6406/12-4 S

General

Well 6406/12-4 S was drilled on the flank of the Frøya High close to the southern end of the Halten Terrace in the Norwegian Sea. The exploration objective was to test Intra Melke sandstone in the Boomerang South West Prospect, younger than the reservoir in the Pil discovery. The well also had as appraisal objective to core the transition into the top of the Pil discovery reservoir close to the established oil-water contact.

Operations and results

Wildcat well 6406/12-4 S was spudded with the semi-submersible installation Transocean Arctic on 23 June 2015 and drilled to TD at 4318 m (3882.9 m TVD) m in Late Jurassic Intra-Melke sandstone. The well was drilled vertical down to 1203 m. From 1203 m to 3660 m, the well was drilled deviated with a sail angle of 41°. From there and through the reservoir to final TD the sail angle was changed to ca 7°. Due to a highly overbalanced mud weight during drilling in the 8 1/2" section, a significant drill break was experienced in the Rogn Formation, with substantial mud losses to the formation at approximately 3746 m. This caused serious mud invasion into the formation. The well was drilled with seawater and sweeps down to 1210 m and with XP-07 oil based mud from 1210 m to TD.

The well encountered 26 m of Rogn Formation of good quality at 3726 m. A 196 m thick package of Spekk shales and siltstones followed down to top Melke Formation at 3946 m. Small amounts of oil was recovered in an RCX fluid sample from the Rogn Formation. Both this oil and pressure data from the Rogn Formation were seriously affected by the mud invasion, making it difficult to conclude on the nature of the oil. The petrophysical logs indicated hydrocarbon saturations of up to 20% across the cored interval in the