Thin Salt Layer Research Articles

Feasibility Evaluation of I–Shaped Horizontal Salt Cavern for Underground Natural Gas Storage

Underground salt cavern gas storage has been widely applied due to its numerous advantages. Most of China’s salt resources are derived from lacustrine deposits. As high–quality resources in the central sedimentary area are gradually exploited, exploring the utilization of thin salt layers at the edges of sedimentary centers is the future development trend. However, the use of thin salt layers faces challenges such as low resource utilization, small cavern volumes, and poor economic feasibility, which limit its engineering applications. Therefore, a comprehensive assessment of constructing gas storage in thin salt layers is necessary. This paper first analyzes the necessity of building gas storage in thin salt layers and surveys cavern construction methods and their applicability. Based on geological seismic data, the feasibility of constructing gas storage in the Pingdingshan thin salt layer is proposed. A novel I–shaped cavern design is introduced, which, according to engineering economic evaluations, reduces investment by 9.6% compared to traditional single–well vertical cavern construction methods. Finally, rock mechanics tests were conducted to study the impact of mudstone interlayers and cyclic operation modes on the stability of the I–shaped cavern under three different injection and production conditions. The analysis shows that multi–cycle injection and production can effectively suppress cavern shrinkage and the development of the rock–relative plastic zone. The safety factor (SF) for different conditions is greater than 1, indicating that the I–shaped cavern has good stability and can adapt to various operational conditions. This study provides valuable insights into the geological conditions and rock mechanics characteristics for the future construction of gas storage in thin salt layers in China.

Feasibility analysis on the utilization of TWH-caverns with sediment space for gas storage: A case study of Sanshui salt mine

Underground salt cavern (USC) has emerged as an optimal location for large-scale energy storage, encompassing oil, gas, hydrogen, carbon dioxide, and compressed air energy storage (CAES), owing to its inherent advantages of substantial capacity, stability, and hermeticity. However, most salt mines in China are characterized by a relatively thin salt layer thickness, a large number of interlayers and low salt layers grade. Consequently, a substantial proportion of the cavernous space resulting from water solution mining becomes progressively covered by insoluble sediment. Herein, the feasibility of gas storage in two butted-well horizontal (TWH) caverns with sediments, located within the Sanshui salt mine in Guangdong Province, China, is comprehensively analyzed through engineering investigation, physical model experimentation, numerical simulation, and theoretical analysis. Firstly, a theoretical model was developed to calculate the volume of caverns based on salt grade (soluble content). Secondly, a joint physical model experiment and numerical simulation were conducted to obtain the most probable shape of the process for forming water-soluble caverns. Moreover, a novel technology was proposed to utilize sediment space for gas storage in TWH-caverns. Ultimately, the support pressure of surrounding rock was determined by using the passive earth pressure theory, and subsequently, an assessment of cavern stability was conducted. Here, the numerical simulation results demonstrated that in the absence of sediment space utilization, there was a limited capacity for gas storage, resulting in significant deformation of the surrounding rock and an increased level of roof instability. On the contrary, sediment can provide structural support to the surrounding rock, thus increasing its stability (the plastic zone expansion was reduced from 1600 % (0.3 σz), 1345 % (0.35 σz) and 1297 % (0.4 σz) to 109 %, 87 % and 78 %, respectively) and enhancing the capacity for gas storage. Accordingly, this study provides valuable guidance for the assessment of gas storage in low-grade salt sedimentary environments, as well as for the design of gas injection and brine discharge, and stability evaluations.

Unveiling the Synergistic Potential of Laser Chemical Solid‐Phase Deposition of Atomic Platinum‐Metal Layer on 2D Materials for Bifunctional Catalysts

AbstractThe formation of high‐density atomic metal layers on 2D materials enhances catalytic device development by providing a large surface area, precise control over active sites, and enhanced reactivity. Here, pulsed laser‐induced chemical solid‐phase deposition (LCSD) is introduced for achieving high‐density atomic metal layers. By leveraging high‐density plasma generated via pulsed nanosecond laser irradiation of thin salt layers on 2D materials, atomic‐scale metals are deposited onto abundant nucleation sites, creating dense atomic‐metal layers. This study engineers layered double hydroxide (LDH) materials layered with atomic platinum‐based alloys, exhibiting exceptional catalytic activity for overall water splitting. LDH's excellent oxygen evolution performance combined with remarkable advances in hydrogen evolution catalysis are achieved. Introducing a second element improves Pt layer dispersion and uniformity, resulting in extraordinary Pt distribution density and minimal overpotential. The LDH and Pt‐metal combination creates powerful synergistic effects, significantly enhancing catalytic performance and enabling superior bifunctional catalysts for water splitting. LCSD effectively fabricates stable nanocomposites designed for electrocatalytic applications, leveraging unique structures of atom‐scale metal‐supported composite 2D materials, enhancing overall electrocatalytic performance. This breakthrough impacts energy conversion and environmental protection, broadening electrocatalysis and revolutionizing atom‐scale metal‐supported composite 2D materials. Its practical applications span various areas, contributing to sustainable energy solutions and environmental preservation.

Structural control of inherited salt structures during inversion of a domino basement-fault system from an analogue modelling approach

Abstract. The geometries of inverted rift systems are different depending on a large variety of factors that include, among others, the presence of decoupling layers, the thickness of the pre- and syn-extension successions, or structural inheritances. Our study focuses on the inversion of an extensional domino-style basement-fault system with a pre-extension salt layer using analogue models to understand the role of pre-existing structural features during inversion. Models investigate how different overburden and salt thicknesses, inherited extensional structures, and salt distributions condition the evolution during inversion. The experimental results show that models with thick salt can partially or totally preserve the extensional ramp–syncline basin geometry independently of the overburden thickness. In contrast, models with a thin salt layer result in a total inversion of the ramp–syncline basins with the development of crestal collapse grabens and extensional faults affecting the overburden. Inversion also triggered the growth or reactivation of salt-related structures such as primary weld reopening and/or obliteration, diapir rejuvenation, salt thickening, or thrust emplacement. The use of analogue modelling allowed us to address the processes that controlled the growth and evolution of these structural elements during the inversion. Experimental results also provide a template of different structural styles resulting from the positive inversion of basins with a pre-extensional salt layer that can help subsurface interpretation in areas with poor seismic imaging.

Temporary clogging effects induced by a sustainable anti-icing hydrogel on the hydraulic conductivity and inertia coefficient of open-graded asphalt pavements

Open-graded asphalt pavements require special winter maintenance procedures to ensure the effectiveness of anti-icing and deicing measures. A recently developed solution for this type of pavement is represented by an environmental friendly thickened bio-based salt hydrogel, which consists of a thermo-sensitive sodium chloride (NaCl) brine admixed with a gellant agent (seaweed fibers) having the ability to form a gel-like structure when hot-sprayed on a cold surface. This thin salt layer results in a long-lasting residual efficacy of the winter maintenance product and in a reduction of salt consumption, but affects the drainage capacity of the pavement. These transient clogging effects were evaluated on laboratory-made specimens through the measurement of their vertical hydraulic conductivity variations before and after the hydrogel application, using a 1-D air permeameter and a constant head water permeameter. The analyses, based on Darcy–Forchheimer model and Darcy model for lower Reynold numbers, revealed a significant short-term reduction of the hydraulic conductivity, that, anyway, tends to be almost totally restored once the critical weather event is over (after about 6 h).

Analogical simulation of salt flow and associated structures in different extensional conditions

The salt layer thickness variability and the timing of salt deposition in relation to rifting (prerift salt, synrift salt, and late synrift/postrift salt) influence salt flow and the resulting growth, geometry, and kinematics of salt bodies under different extensional conditions. We apply analogue modelling to analyze the influence and interplay of each of these parameters through three series of experiments focusing on extensional salt tectonics. The first (Series I) simulates thick-skinned extension of a tabular salt layer in the absence of basement structures and explore the effects of variable salt thicknesses and extensional structural styles. Series II tests the degree of mechanical coupling of sub- and supra-salt faults according to contrasting salt thicknesses over a rotating rift block. Series III explores thin-skinned, gravity-driven deformation implementing models of i) pure-gliding (S1), ii) pure-spreading (S2) and iii) a combination of both (S3). Series I shows that the degree of symmetry and the kinematics of the structures vary due to the influence of the thickness of the salt layer. Thick salt layers tend to nucleate symmetric rifts and associated diapirs, while thin salt layers form rifts that are strongly asymmetric and rotated towards the direction of extension. Series II demonstrates that the number and dimensions of peripheral post-salt grabens, rollers, and reactive diapirs depends on the degree of coupling between sub- and supra-salt, which in turn is controlled by how the salt layer is distributed over active rift structures. Series III shows that deformation is compartmentalized into proximal, transitional, and distal domains which are characterized by extension, translation and contraction, respectively. The style and lateral extent of these domains however vary. In models where deformation is driven exclusively by tilting of the salt layer (S1) and open-toe salt advance, there is development of linear grabens cored by reactive-passive diapirs throughout most of the model length. This produces a more abrupt transition between the extensional and contractional domains and limited downdip salt inflation. In the pure-spreading model (S2), where deformation is driven solely by differential loading there is formation of a wide zone of salt inflation at the toe-of-slope and an overall greater number of contractional structures at the downdip end of the model, beyond the slope. In S3 there is development of a more variable suite of salt and overburden structures as typically observed along salt-bearing passive margins. In this model, deformation is characterized by the development of rollover and normal growth faults in the proximal domain that transition downdip onto upright diapirs associated with bowl-shaped minibasins, halokinetic sequences rotated and megaflaps. Our study improves our understanding of the extensional salt tectonic systems and the controls on different salt and post-salt geometries and kinematics.

Experimental and mechanistic study of mudstone volumetric swelling at the bottom of salt cavern gas storage

Salt cavern gas storage is one of the vital strategic natural gas reserves and emergency peak shaving facilities all over the world. However, rock salt in China is primarily bedded salt, usually composed of many thin salt layers and interlayers (e.g., anhydrite, mudstone, and glauberite). During the water solution mining process of the cavern, the insoluble mudstones fall to the bottom and account for 1/3 up to 2/3 of the storage capacity. The bulk volume of the insoluble mudstones is almost twice its in-suit volume. It is of great urgency to investigate the swelling mechanisms of the bottom insoluble mudstones. Given this, we first analyzed the mineral composition of salt rock and insoluble mudstones by using XRD and SEM methods. Then, experimental studies were carried out considering both clay swelling and physical packing. At last, the zeta potential tests were conducted to reveal the swelling mechanisms of the bottom mudstones. Results show that the volumetric expansion of mudstones is made up of three parts: clay swelling, particle surface bound water volume, and pore space free water volume increase. Because the content of expansive clay in the bottom mudstones is less than 2%, and the high salinity brine in the cavern has excellent clay stability performance, clay swelling is not the main contributor to the volumetric expansion of the bottom mudstones. Measurement results show that the surface of the mudstones is negatively charged after hydration. Electrostatic repulsion can increase the spacing between small rock particles and creates approximately 47.6% of the pore space, which is the main factor in the volumetric expansion of mudstones. This study provides a theoretical basis for the mining solution and capacity enlargement during the construction of bedded salt cavern gas storage in China.

Optimization of shrinkage agents and study of their shrinking mechanism for mudstones in the salt cavern gas storage

Salt cavern gas storage takes up a high proportion of gas storage, which allows a large amount of gas production in one day and flexible market response. It has become one of the world's important strategic natural gas reserves and emergency peak-shaving facilities. However, salt cavern gas storage in China is mainly built in the layered salt formation, which is characteristic of thin salt layers with high contents of insoluble mudstone interlayers. During the construction of this type of gas storage, these insoluble interlayers can be left at the bottom of the storage and reduce the storage by 30%–70%. It is urgent to study how to effectively control the volumetric expansion of insoluble mudstones and enlarge the storage capacity. In view of this, we first characterize and quantify the rock salt, interlayer mudstones, and clay minerals by XRD. Then, 12 kinds of organic and inorganic shrinkage agents were compared in the shrinkage experiments. Five factors affecting the shrinkage are considered, including the concentration and diffusion distance of shrinkage agents, the mass ratio and particle sizes of mudstones, and the temperature. The optimal recipe and concentration of chemical agents suitable for mudstone shrinkage in salt cavern reservoir are obtained. Finally, based on the shrinking performance of mudstones, SEM scanning, EDS analysis and Zeta potential test, the shrinking mechanism of insoluble mudstones at the bottom of the cavern was proposed. The results show that: The content of swelling clay in the target gas storage is low and the clay swelling is not the main reason for the volumetric expansion of mudstones. High valence cationic salts or polymers can shrink. Among which, the order of shrinking effectiveness is: inorganic polymers > Inorganic salts > Organic polymers. When the dosage of PAC-30 is 0.7 g/L, the volumetric shrinkage effect of mudstones is more than 40%. It has a great potential to expand the storage capacity of the salt cavern. The study shows that there is an optimum dosage of the shrinkage agent. The increasing temperature and the small particle sizes of mudstones are beneficial to shrinkage. The shrinking process is a diffusion control process, and the shrinkage agents are easy to form a dense layer on the mudstone surface, which hinders the further diffusion of the shrinkage agents. Mechanism studies show that: After the addition of cationic polymer, the Zeta potential on the mudstone grain surface decreased significantly. The electrostatic repulsion between rock particles was decreased, and flocculation, agglomeration, and compaction occurred, which is the main mechanism of mudstone shrinkage in the gas storage cavern. This study provides a theoretical and practical basis for the volumetric shrinking of mudstones at bottom of bedded salt cavern gas storage.

Kinematic interaction between stratigraphically discrete salt layers; the structural evolution of the Corrib gas field, offshore NW Ireland

The kinematic interaction of thin salt layers during basin evolution has received little attention to date, despite there being several basins which contain multiple thin salt layers across NW Europe. This study utilises high-quality 3D seismic reflection data coupled with borehole data to investigate the evolution of the structure containing the Corrib gas field which is composed of two distinct salt structures. Located in the Slyne Basin offshore NW Ireland, the structure consists of a NE-SW oriented Permian salt anticline which folds the overlying Mesozoic stratigraphy. Upper Triassic salt acts as a second mechanical detachment and forms an elongate salt roller parallel to the crest of the Permian salt anticline. The Upper Triassic salt roller forms the footwall of a listric fault which downthrows the anticlinal crest of the folded Jurassic section to the SE. The Permian salt anticline began rising during the Late Triassic and Early Jurassic driven by low-strain regional extension. During the main phase of rifting, a combination of basement tilting, gravity gliding, and salt welding resulted in a steep increase in the amplitude of the Permian salt anticline. The relief on the salt-cored fold resulted in gravity gliding on the Triassic salt, forming the parallel salt roller and listric fault. The throw distribution on the listric fault is driven by the combined mechanisms of gravity sliding on the Triassic salt and by inflation of Triassic salt in the footwall of the fault. The listric fault is reactivated post-rift, suggesting modification of the Permian and Triassic salt structures. This study improves the understanding of the kinematic interaction of thin salt layers during syn-rift and post-rift deformation, with implications for hydrocarbon exploration on the Irish Atlantic margin and further afield.

Fabrication and characterization of 1-dimensional neodymium-iron-boron fibers using new reduction-diffusion process

A novel method for the synthesis of neodymium-iron-boron (Nd-Fe-B) fibers is demonstrated in this study by adopting three continuous processes: electrospinning, step heat treatment, and a new process comprising facile reduction-diffusion. The structural and crystalline studies revealed that as-spun precursor fibers were transformed into FeNdO3, Fe2O3, and NdBO3 phases by non-isothermal heat treatment; further, the oxide mixture fibers were reduced to a single Nd2Fe14B phase by the facile reduction-diffusion process. A facile reduction-diffusion process in this paper can obtain Nd2Fe14B fibers without brokenness; this is because it leads to the formation of a thin salt layer on Nd2Fe14B fiber surface when reacting to by-product CaO granules. The BHmax of Nd2Fe14B fibers was exhibited by 3.34 MGOe. To our knowledge, this is the first attempt to fabricate 1-D Nd2Fe14B fibers successfully using a new reduction-diffusion process. This work provides a simple way to prepare 1-D hard magnetic Nd-Fe-B fibers with excellent shape anisotropy attributed to a high aspect ratio.

Discrete-element numerical modeling of sub-salt structures in the Central Kelasu fold-thrust belt, Kuqa Depression, northwestern China

Knowledge of the deformation history and dominant factors influencing the formation of sub-salt structures is necessary to understand the formation of sub-salt traps. In this study, the discrete-element method (DEM) is used to assess the deformation mechanism of sub-salt structures in the Central Kelasu fold-thrust belt of the Kuqa Depression. A series of DEM models of the Central Kelasu fold-thrust belt are constructed, the final deformation styles of the models are compared with the real structures in order to determine the fitting degree of each models, and the dominant factors influencing the formation of sub-salt structures are determined. A thin salt layer promotes the deformation in the sub-salt sequence. Salt sub-sags, basal uplifts, and pre-existing faults can also promote the deformation in the sub-salt sequence in the northern part of the models. Large deformations accumulate in pre-existing structures in the northern part of the models, and then subsequent deformations are also transmitted to the salt layer and supra-salt sequence; however, these deformations are hardly transmitted to the sub-salt sequence in the middle and southern parts of the models. Among the eight DEM models constructed in our research, the horizontal-stratum model without any initial structures showed the best fit to actual phenomena. Earlier simple structures of Mesozoic layers can be deformed into the current complex structures under compression effects in the late Himalayan period. By comparing with other regions and analyzing the deformation progress of the DEM model, the sub-salt structures in the Kuqa Depression are considered to be fold-accommodation fault structures.

Feasibility analysis of using horizontal caverns for underground gas storage: A case study of Yunying salt district

Rock salt of Yunying salt district, Hubei province, China, has a typical bedded structure, composed of many thin interlayers and thin salt layers. When the conventional single-well leaching method is used for the construction of caverns, the construction efficiency is low and the usable volume of the caverns is small. However, horizontal caverns (HCs) can be built in the formation with a high salt content, which can eliminate the shortcomings caused by the conventional single-well leaching method. Tests have been carried out on samples prepared from the cores obtained from the target formation to determine their mechanical properties. A 3D geomechanical model of the HC is developed based on the characteristics of Yunying salt district and on the mechanical properties obtained from the tests. The safety of the rock mass surrounding the HC under different conditions is simulated. Taking into account the failure characteristic of rock salt, a comprehensive evaluation index system for the feasibility of HC is proposed, including the displacements, plastic zones, equivalent strains, volume shrinkages and safety factors. The results show that the HC has a good feasibility in Yunying salt district. The internal gas pressure, roof structure and dimensions, and the relative location between HC and tin interlayers are the key factors affecting the safety of the HC, and should be highlighted in the actual design and construction. The study provides the design parameters for the proposed HC in Yunying salt district, and can also be a reference for similar engineering in other areas.

Feasibility analysis of using abandoned salt caverns for large-scale underground energy storage in China

Rock salt in China is primarily bedded salt, usually composed of many thin salt layers and interlayers (e.g. anhydrite, mudstone, and glauberite). Thus, the feasibility analysis of abandoned salt caverns located in salt beds to be used as Underground Gas Storage (UGS) facilities is full of challenges. In this paper, we introduce the feasibility analysis of China’s first salt cavern gas storage facility using an abandoned salt cavern. The cavern is located in Jintan city, Jiangsu province, China. The mechanical properties and permeability of the bedded salts are obtained by experiments. Based on the results of the analyses, it appears to be quite feasible to convert the abandoned salt caverns of Jintan city to UGS facilities. The stability of the cavern is evaluated by the 3D geomechanical numerical simulations, and the operating parameters are proposed accordingly. Results indicate that the maximum volume shrinkage of the cavern is less than 25% and the maximum deformations are less than 2% of the caverns’ maximum diameters after operating for 20years. It is recommended that the weighted average internal gas pressure be maintained as 11MPa to control the extent of the plastic zones to a safe level. Safety factors decrease with operating time, especially those of the interface between rock salt and mudstone layers decrease significantly. Effective strain is generally greater than 2%, and locally is greater than 3% after operating 20years. The maximum pressure drop rate should be kept to less than 0.55MPa/day. Based on above proposed parameters, China’s first salt cavern gas storage facilities were completed, and gas was first injected, in 2007. To check the status of the caverns after operating for 6years, the volumes of the caverns were measured in 2013 by Sonar under working conditions. Measurement results show that the cavern shapes did not change much, and that volume shrinkages were less than 2%. Comprehensive results show that the feasibility analysis method proposed in this paper is reliable.

A new conceptual model for the structural evolution of a regional salt detachment on the northeast Scotian margin, offshore eastern Canada

In this study, we examine, using seismic data in conjunction with numerical modeling, a regional-scale salt detachment and associated synkinematic sediments from the Scotian margin, offshore eastern Canada. This part of the Scotian margin is characterized by an up to 4.5-km (2.8-mi)-thick and approximately 175-km (108-mi)-long synkinematic wedge of Jurassic sediments with internal sigmoidal, landward-dipping reflectors. The synkinematic wedge is laterally extensive, encompassing an area of approximately 30,000 km2 (11,600 mi2), and soles into an interpreted salt detachment. The Jurassic synkinematic wedge, which is interpreted to have formed as an open-ended allochthonous salt nappe, was loaded by prograding sediments during the Jurassic. This loading squeezed the salt seaward and caused the overlying sediments to undergo extension and gravity spreading and gliding, detaching on the salt sheet. The open-ended nappe model provides a mechanism for producing a large amount of extension with very little compensating contraction. Numerical model results indicate that high rates of extension, detaching on even a thin salt layer, can result in similar sigmoidal, landward-dipping strata. Based on the numerical modeling and seismic interpretation results, we propose a new conceptual model for the Jurassic–Paleogene structural evolution of the study area; this model may also have implications for other passive-margin salt basins with regional salt detachments.