7120/12-1

Well 7120/12-1 was, together with Statoil's well 7119/12-1, the first well to be drilled offshore northern Norway in the Norwegian Sea, Troms I area. Based on seismic interpretation and regional geological data the location of the well was planned to test possible sandstone reservoirs of Middle Jurassic, Early Jurassic, and Late Triassic age. Post-Jurassic sediments were not considered prospective due to lack of closure and/or reservoir rocks. The well was planned to be drilled through a seismic marker at 1965 + 90 m and down to 2500 m (+ 300 m).

Operations and results

Exploration well 7120/12-1 was spudded with the semi-submersible installation Treasure Seeker on 1 June 1980 and drilled to TD at 3573 m in Middle Triassic sandstones and shales (Kobbe Formation). When testing the BOP after setting the 20" casing a leakage was detected in the kill line. Three days was spent repairing this before operations could continue. At 1900 m drilling was interrupted by a 35-days labour strike, from 10 July to 14 August. The hole deviation was significant in the 8 3/4" section, building angle from 4 deg at 1875 m to 23 deg at TD. This resulted in a 57 m difference between drilled depth and true vertical depth at final TD. The well was drilled with seawater and hi-vis pills through the 36" and 26" sections down to 710 m and with lignosulphonate/lignite (Spersene/XP-20) mud from 710 m to TD.

The well encountered traces of hydrocarbons in thin sandstone reservoirs of Early Cretaceous and Late Triassic age.

The target seismic marker was reached at 2019 m (the Fuglen Formation). A 450 m thick sequence of sandstones with minor interbeds of shales of Middle to Lower Jurassic and Late Triassic age was penetrated below this marker, from 2047 m to 2497 m (Stø, Nordmela, Tubåen, and Fruholmen Formations). The sandstones in this sequence were water bearing. From log evaluation total net sand in the sequence was 271.5 m with an average porosi