6506/12-5

General

Well 6506/12-5 was the third well drilled on the Smørbukk Sør Discovery (Beta-structure) in block 6506/12, Haltenbanken area. The well was designed to appraise the hydrocarbon potential and define the hydrocarbon-water contacts. Primary target was Middle and Early Jurassic sandstone. The Fangst Group siltstone member was expected to be sealing at this depth. The well would also test if intervals within the Ror and Tilje formations also could be sealing rocks. Secondary target was the Late Cretaceous Lysing Formation of the Cromer Knoll Group.

Prognosed TD was in the Åre formation at 4559 m RKB.

Operations and results

Appraisal well 6506/12-5 was spudded with the semi-submersible installation Dyvi Delta on 17 October 1985 and drilled to TD at 4587 m in the Early Jurassic Åre Formation. The well was drilled with less than 2.5 deg deviation down to 4235 m. There were minor incidents with a failed anchor and lost circulation in the top hole. A poorly cemented 9 5/8" casing required 116 hours amendment before normal drilling could commence. The well was drilled with spud mud down to 393 m. From here a pilot hole was drilled to 1080 m using gypsum/polymer mud, and then opened up using spud mud. Further drilling was with gypsum/polymer mud from 1080 m to 3519 m, and with gel/lignite/lignosulphonate from 3519 m to TD. Shallow gas was not encountered.

Secondary target Lysing Formation came in at 3157 m and primary target Garn Formation at 3948 m. Hydrocarbons were encountered in both. An OWC was found in the Lysing Formation at 3178.2 m, and another OWC in the Garn Formation at 4010.5 m. The Not Formation as well as top of the Garn Formation was found to be sealing in this well.

Cores were cut in the Upper Cromer Knoll Lysing Sands and throughout most of the interval from the lower part of the Viking Group at 3910 m down to 4362 m in the Tilje Formation. A total of 429.43 m was recovered in 27 cores. Core n