# A Review of Evaporite Beds Potential for Storage Caverns: Uncovering New Opportunities
## 3 Properties and Geomechanics of Bedded Evaporites
### Main Geomechanical Considerations in Bedded Evaporite Caverns
#### 3.3.1 Cavern Design  
In thin-bedded salt caverns, three main issues must be addressed during the design phase: the potential fracturing of heterogenous materials, slippage along bedding planes due to differential deformation in various layers, and propagation of damage leading to rock failure around the cavern [186]. A well-thought-out design can mitigate issues such as roof instability, fractures in surrounding formations leading to leakages, and subsidence. A detailed review of cavern behavior, design methods, and stability criteria is provided in [187]. Key parameters such as size, shape, number, distance between caverns (pillar size), and roof thickness are critical for both storage capacity and stability. The storage capacity of a cavern depends on its shape, diameter, and height as shown in a study in [188]. This study used these calculations for selecting hydrogen storage sites in salt caverns in China. With respect to stability, factors like cavern height, diameter, height-to-diameter ratio, and roof thickness were evaluated in the U.S. thin-bedded salt caverns in [186]. The geometry of bedded salts and the impurities in bedded salts of the Midland basin are described in [189]. A methodology for selecting underground salt cavern gas storage sites based on these parameters was developed in [190]. Impurities in salt beds, which can include non-soluble minerals or interlayers, present unique challenges during cavern design. These impurities occupy a large volume of the cavern, reducing storage capacity [191]. These interlayers are also the cause of irregularly shaped caverns [41; 192]. A concept proposed in [22] suggests using pore spaces within these impurities for storage. The study in [193] highlights the stabilizing effect of interlayers on caverns. Various factors affecting the irregular shape of caverns, such as impurities, blanket position and duration, and tubing failure are explored in [194]. Three cavern shapes, including cylindrical, enlarged top, and enlarged bottom, were considered in [195] to investigate their stability. For bedded salts, ref. [107] noted that constructing vertical caverns is challenging due to significant impurities, making horizontal caverns more suitable. U-shaped caverns were proposed in [11] for the disposal of drilling waste in salt beds with high insoluble content. The study in [196] investigated the stability of U-shaped horizontal salt caverns for underground natural gas storage. In addition, the long-term stability of horizontal elliptical cylindrical caverns was analyzed in [197], while ref. [198] developed a design separating caverns into upper and lower sections, with gas pressure dictating cavern shape and dimensions. Based on the comparison performed in [192], ellipsoid-shaped caverns are the most stable, while cylinder-shaped and cuboid-shaped caverns are the least stable. The effects of geological conditions such as depth, thickness, and mineralogy on the shape of caverns are discussed in [131]. The space between caverns, known as pillars, is another crucial factor. Pillar dimensions and cavern stability were studied in [199; 200], while ref. [201] investigated how pillar width and the number of caverns impact stability. Based on this study, a pillar width of 2-3 times the cavern diameter leads to instability in the center of the pillar, while thinner pillars cause instability at the edges. Variations in rock salt properties, as noted in [202],are the main reason for the lack of systematic pillar design. An experimental work in [203] optimized the width between new and old caverns, suggesting a distance of at least twice the maximum diameter of the new cavern. The internal pressure of the cavern is another main parameter to be determined. Studies have shown how internal pressure affects displacements around caverns [19; 20; 204]. Internal pressure is influenced by cavern height as mentioned in [205], while ref. [206] demonstrated its impact on cavern stability.