Comparative Analysis of Layered and Continuous Solution Mining Schemes in Bedded Salt Formations Using Horizontal Interconnected Wells

Abstract

Salt deposits in China predominantly originate from lake deposits, characterized by thin salt beds interspersed with numerous interlayers, collectively termed bedded salt formations. Historically, solution mining practices have adopted the layered solution mining approach, inspired by coal mining techniques. However, this approach fails to account for the unique challenges of salt solution mining. Practical implementation is inefficient, costs escalate post-construction, and cavern geometry is constrained by salt bed thickness. Additionally, resource loss in abandoned beds and stability risks in adjacent mining zones remain unresolved. This study investigates mining scheme selection for low-grade salt deposits in Huai'an Salt Basin, introducing a continuous solution mining method that traverses multiple interlayers. Through comprehensive analysis of plastic deformation in caverns and surrounding rock, volume shrinkage rates, and economic costs comparing continuous and layered solution mining approaches, the results demonstrate that: (1) In the layered solution mining with horizontal interconnected wells scheme, plastic deformation zones propagate unevenly, posing interlayer connectivity risks. Concurrently, roof subsidence and floor heave destabilize the structure; (2) the continuous solution mining with horizontal interconnected wells scheme reduces plastic deformation zones to 3.4% of cavern volume, with volumetric shrinkage below 17%, markedly improving stability; (3) Economically, the continuous solution mining scheme generates caverns 2.43 times larger than the layered solution mining, slashing unit volume costs to 41.1% while enhancing resource recovery and long-term viability. The continuous method demonstrates distinct economic advantages and achieves higher resource utilization efficiency in solution mining compared to layered mining. Furthermore, its superior cavern stability presents strong potential for large-scale implementation.

1. Introduction

Salt rock resources hold significant strategic value for energy storage globally. Current estimates suggest total global reserves of approximately 2.1 trillion tons [1,2], primarily distributed in the United States, Germany, Canada, and China. Marine sedimentary salt domes in Europe and North America exhibit simple structures, extensive distribution (thickness exceeding 3000 m), and high salt purity. These formations are not only suitable for traditional mining but also ideal for large-scale underground storage facilities, such as compressed air energy storage (CAES) [3–5], hydrogen storage [6–8] and oil storage, due to their superior sealing capability, plastic deformation capability and stability. The slender vertical caverns formed by single-well convection with oil/gas blanket solution mining in these regions have proven effective for long-term storage stability.

The salt deposits of China exhibit complex geological features: multilayered interbedded structures dominate in eastern terrestrial basins, while marine sedimentary characteristics persist in western regions like the Tarim Basin. This geological diversity enables underground energy storage development: within bedded salt formations, interlayers serve as natural impermeable barriers, while thick salt beds allow construction of million-cubic-meter-scale storage caverns. However, these conditions demand advanced mining-storage integration. In eastern mines, salt beds lie at depths of 200–1500 m, with thicknesses of 200–250 m and interlayers comprising 10%–30% of the strata, complicating cavern volume optimization and geometry control [9,10].