7117/9-1

General

The wildcat 7117/9-1 was the first well to be drilled in the western part of the Troms I area. It is located on the western margin of the Tromsø Basin close to the Senja High. The primary objectives of the well were to test two possible sandstone reservoirs of assumed Late Cretaceous age. Flat spots indicating fluid contacts were noted in each of these two target horizons. A secondary objective was to test sandstones of assumed Middle to Early Jurassic age. Planned TD was 2500 m in sediments of Triassic age.

Operations and results

The location survey showed the area to be covered with iceberg scars with depths from l m to 10 m. The dominant direction of these scars is ENE-WSW and most of them are filled with sand and silt. The quaternary sediments were about 280 m thick and layered in three main zones. There were no indications of shallow gas in the area.

Exploration well 7117/9-1 was spudded with the semi-submersible installation Treasure Scout on 20 April 1982. Due to excessive hole deviation while drilling to 303 m the rig had to be moved to respud the well on 24 April. In this attempt high torque in extremely hard top layers caused the drill string to twist off at 299 m. The third hole was spudded on 30 April. The drilling progressed without further problems. The last section was drilled with 8 3/8" bit and the well reached TD at 3200 m in Early Cretaceous (Middle Albian to ?Aptian) clay stone. The well was drilled with seawater and hi-vis pills down to 348 m, with seawater/bentonite from 348 m to 817 m, and with gypsum / lignosulphonate from 817 m to 1220 m. From 1220 m the mud was changed to a gel lignosulphonate system as the reactive clays disappeared and the rest of the well was drilled with this mud system.

The more shallow of the two Late Cretaceous target reservoirs was found to be a low velocity clay stone interval of Paleocene age, between 1277 m and 1328.5 m. The flat spot (at 1.4 sec TWT) cou