34/4-7

General

Well 34/4-7 was drilled in the north-eastern margin of the Snorre Field. The Late Triassic - Early Jurassic reservoirs of the Snorre Field are made up of a complete series of rotated fault blocks dipping between 5 and 12 degrees towards west and northwest. The primary purpose of the well was to assess the upper part of the Lunde Formation. The well was located to provide data on the reservoir quality of both oil and water bearing parts of upper Lunde, and to investigate potential changes in porosity and permeability across the oil/water contact. Further objectives were to verify a revised velocity model for the 34/4 part of the Snorre Field and reduce structural uncertainty.

Operations and results

Wildcat well 34/4-7 was spudded with the semi-submersible installation Treasure Saga on 17 February 1987 and drilled to TD at 2950 m in the Late Triassic Lunde Formation. Drilling proceeded without significant problems. The 26" section was drilled first as a 17 1/2" pilot hole down to 915 m as a precaution against shallow gas, then opened up to 26" with an underreamer. The well was drilled with seawater and bentonite down to 470 m, with gel mud from 470 m to 915 m, with gypsum/polymer mud from 915 m to 2407 m, and with KCl mud from 2407 m to TD.

Apart from the Pliocene Utsira Formation at 1062 m and some minor sandy intervals in Middle Oligocene to Late Miocene, the upper section down to Triassic consists mainly of claystones. No Jurassic sediments were encountered in the well. The Triassic Lunde Formation was encountered at 2502 m, 35 m deeper than expected and is composed of sandstones with minor siltstones in the upper part. From 2736 m the Lunde Formation consists of interbedded sandstone, claystone and limestone