30/10-5

General

Well 30/10-5 was drilled on the northern tip of the Frigg Field. Its main purpose was to explore a deep-seated closure at Middle Jurassic level. This structure was targeted already in the 30/10-1 and 30/10-4 wells, but it was not reached because well 30/10-1 was terminated in the Late Cretaceous due to high-pressure problems and well 30/10-4 became junked in the Miocene due to an unrecoverable fish.

Operations and results

Exploration well 30/10-5 was spudded with the semi-submersible steel installation Neptune 7 on 25 August 1974 and drilled to TD at 5185 m in the Late Triassic Hegre Group. Reaming of the 12 1/4" hole to17 1/2" for setting the 13 3/8" casing was delayed due to several twist-offs, junk in hole, pod trouble and weather. After setting the13 3/8" casing drilling was resumed. At 2943 m, lost circulation was encountered, however; after setting a cement plug, drilling was continued without difficulties. Drilling from the sea floor to 747 m was with seawater and gel. Below 747 m a fresh-water Spersene XP 20 (lignosulphonate) mud system was used.

The Oligocene section consisted entirely of siltstone and clay. The Eocene, section contained a sandstone reservoir (Frigg Formation, first informally termed "Frigg Clastic Tongue") from 1964 m to 2150 m. Good gas shows were present from 1965 m to 1974 m and good oil shows from 1974 m to 1978 m. Below 1978 m the section was water wet. The Rogaland Group contained 159 m of potential sandstone reservoirs but no shows were encountered. The Danian consisted of silty limestone and dark grey shale. The Late Cretaceous consisted primarily of interbeds of tight micritic limestone, marl and shale. Numerous gas shows were noted in limestone stringers in the uppermost part of this section. The limestone section between 2917 m and 2943 m was sandy and contained some gas. A second zone between 3628 m and 3534 m also contained some gas. Log analysis indicated