Through production testing of well 34/10-A-8, Statoil Petroleum AS has proven a substantial volume of oil in the Shetland group/Lista formation, which is located above the Gullfaks field in the North Sea. The estimated volume of the deposit is 6—24 m3 (210—850 cubic feet).
The well was originally drilled in 1987 from the Gullfaks A platform as a development well on Gullfaks, but was recompleted in December 2012 for a formation test at the top of the Shetland group above the Gullfaks field. The objective of the test was to investigate pressure conditions and productivity in jointed carbonate rocks in the Shetland group from the Cretaceous Age, as well as in the overlying sandstones in the intra-Lista formation from the Paleocene Age. Due to overpressure, the zone has posed a challenge for many years as regards drilling through to the Gullfaks reservoir.
The well test in 34/10-A-8 shows that the perforated zone has good flow properties here, and the results indicate that production will be supported by a considerable volume. Traces of petroleum in the Lista formation have been registered in several wells in the area, but recoverable oil has never been proven before. The Lista formation consists of relatively thin layers of sand with moderate to poor reservoir properties.
The size of the discovery is associated with considerable uncertainty. Preliminary estimates based on modelling, formation tests and sampling indicate recoverable resources in the area of 6 – 24 million Sm3 of oil equivalents, but the deposit may be considerably larger. The licensees in production license 050 will now carry out test production for data acquisition and studies to clarify the potential and further development of these resources. It may be relevant to investigate additional existing wells on Gullfaks as regards the flow properties of these more shallow reservoirs.
The discovery is particularly interesting because it shows that untraditional and previously overlooked deposits may represent considerable values.
