Burggraf-Bernsdorf – transformation of a potassium mine to a UGS facility

The potassium mine Burggraf-Bernsdorf was established between 1911 and 1913. It was situated at the southwestern flank of the Roßleben saddle (Sachsen-Anhalt) and belonged to the “Unstrut Kalirevier”. About 300.000 tons of carnallitite were extracted. The mined cavity was about 175.000 m³. Due to a reorganization of the German potassium industry the mine was closed in 1921. After a 40 year long period of quietness the abandoned mine was investigated for its suitability as an underground gas storage facility (UGS). The project was regarded as a large-scale test firstly. Safety criteria were developed and investigations were conducted in the fields of rock mechanics, explosion hazards and of physicochemical interactions. The storage phase started in 1970 after installation of an effective seal into both shafts. Due to the small capacity the UGS was used as a buffer store of the regional gas grid. About 1,4 billion m³ of gas were handled during the operating phase. In 2014 the operator decided to close the UGS due to the high wetness of the produced gas and the complexity of a refitting of the facility. Several methods were checked to abandon the UGS. Dry abandonment was compared with flooding with different media. Aspects of rock mechanics, of leaching kinetics and of environmental studies were considered during this procedure. The abandonment of the mine, the removal of the casing and the backfilling of the shafts happened between 2018 and 2020. A five year long monitoring period will finalize the history of the multifunctional mine Burggraf-Bernsdorf.