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Exploration wellbore: 33/9-9

General information

Wellbore history

General

Well 33/9-9 was drilled in the northern part of the Statfjord field, about 1.6 km southeast of 33/9-3 well on the Tampen Spur in the northern North Sea. The objectives were to provide structural and stratigraphic control on the Brent reservoirs, and to provide stratigraphic control and to establish an oil/water contact for the Statfjord reservoir.

Operations and results

Appraisal well 33/9-9 was spudded with the semi-submersible installation Borgny Dolphin on 27 July 1977 and drilled to TD at 3100 m in Late Triassic sediments in the Statfjord Formation. The well was drilled with seawater down to 486 m and with a seawater/lignosulphonate mud system from 486 m to 1993 m. At 1993 m, TD in the 17 1/2" section, the hole was displaced to a freshwater/Lignosulphonate mud system. At the same point diesel was added to free the 13 3/8" casing which had become differentially stuck. After that the mud contained initially 5% diesel decreasing to traces of diesel at to 2489 m. From 2489 m to final TD the freshwater/Lignosulphonate mud system was without measurable diesel.

No hydrocarbon shows were reported above the Brent Group. The Brent Group was found at 2413 m, 77.5 m deeper than prognosed 44.0 m thinner than anticipated in comparison to 33/9-3. Good oil shows were encountered at the top of the Brent Formation and continued throughout the reservoir down to top Dunlin Group at 2504 m. The entire Brent Group was oil-filled and it was above the field oil/water contact of 2609.1 m (2584.1 MSL). Log calculations showed that of the 87.0 m of gross oil section 84.6 m was net sand with 27.5% average porosity and 13.1% average water saturation. The Dunlin Group came in at 2504 m and log interpretation indicated a 23.2 m gross oil bearing reservoir between 2528.4 and 2551.6 m with 17.9 m net oil sand. The interval had 20.2% average porosity and 34.6% water saturation. Oil shows were reported from ditch samples and side wall cores in the Dunlin sand between 2535 and 2575 m. No OWC was established in the Dunlin Group. It was assumed that Brent and Dunlin had a common OWC at 2609.1 m (2584.1 MSL), outside well position. The Early Jurassic Statfjord Formation was penetrated at 2715.0, only 5.0 m deep to prognosis confirming that the Statfjord seismic reflector is a reliable mapping horizon. Good oil shows were reported from the top down to about 2850.0 m. The lowest potential pay sand indicated on the CPI log occurs between 2847.5 and 2852.5 m, but a test in this interval, DST No. 2, produced water with only trace oil. The anticipated oil/water contact was not found. The lowest-known-oil in the well at 2815.0 m (2790.0 m MSL) is 13.1 m above the lowest-known-oil previously established in the 33/12-2, which falls within a section of tight sands and shales in 33/9-9.

A total of 23 cores were cut in the well. Cores no 1 to 8 were taken through the Brent reservoir and into the shaly top of Dunlin, while cores no 9 to 23 were cut in the Statfjord Formation. A significant error in core depth is noted for the first 16 cores. For these 11.3 m must be added to the registered core depths in order to match with the logger's depth. The last seven cores had core-log mismatch within +/- 2 m.

The well was permanently abandoned on 17 November 1977 as n oil and gas appraisal well.

Testing

Six separate zones were successfully tested, requiring a total of nine attempts. The purpose of the tests was to obtain information from six separate zones in the Brent, Dunlin and Statfjord Sands in order to further evaluate the reservoirs. The tests for the first two zones were designed primarily for production data, bottom hole pressures and formation fluid samples, with sustained sand production expected only if very thin unconsolidated sand stringers were present. The last four zones where sand bonding was weak, as calculated from the well log data, had the additional test requirement of measuring the oil rate at which the formation sand broke down.

DST 1 in the interval 2847.5 to 2852.5 m in the Statfjord Formation was a misrun.

DST 2 in the interval 2847.5 to 2852.5 m in the Statfjord Formation produced 215 Sm3 water and only trace oil /day through a 3/4" choke. The recorded bottom hole temperature was 91.1 deg C. Sand was produced throughout the test, at rates from 1200 to 300 pounds/thousand barrels (ptb)

DST 3 in the interval 2800.0 m to 2803.5 m in the Statfjord Formation produced in the final flow period 254 Sm3 oil /day through a 1/4" choke. The GOR was 82 Sm3/Sm3 and the oil gravity was 39.0 deg API. The recorded bottom hole temperature was 86.1 deg C. After the initial cleanup flow no sand was produced.

DST 4 in the interval 2742.0 m to 2745.0 m in the Statfjord Formation was a misrun.

DST 5 in the interval 2742.0 m to 2745.0 m in the Statfjord Formation produced in the final flow period 513 Sm3 oil /day through a 5/16" choke. The GOR was 93 Sm3/Sm3 and the oil gravity was 38.7 deg API. The recorded bottom hole temperature was 89.4 deg C. Sand was produced after each rate change (20 ptb), but cleaned up rapidly. Sand began producing more or less continuously, in bursts, on 5/8" choke (40 ptb) indicating formation was breaking down.

DST 6 in the interval 2742.0 m to 2745.0 m in the Statfjord Formation produced in the final flow period 299 Sm3 oil /day through a 1/4" choke. The GOR was 129 Sm3/Sm3 and the oil gravity was 38.6 deg API. The recorded bottom hole temperature was 193 deg C. No sand was observed other than a few grains upon initial cleanup on 7/16" choke.

DST 7 in the interval 2531.0 m to 2537.0 m in the Dunlin Group produced in the final flow period 442 Sm3 oil /day through a 23/64" choke. The GOR was 117 Sm3/Sm3 and the oil gravity was 34.4 deg API. The recorded bottom hole temperature was 82.8 deg C. On 1 1/4" choke sand production was observed on a continuous basis at about 120 ptb.

DST 8 in the interval 2458.0 m to 2460.7 m in the Brent Group produced in the final flow period 525 Sm3 oil /day through a 24/64" choke. The GOR was 144 Sm3/Sm3 and the oil gravity was 37.6 deg API (measured in the first flow period). The recorded bottom hole temperature was 80.1 deg C. Only small amounts of sand were produced.

DST 9 in the interval 2426.0 m to 2432.8 m in the Brent Group produced in the final flow period 416 Sm3 oil /day through a 22/64" choke. The GOR was 170 Sm3/Sm3 and the oil gravity was 38.5 deg API (measured in the first flow period). No temperature was recorded due to malfunction in the temperature gauge. Small amounts of sand were produced throughout the test. No measurable sand was produced on the highest flow rate (50/64" adjustable choke).

Cuttings available at the NPD

Interval [m]: 254.00 - 3101.00

Cores available at the NPD

Core length [m]: 258.67

Scanned core photos

24414-2416m	2416-2419m	2419-2421m	2421-2424m	2424-2426m
2426-2429m	2429-2432m	2432-2432m	2432-2434m	2434-2437m
2437-2439m	2439-2443m	2442-2444m	2444-2446m	2446-2448m
2448-2451m	2451-2453m	2453-2455m	2455-2458m	2458-2460m
2460-2463m	2463-2465m	2465-2465m	2468-2470m	2470-2473m
2473-2475m	2475-2478m	2478-2480m	2480-2481m	2481-2484m
2484-2487m	2487-2490m	2490-2492m	2492-2495m	2495-2498m
2498-2500m	2500-2503m	2503-2505m	2505-2508m	2508-2522m
2511-2513m	2513-2516m	2516-2516m	2719-2722m	2722-2725m
2725-2727m	2727-2732m	2732-2734m	2734-2737m	2737-2740m
2740-2742m	2742-2745m	2742-2745m	2745-2748m	2748-2750m
2750-2754m	2754-2757m	2757-2760m	2760-2762m	2762-2765m
2765-2768m	2768-2774m	2774-2776m	2776-2779m	2779-2782m
2782-2784m	2784-2786m	2786-2789m	2789-2791m	2791-2793m
2793-2795m	2795-2798m	2798-2807m	2807-2810m	2810-2812m
2812-2815m	2815-2818m	2818-2821m	2821-2823m	2823-2826m
2826-2828m	2828-2831m	2831-2834m	2834-2837m	2837-2840m
2840-2842m	2842-2845m	2845-2847m	2847-2850m	2850-2853m
2858-2861m	2853-2856m	2856-2858m	2861-2863m	2863-2866m
2866-2868m	2868-2871m	2871-2874m	2874-2876m

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 (intervals and pressures)

Drill Stem Test (recovery)

Available logs

Lithostratigraphy

Composite log

No composite log presently available.

Geochemical information

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

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Old NPD WDSS reports, NPD papers and other related documents

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