30/6-17 A

General

Well 30/6-17 A is a sidetrack to well 30/6-17 R on the western side of the Oseberg Field. Well 30/6-17 R did not penetrate the Statfjord Formation in a high structural position as planned. The sidetrack was drilled to fulfil the objective. Secondary objectives were to appraise the Cook Formation discovery and the gas sands around BCU found in 30/6-17 R. Finally, a minifracture test would be conducted to obtain minimum-horizontal-stress data that could improve drilling efficiency in Eocene clays in the Oseberg area. Prognosed depth of the well was 3532 m (2690 m TVD), 50 m into the Statfjord Formation.

Operations and results

Well 30/6-17 was re-entered with the semi-submersible installation Treasure Hunter on 4 February 1986. Sidetrack 30/6-17 A was kicked off due west from below the 13 3/8" casing, with kick off point at 1633 and drilled to TD at 2686 m (2528 m TVD) in the Early Jurassic Statfjord Formation. Drilling proceeded without significant problems. It was drilled with KCl/polymer mud from kick off to 2335 m and with NaCl/polymer mud from 2335 m to TD.

The well encountered a gas bearing Cook Formation while the Statfjord Formation was found water bearing. Hydrocarbon shows seen in Tertiary and Cretaceous limestones similar to in 30/6-17 R, and also in a ca 5 meter thick sandstone bed associated with the Base Cretaceous Unconformity. The Cook Formation (2460 - 2488 m, 2357.5-2379 m TVD) is developed as an overall coarsening upward sequence. The grain size is fine to medium at the upper part, becoming very fine to fine with increasing silt content downwards. The whole of the Cook Formation was found gas bearing with a net pay of 27.9 m. No oil/gas contact was thus seen. The average porosity is 24.1% and the average