25/8-7

General

Exploration Well 25/8-7 is located East North-East of the Jotun Field. The two main objectives for drilling well 25/8-7 were to test the hydrocarbon potentials of the sandstones in the Lower Palaeocene Heimdal Formation (Krap prospect) and in the Middle Jurassic Hugin Formation.

Operations and results

Well 25/8-7 was spudded with the semi-submersible installation "Dyvi Stena" on 21 July 1995 and drilled to a total depth of 2380 m, 40 metres into the Early Jurassic Amundsen Formation. The well was drilled with seawater and high viscous pills through the 36" and 17 1/2" hole sections down to 1070 m. After setting the 13 3/8" casing the mud system was changed to a 1.27 SG KCL/ polymer system with 3 - 4 % glycol added for drilling the 12 1/4" and 8 1/2" sections to final TD. No shallow gas or boulder beds were encountered in the uppermost well section.

The well penetrated mainly clays and claystones in the Nordland, Hordaland and Rogaland groups. Grid Formation sands were encountered from 1293 m to 1348 m and 1484 m to 1504 m. Minor thin distal remnants of the Heimdal Formation sands were encountered between 2050 and 2061.5 metres, however these proved water wet. Top Ty Formation was reached at 2157 m, consisting of clean sandstone divided by a thin shale bed. It continued down to top Shetland Group at 2209 metres. No hydrocarbons were found in the Ty Formation. The Shetland Group consisted mainly of chalk with the Cromer Knoll Group consisting of limestones interbedded with claystones and marls. The Hugin Formation sandstones came in at 2318 m and were found to be water bearing. Traces of dark brown tarry dead oil staining together with weak, dull yellow fluorescence and slight petroliferous odour was seen in the Heimdal Formation sands and claystones from 2050 m to 2061.5 m. Similarly traces of dark brown tarry dead oil stained grains were described at the top of the Hugin Formation at 2318