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Exploration wellbore: 34/8-4 S

General information

Wellbore history

General

Well 34/8-4 S is located on the Visund Field, A structure where previous wells 3/8-1, 3/8-3, and 3/8-3 A had proved hydrocarbons in the Brent Group. The main target in 34/8-4 S was the hydrocarbon potential in the Lomvi Formation on the A-structure. Secondary targets were the hydrocarbon potentials of the Statfjord and Lunde B/C formations on the A south compartment. Pressure measurement should be acquired from the Lunde- and Lomvi Formations in order to evaluate the sealing potential of the Middle to Late Triassic sequence. The well was designed for temporary abandonment and re-entry as a subsea producer. The well was planned as a deviated hole to penetrate top Statfjord, Lunde B/C and the Lomvi Formations within structural closure, leaving more than 10 mill Sm3 oil untested up-dip. Boulders could be encountered between 350 m and 395 m. Two intervals with possibility for shallow gas were identified at 446 m and 477 m.

Operations and results

Wildcat well 34/8-4 S was spudded with the semi-submersible installation Maersk Jutlander on 6 Desember 1991 and drilled to TD at 4150 m in rocks of Triassic age. Drilling started with an 8 1/2" pilot hole checking for shallow gas. No boulders or shallow gas was encountered. Significant technical problems were encountered during drilling of this well and one third of the total rig time was counted as down time. The longest period of down time occurred after TD in the 17 1/2" hole where 31.6 days were spent repairing the BOP and wellhead. The planned TD at 4478 m was not reached due to operational problems. The pipe was backed off at 3936 m and the borehole was logged from this depth and up to the 9 5/8" casing shoe. The well was drilled vertical down to ca 2310 m where it started to build angle up to 30 & at ca 2680 m. From here to TD the deviation varied between 30 & and 50 &.& The well was drilled with spud mud and seawater down to 1165 m, with KCl / polymer mud from 1165 m to 3781 m, and with a dispersed high-temperature tolerant mud system from 3781 m to TD.

Hydrocarbons were encountered in the Brent Group, Rannoch sandstones, and in thickly developed Triassic sandstones of the Hegre Group's Lunde Formation. No fluid contacts were observed in either Groups. The Lomvi Formation proved to be water bearing. Oil shows on sandstones started at Top Brent Group, 2903 m, and ended at 3697 m in Late Triassic, Lunde Formation. One of the secondary targets, the Statfjord Formation, was not encountered in the well. A total of seventeen cores were cut: sixteen in the Lunde Formation and one in the Lomvi Formation. RFT formation pressures were obtained in five runs, three of which were cased hole RFT runs. A gas gradient was defined from pressures obtained in the Brent Group and a common hydrocarbon gradient of 0.045 bar/m (0.46 g/cc) could be inferred throughout the Lunde Formation. A total of 60 sidewall cores were requested in two runs and 37 were recovered. The well was suspended on 9 June 1992 a gas and condensate discovery in the Lunde Formation.

Testing

Five production tests were performed, four gas/condensate tests in the Lunde Formation and one gas test in the Rannoch Formation. Production test data quoted refer to maximum rates at the specified choke sizes.

Test 1 was performed in the interval 3219.0 - 3241.0 in Lunde D. It flowed at a condensate rate of 441 Sm3/d and a gas rate of 410280 Sm3/d on a 15.87 mm choke. The GOR was 930 Sm3/Sm3. The condensate gravity was 0.782 g/cc and the gas gravity was 0.728 (air = l). The test produced 2.0 % CO2 and no H2S.

Test 2 was aborted due to tool failure shortly after running the test string.

Test 2A was performed in the interval 3133.0 - 3143.0 m in Lunde B/C. It flowed at a condensate rate of 754 Sm3/d and a gas rate of 605090 Sm3/d on a 17.46 mm choke. The GOR was 803 Sm3/Sm3. The condensate gravity was 0.788 g/cc and the gas gravity 0.734 (air = 1). The test produced 0.7 % CO2 and no H2S.

With the test string still in position after Test 2A, Test 2B1 was initiated by perforating three additional intervals. However, it was aborted due to problems with the subsea test tree and lubricator valves.

Test 2B2 perforated the four intervals 3132.5 - 3142.5 m, 3112.5 - 3127.5 m, 3094.5 -3104.5 m, and 3066.5 - 3082.0 m in Lunde B/C. It flowed at a condensate rate of 985 Sm3/d and a gas rate of 792950 Sm3/d on a 20.63 mm choke. The GOR was 805 Sm3/Sm3. The condensate gravity was 0.785 g/cc and the gas gravity 0.739 (air = l). The test produced 0.5 % CO2 and no H2S.

Test 3 perforated the interval 3000.7 - 3017.7 m. It flowed at a condensate rate of 908 Sm3/d and a gas rate of 708500 Sm3/d on a 21.43 mm choke. The GOR was 781 Sm3/Sm3. The condensate gravity was 0.777 g/cc and the gas gravity 0.738 (air-1). The test produced 0.1 % CO2 and no H2S.

Test 4 perforated the interval 2903.4 - 2917.4 m, top section of the Rannoch Formation. It flowed at a condensate rate of 205 Sm3/d and a gas rate of 480000 Sm3/d on a 25.40 mm choke. The GOR was 2418 Sm3/Sm3. The condensate gravity was 0.770 g/cc and the gas gravity 0.690 (air = l). The test produced 1.0% CO2 and 0.6 ppm H2 S.

Note that for this well the "bottle depths" quoted for the oil samples available from the NPD are in m TVD MSL.

Cuttings available at the NPD

Interval [m]: 1170.00 - 4150.00

Cores available at the NPD

Core length [m]: 355.50

Scanned core photos

3005-3010m	3010-3015m	3015-3019m	3067-3072m	3072-3077m
3077-3082m	3082-3084m	3096-3101m	3101-3106m	3106-3111m
3111-3116m	3116-3121m	3121-3122m	3123-3128m	3128-3133m
3133-3138m	3138-3142m	3176-3181m	3181-3186m	3186-3188m
3190-3195m	3195-3200m	3200-3205m	3205-3207m	3208-3213m
3213-3218m	3218-3223m	3223-3228m	3228-3233m	3233-3235m
3255-3260m	3260-3265m	3265-3270m	3270-3272m	3276-3281m
3281-3285m	3292-3297m	3297-3302m	3302-3307m	3307-3312m
3312-3317m	3317-3318m	3319-3324m	3324-3329m	3329-3332m
3333-3338m	3338-3343m	3343-3348m	3348-3353m	3353-3358m
3358-3359m	3385-3390m	3390-3395m	3395-3400m	3400-3405m
3405-3410m	3410-3412m	3412-3417m	3417-3422m	3422-3427m
3427-3432m	3432-3437m	3437-3438m	3439-3444m	3444-3449m
3449-3454m	3454-3459m	3459-3464m	3464-3465m	3464-3471m
3471-3476m	3476-3481m	3481-3485m	4044-4049m	4049-4054m
4054-4059m	4059-4064m	4064-4069m	4069-4071m

Palynological slides available at the NPD

Oil samples available at the NPD

Casing and leak-off tests

Mud

Drill stem test (intervals and pressures)

Drill Stem Test (recovery)

Available logs

Lithostratigraphy

Composite log

Composite log (Format:PDF. Size: 0.642 Mb)
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Geochemical information

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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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