Drilling for an energy storage in the city of Lund in the south of Sweden was performed by the contractor Skånska Energi AB. A total of 17 holes were first casing advanced to 90 meter and then drilled down to a total depth of 250 meter. Casing OD was 168 mm and hole diameter 140 mm. The hammer used was the W120.

Geology was a mix of shale, clay, sand and sandstone. When drilling in this geology the return water from the hole contains a large fraction of particles in the micron range which are very difficult to sediment out from the return water. Since there were strict restrictions on the solids content in the water returned to the sewage system (in the order of 40 mg/liter) a solution had to be found.

The solution was to rent a centrifuge from Noxon, see www.noxon.com, which reduced the solids content in the return water to a level acceptable to the environmental authorities.

Equipment used