2/1-11

General

Well 2/1-11 is located on the Hidra High in the Central Graben of the North Sea. It was drilled to investigate the possibility of commercial quantities of hydrocarbons in the Jurassic J60/J70 sandstones (Ula Formation). A secondary objective was to assess the reservoir potential of the older J50 Jurassic sandstone sequence.

Operations and results

Wildcat well 2/1-11 was spudded with the semi-submersible installation Mærsk Jutlander on 14 January 1997 and drilled to TD at 4725 m (4697 m TVD) in the Late Triassic Smith Bank Formation. At a depth of 724 m, while drilling riserless, the well was observed by the ROV to be flowing. Evidence of this flow was observed in the moon pool - a patch of light coloured water being apparent. The well was circulated with seawater while additional kill mud was built. A pilot hole was then drilled to the section TD of 1151 m with further flows being observed at 736 m, 802 m, 900 m, 939 m, 1112 m and 1121 m. Most likely the gas in all instances came from an interval between 650 and 724 m, which after drilling was correlated to a shallow biogenic gas warning at 638 identified in the site survey. The shallow gas problems led to a delay in installing a new cuttings handling system on the rig, required because of a late decision to use oil based mud in the 12 1/4" hole. No serious harm was done by the shallow gas but considerable rig time was spent. The well was planned vertical but a slight deviation is seen in the deviation survey, starting at ca 3600 m (3 deg deviation). At 4350 m the deviation had reached 10 deg, and at TD it was 30 deg. As a result MD is more than 5 m larger than TVD below 4450 m, and the difference is as much as 28 m at TD. The well was drilled with seawater and hi-vis sweeps down to 1162 m and with ENVIROMUL oil based mu