Tight Ultra-deep Gas Field Production Optimisation – Development Optimisation and CO2 Enhanced Gas Recovery Potential of the Schoenkirchen Uebertief Gas Field, Austria

The Schoenkirchen Uebertief gas field is situated in the Vienna Basin, a pull-apart basin east of Vienna in Austria. The field is located inside the Mesozoic Northern Calcareous Alps thrust belt which is buried at this location by 3000m Neogene basin fill sediments. The gas was trapped in a steeply inclined thrust unit which is enveloped by Early Tertiary intraorgenic sediments. The top of the structure was encountered at a depth of 5050 m and the original gas/water contact at 5780 m. The field was and still is invisible on seismic - hence the discovery was purely based on a geologic model that was derived from outcrop studies along the western basin margin.

The field consists of intensively fractured dolomite with 3.7 % porosity and low permeability of around 3 mD. The initial reservoir pressure was 598 bar and the field contained gas with a CO₂ content of about 12 %. Gas Initially In Place (GIIP) was 20 Bm3. Production from the field commenced in 1969. Until 2008, 12.2 Bm3 of gas have been produced. By optimising the production system, the expected ultimate recovery factor is 88 %.

The field has been produced by three wells located at one end of the15 km long and only 2.2 km wide structure. The proximity of the field to CO₂ sources (refinery) and the well design which accounted for the high CO₂ content in the produced gas makes the field a good candidate for CO₂ geological storage.

CO₂ injection into the field far away from the producers to optimise sweep efficiency was studied by performing compositional simulation runs. The results indicate that about 1 % incremental gas of the GIIP could be recovered in addition to avoiding CO₂ emissions of 37 million tons of CO₂.