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Exploration wellbore: 30/9-12

General information

Wellbore history

General

The well 30/9-12 is located on the southern part of the Alpha and Gamma structure in the Oseberg Sør area, some 4 km south of well 30/9-2, and approximately 100 m to the south of the licence boundary PL 079/104. The main target of the well was to appraise the southern extension of the Oseberg field, i.e. to improve the seismic mapping of the Alpha South/Gamma structural complex; to improve stratigraphical mapping and control of the hydrocarbon bearing Brent Group in the area; to test an oil/water contact in relation to the Oseberg Field and the C-structure; and to test communication relations in the Oseberg Field.

Operations and results

Appraisal well 30/9-12 was spudded with the semi-submersible installation Vildkat Explorer on the 7 April 1991 and drilled to TD at 2994 m in the Cook Formation of the Dunlin Group. The well was drilled with spud mud to 1016 m and with KCl polymer mud from 1016 m to TD. Shallow gas predicted at 184 m proved to be the base of a boulder zone, probably a glacially eroded horizon.

The well proved a column of 10.3 m of moveable hydrocarbons oil in the Tarbert Formation with an oil down-to contact at 2674.5 m, However, as no oil/water contact was established, uncertainty remained as to the amount of hydrocarbon resources within the southern part of the Alpha South structure. A total of 70.4 m of net sand was calculated for the Brent sequence, with an average porosity of 21.5% and calculated average Sw of 26.1% in the Tarbert Formation.

The pressure data obtained from the well indicated a significant depletion caused by production from Oseberg B.

Good oil shows were recorded on cuttings from limestone stringers in the interval 2325 m to 2554 m in the Cretaceous and on sandstones (conventional and sidewall cores) in the interval 2658 m to 2673 m in the Tarbert Formation. A total of 10 conventional cores were cut, one in the Heather Formation and nine through the entire Brent sequence and into the top Dunlin. A total of 30 sidewall cores were attempted in the interval 2580 m to 2969.5 m. and 25 were recovered. One wire line RFT fluid sample was taken at 2667 m in the Tarbert Formation. It recovered 5 l of 0.87 g/cm3 oil and some gas.

The well bore was plugged back to 950 m for sidetracking and permanently abandoned on 9 May 1991 as an oil appraisal.

Testing

No drill stem test was performed

Cuttings available at the NPD

Interval [m]: 1030.00 - 2992.00

Cores available at the NPD

Core length [m]: 140.70

Scanned core photos

2617-2622m	2622-2627m	2627-2632m	2632-2637m	2637-2666m
2666-2671m	2671-2676m	2676-2681m	2681-2686m	2686-2690m
2691-2696m	2696-2701m	2701-2708m	2708-2713m	2713-2718m
2718-2723m	2723-2725m	2726-2730m	2730-2735m	2735-2739m
2739-2744m	2744-2749m	2749-2752m	2758-2763m	2763-2768m
2768-2773m	2773-2778m	2778-2783m	2783-2790m	2790-2795m
2795-2800m	2800-2804m

Palynological slides available at the NPD

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

Composite log (Format:PDF. Size: 0.395 Mb)
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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.

Old NPD WDSS reports, NPD papers and other related documents

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