25/11-18

General

Well 25/11 -18 was drilled to appraise the 25/11-15 Grane discovery drilled in 1991. The primary objectives of 25/11-18 were to confirm beyond reasonable doubt recoverable oil reserves greater than 30 million Sm3 in the Heimdal Formation in the Grane Discovery prior to initiating PDO activities; to obtain an Utsira formation water sample and water production rates in order to design the water injection system for the Grane Field; to confirm top and base reservoir, reservoir development, continuity, and quality of Heimdal sand in order to reduce the uncertainties in the resource estimates; to obtain velocity information as input to depth conversion model for the Grane Field; and to test coiled tubing drilling/coring technology as concept for future cost savings.

Operations and results

Appraisal well 25/11-18 was spudded with the semi-submersible installation "West Vanguard" on 10 August 1994 and drill to a total depth of 1875 m in the Late Cretaceous limestones of the Hod Formation. Due to technical problems it was not possible to do wire line logging at TD of the original well. The well was technically sidetracked (25/11-18 T2) with kick-off at 1390 m. The well was drilled with spud mud through the 36" and 24" sections down to 563 m, with polymer mud through the 17 1/2" section to 1183 m, with "ANCO 2000" mud from 1183 through the 8 1/2" section and into the slim 4 1/8" section down to 1690 m where the hole was displaced to "AQUACOL" mud.& Drilling of the 4 1/8" section continued with "AQUACOL" mud down to TD at 1860 m. The technical sidetrack was drilled as a 6" hole to final TD at 1875 m using KCl / Polymer mud. Coiled tubing drilling and coring and slim hole logging was proven possible from an offshore floater with acceptable quality on geological information. Operations, however, were hampered by problems related to junk and hole instability due to low mud