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Exploration wellbore: 2/1-11

General information

Wellbore history

General

Well 2/1-11 is located on the Hidra High in the Central Graben of the North Sea. It was drilled to investigate the possibility of commercial quantities of hydrocarbons in the Jurassic J60/J70 sandstones (Ula Formation). A secondary objective was to assess the reservoir potential of the older J50 Jurassic sandstone sequence.

Operations and results

Wildcat well 2/1-11 was spudded with the semi-submersible installation Mærsk Jutlander on 14 January 1997 and drilled to TD at 4725 m (4697 m TVD) in the Late Triassic Smith Bank Formation. At a depth of 724 m, while drilling riserless, the well was observed by the ROV to be flowing. Evidence of this flow was observed in the moon pool - a patch of light coloured water being apparent. The well was circulated with seawater while additional kill mud was built. A pilot hole was then drilled to the section TD of 1151 m with further flows being observed at 736 m, 802 m, 900 m, 939 m, 1112 m and 1121 m. Most likely the gas in all instances came from an interval between 650 and 724 m, which after drilling was correlated to a shallow biogenic gas warning at 638 identified in the site survey. The shallow gas problems led to a delay in installing a new cuttings handling system on the rig, required because of a late decision to use oil based mud in the 12 1/4" hole. No serious harm was done by the shallow gas but considerable rig time was spent. The well was planned vertical but a slight deviation is seen in the deviation survey, starting at ca 3600 m (3 deg deviation). At 4350 m the deviation had reached 10 deg, and at TD it was 30 deg. As a result MD is more than 5 m larger than TVD below 4450 m, and the difference is as much as 28 m at TD. The well was drilled with seawater and hi-vis sweeps down to 1162 m and with ENVIROMUL oil based mud from 1162 m to TD.

All principal seismic horizons were penetrated within their error bars. A poorly developed Forties Formation Equivalent sand encountered at 3139.5 m had minor associated gas shows. Top Vidar Formation was 67 m shallow to prognosis, Ekofisk Formation 19 m shallow and the Cromer Knoll Group on prognosis. There were no shows in the Vidar and Ekofisk Chalk Formations. The Base Cretaceous pick, identified as the Farsund Formation, was 10 m shallow to prognosis. The Mandal Formation (Late Jurassic, J73 - J71) was absent as prognosed. No significant J70 - J60 (Ula Formation) sandstones were encountered, but minor sandstones were present. Hydrocarbon shows were limited to gas peaks with compositions up to C5. A sidewall core at 4316m had oil staining and fluorescence. Biostratigraphic data suggested a J50 sequence boundary at 4483 m at the base of the Haugesund Formation, 69 m shallow to prognosis, but was seen only as a condensed sequence. The interval 4500 - 4535 m, within the J40 - J20 Bryne Formation, was oil bearing with fluorescence in cuttings samples and drilled gas with the compositional range of Cl - C5. The Triassic was picked at 4617 m, 92 m high to prognosis. There were no hydrocarbon shows in the Triassic.

No cores were cut and no wire line fluid samples were taken.

The well was plugged and suspended on 7 May 1997 as an oil discovery.

Testing

No drill stem test was performed.

Cuttings available at the NPD

Interval [m]: 1170.00 - 4125.00

Cores available at the NPD

No cores in this wellbore.

Scanned core photos

No scanned core photos available

Palynological slides available at the NPD

No palynological slides in this wellbore.

Oil samples available at the NPD

No oil samples available.

Casing and leak-off tests

Mud

Drill stem test

No drill stem test in this wellbore.

Available logs

Lithostratigraphy

Composite log

No composite log presently available.

Geochemical information available at the NPD

No geochemical data presently available. Regional geochemical studies which include data from this well may however be filed on a different well.

Documents reported by the licencees (period for duty of secrecy expired)

No documents presently available.