Field experiment research on the penetrability of insoluble sediment in high-impurity salt mine caverns

The solution mining salt caverns in impure salt mines include generally two parts: the above clear brine space and the down sediment/brine mixed space. Gas storage by displacing brine in the sediment as well as in the above space is an optimal pathway to overcome barriers of building caverns in high-impurity salt mines and to achieve large-scale underground energy storage. Field experiments of sediment connectivity were carried out in a butted well salt cavern to determine the connectivity of voids within the sediments. Through a combination of sonar and downhole television surveys, as well as drilling exploratory wells, the height and spatial occupancy of the sedimentary deposits, the three-dimensional salt cavern morphology, and the undetectable horizontal section locations due to sediment burying were revealed. Based on this, a test plan for sediment void connectivity was designed, with real-time monitoring of wellhead pressure, temperature, and flow rate using sensors during the experiment. The analysis of field experiment results indicates that over 95 % of the target salt cavern space is occupied by sediments, but the sediment voids have good connectivity, with approximately 1 kPa/m pressure loss during brine flow. The sediment permeability ranges from 10⁻⁹ m² to 10⁻¹¹ m², and the void ratio can reach up to 40 %.

Implementing gas storage in sediment voids has many advantages and promising application prospects, 1) 4.5 times capacity expansion compared to conventional salt cavern gas storage; 2) Faster gas storage compared to new cavern construction; 3) Additional surrounding rock support to reduce salt cavern creep; 4) Reduced demand for precise cavern measurements, lowering technical complexity and costs. This research provides field experiments and data support for gas storage in high-impurity salt mine sediment voids, contributing to expanded salt cavern site selection and increased storage capacity.