25/2-10 S

General

Well 25/2-10 S was designed to drill the Gamma Structure, one of the Frigg satellites, east of the East Frigg Beta Structure. The primary objective of the well was to test whether the gamma structure is an eastward extension of the East Frigg Beta structure. The main target was the Lower Eocene Frigg Formation; secondary targets were the Balder and Ekofisk Formations. In addition a possible gas accumulation was expected in a thin sand body of late Oligocene age.

Shallow gas indications at 256 m MSL, and a disturbed zone on the seismic from seabed to the Frigg Formation demanded a deviated well in order to reach the Frigg Formation at its highest structural position.

Operations and results

Wildcat well 25/2-10 S was spudded 2 December 1985 by Sonat Offshore A/S semi-submersible rig Henry Goodrich. The well terminated in Limestone of the Early Paleocene Ekofisk Formation at a depth of 2967 m (2643 m TVD RKB).

Due to shallow gas indication on the chosen locality, the well was spudded 1100 m north and 200 m east of the TD position. Drilling proceeded without significant problems down to 1049 m here mud was lost.

An Oligocene sand, now re-dataed to be of Lower Miocene age, was confirmed in the interval 1115 m to 1148.5 m (1006.5 m to 1031 m TVD RKB) with gas from top sand at 1115 m down to a GOW at 1136.5 m (1006.5 m to 1022.5 m TVD RKB). From 1095 m to 1150 m (992 m to 1030 m TVD RKB) strong yellowish green to yellow ocher direct fluorescence and milky yellow cut were observed on cuttings and SWC. Pressure measurements suggest an oil gradient of ca 0.72 g/cc below the gas with a tentative OWC at 1162 m (1041.5 m TVD RKB). Top Frigg Formation came in at 2230 m (1943 m TVD RKB) with minor amounts of oil and gas. The GOC in the Frigg reservoir was found at 2243.6 m (1956 m TVD RKB) and the OWC at 2259.6 m (1971 m TVD RKB). Brown oil staining was reported on the cores from 2243.5 m to 2257 m. In the Frigg Forma