25/11-4

General

Well 25/11-4 was drilled ca 2.6 km south-south west of the 25/11-1 Balder discovery well on the Utsira High in the North Sea. The objective was to define the continuity of oil bearing sands of Early Eocene age that were present in 25/11-1 well.

Operations and results

Appraisal well 25/11-4 was spudded with the vessel Glomar Grand Isle on 15 October 1970 and drilled to TD at 1896 m in the Early Paleocene Ekofisk Formation. Drilling operations were normal down to 963 m and at that depth problems with the Hydril necessitated pulling the riser and upper part of the B.O.P. stack. While drilling at 1753 m weather conditions hampered drilling and it was necessary to again pull the riser and upper part of the stack. After losing several days due to weather conditions the well was completed, however, during the midst of the logging operations, storm warnings made it necessary to shorten the program and the planned velocity survey was not made. Initial drilling from the seafloor to 179 m was with sea water and gel. Below 179 to a depth of 948 m, the mud system consisted of seawater, Spersene XP-20 Salinex. From 948 m to TD fresh water Spersene XP-20 mud was used.

The well penetrated the Utsira Formation and several Skade Formation sand units and then entered a ca 500 m thick section of shales belonging to the lower Hordaland Group before top Balder formation was encountered at 1695 m. The Balder Formation (Early Eocene) proved almost void of reservoirs. It was all silty shale except a 4 foot sand section between 1740 and 1742 m. This sand had a good oil stain, bright yellow fluorescence and a bright yellow cut. The only massive reservoir present was the Paleocene Hermod Formation sand from 1792 to 1816 m. This sand had no hydrocarbon