Rock Salt Formations Research Articles

Shear-induced fluid localization, episodic fluid release and porosity wave in deformable low-permeability rock salt

Understanding fluid distribution and migration in deformable low-permeability rock salt is critical for geologic disposal of nuclear waste. Field observations indicate that fluids in a salt formation are likely compartmentalized into relatively isolated patches and fluid release from such a formation is generally episodic. The underlying mechanism for these phenomena remains poorly understood. In this paper, a hydrological-mechanical model is formulated for fluid percolation in a rock salt formation under a deviatoric stress. Using a linear stability analysis, we show that a porosity wave (a train of alternating high and low porosity pockets) can emerge from positive feedbacks among intergranular wetting, grain boundary weakening and shear-induced material dilatancy. Fluid localization or episodic release can be viewed as a stationary or propagating porosity wave respectively. Fluid pockets transported via a porosity wave remain relatively isolated with minimal mixing between neighboring pockets. We further show that the velocity of fluid flow can be significantly enhanced by the emergence of a porosity wave. The concept and the related model presented in this paper provide a unified consistent explanation for the key features observed in fluid flow in rock salt. The similar process is expected to occur in other deformable low-permeability media such as shale and partially molten rocks under a deviatoric stress. Thus, the result presented here has an important implication to hydrocarbon expulsion from shale source rocks, radioactive waste isolation in a tight rock repository, and caprock integrity of a subsurface gas (CO2, H2 or CH4) storage system. It may also help develop a new engineering approach to fluid injection into or extraction from unconventional reservoirs.

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.

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.

Experimental study of geophysical and transport properties of salt rocks in the context of underground energy storage

AbstractArtificial caverns in salt rock formations play an important role in the net‐zero energy transition challenge, both for covering short‐term fluctuations in energy demand and serving as safe locations for long‐term underground gas storage both for hydrogen and natural gas. Geophysical tools can serve for monitoring geomechanical changes in the salt cavern during selection and development, and during gas storage/extraction activities, but the use of common geophysical monitoring techniques has been very limited in this area. Here, we present experimental work on physical and transport properties of halite rocks within the energy storage context and assess the potential of seismic and electromagnetic data to monitor gas storage activities in salt formations. First, we analysed the stress‐dependency of the elastic and transport properties of five halite rocks to improve our understanding on changes in the geological system during gas storage operations. Second, we conducted two dissolution tests, using cracked and intact halite samples, monitored with seismic (ultrasonic P‐ and S‐waves velocities and their attenuation factors) and electromagnetic (electrical resistivity) sources to evaluate (i) the use of these common geophysical sensing methods to remotely interpret caverning development and (ii) the effect of structural discontinuities on rock salt dissolution. Elastic properties and permeability showed an increasing trend towards rock sealing and mechanical enhancement with increasing pressure for permeabilities above 10−21 m2, with strong linear correlations up to 20 MPa. In the dissolution tests, the ultrasonic waves and electrical resistivity showed that the presence of small structural discontinuities largely impacts the dissolution patterns. Our results indicate that seismic and electromagnetic methods might help in the selection and monitoring of the caverning process and gas storage operations, contributing to the expected increase in demand of large‐scale underground hydrogen storage.

Site selection evaluation for salt cavern hydrogen storage in China

Salt caverns are ideal for hydrogen storage. Rock salt formations are widely distributed in China, but geological conditions vary widely. It is necessary to evaluate the suitability of salt mines to build salt cavern hydrogen storage (SCHS). In this paper, an evaluation model based on Entropy-Weighted Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) for SCHS site selection is established. The Entropy Weight Method (EWM) is used to calculate the weights of the evaluation indexes, and the suitability of SCHS is evaluated based on TOPSIS. Finally, the hydrogen storage capacity of the preferred site and the demand for SCHS are considered. According to the evaluation, Jintan and Qianjiang are currently the most suitable sites in China for SCHS, with single-cavern hydrogen storage capacities of 69.56 GWh and 237.00 GWh respectively. To meet China's hydrogen consumption demand in 2060, a minimum of 84.76 km2 or 41.12 km2 of mine area would need to be planned for SCHS in Jintan or Qianjiang, respectively.

Wellbore pressure model for drilling fluid in ultra-deep rock salt formations at high temperatures and pressures

The Kuqa Mountain front area of Tarim is rich in oil and gas resources, but the development of ultra-deep rock salt formation is common, leading to a narrow safety density window and significant impacts on engineering operation safety and wellbore quality, such as overflow and leakage. Managed pressure drilling (MPD) is an effective solution to the problem of drilling in narrow density windows, and a precise wellbore pressure calculation method is essential to ensure the reasonable determination of MPD parameters. Conventional wellbore pressure models treat fluid properties as constant and do not consider the impact of ultra-deep rock salt formation on wellbore pressure calculation, leading to incomplete calculation accuracy that cannot fully meet engineering requirements. In this paper, an improved wellbore temperature field model coupled with the rock salt formation is established. Additionally, rheological experiments on drilling fluids used in the field are conducted and a prediction model for shear stress and density is established based on the varying degrees of temperature and pressure influences. Based on the temperature field of the wellbore and the rheological experimental, a wellbore pressure prediction model is established, and field application is conducted in Keshen Well X. By comparing the measured values, the overall error does not exceed 5%. Compared with neighboring blocks, the rate of penetration has been increased by 73.8%, and the drilling efficiency has been significantly improved. The use of wellbore pressure calculation method, which is studied in this paper, has facilitated efficient operations in drilling ultra-deep rock salt formation.

Effects of creep of the salt rock formation on the failure of cement sheath integrity

Salt rock has a good sealing ability for oil and gas, but the creep of salt rock may cause wellbore integrity failure, and even cause safety accidents and economic losses in serious cases. Based on the creep law of salt rock obtained from the creep experiment of salt rock, the finite element model of casing-cement sheath-formation combination in salt rock formation is established. The effect of formation creep on the integrity of cement sheath under different uniform in-situ stress conditions is studied. The results show that the creep of salt rock will cause the shear failure of the cement sheath; reducing the elastic modulus of the cement sheath and increasing the Poisson's ratio of cement sheath will reduce the risk of shear failure of the cement sheath.

Parameter design of the compressed air energy storage salt cavern in highly impure rock salt formations

Compressed air energy storage (CAES) salt caverns are suitable for large-scale and long-time storage of compressed air in support of electrical energy production and are an important component for realizing renewable energy systems. In this paper, the use of sediment voids in highly impure rock salt formations for CAES is proposed. The interaction between the insoluble sediment and the cavern wall is analyzed. A geomechanical model is established to optimize the design parameters of CAES salt caverns. The simulation results show that as the cavern height increases, the displacement decreases in the bottom sediment region and increases in the waist. As the internal air pressure increases, the safety factor increases, while the volume shrinkage and displacement decrease. The plastic zone and the strength utilization rate decrease, and the safety factor increases with increasing pillar width. Based on the above results, the long cylindrical cavern is recommended to have a height in the range of 260–280 m and a diameter of 80 m. The minimum internal air pressure is 10–12 MPa, and the maximum internal air pressure is 16–18 MPa. The pillar widths between caverns are approximately 2.0–2.5 times the cavern diameter. In this study, for a single cavern with a diameter of 80 m and a height of 260–280 m, the upper free volume (excluding sediment) and the lower sediment filled volume of a single cavern are approximately 4.6–5.0 × 105 m3 and 7.2–7.8 × 105 m3, respectively. The sediment voids used for storing compressed air increase by at least approximately 3.6 × 105 m3, which is approximately 0.8 times the upper free cavern volume. The results show that the CAES salt cavern in highly impure rock salt is feasible and has great potential.

Creep behavior of layered salt rock under triaxial loading and unloading cycles

Abstract This paper presents an extensive laboratory investigation of layered salt rocks under triaxial loading and unloading cycles aiming to better understand their viscoelastic plasticity strain characteristics. Specifically, creep curves were obtained from the triaxial loading and unloading tests and analyzed using the Burgers model. The microstructure of the layered salt rocks before and after the creep test was comparatively analyzed using the dry grinding optical diagram. The results show that the creep deformation of layered salt rocks is mainly viscoelastic under a low deviatoric stress and contains both viscoelastic and viscoplastic deformations when the deviatoric stress is high. With the increase of deviatoric stress, both the instantaneous elastic and plastic strains increase, and the increasing rate becomes lower as the deviatoric stress increases. The creep curves of layered salt rocks can be well represented with the Burgers model. Since the creep leads to fracturing and interlayer rupturing and producing new fluid seepage channels in layered salt rocks, this study has great value for understanding the long-term performance of gas and hydrocarbon liquid storage caverns in layered salt rock formation.

Compaction of crushed salt for safe containment – a summary of the KOMPASS projects

Abstract. For the underground disposal of high-level nuclear waste in rock salt formations, the safety concept includes the backfilling of open cavities with crushed salt. For the prognosis of the sealing function of the backfill for the safe containment of the radioactive waste, it is crucial to have a comprehensive process understanding of the crushed-salt compaction behavior. The crushed-salt compaction process is influenced by internal properties (e.g., grain size, mineralogy, and moisture content) and boundary conditions (e.g., temperature, stress state, and compaction rate) and, therefore, involves several coupled thermal–hydro–mechanical (THM) processes (Hansen et al., 2014; Kröhn et al., 2017). With the paradigm shift from the limited release of radionuclides to safe containment due to the German Repository Site Selection Act passed in 2017, the importance of crushed salt as geotechnical barrier has increased, with a focus on the evolution of its hydraulic properties. Based on the knowledge gaps in the current process understanding, the “Compaction of crushed salt for safe containment” (KOMPASS) projects were initiated to improve the scientific basis behind using crushed salt for the long-term isolation of high-level nuclear waste within rock salt repositories. The efforts to improve the prediction of crushed-salt compaction begun during the first phase of the KOMPASS projects (Czaikowski et al., 2020) and were followed up in a second phase ending in June 2023. The primary achievements of the projects are as follows (Czaikowski et al., 2020; Friedenberg et al., 2022): specification of the KOMPASS reference material, an easily available and reproducible synthetic crushed-salt material, for generic investigations; development of pre-compaction methods and successful production of samples in the short term and under in situ loading conditions; formulation of an extended laboratory program addressing the isolated investigation of known relevant factors influencing the compaction behavior of crushed salt (Düsterloh et al., 2022); execution of long-term compaction tests addressing isotropic and deviatoric load changes, temperature, and compaction state; construction of a backfill body using the KOMPASS reference material in the Sondershausen mine through collaboration with the SAVER (Entwicklung eines salzgrusbasierten Versatzkonzepts unter der Option Rückholbarkeit) project (Schaarschmidt and Friedenberg, 2022); advancement of the tools for microstructure investigation methods (Svensson and Laurich, 2022); generation (first stages) of a microphysical process list combining literature research with our own findings; benchmarking of long-term compaction test for model development and optimization of various existing models as well as the development of new models; application of a virtual demonstrator (2D model representing a backfilled drift in rock salt) for the visualization of developments and the quantification of the models (Rabbel, 2022). In summary, the KOMPASS projects contributed to the reduction of uncertainties and the strengthening of the safety case for using crushed salt within rock salt repositories.

Large-scale CAES in bedded rock salt: A case study in Jiangsu Province, China

To efficiently utilize renewable energy sources primarily consisting of wind and solar power, large-scale compressed air energy storage (CAES) can be implemented using underground salt caverns. In this paper, the abundant wind and solar energy resources and the geological conditions of the three major salt mines in Jiangsu Province are introduced. A geomechanical model is established based on the Huai'an rock salt formation. The simulation results show that as the internal air pressure (IAP) increases, the safety factor increases, and the displacement, plastic zone, volume shrinkage, and equivalent strain decrease. Based on the above results, the minimum IAPs of caverns AN 13 and AN 21 are recommended to be 10–12 MPa. According to estimates, to store 15% of wind and solar power in Jiangsu Province through CAES by 2050, a 9894.0 × 104 m3 salt cavern volume is needed, of which at least 77.8 million m3 can be provided by salt mining enterprises. The cost of reconstructing an underground salt cavern is 12.1 billion yuan, while the investment in surface equipment is 746.7 billion yuan. We provide an economical and feasible solution for achieving carbon neutrality in Jiangsu Province in this study.

Theoretical and Technological Challenges of Deep Underground Energy Storage in China

Deep underground energy storage is the use of deep underground spaces for large-scale energy storage, which is an important way to provide a stable supply of clean energy, enable a strategic petroleum reserve, and promote the peak shaving of natural gas. Rock salt formations are ideal geological media for large-scale energy storage, and China is rich in salt rock resources and has a major shortage of energy storage space. Compared with the salt domes in other countries, the salt rock formations in China are typical lacustrine bedded salt rocks characterized by thin beds, high impurity content, and many interlayers. The development of large-scale energy storage in such salt formations presents scientific and technical challenges, including: ① developing a multiscale progressive failure and characterization method for the rock mass around an energy storage cavern, considering the effects of multifield and multiphase coupling; ② understanding the leakage evolution of large-scale deep underground energy storage caverns; ③ understanding the long-term performance evolution of large-scale deep underground energy storage caverns; ④ developing intelligent construction technologies for the deep underground salt caverns used for energy storage; and ⑤ ensuring the long-term function of deep underground energy storage spaces. The solution to these key scientific and technological problems lies in establishing a theoretical and technical foundation for the development of large-scale deep underground energy storage in China.

Shape prediction and parameter optimization of single-well retreating horizontal salt cavern for energy storage

The single-well retreating horizontal (SWRH) salt rock energy storage has the advantages of high construction efficiency and low cost. However, there needs to be a unified standard for key parameters such as water injection rate, direction and retreat distance in the SWRH leaching process. To solve such a problem, a multi-field coupling numerical model was established, including flow, concentration, temperature fields, and cavern boundary development. The correctness of the numerical model was verified by physical simulation experiments. Before parameter optimization, evaluation criteria of leaching efficiency, water-saving capacity, salt rock formations utilization, and shape regularity coefficient were proposed. The effects of water injection rate, direction, and retreat distance in the SWRH leaching process were analyzed. The feasibility of using air isolation was discussed to deal with the height limitation of salt rock formation. The results showed that increasing the water injection rate led to higher leaching efficiency, higher utilization of salt rock formations and a more regular cavern shape but consumed more freshwater and energy. An upward injection direction increased the leaching efficiency by 5 %–13 % but reduced the shape regularity coefficient and water-saving capacity by 8.3 %–12.3 % and 50 %–67 % relative to a rightward injection direction. The retreat distances were closely related to water injection rates. After air injection, air isolation increased the dissolution rate near the gas-liquid interface 5.41 times due to the brine concentration near the gas-liquid interface being only 44.34 % before air injection. A variable water injection rate, a rightward water injection direction, a retreating distance matching the maximum water injection rate, and a high-frequency gas isolation adjustment were suggested for the SWRH leaching process. The finding promises a broad prospect for the SWRH salt rock energy storage.

Hydrogen geo-storage in rock salt formations: petrophysical characterisation and geomechanical testing of a potential host formation in Western Australia

Hydrogen geo-storage in rock salt formations: petrophysical characterisation and geomechanical testing of a potential host formation in Western Australia

A prediction method of the effective volume in sediment-filled salt cavern

An emerging trend in China is to build gas storage in salt rock formations with a large number of interlayers. However, the sediments formed after the collapse of the interlayers may occupy >80 % of the volume of the salt cavern. The effective volume of salt cavern cannot be investigated by sonar in such cavities. Therefore, a method to predict the effective volume in sediment-filled salt cavern is proposed based on a liquid injection test. First, the bulk modulus of brine and the salt cavern compressibility factor were used to characterize the brine compression and the salt cavern expansion during liquid injection. The volume equilibrium relationship for the liquid injection test was derived. Second, a liquid injection test was conducted for a salt cavern in China. The compressibility factor of this salt cavern is calculated based on the prediction method of the cavern morphology proposed in this paper. The effective volume of the salt cavern is derived. The method was validated by numerical simulation, and the deviation between the two was 0.79 %. For the construction of salt cavern gas storage, this method has the significance of guidance and reference.

Failure mode of cement sheath in salt cavern gas storge wellbore based on coupling plasticity and damage evolution

In this paper, the failure mechanism of the cement sheath in gas storage salt caverns under the cyclic internal pressure and cavity shrinkage was explored. First, an elastoplastic damage evolution model for the completion cement was established and further developed as a constitutive equation for numerical calculation. Second, the verification of the model is completed by mechanical tests and numerical examples, respectively. The uniaxial and triaxial compression tests, Brazilian splitting tests, and cyclic loading tests were performed to verify the theoretical stress-strain curves. Numerical examples were performed to verify the stability of the constitutive equation in numerical simulations. Finally, the constitutive equation is applied to the engineering, and the numerical model calculation of wellbore fatigue damage and salt cavity shrinkage was performed. The following conclusions are obtained: cyclic loading will increase the plastic strain of the cement sheath, and micro-annuluses will form on the inner surface after 25 years of operation. The shrinkage of the salt cavity will debond the outer side of the cement sheath near the open well. With the increase of cavity shrinkage, the range of wellbore failure increases upwards. When the cavity shrinkage rate exceeds 10%, partial debonding will occur on the cemented surface between the cement sheath and the rock salt formation, which may provide a channel for natural gas leakage.

Computing safety drilling fluid density of ultra-deep rock salt formation

Computing safety drilling fluid density of ultra-deep rock salt formation

Potential for Underground Storage of Liquid Fuels in Bedded Rock Salt Formations in Poland

The paper aims to give a universal methodology for assessing the storage capacity of a bedded rock salt formation in terms of the operational and strategic storage facilities for liquid fuels. The method assumes the development of a geological model of the analyzed rock salt formation and the determination of the salt caverns’ size and spacing and the impact of convergence on their capacity during operation. Based on this method, the paper presents calculations of the storage capacity using the example of the bedded rock salt formations in Poland and their results in the form of storage capacity maps. The maps show that the analyzed rock salt deposits’ storage capacity in northern Poland amounts to 7.1 B m3 and in the Fore-Sudetic Monocline to 10.5 B m3, in the case of strategic storage facilities. The spatial analysis of the storage capacity rasters, including determining the raster volumes and their unique values, allowed us to quantify the variability of the storage capacity in the analyzed rock salt deposits.

Исследование содержания галопелитов в пласте каменной соли Б-В Верхнекамского месторождения калийно-магниевых солей

The paper presents the results of studying halopelite content in the B–V rock salt layer in conditions of the Verkhnekamsk potassium-magnesium salt deposit in terms of gas-dynamic hazard during mining of the AB potassium layer. Presence of halopelite bands in the interformational B-V rock salt layer is considered as the factor which causes reduction of both rock tensile strength and cohesion between individual rock layers in the roof of the mine workings that leads to its intensive exfoliation. In case of free gas accumulation or its infiltration from the enclosing rocks into the formed voids this can cause gas-dynamic phenomena, i.e. the roof rocks collapse accompanied by gas emission. Forecasting of the gas-dynamic hazards is extremely important both in mining of potash beds and in the development of oil and potash deposits that coincide laterally. In the course of the research, the content of halopelite within the B-V rock salt formation was taken into account using such a quantitative indicator as the content of water insoluble residue (IR). Analysis of statistical dependence of insoluble residue content as a quantitative characteristic of halopelite content in the B–V formation with the other formation characteristics such as calcium sulphate content, formation thickness and absolute roof elevation was performed. The regression equations were obtained that characterize the correlation relations between the IR and CaSO4, IR and Hcr with regard to the three studied options. Analysis of correlation coefficient values was executed between the IR by CaSO4, as well as the type of the regression equations for free and angular members.

Catalysis of ceria incorporated magnesium hydride: A follow up study

In continuation with the results explored in our recent previous study (https://doi.org/10.1016/j.apsusc.2021.150062), the current work sheds more light regarding the active in situ catalytic species in ceria additive loaded hydrogen storage system, MgH2. For this study, two samples, MgH2+0.167CeO2 and MgH2+0.5CeO2 were processed through mechanical milling (5 h/200 rpm) and tests were conducted at various stages of hydrogenation/dehydrogenation cycles (cycles: 1, 5 and 10). Evidence for mild chemical interaction between MgH2 and CeO2 is observed at the time of mechanical milling, whereas strong redox type interaction is witnessed in the cycle tested samples. In-situ X ray diffraction study confirms that the thermally activated interaction between MgH2 and CeO2 does not produce MgO. In situ Raman spectra provide crucial evidence that reduced cerium oxides exist at all stages of interactions in the MgH2/CeO2 hydrogen storage system. Detailed advanced electron microscopic observations concur well with the in-situ X ray diffraction and Raman spectroscopy studies. Although Gibbs free energy calculations reveal the possible existence of cerium hydrides, owing to the structural similarities between CeHx and CeOx phases, the chemical identity of the most abundant catalytic product remains debatable. Regarding the catalytic mechanism, suppression of MgO rock salt formation is identified to be a key step where the role of CeHx/CeOx interfaces gains more importance.