Solution mining technology
The role of salt in cavern construction
Solution mining technology turns a borehole into a cavern. The first step is to install concentric leaching strings in the casings of the well. Then, water is injected through one of the two strings. The salt is dissolved by the water and pumped to the surface in the form of brine. The upper part of the cavern, the so-called cavern roof, is protected by a blanket medium (typically nitrogen or crude oil).
During the entire leaching phase, which ranges from 2.5 to 4 years, the shape of the cavern can only be influenced by parameters such as the following:
- The leaching rate, i.e. the amount of water injected;
- Direct or indirect leaching process, i.e. injecting water through the internal or the external leaching string;
- Depths of the leaching strings;
- Depth of the blanket interface;
- Duration of the leaching intervals.
These parameters can be used to optimise the technical and economical properties of the cavern shape. Rock-mechanical aspects that are relevant for safety as well as geological conditions are also taken into account here. A 3D simulation program is used to analyse the different cavern leaching phases.
In short, cavern leaching requires thorough planning and constant monitoring. All activities are managed at the cavern site where the leaching concept is implemented. The development of the shape and size of the cavern is monitored by constantly analysing the brine and performing sonar measurements.