34/10-33 A

General

Well 34/10-33 A is a sidetrack from appraisal well 34/10-33, which found oil in a down-to situation in the Gullfaks South Discovery. The main objectives were to locate the gas-oil contact in the Tarbert Formation and the oil-water contact, which was not seen in the primary well. Further objectives were to acquire more pressure data over the reservoir in order to evaluate if the pressure shift in the oil zone seen in the primary well could be explained by tight faults and/or a lateral continuous barrier within in the Ness Formation, and also to test if the Tarbert and Ness formations were in a common pressure regime. Finally, the well should provide water samples from the Brent Group and gather information for an optimal placing of a horizontal test well as a new sidetrack from well 34/10-33.

Operations and results

Well 34/10-33A was kicked off on 15 December 1988 from the vertical well 34/10-33 at 2698 m. The sidetrack was drilled to TD at 3851 m in the Middle Jurassic Rannoch Formation using the semi-submersible installation West Delta.

Due to severe technical problems during drilling, the logging programme was not fulfilled, and several of the well objectives could not be met. The well was drilled with gel/lignosulphonate/lignite mud from kick-off to TD.

The Brent Group was encountered at 3347 m. The logs showed a gas/oil contact at 3427 m (3295 m TVD MSL) in the Tarbert Formation and suggested an oil/water contact at ca 3625 m (3430 m TVD MSL) in the Ness Formation. In addition the well encountered a thin hydrocarbon bearing sand layer 3040 m (3001 m TVD MSL) in the Draupne Formation.

No cores were cut in this well and n