6507/3-1

General

Well 6507/3-1 is located west-southwest of the Norne Field on the Dønna Terrace offshore Mid Norway. The prospect, called the Alpha structure, was defined as a horst structure oriented in a northeast - southwest direction on the Dønna Terrace, west of the Nordland Ridge in the northern part of the block. The northern part of the structure extended into block 6607/12. The well was expected to penetrate rocks of Cenozoic-, Cretaceous-, and Jurassic age. The primary objective of the well was to test the hydrocarbon potential of the Middle to Early Jurassic Fangst and Båt Groups. Secondary objectives were to test possible reservoirs in the Early Cretaceous (Cromer Knoll Group) and Late Jurassic (Rogn Formation sands). The commitment of the well was to drill into rocks of Triassic age or to 5000 m.

Operations and results

Wildcat well 6507/3-1 was spudded with the semi-submersible installation Ross Rig on 12 May 1990, and drilled to TD at 4757 m in Late Triassic sediments of the Åre Formation. After having set the 9 5/8" casing with shoe at 3167 m, an 8 1/2" hole was drilled to 4080 m. This hole, especially the Melke Formation, became very unstable and caused serious drilling problems. After having worked with stuck pipe and fish, the hole was finally plugged back to the 9 5/8" casing shoe and sidetracked from 3177 m, (a technical bypass) and drilled to TD. Due to the problems encountered the first hole was logged from 3850 m to hole TD at 4080 with MWD only, while the sidetracked hole was not logged below 4506 m. The Directional survey shows a practically vertical well with TVD only one meter short of MD down to this depth. The well was drilled with seawater and CMC hi-vis pills down to 900 m, with gypsum/polymer mud from 900 m to 3183 m, with gel/lignosulphonate mud from 3183 m to 3974 m, and with Kemseal/PAC/Miltemp mud from 3974 m to final TD.

Top of the Garn formation was penetrated at 3608 m. Above this level no