7/12-6
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General information
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Wellbore history
GeneralWell 7/12-6 was drilled as an appraisal well on the Ula Field in the southern North Sea. The objective was to determine sand distribution in northern part of the Ula field, and production and injection properties of reservoir and aquifer.Operations and resultsAppraisal well 7/12-6 was spudded with the semi-submersible installation Sedco 707 on 10 April 1981 and drilled to TD at 3700 m in the Triassic Skagerrak Formation. Some hole problems and excessive cavings due to underbalanced drilling occurred in the 12 1/4" section between 2633 and 3353 m, otherwise the well was drilled without significant technical problems or delay. The well was drilled with gel/seawater and fluid loss additives down to 480 m and with gypsum/lignosulphonate and fluid loss additives from 480 m to TD.The Ula Formation sandstones were penetrated at 3406 m. The sandstones were 115 m thick, very fine to fine grained with porosities from 10 to 25% and permabilities from 1 to 2000 mD. The reservoir was oil bearing throughout, no OWC was established. An unexpected Triassic reservoir of good quality was found below the Ula Formation. The well drilled 179 m into it without reaching the OWC. The reservoir consisted of various types of micaceous sandstones with porosities from 4 to 23% and permabilities from 0.03 to 2600 mD. The first hydrocarbon indication was recorded as a weak oil show at 2440 in siltstone. Further shows were recorded in the Late Cretaceous between 3010 m and 3060 m, however the logs did not indicate any significant mobile hydrocarbon. Hydrocarbon shows were recorded throughout the Upper Jurassic Ula Formation between 3407 m and 3521 m. Patchy shows were recorded in the Triassic interval between 3521 m and TD.A total of 240 m core was cut in 9 cores over the interval 3407.7 to 3647.17 m in the Ula and Skagerrak formations. RFT fluid samples were taken at 3437 m (oil), 3533.5 m (mud filtrate), and at 3530.5 m (mud filtrate).The well was permanently abandoned on 24 July 1981 as an oil appraisal well.TestingBoth reservoirs were tested.DST 1C in the Triassic Skagerrak Formation reservoir (3543 - 3612 m) flowed 160 Sm3 oil and 5720 Sm3 gas through a 12/64" choke. The GOR was 36 Sm3/Sm3. The oil density was 0.810 g/cm3 and the separator gas gravity was 0.806 (air = 1). The bottom hole temperature measured at 3531 m, was 149.4 deg C.DST 2 in the Ula Formation sandstone reservoir (3434 - 3511 m) flowed 1269 Sm3 oil and 84526 Sm3 gas through a 32/64" choke. The GOR was 67 Sm3/Sm3. The oil density was 0.842 g/cm3 and the separator gas gravity was 0.840 (air = 1). The bottom hole temperature measured at 3425 m, was 143.3 deg C.DST 2 was followed by an injection test. The maximum injection rate was 1407 Sm3/day at a wellhead injection pressure of 3100 to 3200 psi. As no OWC was seen the no injection test could be performed in the aquifer. -
Cuttings at the Norwegian Offshore Directorate
Cuttings at the Norwegian Offshore Directorate Cuttings available for sampling?NOCuttings at the Norwegian Offshore Directorate Cutting sample, top depth [m]Cutting samples, bottom depth [m]180.003632.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom13406.73434.3[m ]23434.33461.3[m ]33461.63488.6[m ]43488.63515.5[m ]53515.53542.8[m ]63542.83569.8[m ]73569.83596.8[m ]83596.83624.3[m ]93624.33647.2[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]240.1Cores at the Norwegian Offshore Directorate Cores available for sampling?YES -
Core photos
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Oil samples at the Norwegian Offshore Directorate
Oil samples at the Norwegian Offshore Directorate Test typeBottle numberTop depth
MD [m]Bottom depth
MD [m]Fluid typeTest timeSamples availableDSTTEST20.003511.0016.07.1981 - 00:00YESDST0.000.0029.06.1983 - 00:00YES -
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 typeCONDUCTOR30167.036172.00.00LOTSURF.COND.18 5/8465.017 1/2480.01.88LOTINTERM.13 3/81684.017 1/21696.01.83LOTINTERM.9 5/83337.012 1/43350.01.97LOTLINER73688.08 1/23700.00.00LOT -
Drill stem tests (DST)
Drill stem tests (DST) Test numberFrom depth MD
[m]To depth MD
[m]Choke size
[mm]1.0354436124.72.03434351112.7Drill stem tests (DST) Test numberFinal shut-in pressure
[MPa]Final flow pressure
[MPa]Bottom hole pressure
[MPa]Downhole temperature
[°C]1.01492.0143Drill stem tests (DST) Test numberOil
[Sm3/day]Gas
[Sm3/day]Oil density
[g/cm3]Gas grav. rel.airGOR
[m3/m3]1.016057200.8160.806362.01270845260.8420.84066 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]CBL31253632CCL160195CCL31003508CCL33003525CCL33003390DLL MSFL33373703FDC CNL CAL GR33373704HDT SL33373703ISF BHCS GR MSFL CAL4651692ISF BHCS GR MSFL CAL16843351ISF BHCS GR SP93477ISF BHCS SP GR33373702RFT GR34153670RFT GR34163570VELOCITY2003650 -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit941672253925392564260526612702271027302730281030023071308530923092329232923332340635213521 -
Geochemical information
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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]pdf18.37pdf2.34pdf29.48pdf27.74pdf0.30pdf37.34pdf5.33pdf3.87pdf3.95pdf3.98pdf2.60pdf29.48pdf4.31pdf1.66pdf1.81pdf0.68pdf45.04pdf13.49pdf3.88pdf0.99pdf11.31pdf2.96pdf2.67pdf207.05pdf9.83pdf10.26pdf11.87 -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured3901.1485.0waterbased16801.3058.0waterbased19901.4248.0waterbased26301.5059.0waterbased33901.5051.0waterbased