Background Under the guidance of the strategies to achieve the goals of peak carbon dioxide emissions and carbon neutrality, salt cavern storage facilities, serving as key infrastructure for clean energy strategic reserves, have emerged as a core approach to promoting the transformation and upgrade of the salt industry and to building a low-carbon energy system in China. Jiangxi Province, located in the middle part of the Yangtze River Economic Belt, is endowed with abundant salt rock resources, making it a national priority zone for developing resources for salt cavern storage. However, traditional methods for the siting of the facilities rely on drilling and coring, facing bottlenecks such as high costs and inadequate vertical continuity assessment. Therefore, there is an urgent need to develop efficient and precise geological evaluation techniques to provide support for the scientific siting of salt cavern storage.

Objective and Method This study investigated the borehole ZK01 used for the preliminary feasibility study of the salt cavern storage project of the Qingjiang Salt Mine. By integrating multiparameter geophysical logging and the geological records of cores, this study systematically analyzed the structural characteristics of salt-bearing strata and selected the optimum target horizons for salt cavern storage. By highlighting the identification of the log response characteristics of varying lithologies, this study established a mineral composition inversion model and extracted key parameters including ore-bearing coefficient, ore grade, interlayer distribution, and the properties of roof, floor, and cap rocks.

Results The salt rocks showed typical log responses characterized by low gamma-ray (GR) values, low sonic interval transit time, low compensated neutron log (CNL) values, and high three lateral resistivity. In contrast, the mudstones showed log responses featuring high GR values, high CNL values, high sonic interval transit time, and low three lateral resistivity. Additionally, the transition rocks exhibited a continuously gradational trend in their petrophysical property parameters. Compared to curve overlapping and reconstruction methods, the GR-CNL cross plots significantly enhanced the lithological identification efficiency, achieving semi-quantitative identification of four lithologies. The interval at depths ranging from 906 m to 1 095 m exhibited an ore-bearing coefficient of 51.1%, an average NaCl grade of 69.46%, a predominance of 2‒4-m-thick mudstone interlayers, thick mudstone roof and floor, and tight salt rocks as cap rocks. Therefore, this interval was identified as the optimum target horizon for salt cavern storage.

Conclusions Geophysical logging technique enables the quantitative characterization of the structural characteristics and mineral assemblages of salt-bearing strata, providing key geological parameters and a basis for scientific decision-making for the siting of salt cavern storage. This methodology proves universally applicable to salt-bearing basins with high tectonic stability and simple mineral assemblages. For areas with complex geological settings, it is necessary to conduct adaptive optimization using high-resolution logging techniques.