A regional-scale engineering geological study for selecting suitable rock masses for constructing unlined oil storage caverns in Southern Zagros, Iran

The southern section of the Zagros zone in southwestern Iran, a well-known sedimentary basin, was investigated to address two key questions: (1) whether it would be feasible to construct large unlined rock caverns (URCs) in moderate-quality sedimentary rocks of this area for the storage of crude oil, and (2) which parts of this wide area were most suitable for constructing such huge underground structures. To answer these questions, first, the geological, hydrogeological and engineering geological properties of typical rock units in the area were investigated, and preliminary analyses were performed to check the stability, permeability and water circulation conditions of typical rock masses at depth. Next, geographical information system (GIS) techniques were applied to select the best regions for constructing the URCs. Parameters including geological characteristics, governmental restrictions, and proximity to facilities were selected as important factors for area zonation and for preparing a suitability map for constructing URCs for storing crude oil. The results of the study indicated that limestone units of the Asmari and Sarvak Formations at a moderate depth (200–300 m) were the most appropriate rock units for construction of URCs with a cross-section area of around 500 m². In addition, the suitability map showed that two small regions in the central and northern parts of the study area were best suited for URC construction. The key advantages of these regions include a wide distribution of surface exposures of good-quality stratigraphic units (Asmari and Sarvak Formations), limited distribution of active tectonic structures such as salt domes and faults, and proximity to crude oil facilities.