Halite cementation in sandstone from the middle triassic bunter formation in north-west germany (Hengstlage and dotlingen gas fields)

摘要

Halite cementation has been observed in the porous Solling sandstone (Middle Triassic Bunter Formation) in numerous wells of the Hengstlage and Dotlingen gas fields/underground storage (south of the city of Oldenburg). This is due to halite saturated formation brines, as the formation water is in contact with adjacent salt domes. In addition, halite cementation is caused by a temperature and pressure decline during gas production and the injection of dry gas into the underground storage. The Solling sandstone is either salt cemented from bottom to top or solid salt is present in the deeper part of the sequence only. Its occurrence is independent of the lithofacies, and is probably related to a palaeo gas-water contact. From petrographic observations and mercury porosimetry data it could be proved that larger pores in coarser laminae are preferentially halite-filled. Pores in the finer laminae are open and thus preserve residual porosity. A possible explanation is that fluids in small pores can maintain a higher supersaturation with respect to crystallisation.