34/7-1

General

The wildcat 34/7-1 was drilled on the E-structure northeast in block 34/7, on a location ca 9 km south-south west of the 34/4-1 Snorre Discovery well in the northern North Sea. The continuation of this structure was explored by well 34/4-4. The main objective of 34/7-1 was Late Triassic sandstones, which proved hydrocarbon bearing in 34/4-1 and 34/4-4.

Operations and results

Well 34/7-1 was spudded with the semi-submersible installation Vildkat on 9 May 1984 and drilled to TD at 2905 m in the Late Triassic Lunde Formation. The 26" hole was drilled and logged first as a 17 1/2" pilot hole to 1106 m as a precaution against shallow gas then opened up to 26" by using underreamer. Tight spots occurred in the 26" hole section. In the 17 1/2" hole the string got stuck at 1274 m. The string had to be backed off and was fished out of the hole. Some tight spots occurred in this section too. When running the 9 5/8" casing, lost returns were experienced three times and the casing was pulled out of the hole. A velocity log was run, and the well was plugged back to 2640 m by setting two cement plugs and the 9 5/8" casing was landed at 2632 m. The well was drilled with seawater and bentonite down to 1106 m and with polymer/KCl mud from 1106 m to TD.

The Tertiary and Cretaceous sections were mainly composed of claystones, with sand development in lower the Pliocene and in the Late Miocene. The Triassic consisted of sandstones alternating with siltstones, claystones and minor marl.

A major unconformity is observed at 2392 m between the Late Triassic and the Lower Cretaceous. Apart from this, four other unconformities are observed in the well, one in Cretac