Sønderborg

The plant was established in 2013, and it includes one production well and one injection well. The figure above illustrates the position of wells and filters.

Reservoir(s): The producing reservoir consist of sandstones, i.e. sandstones belonging to the Upper Triassic – Lower Jurassic Gassum Formation. Average porosity of the sandstones: 28%.

Reservoir depth: 1100–1200 m.

Reservoir temperature: approx. 47 °C.

Problems observed: It is suspected that release of mill scale from the injection well casing (Fe) combined with deposition of rust flakes (Fe) could clog perforations. Both rust flakes and grains with sulphides (PbS, ZnS, FeS) are observed in filter extracts. Trouble shouting of the injection problem is still ongoing and there could be other causes of the problems (clogging of formation, bad well connection, precipitation of iron (Fe) and iron-rich minerals due to corrosion etc.).

Geological model for the Sønderborg geothermal reservoir: The reservoir section consists of two pronounced sandstone layers separated by a clayey interval. The Sønderborg plant produces from sandstones belonging to the Upper Triassic–Lower Jurassic Gassum Formation. The Gassum Formation is present in most of the Norwegian–Danish Basin, except where major salt structures occur and on the basement blocks of the Ringkøbing–Fyn High. The formation was deposited in a humid climate and consists of marine and fluvial sandstones interbedded with marine and lagoonal mudstones. In general, the sandstones are considered to be widespread with relatively good lateral continuity – and most likely, the Gassum Formation sands have been exposed to long transport distances.