared to natural gas storage, signifying a higher level of danger. (3) At the same storage pressure, the displacement at the cavity top for hydrogen storage is greater than that for natural gas storage. The displacement difference between the two is greatest at 9 MPa, amounting to 0.026 m. (4) Due to hydrogen’s lower dynamic viscosity and higher permeability, the depth and extent of the plastic zones within the interlayers are greater compared to natural gas. When the storage pressure is 15 MPa, the depth of the plastic zone within the interlayer can be up to 2.1 m greater than when storing natural gas, occurring in the third interlayer from the top. These research findings may serve as a valuable reference for determining the operational parameters of on-site salt cavern hydrogen storage facilities.

Research of interlayer dip angle effect on stability of salt cavern energy and carbon storages in bedded salt rock

In order to clean and decarbonize energy, large-scale underground energy storage in salt caverns can be utilized. The construction and safety evaluations for these caverns are crucial, especially for salt caverns with significant interlayer dip angles. Aimed at the bedded salt rocks for energy and carbon storage, this study focuses on the impact of different interlayer dip angles on the stability of underground energy and carbon storage caverns in bedded salt rock formations in China. Four salt caverns with varying interlayer dip angles of 0–30° were established for stability comparison. Numerical simulations reveal that caverns with high interlayer dip angles demonstrate low volume shrinkage, general deformation resistance and small equivalent strain, while exhibiting a larger volume of plastic zones compared to caverns with lower interlayer dip angles. It is important to consider the deformation of the cavern wall rock in the down-dip direction for caverns with high interlayer dip angles. The presence of inclined interlayers affects the symmetry of the contour distribution of deformation, safety factor and equivalent strain. Furthermore, recommendations are provided for the construction of salt caverns in salt rock formations with high interlayer dip angles.

Effects of cushion gas pressure and operating parameters on the capacity of hydrogen storage in lined rock caverns (LRC)

Hydrogen storage in lined rock cavern (LRC) provides versatile site selection, safety, and stability, making it a crucial option. In this study, a thermodynamic mathematical model was established to describe hydrogen storage in LRC. This model is based on the principles of mass, momentum, and energy conservation while accounting for the authentic compressibility of hydrogen. The thermodynamic fluctuations throughout the seasonal cycle in LRC were computed using the COMSOL Multiphysics software. The results indicate that when the hydrogen storage reaches the operating pressure, the lower the cushion gas pressure, the greater the hydrogen injection amount, and the higher the utilization rate of storage capacity. With a cushion gas pressure of 3 MPa, the storage capacity utilization rate exceeds that at 15 MPa by 41 %. The injection rate of 0.5 kg/s results in a temperature increase of 12 °C compared to 0.27 kg/s, indicating twice the temperature rise at the 0.27 kg/s injection rate. An increase in injection temperature corresponds to higher temperature within the hydrogen storage cavern upon completion of gas injection, thereby reducing the time needed for gas injection to reach maximum operating pressure. A lower initial cavern temperature results in a longer time for hydrogen storage to reach maximum operating pressure.

Lotsberg Formation: lithological and geochemical constraints for a prime H2 cavern target in Alberta, Canada

Abstract Homogenous and thick (approximately 40–170 m) halite intervals in the upper part of the Lotsberg Formation are most favored targets for hydrogen (H2) storage caverns in Alberta. However, repurposing cavern-making technologies for H2 storage must consider higher diffusivity and higher reactivity of H2, including its known dissolving effect on sulfate minerals and intense production of H2S through bacterial sulfate reduction. New core observations, geochemical and XRD data made on a continuous core through the upper informal member of the Lotsberg Formation and overlying red beds elucidate high content of anhydrite nodules and partings in these red beds, whereas the thick (42.9 m in our test well), exceptionally clean and homogeneous upper halite in this succession contains anhydrite only in trace amounts. A dolomarl-rich interval at 1894.0–1899.45 m, traced regionally as the L2 marker, represents a solution-collapse breccia, thus indicating an intraformational unconformity and an episode of meteoric salt removal prior to deposition of the upper-most halite of the Lotsberg Formation. If the cavern roof is made close to the overlying anhydritic dolostone of the Ernestina Lake Formation, reactivity of H2 may cause rapid dissolution of anhydrites leading to roof collapse, as well as accumulation of H2S through bacterial sulfate reduction. We infer that preserving a thick salt roof during cavern making may be a solution to prevent these damaging effects. Reactivity of H2 with carbonates in the caprock should also be considered. Anhydrite nodules also occur in the basal one-third of the upper Lotsberg, the interval containing more non-halite impurities than the upper salt unit of this member. In this part of the section, anhydrites do not seem to represent the same concern as they will be exposed to cavern-floor sump and cushion gas, whereas H2 reservoir can be operated within the limits of the clean and homogeneous upper halite of the upper Lotsberg Formation. Emplacement of horizontally elongated two-well caverns may represent an adequate way to overcome cavern size limitations, especially in overlying, thinner-bedded halites of the Prairie Evaporite Formation. Résumé Des intervalles homogènes et épais (d’environ 40 m à 170 m) d’halite dans la partie supérieure de la Formation de Lotsberg sont parmi les plus ciblés pour stocker l’hydrogène (H2) dans des cavités en Alberta. Cependant, adapter les technologies pour créer des cavernes de stockage de H2 doit considérer la diffusivité et la réactivité plus élevées de l’H2, y compris son effet dissolvant connu sur les minéraux sulfatés et son intense production de H2S par la sulfatoréduction bactérienne. De nouvelles observations sur les carottes avec données géochimiques et diffractions de rayon X faites sur une carotte continue à travers le membre supérieur officieux de la Formation de Lotsberg et des lits rouges sus-jacents élucident le contenu élevé de nodules et d’inclusions stériles dans ces lits rouges, tandis que le plan d’halite (de 42,9 m d’épaisseur de notre puits d’essai) de la partie supérieure de cette succession se révèle exceptionnellement propre et homogène et ne contient que des traces d’anhydrite. Un intervalle riche en marne dolomitique dans la partie comprise de 1894,0 m à 1899,45 m est l’horizon marqueur L2 au niveau régional. Celui-ci représente une brèche d’effondrement par dissolution, ce qui indique par conséquent une discordance intraformationnelle et un épisode d’élimination saline par météorisation avant le dépôt d’halite le plus élevé de la Formation de Lotsberg. Si le toit de la cavité est créé près de la dolomie anhydritique sus-jacente de la Formation d’Ernestina Lake, la réactivité de l’H2 pourrait causer une dissolution rapide des anhydrites et entraîner l’effondrement du toit, ainsi qu’à l’accumulation de H2S par la sulfatoréduction bactérienne. Nous supposons que la préservation d’un épais toit salin durant la création de cavités serait la solution pour prévenir ces effets dommageables. Nous devrions également considérer la réactivité de l’H2 avec les carbonates de la roche couverture. De plus, les nodules d’anhydrite se présentent également dans la tierce partie basale de la Formation de Lotsberg, l’intervalle contenant plus d’impuretés non liées à l’halite que l’halite de la partie supérieure de Lotsberg. Dans la partie de cette section, l’anhydrite ne semble pas représenter les mêmes préoccupations puisqu’elle sera exposée au puisard du fond de la cavité et au gaz-coussin, tandis que le réservoir H2 peut être exploité dans les limites de l’halite supérieure propre et homogène de la Formation de Lotsberg supérieure. L’emplacement de cavités à deux puits horizontaux allongés peut représenter un moyen adéquat pour résoudre les limites quant à la grandeur des cavités, en particulier lorsqu’il s’agit de minces lits d’halites sus-jacents de la Formation d’halite des Prairies. Michel Ory ACRONYMY AB Alberta AIHA Alberta’s Industrial Heartland Association CRM Critical Raw Minerals EPG Elk Point Group LNG Liquefied Natural Gas LPG Liquefied Petroleum Gas R&D Research and Development SK Saskatchewan UHS Underground Hydrogen Storage XRD X-ray diffraction WCSB Western Canada Sedimentary Basin

Experimental investigation on the oil extraction process for a novel underground oil storage method: Oil storage in salt cavern insoluble sediment voids

Large-scale underground oil storage is vital for addressing the energy crisis. Leveraging the insoluble sediment space at the bottoms of salt caverns for oil storage is particularly effective in high-impurity salt mines, enhancing oil storage capacity. The process of extracting oil from the sediment void is essential for utilizing this resource. Three experimental devices were developed to investigate this extraction process. We conducted experiments on oil extraction processes and rates for various oil types, analyzing weight changes and influencing factors. The sediment and water content in the extracted oil were also evaluated. Results indicated that extracting oil from the sediment void is feasible, yielding average recovery rates over 90.0 %. High-viscosity oil at 50 °C exhibited three stages: initial stability, a rapid rise, and final stability. Low-viscosity oil correlated with brine injection rates, displaying a rapid rise, stable phase, and subsequent decline. Petrolatum extraction was easier than diesel extraction, and ground temperature improved recovery rates. Changes in water and sediment content had minimal impact on oil quality. This research provides insights for large-scale underground energy storage.

Microstructural evolution and mechanical behaviors of rock salt in energy storage: A molecular dynamics approach

The microstructure of rock salt significantly influences its macroscopic mechanical behaviors and deformation phenomena. Understanding the deformation and failure characteristics of rock salt at multiple scales is crucial for the secure and efficient functioning of energy storage in salt caverns. Although the macroscopic behaviors of rock salt are well understood, the microstructural changes occurring under uniaxial compression have not been thoroughly investigated. This study aims to investigate the evolving laws of rock salt microstructure and mechanical properties during the damage process, thereby providing a fundamental understanding of the underlying mechanism. To achieve this, a series of characterization tests on rock salt were conducted to study its microstructure and defects. Building on this, molecular dynamics simulations were utilized in rock mechanics to elucidate the mechanical behaviors, structural evolutions, and dislocation motions of rock salt during the damage process. The rock salt obtained from Qianjiang, China, is a polycrystalline material with an average subgrain size of 46 nm and an average dislocation density of 4.76 × 10−6 1/Å2. Uniaxial compression of single crystal NaCl exhibits three stages: elastic compression, rapid dislocation multiplication, and forest hardening. Scattered dislocations and isolated dislocation tangles trigger further plastic slippage, leading to decreased strength. Later, the formation of a dislocation cell network hinders further slip and reinforces the strength of rock salt. Plastic deformation is found to be a dominant factor in grain refinement and the formation of polycrystalline structures. Intergranular cracking results from cross-patterned dislocation lines on grain boundaries, which become vulnerable areas of the structure. This study describes the evolutionary process of rock salt microstructures and mechanical properties, identifies the micro-destruction mechanisms during the damage process at the ionic level, and provides insights into the micro-mechanical behavior of rock salt and for the design and stability assessment of underground energy storage facilities.

Airtightness evaluation of lined caverns for compressed air energy storage under thermo-hydro-mechanical (THM) coupling

Large-scale compressed air energy storage (CAES) technology can effectively facilitate the integration of renewable energy sources into the power grid. The airtightness of caverns is crucial for the economic viability and efficiency of CAES systems. This paper presents a new thermo-hydro-mechanical (THM) model for investigating the effects of complex thermodynamic changes on air leakage in concrete-lined rock caverns. The model is validated using field measurement data, numerical simulations, and analytical solutions. Subsequent simulations were conducted to analyze air leakage, pore pressure, and leakage range under various operating conditions. Finally, the impacts of different parameters on air tightness were assessed. The results indicate that the daily air leakage mass percentage (TDALMP) in the concrete-lined CAES cavern is 0.60 % under the operating pressure of 4.5–10 MPa, which meets the tightness requirement. The permeability of the lining is a key parameter for airtightness, in this case, the permeability of the concrete lining cannot exceed 1 × 10−19 m2. The daily air leakage rate can be reduced by modestly increasing the cavern radius, lowering the temperature of the injected air, and decreasing the maximum operating pressure. These results can provide a reference for the study and construction of CAES caverns in similar projects.

Flexibility provision in the Swiss integrated power, hydrogen, and methane infrastructure

The renewable energy transition hinges on balancing energy supply and demand across seasons. This paper investigates the potential flexibility of Switzerland’s integrated power, hydrogen, and methane infrastructure to balance temporal mismatches while complying with national energy policies for sustainability and security. It develops an optimization method for energy system expansion and operation planning, filling crucial research gaps by (1) explicitly modeling power and gas transmission networks to guide technology placement and pinpoint network expansions, and (2) incorporating flexibility in power demand via shedding and shifting and in hydrogen and methane demands via price elasticity. The findings suggest that a 6.7-fold capacity expansion of variable renewables (i.e., photovoltaic, wind, run-of-river) by 2050 offsets nuclear phase-out and demand growth. The winter power gap is filled by power imports, hydropower generation, and gas turbines fueled by cost-effective hydrogen or methane imports. However, fuel embargoes escalate winter hydrogen and methane prices, reducing demand by 3.8%–10.4% and increasing domestic fuel production from biomass and excess renewable power in summer. To bridge the seasonal hydrogen and methane supply–demand gaps, up to 1.9 terawatt-hours of gas cavern storage is deployed in geologically viable locations, while costly tank storage plays a minor role. Power-to-gas requirements and power trade restrictions necessitate further renewable expansion, including 8.0 to 9.5 gigawatts of wind installations.

Gas tightness around salt cavern gas storage in bedded salt formations

Underground salt cavern storage has become the preferred medium for storing gas energy and strategic substances. Salt caverns are suitable for storing small molecular gases due to the low porosity and permeability of salt rocks. This paper comprehensively analyzes the physical properties of four gases - hydrogen, helium, methane, and carbon dioxide - under subsurface temperature and pressure conditions. It categorizes the flow regimes of these gases in salt rocks under geological pressure conditions based on the Knudsen number. In a typical 1000 m salt cavern, the predominant permeation flow regime of four gases in the surrounding rock is Klinkenberg flow, with helium potentially undergoing transitional flow at low operation pressures. A 3D numerical model is established for an actual salt cavern to compare the permeation and leakage characteristics of these gases within salt rock formations. Results indicate that, under identical operation conditions, the permeation range of the gases decreases in the following order: hydrogen > methane > helium > carbon dioxide. Under the cyclic operation pressures, the cumulative leakage amount of hydrogen, helium, and methane increases over time, while that of carbon dioxide initially rises and then decreases. This behavior is attributed to the fact that the reverse-permeation rate of carbon dioxide at low pressures exceeds its permeation rate at high pressures. Over 30 years cyclic operation, the leakage ratios of the gases are as follows: hydrogen (13.29 %), methane (9.34 %), helium (7.47 %), and carbon dioxide (0.93 %), with hydrogen exhibiting the highest and carbon dioxide the lowest leakage ratios. Larger permeability results in a larger permeation range, while larger porosity leads to a smaller permeation range. When the permeability of salt layer is greater than 1e-20 m2, the permeation range of hydrogen significantly increases. Gas leakage ratios increase with permeability nonlinearly and increase with porosity linearly. The impact of salt layer permeability on leakage ratios is greater than that of porosity. This study provides crucial guidance for the selection of geological formations for storing hydrogen, helium, methane, and carbon dioxide in salt caverns, as well as the investigation of gas permeation characteristics in salt layers.

Overview of Salt Cavern Oil Storage Development and Site Suitability Analysis

Salt cavern storage, characterized by its safety, stability, large scale, economic viability, and efficiency, stands out as a cost-effective and relatively secure method for large-scale petroleum reserves. This paper provides an overview of the current development status of salt cavern storage technologies both domestically and internationally, analyzes the advantageous conditions and numerous challenges faced by salt cavern Strategic Petroleum Reserve (SPR) storage in China, and forecasts the development trends of this technology. The conclusions indicate that China possesses all of the necessary conditions for the development of salt cavern storage. Moreover, utilizing the Analytical Hierarchy Process (AHP), a macro suitability hierarchical evaluation system is constructed for the site selection and construction of salt cavern storage facilities. This system quantifies various site selection indicators, integrating expert opinions and findings from relevant theoretical research to establish grading standards for the suitability indices of salt cavern storage construction. Applied to the site evaluation of salt cavern storage at the Jintan Salt Mine in Jiangsu, the results indicate its high suitability for storage construction, making it an ideal location for establishing such facilities. The evaluation results are consistent with expert opinions, demonstrating the rationality of this method.

Integrating 1D and 3D geomechanical modeling to ensure safe hydrogen storage in bedded salt caverns: A comprehensive case study in canning salt, Western Australia

The viability of hydrogen storage in bedded salt caverns hinges on understanding the geomechanical challenges posed by the anisotropic stress states and complex geology of such environments. This study presents a comprehensive geomechanical analysis focusing on a proposed cavern within the Carribuddy Formation in Western Australia, characterized by its interbedded salt layers. This paper introduces a new geomechanical workflow, encompassing 1D and 3D modeling techniques to provide detailed changes of mechanical properties and stress state in interbedded salt formation allowing to identify the initial optimal operational pressures for underground hydrogen storage. Initial 1D models evaluated mechanical properties and in-situ stresses, while subsequent 3D simulations, enriched by data from neighboring wells, detailed the stress, strain, and displacement responses of the cavern walls to internal pressure changes. The analysis pinpointed an initial safe gas pressure range between 3000 and 4000 psi, attributing this margin to the robust characterization of the mechanical and in-situ stress of the formation. Our findings underscore the significance of high-resolution geomechanical modeling in identifying initial optimal operational pressures for hydrogen storage in salt caverns, ensuring both safety and structural integrity.

Integration of a Hydrogen Storage Cavern into the Carbon2Chem® Project

AbstractUnderground salt caverns allow large hydrogen storage capacities at low specific costs. Such storage is required to balance fluctuating hydrogen supply and constant demand of large consumers as a methanol plant from the Carbon2Chem® project. The geological and technical feasibility for developing up to 168 Mio. m3 (n.c.) or 595 GWh of working gas capacity until 2040 at a location in the Lower Rhine Bay is described. Various options for realization as well as a novel process for cavern leaching parallel to hydrogen storage operation are evaluated. Further work is required including geological exploration and optimization of brine production. The main hurdles for investment decisions are the political uncertainties on the hydrogen storage market design and on the ramp‐up of the hydrogen market.

Opportunities and constraints of hydrogen energy storage systems

Abstract In contrast to battery storage systems, power-to-hydrogen-to-power (P-H2-P) storage systems provide opportunities to separately optimize the costs and efficiency of the system’s charging, storage, and discharging components. The value of capital cost reduction relative to round-trip efficiency improvements of P-H2-P systems is not well understood in electricity systems with abundant curtailed power. Here, we used a macro-energy model to evaluate the sensitivity of system costs to techno-economic characteristics of P-H2-P systems in stylized wind-solar-battery electricity systems with restricted natural gas generation. Assuming current costs and current round-trip P-H2-P efficiencies, least-cost wind and solar electricity systems had large amounts of excess variable renewable generation capacity. These systems included P-H2-P in the least-cost solution, despite its low round-trip efficiency and relatively high P-H2-P power discharge costs. These electricity system costs were not highly sensitive to the efficient use of otherwise-curtailed power, but were sensitive to the capital cost of the P-H2-P power discharge component. If the capital costs of the charging and discharging components were decreased relative to generation costs, curtailment would decrease, and electricity system costs would become increasingly sensitive to improvements in the P-H2-P round-trip efficiency. These results suggest that capital cost reductions, especially in the discharge component, provide a key opportunity for innovation in P-H2-P systems for applications in electricity systems dominated by wind and solar generation. Analysis of underground salt cavern storage constraints in U.S.-based wind and solar scenarios suggests that ample hydrogen storage capacity could be obtained by repurposing the depleted natural gas reservoirs that are currently used for seasonal natural gas storage.

Well Integrity in Salt Cavern Hydrogen Storage

Underground hydrogen storage (UHS) in salt caverns is a sustainable energy solution to reduce global warming. Salt rocks provide an exceptional insulator to store natural hydrogen, as they have low porosity and permeability. Nevertheless, the salt creeping nature and hydrogen-induced impact on the operational infrastructure threaten the integrity of the injection/production wells. Furthermore, the scarcity of global UHS initiatives indicates that investigations on well integrity remain insufficient. This study strives to profoundly detect the research gap and imperative considerations for well integrity preservation in UHS projects. The research integrates the salt critical characteristics, the geomechanical and geochemical risks, and the necessary measurements to maintain well integrity. The casing mechanical failure was found as the most challenging threat. Furthermore, the corrosive and erosive effects of hydrogen atoms on cement and casing may critically put the well integrity at risk. The research also indicated that the simultaneous impact of temperature on the salt creep behavior and hydrogen-induced corrosion is an unexplored area that has scope for further research. This inclusive research is an up-to-date source for analysis of the previous advancements, current shortcomings, and future requirements to preserve well integrity in UHS initiatives implemented within salt caverns.

Mechanical Properties of Rock Salt from the Kłodawa Salt Dome-A Statistical Analysis of Geomechanical Data.

Rock salt is a potential medium for underground storage of energy resources and radioactive substances due to its physical and mechanical properties, distinguishing it from other rock media. Designing storage facilities that ensure stability, tightness, and safety requires understanding the geomechanical properties of rock salt. Despite numerous research efforts on the behaviour of rock salt mass, many cases still show unfavourable phenomena occurring within it. Therefore, the formulation of strength criteria in a three-dimensional stress state and the prediction of deformation processes significantly impact the functionality of storage in salt caverns. This article presents rock salt's mechanical properties from the Kłodawa salt dome and a statistical analysis of the determined geomechanical data. The analysis is divided into individual mining fields (Fields 1-6). The analysis of numerical parameter values obtained in uniaxial compression tests for rock salt from mining Fields 1-6 indicates an average variation in their strength and deformation properties. Upon comparing the results of Young's modulus (E) with uniaxial compressive strength (UCS), its value was observed with a decrease in uniaxial compressive strength (E = 4.19968·UCS2, R-square = -0.61). The tensile strength of rock salt from mining Fields 1-6 also exhibits moderate variability. An increasing trend in tensile strength was observed with increased bulk density (σt = 0.0027697·ρ - 4.5892, r = 0.60). However, the results of triaxial tests indicated that within the entire range of normal stresses, the process of increasing maximum shear stresses occurs linearly ((σ1 - σ3)/2 = ((σ1 + σ3)/2)·0.610676 + 2.28335, r = 0.92). A linear relationship was also obtained for failure stresses as a function of radial stresses (σ1 = σ3·2.51861 + 32.9488, r = 0.73). Based on the results, the most homogeneous rock salt was from Field 2 and Field 6, while the most variable rock salt was from Field 3.

Relative permeabilities for two-phase flow through wellbore cement fractures

Multiple fluids are likely to exist in fractures and flow paths associated with leaky wellbores, including liquids (e.g., crude oil) and gases (e.g., gas exsolved from liquid). These fluids occupy and move through different portions of the pore spaces within the fractures depending on many factors, including fluid properties, fracture size, and the amount of the different fluids. Upward leakage of any phase, through the fracture, can contaminate water-bearing formations, create hazardous surface conditions, and compromise the functionality of the wellbore. Early signs of wellbore leaks may be expressed by anomalous pressure behavior at surface monitoring points on cavern storage wells. These pressure anomalies are difficult to interpret, necessitating knowledge of the factors that affect the multiphase flow in fractures and porous media. These parameters are critical to modeling multiphase flow in fractures. This insight can guide further diagnosis and maximize leak remediation. Our study focuses on the relationship of the liquid–gas relative permeabilities for representative variable-aperture wellbore cement fracture. To obtain the relative permeability of each phase, two-phase flow tests were conducted where both fluids were flowing simultaneously through a fractured wellbore cement specimen under a range of factors, namely (1) aperture size, (2) capillary numbers, and (3) viscosity ratio. The flow experiments were conducted under a range of confining stresses and flow velocities, using nitrogen gas and silicone oils (of different viscosities) in a specially designed pressure vessel. The sum of gas and oil relative permeabilities were found to be less than one under all conditions, which indicates that the presence of one phase affects the permeability of the other phase, and vice versa. Since the gas phase flow conditions include a significant inertial flow component in addition to viscous flow, the inertial flow coefficients at different saturation states are presented. The factors affecting the relationship between the relative permeabilities are discussed in detail. A new mathematical model for estimating the relative permeability of wellbore cement fracture is presented and experimentally validated.