Det norske oljeselskap AS, operator of the Ivar Aasen field in the North Sea, has completed the drilling of three appraisal wells, 16/1-22 S, 16/1-22 A and 16/1-22 B.
The field is located in the central part of the North Sea and was proven in 2008.
According to the Norwegian Petroleum Directorate (NPD), the size of the field prior to drilling the appraisal wells was 24 million standard cubic metres (Sm3) of recoverable oil, 1 million Sm3 of recoverable condensate and 4.5 billion Sm3 of recoverable gas.
The objective of well 16/1-22 S was to investigate reservoir rocks and reservoir quality, as well as secure depth control along the west flank of the field in Middle Jurassic to Upper Triassic reservoir rocks (the Hugin, Sleipner and Skagerrak formations) in order to optimise well sites with a view to the drainage strategy. Sidetracks 16/1-22 A and 16/1-22 B were drilled 1000 metres northeast and 1350 metres north, respectively, of 16/1-22 S in order to investigate reservoir rocks and perform additional data acquisition. 16/1-22 A also aimed to investigate an underlying seismic anomaly.
16/1-22 S encountered a 3-metre oil column in sandstone of good to very good reservoir quality in the Skagerrak formation. The oil is saturated with a gas/oil ratio of about 160 Sm3/Sm3, as is the case otherwise in the western part of the field (16/1-11, 16/1-11 A and 16/1-9). The oil/water contact was not encountered, but was calculated at about 2435 metres, which is deeper than the previously calculated oil/water contact for the Skagerrak formation (16/1-11 A).
16/1-22 A encountered a total oil column of about 55 metres in the Skagerrak formation, 30 metres of which was in sandstone of varying reservoir quality, from moderate to very good. The oil/water contact was not encountered. The seismic anomaly is linked to the top of a total oil column of about 25 metres in underlying sandstone (alluvial fan), 15 metres of which had moderate reservoir properties. The oily part of the alluvial fan is not included in the field’s previously reported reserves.
16/1-22 B encountered a total oil column of about 45 metres in the Skagerrak formation, 25 metres of which was in sandstone of good to very good reservoir quality. The oil/water contact was not encountered.
The NPD noted that none of the wells were formation-tested, but comprehensive data collection and sampling was conducted.
The NPD added that the results have yielded valuable information as regards the final location of production and water injection wells. Gas was not encountered in the wells.
PDO & drilling rig
The Plan for Development and Operation (PDO) of the Ivar Aasen field was submitted to the Ministry of Petroleum and Energy on December 21, 2012.
Wells 16/1-22 S, 16/1-22 A 16/1-22 B were drilled to measured depths of 2640, 2896 and 3215 metres, respectively, and vertical depths of 2562, 2468 and 2501 metres below the sea surface. They were all terminated in the Skagerrak formation in the Upper Triassic. The wells have been permanently plugged and abandoned. Water depth at the site is 113 metres.
The wells were drilled by the Maersk Interceptor jack-up drilling rig, which will now continue production drilling on the Ivar Aasen field once the platform’s jacket has been installed.