2/7-26 S
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General information
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Wellbore history
GeneralWell 2/7 26 S is located on the Embla Field in the Central Graben of the North Sea. It was designed to test the pre-Jurassic sandstones, which had shown commercial quantities of hydrocarbons in the 2/7-20, 2/7-21 S, and 2/7-23 S wells. The objective of the well was to confirm the presence of hydrocarbon bearing sandstones in the western fault block of the structure and to establish the productivity of this reservoir section through a program of well testing and coring. Well location and TD was chosen so that both the upper and lower sandstone members of the pre-Jurassic sequence would be penetrated. The target location was 300 m to the south of the 2/7-9 well at Base Cretaceous level. The reservoir section was expected to be highly fractured and over-pressured. Shallow gas was expected since gas had been encountered in all wells drilled from the template location over the 2/7-20 well.Operations and resultsAppraisal well 2/7 26 S was spudded with the semi-submersible installation West Delta on 20 March 1991 and drilled to TD at 4848 in Devonian rocks. The well was drilled deviated from a template located over the 2/7-20 well to penetrate the target reservoir section in the western fault block of the Embla structure. Minor shallow gas was detected in sandy zones with an increase in background gas from 4 to 64 units. Apart from some failures when logging and some stuck pipe experiences, drilling proceeded without significant problems. The well was drilled with seawater and hi-vis sweeps down to 575 m, with KCl/PAC mud from 575 m to 4125.5 m, and with Enviromul oil based mud from 4125.5 m to TD.The 9 5/8" casing was set in claystones of the Lower Cretaceous, Rødby Formation. The remaining Lower Cretaceous section including Sola, Tuxen and Åsgård Formations was penetrated, followed by a Late Jurassic sequence consisting of 3 m Mandal Formation and 82 m Farsund Formation. The top of the reservoir sands were encountered at 4386 m (4226 m TVD), 58 m higher than prognosed. As in the other Embla wells the reservoir was undefined, Pre-Jurassic stratigraphy. Both the upper and the lower sandstone units were present in the well as predicted. The reservoir was oil bearing. No definite OWC was defined, however RFT pressure data, logs and DST results indicated oil-filled porous sandstones from top reservoir and down to at least 4606 m (4465 m TVD).The cuttings in the intervals between 1520 - 1680 m and 1730 - 1830 m (Base Nordland Group / upper Hordaland Group) showed 30-100% pale to bright yellow fluorescence accompanied by oil in the mud. The cut was blooming to streaming yellow, and the odour was good to strong. Good to excellent oil shows were seen in the interval 3111.4 m to 3973 m with 35% fluorescence in marls/limestones from 3111.4 m and rapidly increasing to 70% by 3018.1 m. Shows up to 80%, with bright yellow fluorescence and yellow fast streaming cut, were seen from 3124.2 to 3230.9 m. Shows were also seen at 3550.9 m, 5% -10% with dull yellow fluorescence and hazy crushed cut. From 3627.1 to 3834.4 m shows of 20% to 80% with a dull fluorescence were seen. The cut was pale blue yellow and slightly streaming. Shows further down in the well, including the pre-Jurassic reservoir section were weak and most likely caused by the oil-based mud.A total of 18 cores were cut in the well. The first was cut at 3200.4 - 3214.3 m in the Tor Formation. The second core was cut through the Mandal Formation and into the upper part of the Farsund Formation. A total of 16 cores were cut in the reservoir interval including a core in the rhyolittic rocks at TD. A total of 90 sidewall cores were attempted and 28 sidewall cores were recovered. No wire line fluid samples were taken.The well was suspended on 13 September 1991 as an oil appraisal well and reclassified to development well 2/7-D-26TestingTwo DST tests were performed in this well.DST 1 was conducted over the interval 4605.5 - 4696.9 m (4465.0 - 4552.2 m TVD). It flowed in the range of 48 Sm3 (300 STB) /day, with signs of unstable flow, at pressures less than 1000 psi.DST 2 was conducted over a gross interval from 4309.8 - 4538.4 (4184 - 4401 m TVD).The well was tested on a 16/64" choke with flowing rates of 223 Sm3 oil and 61447 Sm3 gas/day. The GOR was 275 Sm3/Sm3, the oil density was 0.81 g/cm3 (43 deg API), and the gas gravity (air = 1) was 0.81 with 6% CO2 and 20 ppm H2S. A stable down-hole temperature of 160 deg C was measured in the test. -
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]579.004547.60 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom110500.010545.5[ft ]214103.014153.9[ft ]314417.014453.1[ft ]414457.014480.8[ft ]514481.014545.8[ft ]614558.014581.6[ft ]714586.014592.1[ft ]814598.014635.6[ft ]914636.014658.0[ft ]1014660.014693.6[ft ]1114696.014743.8[ft ]1214746.014807.2[ft ]1314807.014848.0[ft ]1414854.014903.6[ft ]1514903.014935.6[ft ]1615312.015403.6[ft ]1715404.015495.1[ft ]1815844.015907.7[ft ]Cores at the Norwegian Offshore Directorate Total core sample length [m]250.7Cores 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 availableDSTDST 14605.504696.9024.08.1991 - 00:00YESDSTDST 24309.804538.4003.09.1991 - 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 typeCONDUCTOR30158.036160.00.00LOTINTERM.20571.026573.00.00LOTINTERM.13 3/82130.017 1/22133.01.91LOTINTERM.9 5/84117.012 1/44120.02.16LOTINTERM.6 5/84847.08 1/84848.00.00LOT -
Drill stem tests (DST)
Drill stem tests (DST) Test numberFrom depth MD
[m]To depth MD
[m]Choke size
[mm]1.0460646976.32.0431045386.3Drill stem tests (DST) Test numberFinal shut-in pressure
[MPa]Final flow pressure
[MPa]Bottom hole pressure
[MPa]Downhole temperature
[°C]1.01332.0Drill stem tests (DST) Test numberOil
[Sm3/day]Gas
[Sm3/day]Oil density
[g/cm3]Gas grav. rel.airGOR
[m3/m3]1.053101230.8191912.0223614470.8190.810279 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]CST GR41454829CST GR41474777DLL MSFL BHC GR AMS21334104FMS GR31124083LDL CNL GR AMS30884070LDL CNL NGL AMS42564859MWD - GR RES DIR2744394OBDT GR41204857PIL ASL GR AMS39774856RFT GR31343530RFT GR41744715VELOCITY22554800 -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit10016062966296629833038309131183118320033213981398940574057416341824299429943024386 -
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]pdf2.75pdf38.80 -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured1181.05WATER BASED1601.05WATER BASED1801.05WATER BASED2941.05WATER BASED5761.20WATER BASED6941.3235.0OIL BASED11781.3238.0OIL BASED16281.5642.0OIL BASED19911.7032.0OIL BASED21431.7026.0OIL BASED21461.7038.0OIL BASED22881.7018.0OIL BASED24731.7018.0OIL BASED26301.7020.0OIL BASED27241.7019.0OIL BASED28741.7321.0OIL BASED29831.7322.0OIL BASED29871.7322.0OIL BASED29981.7323.0OIL BASED30471.7321.0OIL BASED31251.7322.0OIL BASED31381.7322.0OIL BASED32001.7321.0OIL BASED32191.7326.0OIL BASED33411.7321.0OIL BASED33851.7320.0OIL BASED34871.7324.0OIL BASED34981.7324.0OIL BASED35321.7322.0OIL BASED36251.7326.0OIL BASED36781.7326.0OIL BASED37491.7327.0OIL BASED37721.7326.0OIL BASED37781.7326.0OIL BASED37831.7526.0OIL BASED39871.7524.0OIL BASED39991.7524.0OIL BASED40621.7526.0OIL BASED40731.7523.0OIL BASED41131.9335.0WATER BASED41161.7522.0OIL BASED41261.7626.0OIL BASED41462.0052.0WATER BASED42082.0253.0WATER BASED42562.0249.0WATER BASED42792.0446.0OIL BASED42992.0244.0WATER BASED43142.0244.0WATER BASED43152.0445.0WATER BASED43312.0445.0WATER BASED43622.0649.0WATER BASED43942.0650.0WATER BASED43942.0649.0WATER BASED44072.0455.0WATER BASED44142.0649.0WATER BASED44362.0650.0WATER BASED44502.0650.0WATER BASED44682.0649.0WATER BASED44792.0649.0WATER BASED45232.0654.0WATER BASED45422.0448.0WATER BASED45532.0453.0WATER BASED45542.0452.0WATER BASED46022.0446.0WATER BASED46572.0443.0OIL BASED47232.0446.0WATER BASED48492.0442.0WATER BASED48492.0442.0OIL BASED