25/8-9

General

Well 25/8-9 is located East-Northeast of the Jotun Field. The two main objectives for drilling well 25/8-9 were to test the hydrocarbon potential of Early Palaeocene Heimdal Formation sandstones (Krap prospect) and secondly sandstones of the Middle Jurassic Hugin Formation. The well found oil in the Early Heimdal Formation and it was decided to sidetrack (25/8-9 A) to appraise and test the hydrocarbon potential in this discovery.

Operations and results

Exploration well 25/8-9 was spudded with the semi-submersible installation "Byford Dolphin" on 5 January 1997 and drilled to TD at 2548 m in the Early Jurassic Amundsen Formation. The well was drilled with seawater and pre-hydrated bentonite sweeps down to 1110 m and with "Ancovert" oil based mud from 1110 m to TD. No shallow gas or boulder beds were encountered in the uppermost well section. Well 25/8-9 penetrated mainly clays and claystones in the Nordland, Hordaland, and Rogaland groups with both the Utsira (694 m to 905 m) and Grid (1300.5 m to1345.0 m) Formation sandstones being present. Interbedded shales and thin Heimdal Formation sands were encountered between 2096 and 2189 m and hydrocarbons were found present in the uppermost reservoir section, however reservoir quality proved very poor. A FWL/OWC was not possible to define either from MDT (pressure) or logs, but an ODT at 2069 m TVD SS was established. Top Ty Formation was reached at 2228 m, consisting of upper clean sand divided by a shaly unit from a lower clean sandstone divided by a thin shale bed. It continued down to top Shetland Group at 2323 m. 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 2432 m and were found to be water bearing. One core totalling 27 metres was cut in the