2/4-21

General

Well 2/4-21 was drilled on the King Lear prospect in the Central Graben of the Norwegian North Sea, approximately 20 km north of the Ekofisk Field. The prospect was considered a part of the same reservoir as in the 2/4-14 well that ultimately ended up in a major underground blowout in 1989. The main objective of the well was to prove commercial hydrocarbons in intra-Farsund Formation sandstone units.

Operations and results

Well 2/4-21 was spudded with the jack-up installation Mærsk Gallant on 19 Jan.2012 and drilled to TD at 5395 m in the Late Jurassic Farsund Formation. No over-pressured shallow gas was seen, but a 2-3 m thick sand at 627 m contained normal-pressured gas with a composition consistent with a biogenic origin. The well was planned as an HPHT well with pressure prognosis based on results from the 2/4-18 well. Pressures proved to be even higher than prognosed and at 5029 m influx of gas occurred. The well was shut in and after several days control operations the mud was weighted up to 2.1 g/cm3 and drilling continued to TD. Well 2/4-21 was plugged back after having reached TD. All data acquisition was carried out in the main track, but it was decided to drill a parallel vertical sidetrack (2/4-21 T2) for the purpose of achieving good cores from the main reservoir level (the Farsund II sandstone). The sidetrack was kicked off successfully at 4933m and the operations were carried out according to plan. The well was drilled with sea water/spud mud down to 248 m, with spud mud/KCl/Polymer mud from 248 to 453 m, with KCl/polymer/GEM mud from 453 to 1019 m, with oil based XP07-low ECD mud from 1019 m to 3022 m, and with oil based XP07-HPHT mud from 3022 m to TD. Oil based XP07-HPHT mud was used also in the coring side track.

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