7/12-11
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General information
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Wellbore history
GeneralWell 7/12-11 was designed to test 7/12-JU6 prospect, a Late Jurassic Ula Formation sand in a structural prospect some 7 km east of the Ula Field. Well 7/12-11 was located close to the edge of the perceived Late Jurassic Ula Trend fairway.The prospect was defined as a structural trap with fault closure to the east and north, and dip closure to the southwest. Lateral seal to the east was thought to be provided by cross-fault seal of Late Jurassic reservoir against Triassic shales and siltstones. The key element of risk was trap effectiveness, as the prospect relied on a shattered sub-seismic fault zone in the northeastern corner. The results might have implications for further prospectivity in the licence.The primary objective for the 7/12-11 well was to prove a volume of oil that was commercial as a tieback development to the Ula Platform. Secondary objectives were the uppermost part of the Triassic rocks and the Middle Jurassic Bryne Formation.Operations and resultsWildcat well 7/12-11 was spudded with the semi-submersible installation Ross Isle on 31 August 1991 and drilled to TD at 3865 m in the Triassic Skagerrak Formation. A 9 7/8" pilot hole was drilled to 950 m, and some shallow gas was detected by ROV sonar and observation of some surface bubbles at 518 m. The 17 1/2" hole was drilled with the experimental mud system RCS/DF+. In the 12 1/4" hole this mud was gradually diluted and displaced to a KCl/IOBOND mud. Drilling proceeded without significant problems to TD.The Ula sandstones came in at 3787.5 m, 39.5 m deeper than prognosed. It was only 12.5 m thick which was 78 m thinner than prognosed. The Bryne Formation was absent. Very weak hydrocarbon fluorescence was observed in sand stringers of the Lista Formation. Minor gas shows were observed in the Mandal Formation. Occasional oil stained grains with very weak cut fluorescence were seen in the cuttings of the Ula Formation. No shows were observed in the sidewall cores. One 10 m conventional core was cut in the Triassic Skagerrak Formation. A total of 21 sidewall cores were attempted, and 14 were recovered. Two RFT fluid samples were taken at 3797.5 m. No gas or oil was recovered in these samples, only water. The well was permanently abandoned on 6 November 1991 as a dry hole with weak hydrocarbon shows.TestingNo drill stem test was performed -
Cuttings at the Norwegian Offshore Directorate
Cuttings at the Norwegian Offshore Directorate Cuttings available for sampling?YESCuttings at the Norwegian Offshore Directorate Cutting sample, top depth [m]Cutting samples, bottom depth [m]950.003865.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom13802.73812.0[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]9.3Cores at the Norwegian Offshore Directorate Cores available for sampling?YES -
Core photos
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Casing and leak–off tests
Casing and leak–off tests Casing typeCasing diam.
[inch]Casing depth
[m]Hole diam.
[inch]Hole depth
[m]LOT/FIT mud eqv.
[g/cm3]Formation test typeCONDUCTOR30163.036165.00.00LOTINTERM.20935.026937.01.70LOTINTERM.13 3/82735.017 1/22737.01.90LOTOPEN HOLE3868.012 1/23868.00.00LOT -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]DLL LSS GR CAL SP752746DLL MSFL SDT GR SP CAL27383872LDL CNL NGT GR27383871MSCT GR37643806MWD903865RFT HP GR37913833SHDT GR27383872WST GR5003871 -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit9018372708270827412822295329622973297331243387348634863569358635963728372837533788378838003800 -
Composite logs
Composite logs Document nameDocument formatDocument size [MB]pdf0.47 -
Documents – reported by the production licence (period for duty of secrecy expired)
Documents – reported by the production licence (period for duty of secrecy expired) Document nameDocument formatDocument size [MB]pdf61.28 -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured2061.03WATER BASED9461.2023.0WATER BASED9501.0539.0WATER BASED9621.2017.0WATER BASED12221.3930.0WATER BASED14051.6054.0WATER BASED14131.6035.0WATER BASED15951.6060.0WATER BASED17641.7055.0WATER BASED19071.6048.0WATER BASED20511.6045.0WATER BASED22051.6036.0WATER BASED23131.6040.0WATER BASED23801.6031.0WATER BASED23861.6034.0WATER BASED25221.6044.0WATER BASED26591.6044.0WATER BASED26671.6034.0WATER BASED27371.6031.0WATER BASED27431.6028.0WATER BASED27671.5836.0WATER BASED28731.5532.0WATER BASED29721.5534.0WATER BASED30151.5530.0WATER BASED30551.5527.0WATER BASED30871.5531.0WATER BASED31091.5532.0WATER BASED31681.5532.0WATER BASED32031.5532.0WATER BASED33261.5538.0WATER BASED34741.5536.0WATER BASED35571.5535.0WATER BASED35871.5535.0WATER BASED35961.5534.0WATER BASED36241.5538.0WATER BASED36401.5536.0WATER BASED36741.5539.0WATER BASED37231.5528.0WATER BASED37301.5533.0WATER BASED38021.5532.0WATER BASED38651.5538.0WATER BASED -
Palynological slides at the Norwegian Offshore Directorate
Palynological slides at the Norwegian Offshore Directorate Sample depthDepth unitSample typeLaboratory3733.0[m]DCPETROSTR3739.0[m]DCPETROS3745.0[m]DCPETROS3751.0[m]DCPETROS3757.0[m]DCPETROS3763.0[m]DCPETROS3769.0[m]DCPETROS3775.0[m]DCPETROS3781.0[m]DCPETROS3787.0[m]DCPETROS3793.0[m]DCPETROS3799.0[m]DCPETROS