1/5-3 S

General

Block 1/5 is situated in the Norwegian Central Trough at the transition of the Feda Graben and the Breiflabb Basin. Well 1/5-3 S was planned as an exploration well with TD at 2910 m in the Tor Chalk Formation. The well was positioned in a seismically defined "gas chimney" on the crest of a salt induced diapir and was the first well drilled on this diapir. Similar cases have been drilled successfully by STATOIL on the Tommeliten Discovery 1/9-2 and 1/9-3 wells. The primary objective of well 1/5-3 S was to test the presence of moveable hydrocarbons in fractured, reservoir quality chalk of the Ekofisk and Tor formations along the southwestern flank of the diapir. A secondary potential objective was in the Paleocene Rogaland Group. A total depth of 1566 m was reached in the 12 1/4" hole section on June 29, 1998 before deciding to permanently abandon the well due to increasing pore pressure, without fulfilling any of the well objectives.

Operations and results

Exploration 1/5-3 S well was spudded with the semi-submersible "Byford Dolphin" on 10 June 1998 and drilled to TD at 1566 m in rocks of Late Miocene age (undifferentiated Nordland Group). The well was drilled with seawater and hi-vis pills down to 792 m and with Baroid "BARASILC" silicate / KCl glycol enhanced ("GEM GP") mud from 792 m to TD. Due to possible shallow gas hazard at 466 m, a 9 7/8" pilot hole was drilled below the 30" conductor to 780 m. The 9 7/8" hole was opened up to 26" at 792 m prior to setting 20" casing at 785 m. No shallow gas was observed from the MWD resistivity in this hole section.

Record setting overpressures were experienced in the 17 1/2" hole section in well 1/5-3 S. Abnormal pressures were indicated first at 700 - 800 m. Pore pressures built quickly to 1.4 g/cc due to gas just below 1000 m in. Having passed that depth, the hole drilled without problems until below 1200