2/10-2

General

Well 2/10-2 is located in the western area of block 2/10 in PL163, in an inverted half graben structure at the Grensen Spur. The block, being the southernmost in the Norwegian North Sea sector, borders both the UK and Danish sector lines, and held only one previously drilled exploration well at the time of drilling

The main objective of the well was to test the hydrocarbon potential of Late Jurassic sandstones, prospect-A, a combined structural and stratigraphic trap located in the hanging wall of a half graben structure. The well should also test the prospectivity of the Shetland Group, which held oil in the Tor Formation in well 2/7-2; the reservoir potential of the Cromer Knoll Group in stratigraphic closures formed by pinch outs against Base Cretaceous Unconformity; and possible hydrocarbon potential of the pre-Triassic/Rotliegendes Group.

Operations and results

Exploration well 2/10-2 was spudded with the semi-submersible installation "Treasure Saga" on 16 February and drilled to TD at 4164 m in rocks of undefined age. The well was drilled with spud mud down to 1169 m, with KCl mud from 1169 m to 3681 m, and with "HI TEMP" polymer mud from 3681 m to TD. The Tor and Hod limestones slowed down the penetration rate in the 12 1/4" section. Drill string vibrations and torque fluctuations were created which ruined several bits and resulted in one drill string failure.

The 8 3/8" section was surprisingly easy to drill. It was easy to achieve penetration rates of 15 m/hr, but due to geological and pressure control, the penetration rate had to be controlled through most of the section. The pore pressure increased very rapidly at top of the Mandal Formation, and the mud weight had to be adjusted accordingly. The mud weight was increased from 1.70 SG to 1.95 SG over an interval of approximately 30 m. Maximum estimated bottom hole static temperature was approximately 150°C based on Horner p