31/2-8
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General information
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Wellbore history
GeneralWell 31/2-8 was drilled in the northern part of block 31/2, some 3 km NW of the Troll Field boundary, to test a downthrown Jurassic fault-block outside the Troll Field. The primary objective was the Late Jurassic, shallow marine sands of the Viking Group, especially the Sognefjord Formation. The Early Jurassic was secondary objective and would be evaluated by drilling into Triassic sediments.Operations and resultsWildcat well 31/2-8 was spudded with the semi-submersible installation Borgny Dolphin on 16 June 1982 and drilled to TD at 3375 m in the Triassic Hegre Group. A gas zone (confirmed by logs) between 510 - 530 m did not cause any problems during drilling of the 14 3/4" pilot hole. Maximum gas reading through this zone was 10 %. The hole was drilled to 840 m and under-reamed to 26" without incident. The 17 1/2" section was drilled first by an 8 1/2" pilot hole down to 1063 m to provide better control when drilling through a potential gas charged fault plane. No indications of gas were seen. 3 cores were taken in the 12 1/4" section. Two washouts occurred when drilling the 8 1/2" hole below 3317 m. The well was drilled with seawater gel down to 840 m, with KCl/polymer from 840 m to 1745 m, with seawater and Drispac from 1745 m to 2743 m and wit Drispac/lignosulphonate from 2743 m to TD.Only 13 m of Shetland Group chalk was found on top of the Kimmerian unconformity at 1821 m. The Viking Group contained a 15.5 m thick Draupne shale on top of a 680 m thick sequence of sandstone units interbedded in the Heather Formation. The Middle to Early Jurassic was also well developed. Shows occurred sporadically in limestones, siltstone, and claystones through the Early Tertiary and Late Cretaceous. When entering into the Late Jurassic reservoir sands at 1836.5 m (Sognefjord Formation) ditch gas readings went up to more than 4% from a background lower than 1%, but without oil indications in the uppermost section. On the cores taken, very good oil shows were observed in the coarser grained, clean sands between 1841.8 m and 1854.8 m. In the carbonate-cemented band down to 1856.6 m, direct fluorescence became patchy. In the deeper, very fine to fine, micaceous sands the quality of the shows deteriorated further until they disappeared completely around 1872 m. Below the Sognefjord Formation, the only shows encountered was in a sidewall sample at 3050.5 m (at the top of the Statfjord Formation). From log analysis the Jurassic sands were interpreted to be oil bearing from 1836.5 m to ca. 1868 m; below this depth no hydrocarbons were seen.Three conventional cores were cut in the interval 1841.8 m to 1888.5 m in the Late Jurassic. One RFT sample at 1849 m recovered 1800 ml mud contaminated formation water and 100 ml of emulsified hydrocarbons.The well was completed on 18 August 1982 as a well with shows.TestingOil shows on cores and preliminary log interpretation led to a DST in the interval 1843 m to 1848 m in Late Jurassic sandstone. After some technical problems the well was flowed for 2 minutes followed by a one-hour build-up. The well was then flowed until it died after having produced approximately 33 barrels of formation fluid with a trace of oil. A wire line sandballer found 22 m of sand on top of the bridge plug. -
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]500.003375.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom11841.81851.5[m ]21852.51869.7[m ]31870.01888.9[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]45.8Cores at the Norwegian Offshore Directorate Cores available for sampling?YES -
Core photos
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Palynological slides at the Norwegian Offshore Directorate
Palynological slides at the Norwegian Offshore Directorate Sample depthDepth unitSample typeLaboratory1821.7[m]SWCSHELL1826.0[m]SWCSHELL1830.5[m]SWCSHELL1832.8[m]SWCSHELL1836.0[m]SWCSHELL1837.2[m]SWCSHELL1839.5[m]SWCSHELL1857.5[m]CSHELL1858.4[m]CSHELL1860.7[m]CSHELL1863.4[m]CSHELL1864.3[m]CSHELL1868.8[m]CSHELL1870.9[m]CSHELL1873.6[m]CSHELL1878.1[m]CSHELL1880.8[m]CSHELL1881.7[m]CSHELL1937.5[m]SWCSHELL1941.5[m]SWCSHELL1964.5[m]SWCSHELL1965.5[m]SWCSHELL1969.8[m]SWCSHELL1979.7[m]SWCSHELL1989.5[m]SWCSHELL2003.0[m]SWCSHELL2015.5[m]SWCSHELL2032.0[m]SWCSHELL2043.5[m]SWCSHELL2055.0[m]SWCSHELL2068.5[m]SWCSHELL2082.6[m]SWCSHELL2093.0[m]SWCSHELL2107.5[m]SWCSHELL2120.0[m]SWCSHELL2133.8[m]SWCSHELL2145.2[m]SWCSHELL2160.5[m]SWCSHELL2168.5[m]SWCSHELL2181.5[m]SWCSHELL2198.5[m]SWCSHELL2217.5[m]SWCSHELL2250.5[m]SWCSHELL2267.1[m]SWCSHELL2285.2[m]SWCSHELL2314.5[m]SWCSHELL2330.5[m]SWCSHELL2349.5[m]SWCSHELL2355.6[m]SWCSHELL2368.0[m]SWCSHELL2385.8[m]SWCSHELL2398.5[m]SWCSHELL2407.1[m]SWCSHELL2424.5[m]SWCSHELL2436.0[m]SWCSHELL2452.0[m]SWCSHELL2473.5[m]SWCSHELL2491.5[m]SWCSHELL2497.0[m]SWCSHELL2516.0[m]SWCSHELL2532.5[m]SWCSHELL2548.0[m]SWCSHELL2565.9[m]SWCSHELL2575.0[m]SWCSHELL2578.0[m]SWCSHELL2581.5[m]SWCSHELL2595.5[m]SWCSHELL2612.0[m]SWCSHELL2618.0[m]SWCSHELL2632.5[m]SWCSHELL2642.5[m]SWCSHELL2665.5[m]SWCSHELL2672.5[m]SWCSHELL2687.0[m]SWCSHELL2709.3[m]SWCSHELL2722.3[m]SWCSHELL2725.0[m]SWCSHELL2773.9[m]SWCSHELL2778.0[m]SWCSHELL2784.2[m]SWCSHELL2792.3[m]SWCSHELL2815.0[m]SWCSHELL2840.9[m]SWCSHELL2867.5[m]SWCSHELL2892.4[m]SWCSHELL2920.9[m]SWCSHELL2943.8[m]SWCSHELL2968.8[m]SWCSHELL2977.7[m]SWCSHELL3035.5[m]SWCSHELL3046.5[m]SWCSHELL3056.8[m]SWCSHELL3065.8[m]SWCSHELL3228.0[m]SWCSHELL -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit371772142814281472151418081821182118371999218922542266251727202720282528962967303530483274 -
Composite logs
Composite logs Document nameDocument formatDocument size [MB]pdf0.64 -
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]PDF11.09pdf1.07pdf1.22pdf2.28pdf2.91pdf0.17pdf0.64pdf0.76pdf0.13pdf0.12pdf1.35pdf6.69pdf0.53pdf0.72pdf0.27pdf3.34pdf1.61pdf1.45pdf1.83 -
Drill stem tests (DST)
Drill stem tests (DST) Test numberFrom depth MD
[m]To depth MD
[m]Choke size
[mm]1.0184318480.0Drill stem tests (DST) Test numberFinal shut-in pressure
[MPa]Final flow pressure
[MPa]Bottom hole pressure
[MPa]Downhole temperature
[°C]1.0Drill stem tests (DST) Test numberOil
[Sm3/day]Gas
[Sm3/day]Oil density
[g/cm3]Gas grav. rel.airGOR
[m3/m3]1.0 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]CBL VDL4691735CBL VDL7922725CST15771601CST17512725CST27323373DLL MSFL CAL17352729FDC CNL GR27323379FDC CNL GR CAL469834FDC CNL GR CAL7771742FDC CNL GR CAL17352740HDT17352740HDT27323379ISF BHC GR370833ISF BHC GR7751741ISF BHC GR17352738ISF BHC GR27323378LDT CNL NGT27323379LDT NGT17352729RFT00RFT13WST5753370 -
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 typeCONDUCTOR30469.536480.00.00LOTSURF.COND.20826.026840.01.80LOTINTERM.13 3/81734.017 1/21745.01.61LOTINTERM.9 5/82732.012 1/42743.01.89LOTOPEN HOLE3375.08 1/23375.00.00LOT -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured4851.0752.0waterbased8451.2751.0waterbased17451.3655.0waterbased18701.2149.0waterbased27431.2350.0waterbased33751.2450.0waterbased -
Pressure plots
Pressure plots The pore pressure data is sourced from well logs if no other source is specified. In some wells where pore pressure logs do not exist, information from Drill stem tests and kicks have been used. The data has been reported to the NPD, and further processed and quality controlled by IHS Markit.Pressure plots Document nameDocument formatDocument size [MB]pdf0.24