Rock Salt Deposits Research Articles

Effect of pillar width on the stability of the salt cavern field for energy storage

Abstract Effective planning of the cavern field involves determining the optimal pillar width between the caverns and the feasible number of caverns based on geological and mining conditions. The proper design of the pillar width is crucial to ensure the stability of the cavern field and the rational utilization of the rock salt deposit. The stability of the pillars is a complex problem influenced by various factors, including rock salt creep, changes in the cavern pressure during operational cycles, mechanical parameters, and failure criteria of the rock salt. To address this problem, the stability of the cavern field in relation to the number of caverns and pillar widths is evaluated. The evaluation is based on the following criteria: displacements, von Mises stress, strength/stress ratio, and safety factor. Three variations of pillar width and three variants of cavern fields, differing in the number of caverns, are considered. Results show that the allowable pillar width is affected by the number of caverns in the cavern field. Moreover, the stability analysis reveals uneven stress and deformation distribution in the cavern field. When the pillar width is 2.0–3.0 times the diameter of a cavern, pillars at the centre exhibit poorer stability than those at the edges of the cavern field. However, with a narrower pillar width, the highest displacements occur at the field's edges. The findings of this study provide a valuable date in the planning, design, and operation of new cavern fields for the underground storage of energy sources such as oil, natural gas, hydrogen, and compressed air in rock salt deposits.

Artificial intelligence-driven assessment of salt caverns for underground hydrogen storage in Poland

This study explores the feasibility of utilizing bedded salt deposits as sites for underground hydrogen storage. We introduce an innovative artificial intelligence framework that applies multi-criteria decision-making and spatial data analysis to identify the most suitable locations for storing hydrogen in salt caverns. Our approach integrates a unified platform with eight distinct machine-learning algorithms—KNN, SVM, LightGBM, XGBoost, MLP, CatBoost, GBR, and MLR—creating rock salt deposit suitability maps for hydrogen storage. The performance of these algorithms was evaluated using various metrics, including Mean Squared Error (MSE), Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), Root Mean Square Error (RMSE), and Correlation Coefficient (R2), compared against an actual dataset. The CatBoost model demonstrated exceptional performance, achieving an R2 of 0.88, MSE of 0.0816, MAE of 0.1994, RMSE of 0.2833, and MAPE of 0.0163. The novel methodology, leveraging advanced machine learning techniques, offers a unique perspective in assessing the potential of underground hydrogen storage. This approach is a valuable asset for various stakeholders, including government bodies, geological services, renewable energy facilities, and the chemical/petrochemical industry, aiding them in identifying optimal locations for hydrogen storage.

HYDRODYNAMIC MODEL OF SOLOTVYN ROCK SALT DEPOSIT

Rock salt development brings risks of harmful impact on water resources, in particular the Tysa River, posing a threat of cross-border spread of saline pollution on the border between Ukraine and Romania (Solotvyn rock salt deposit, Transcarpathia, western Ukraine). The impact of technogenic load (underground mining of rock salt) within the deposit led to deformation of the structure and nature of water exchange, intensification of suffusion and karst processes, ground surface deformations, catastrophic inflows of groundwater into mines, and, as a result, to the cessation of development of this deposit in 2010. However, the suspension of salt mining did not stop the development of the above-mentioned hazardous geological processes caused by both natural and man-made factors. In order to justify measures for prevention pollution of the Tysa River basin, a hydrogeological model of the Solotvyna rock salt deposit and surrounding areas was created, which allowed to predict the direction and flow rate of fresh and saline groundwater. The model was developed using new data on the geological structure and hydrogeological conditions of the study area (groundwater monitoring data). The modernised hydrodynamic model includes five layers (main aquifers and confining layers). As a result of modelling, maps of the velocity vectors and head contours for two aquifers (Quaternary and Tortonian) were obtained. Based on the results of solving a number of inverse problems, the functional correspondence of the model to natural and anthropogenic conditions was proved. According to the preliminary calculations of the actual groundwater filtration velocity and the path lines of the inert pollutant spreading, it was found that the time of its migration from the salt contour to the Tysa River is approximately 2–3 years. The developed groundwater flow model will be used to substantiate the network of hydrological and hydrogeological observation points in order to optimise the monitoring of water pollution processes.

Hydrogen storage capacity of salt caverns and deep aquifers versus demand for hydrogen storage: A case study of Poland

Geological structures in deep aquifers and salt caverns can play an important role in large-scale hydrogen storage. However, more work needs to be done to address the hydrogen storage demand for zero-emission energy systems. Thus the aim of the article is to present the demand for hydrogen storage expressed in the number of salt caverns in bedded rock salt deposits and salt domes or the number of structures in deep aquifers. The analysis considers minimum and maximum hydrogen demand cases depending on future energy system configurations in 2050. The method used included the estimation of the storage capacity of salt caverns in bedded rock salt deposits and salt domes and selected structures in deep aquifers. An estimation showed a large hydrogen storage potential of geological structures. In the case of analyzed bedded rock salt deposits and salt domes, the average storage capacity per cavern is 0.05–0.09 TWhH2 and 0.06–0.20 TWhH2, respectively. Hydrogen storage capacity in analyzed deep aquifers ranges from 0.016 to 4.46 TWhH2. These values indicate that in the case of the upper bound for storage demand, there is a need for the 62 to 514 caverns, depending on considered bedded rock salt deposits and salt domes or the 9 largest analyzed structures in deep aquifers. The results obtained are relevant to the discussion on the global hydrogen economy, and the methodology can be used for similar considerations in other countries.

The Interaction Principle in the Assessment of Pillars’ Secondary Stress-Deformation State

Abstract In the field of mining, one of the exploitation methods that is still the most used in rock salt, potassium, and magnesium salt deposits is the method with the room and abandoned pillar. The salt mining method with rooms and pillars represents a unique spatial system for which the establishment of an optimal correlation between the parameters of the room, pillar, and rock massif is required in any given situation. Thus, the dimensioning of the most requested element in the system is followed, and depending on its parameters, the other parameters of the system are established. Considering the exploitation method with rooms and pillars, the pillars are certainly the elements that are subjected to the greatest loads. In the situation where the deep exploitation of salt is done with square pillars, the evaluation of the optimal parameters of the elements of the exploitation system requires: establishing the loads that appear in the surrounding salt massif (the natural stress state); the qualitative-quantitative determination of the way of distribution of the secondary stress state in the pillars; evaluating the bearing capacity of the pillars; and establishing their geometric elements. Solving this problem can be achieved by different methods: based on the theory of limit equilibrium, taking into account the effective stress in the pillars; methods of the mechanics of the continuous system based on the analytical models for evaluating the secondary stress and deformation state of pillars and floors; and numerical methods combined with the results and measurements from the laboratory and in situ tests. A methodology based on the pillar–room–salt massif interaction principle was proposed for the analytically achievable stability exploitation system of rock salt by the dry method as the depth increased. Applying this method, the secondary stress-deformation state in the pillar can be established by taking into account the rheological behaviour of the salt, changing the pillar shape, and the extraction technology. The presented algorithm can be extended in the field of exploitation, where the room and pillar exploitation methods are used.

Commercialization of Construction and Operation Stages of Large-Scale Underground Accumulators of Gas and Liquid Energy Carriers

The article describes the relevant issues associated with the reduction of capex and opex of large-scale underground accumulators of gas and liquid energy carriers by commercializing the stages of their construction and operation. It is shown that during the construction of underground storage, the generated construction brine, which is a waste product, can be a raw material for the creation of products of high consumer value for the country’s economy. Technological schemes for the production of economically useful products in cooperation with the process of constructing underground storage in rock salt deposits and the operation of an underground accumulator of natural gas are presented. All the technological schemes are developed based on highly efficient production of common and technical salt, calcined soda, chlorine, glass, hydrogen (methane-hydrogen mixture), ammonia, carbamide. It is shown that the implementation of the developed schemes of cooperation of technological complexes for the production of essential and useful for the country’s economy products significantly reduces total capital and operational costs and, consequently, the cost of the output product.

GIS-based analysis of rock salt deposits’ suitability for underground hydrogen storage

The paper discusses the suitability of bedded salt deposits for underground hydrogen storage facilities. The presented research is an example of multi-criteria decision analysis coupled with spatial data analysis undertaken using GIS (Geographic Information System). The aim of this study is to develop a methodology for selecting the best locations for hydrogen storage in salt caverns. In the analysis, we take into account the results of previous studies of the storage capacity of rock salt deposits. The presented methodology allows the creation of rock salt deposit suitability maps for underground hydrogen storage. The results show that the applied method significantly influences the resulting map image, helping to identify optimal locations for hydrogen storage facilities. The presented approach may be of value to governmental institutions considering underground hydrogen storage, geological services, power plants producing electricity from renewable energy sources, and chemical and petrochemical plants.

Influence of Temperature and Deviatoric Stress on Creep Behavior of Rock Salt

Rock salt deposits are used as depositories for hazardous wastes and oil due to their excellent mechanical properties for depositories such as low permeability and self-healing. The creep behavior of rock salt plays a major role in the long-term stability of rock salt depositories. Temperature and deviatoric stress significantly impact the creep behavior of rock salt. This paper studies the influences of temperature and deviatoric stress on the creep behavior of natural single-crystal rock salt specimens using creep experiments. A special triaxial thermal cell was developed to conduct the experiments. Prismatic specimens were cut out of a large mass of a sample that was acquired from Windsor Salt Mine, Ontario, Canada. The prepared specimens were tested in one-dimensional creep experiments at 20, 100, and 150° C temperatures and under 1 MPa confining pressure. Constant deviatoric stresses (σd ) of 4, 10, and 12 MPa were applied to the specimens. Increasing the applied deviatoric stress and temperature caused an increase in the accumulated strain during the experiments and resulted in higher steady-state strain rates. Although the transient strain rate is increased at elevated temperatures, it appears to be insensitive to the applied deviatoric stress.

Analysis of the Influence of the Vertical Coaxiality of the Pillars on the Stability of the Resistance Structures, from the Ocnele Mari Saline

Abstract The Ocnele Mari rock salt deposit is exploited with small rooms and square pillars, on the horizons +226 m and 210 m. Following the exploitation of the lower horizon +210 m, the floor between the two horizons suffered instability phenomena, marked by fractures and cracks and local degradation of the pillars.Since the pillars at the two horizons have certain deviations from the coaxiality, the question was raised whether the instability phenomena were generated by the deviations from the coaxiality.This article presents the stability analysis of bearing structures, taking into account the actual geometry of pillars, 3D finite element analysis and analysis of safety factors at the ceiling level, calculated from 2D finite element models. The final conclusion is that the instability phenomena that occurred at the Ocnele Mari Saline were generated by the state of stresses and strains, produced by the spatial distribution of the underground voids and the geomechanical characteristics of the rock salt and insignificantly, by the deviation from the coaxiality of the pillars.

Shape design and safety evaluation of salt caverns for CO2 storage in northeast Thailand

Salt caverns are an adequate solution for the sequestration of CO2 (large capacity, safety and long-term operation). The large rock salt deposits of the Maha Sarakham Formation represent a very promising location. Designing salt caverns is still a complex issue. In this paper, the stability of typical cavern shapes (spherical, cylindrical, teardrop, bulb, and pear) was evaluated based on displacement, von Mises stress, safety factor, and volume change. The analysis aimed to find the optimal cavern shape for salt deposits at Ban Nong Plue, Borabue district, Maha Sarakham province, northeast Thailand. The Finite Element simulations investigating the cavern stability are carried out for a time span of 600 years (> 500 years is considered permanent storage). The bulb-shaped cavern yielded the best results, indicating that it constitutes the optimal shape in the given geological conditions. The stability of all analyzed caverns showed a dependence on the operating stage. Each stability factor exhibited large differences between the periods of cavern construction/brine discharge and pre-pressurization by CO2 injection. A lower cavern pressure negatively affected the evaluated factors. The results can be useful in planning future cavern fields for CO2 storage (and other gases) in salt deposits.

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.

Impact of the brine discharge on the bottom ecosystem of the Sambia Peninsula coast (South-Eastern Baltic Sea)

The first underground gas storage facility in Russia, built in rock salt deposits, was developed in the coastal zone of the Kaliningrad Region. Since 2018, seawater for erosion of rock salt is taken from the Baltic Sea, and after appropriate treatment, brine is discharged back to the sea. The aim of the work was to assess the impact of the brine discharge on the bottom ecosystem of the coastal shallow area. A comprehensive study was carried out on the possible path of salt brine propagation, including a bathymetric survey, CTD sounding of the water, sampling of bottom sediments and zoobenthos, determination of heavy metals in sediments. The main pathways for the spread of brine along the bottom were determined, and the additional supply of salt to the coastal zone naturally led to local changes in the existing bottom ecosystem of the coastal shallow water, including changed in the structure of zoobenthos.

SUBSTANTIATION OF THE ARRANGEMENT AND OPERATION OF THE MOZYR UNDERGROUND GAS STORAGE FACILITY

The relevance and importance of underground gas storages for the energy security of the Republic of Belarus is denoted. The types of underground gas storage facilities in operation on the territory of the republic are indicated.
 The geological conditions of the Mozyr salt massif in the area of the mine workings are given. The features of the structure of the Mozyr salt dome are considered. Information about the rock salt deposits of the Zalessky layers suitable for creating caverns is given. Mining and geological conditions are described and favorable factors of an underground gas storage creation in rock salt deposits under the conditions of the Mozyr salt dome are denoted. Information about the screening effect of the roof strata is given. Mathematical modeling was carried out and the assessment of the suitability of the existing
 salt caverns is given. During the conversion of existing and the creation of new caverns, as well as in the process of their operation (injection-storage-selection) long-term sustainability to the effects of pressures emerging has been confirmed.
 Formulas for determination the maximum gas pressure limit, the permissible maximum and minimum operating pressure as well as the required span of the cavern are given. The test pressure range for determining the tightness of the caverns is indicated. The conditions for choosing the minimum operating pressure in the cavern as well as the safety margin factor in relation to specific conditions are determined. In fact, the suitability and prospects of creating underground gas storage facilities in the salt domes of the Pripyat trough have been confirmed.

Rock splitting techniques for reducing undesirable cracks and fissures in rock salt blocks

Massive deposits of rock salt are mined in the Salt Range area of Pakistan. The main export products of rock salt include salt lamps, blocks, and tiles, while local consumption includes the chemical industry and domestic use. The profitable production of salt for value addition depends on the quality, size, and shape of the block. Salt processing for value addition is easier when very few cracks are present in the blocks. The current salt mining practice involves drilling and blasting, which introduces undesired fractures in the material. This paper focuses on the extraction of rock salt blocks by applying conventional cuboid-shaped block mining methods used in quarries. The techniques include wedges and feathers, expansion chemicals, and blasting with low-yield explosives. Experimental work involved both laboratory-scale and in-situ field testing. Laboratory experiments assisted with the determination of splitting force, load-deformation curves, and other rock mechanics parameters. Regression analysis proposes a relationship for the estimation of radial strain from the load in the case of the wedges and feathers method. The splitting force obtained from the laboratory tests was used to confirm the accuracy of the already published empirical relationship. The results of the laboratory as well as in-situ tests showed that the wedges and feathers technique is the most suitable method for mining rock salt blocks of the desired size, shape, while minimizing cracking.

Assessment of the potential for underground hydrogen storage in salt domes

The study concerns the critical issue of large-scale hydrogen storage in salt domes. The article aims to present the methodology for the hydrogen storage potential assessment for salt domes. The method considers the size of storage caverns, their depth, the influence of convergence, and the geological structure of the selected salt domes. Statistical analysis of data from the underground cavern storage facility in the Mogilno salt dome allows determining the probability of constructing a salt cavern of a specific volume and depth in the selected salt domes. Estimates based on the developed methodology indicate that the average hydrogen storage potential for the analyzed salt domes ranges from 125.7 TWht after the first filling to 83.8 TWht after 30 years of operation. The maximum storage potential ranges from 178 to 155 TWht, respectively. In the case of the largest analyzed salt dome, where one may construct salt caverns at a depth that ensures moderate convergence, the storage potential amounts to 34.3 TWht after first filling. The presented methodology is the next phase of the research, which refines the previous estimates, allowing for more accurate forecasts of rock salt deposit capacity in terms of hydrogen storage. The presented problems are of interest to countries considering large-scale hydrogen storage, geological survey organizations, companies producing electricity from renewables, and petrochemical companies considering underground hydrogen storage in salt caverns.

Evolution of texture and internal stresses within polycrystalline rock salt using in situ 3D synchrotron computed tomography and 3D X-ray diffraction

Rock salt caverns have been extensively used as reliable repositories for hazardous waste such as nuclear waste, oil or compressed gases. Undisturbed rock salt deposits in nature are usually impermeable and have very low porosity. However, rock salt formations under excavation stresses can develop crack networks, which increase their porosities; and in the case of a connected crack network within the media, rock salt may become permeable. Although the relationship between the permeability of rock salt and the applied stresses has been reported in the literature, a microscopic study that investigates the properties influencing this relationship, such as the evolution of texture and internal stresses, has yet to be conducted. This study employs in situ 3D synchrotron micro-computed tomography and 3D X-ray diffraction (3DXRD) on two small-scale polycrystalline rock salt specimens to investigate the evolution of the texture and internal stresses within the specimens. The 3DXRD technique measures the 3D crystal structure and lattice strains within rock salt grains. The specimens were prepared under 1D compression conditions and have shown an initial {111} preferred texture, a dominant {110}〈110〉 slip system and no fully connected crack network. The {111} preferred texture under the unconfined compression experiment became stronger, while the {111}〈110〉 slip system became more prominent. The specimens did not have a fully connected crack network until applied axial stresses reached about 30 MPa, at a point where the impermeability of the material becomes compromised due to the development of multiple major cracks.

An Overview of Pakistan Rock Salt Resources and Their Chemical Characterization

Rock salt is of importance for both humans and industries. In this study, we discussed the main salt deposits in Pakistan by evaluating the total reserves as well as the rock salt annual production and by characterizing their chemical composition (Na+, Ca2+, Mg2+, K+, B+, K+, Li+, Cl-, SO42-, Br- and NO3-). Our objectives were to document their impurity, water-insoluble matter and moisture contents to ultimately discuss whether the halite in Pakistan, in its natural form, is safe for human consumption. Pakistan rock salt deposits are located in two distinct regions: the Salt Range area in the Potwar sub-basin with huge Precambrian salt deposits and the Eocene Bahadurkhel/Kohat salts in the Kohat sub-basin. Total reserves are estimated over tens of billion tons with an annual production of about 3,534,075 metric tons in 2017-Results show that the halite of the salt range area is purer than the Bahadurkhel/Kohat salts with purity levels (expressed as NaCl) of 99 and 95 wt. %, respectively. Gypsum represents one of the main impurities in halite for both regions, while potash salts (>9 wt. %) are observed in the Salt Range area, K contents are very low in the Kohat salts. Although the halite moisture content is similar for both regions, impurities contents are higher (>5%) for the Kohat salts, arising the need for their purification prior to eventual human consumption.
 

SALT PROCESSING AT THE NAKHICHEVAN SALT DEPOSIT

One of the topical issues is the study of the formation conditions, geological structure, chemical composition and methods of development of the "Duzdag" salt deposit, formed in the Babek region of the Nakhchivan depression on the territory of Azerbaijan, in order to meet the salt needs of the population. The field is divided into two sections: southern - Nakhchivan and Sust, located 4.5 km north-west of it. The physical and mechanical properties of both sections are close to each other. Losses are allowed during field development due to the fact that salt layers alternate with clay layers. The constantly growing demand for salt has predetermined the need to develop more advanced and progressive production methods based on the mechanization of technological processes, the use of new technologies and world experience. Depending on the formation of salt deposits, different methods of salt extraction are used in world practice. The main method of production of table salt in the world should be its extraction in the form of a solution and evaporation in the sun. The share of each of these methods is about 35%, and about 30% of the salt is extracted from an underground mine. The productive layer of the Nakhchivan rock salt deposit is 93-95% halite and is of high quality. The excess content of clay minerals in the field forces them to be used only in animal husbandry. Frosts drilled in the Nakhchivan rock salt deposit can be widely used in the treatment of liver diseases. The mountain has 130 million tons of natural salt reserves that are effective in treating respiratory ailments. Since the ice is horizontal, patients adapt to the underground part. To open new production facilities and treatment facilities in Duzdag, it is necessary to continue the installation of equipment that meets modern standards, the introduction of mines into a fully automated, controlled technological regime, equipped with a modern ventilation system. Keywords: Nakhchivan salt deposit, processing methods, salt beds.

Spatial Structure and Chronological Development of the Prehistoric Salt-production Complex of Provadia-Solnitsata

The prehistoric complex of Provadia-Solnitsata is located close to the modern-day town of Provadia in Northeastern Bulgaria. The remains represent the oldest salt-production site in Europe (5600 – 4350 BC) from which emerged the earliest prehistoric urban settlement on the continent (4700 – 4350 BC). The complex occupies an area of approximately 30 hectares. The emergence and development of the site were closely related to the largest and in fact the only rocksalt deposit in the Eastern Balkans, the so-called Mirovo salt deposit on which the settlement sits. Salt production on the site was based on the brine (thick saline water) that flowed out of this salt deposit. Brine boiling in ceramic pots at Provadia-Solnitsata is the earliest example on record in Europe for the use of this technology in salt production. It was practiced on this site for longer than one millennium. The heat needed for the process was generated in advance in a special installation or alternatively, was directly provided by an open fire, in both cases by burning firewood. At the end of the Chalcolithic, a change of technology had to be introduced – the water from the brine was then evaporated in a large ‘basin’ by using heat from solar radiation. The development of the five parts of the complex is presented: the tell with deposits from the Late Neolithic and the Chalcolithic, a cemetery from the Early Bronze Age, a Thracian ‘ruler’s residence’ from the 2nd – 1st centuries BC and a very large tumulus on top; a salt-production center from the Late Neolithic and the Chalcolithic together with ritual facilities from that time; a Late Neolithic pit sanctuary and a cemetery from the Middle Chalcolithic over it; a pit sanctuary from the Late Chalcolithic; a cemetery from the Late Chalcolithic.

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