30/3-9

General

The purpose of well 30/3-9 was to prove minimum economical volumes of hydrocarbons in the Brent Group within the C-prospect, and to possibly identify a down flank hydrocarbon/water contact within the Brent Group. The C-prospect is situated within an easterly dipping terrace, north of the Oseberg platform. The 30/3-9 well was the first well drilled on this structural segment.

Operations and results

Wildcat well 30/3-9 was spudded on 24 April 2000 with the semi-submersible installation "West Alpha" and drilled to a total depth of 4015 m in the Early Jurassic Drake Formation. No shallow gas was encountered. The well was drilled with seawater with hi-vis pills and bentonite mud down to 1027 m, and with KCl/polymer/glycol mud ("Glydril" with 3.5 % glycol) from 1027 m to 2466 m. The well was then displaced to oil based "VersaPro" mud and drilled with this mud through the 12 1/4" section to 3712 m. Circulation was lost at 3644 m and 294 m3 "VersaPro" was lost to the formation. The 8 1/2" section (3712 m to TD) was drilled with KCl/polymer/glycol mud ("Glydril" with 2.5 % glycol). Thin gas-charged stringers were encountered at 2113 m (sandstone in the Lista Formation), 2526 m and 2541 m (limestone in the Jorsalfare Formation). The reservoir of the Brent Group was expected to comprise a complete set of formations. However, only the Ness and Oseberg Formations were conclusively present. The absence of the Tarbert Formation is due to erosion. From the image log (FMI), a fault zone was recognized within the Brent Group in the interval between 3900 m and 3909 m. The absence of the Etive/Rannoch Formations (and possibly, the upper part of the Oseberg Formation) is due to faulting. It is possible that the uppermost 3 m of the 19 m thick lower sand (from 3904 to 3907 m) in the reservoir represents the Etive Formation. However, this is not conclusive and the sands are thus assigned to the Oseberg Formation in this report.

The uppermost sand