15/3-8
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General information
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Wellbore history
GeneralThe Gudrun structure is situated on the east flank of the South Viking Graben and west of the Utsira High in the North Sea. Well 15/3-8 was drilled on the western flank of the structure, approximately 9 km east of the UK border. New seismic data and results from well 15/3-7 had revealed uncertainties regarding the Late Jurassic reservoir section in the Gudrun structure. The main purpose of well 15/3-8 was to gather the necessary information required to ascertain whether the Intra-Draupne Formation reservoir rocks of the Gudrun Discovery could be developed commercially. This included reservoir pressure data, petrophysical data including taking cores, fluid sampling for fluid characteristics, and production properties by drill stem testing.Operations and resultsAppraisal well 15/3-8 was spudded with the semi-submersible installation Transocean Leader on 11 April 2006 and drilled to TD at 4592 m in Late Jurassic Intra-Draupne Formation sandstone. No significant technical problems were encountered in the operations and the well was completed within planned time frame. The well was drilled with seawater/bentonite/hi-vis pills down to 1010 m, with Glydril mud from 1010 m to 2765 m, and with Paratherm oil based mud (paraffin base) from 2765 m to TD.Top Viking Group was encountered at 3932.5 m and consisted of the interbedded lithologies of sandstone, claystone and limestone, with varying thicknesses from laminas to stringers and massive layers. The first 140 m was Draupne Formation claystone. The target reservoir section, Intra Draupne Formation sands, was encountered at 4072.5 m, 38.9 m deeper than expected. Three intra Draupne Formation sandstone units were identified, SST1 from 4072.5 m to 4212.5 m, SST2 from 4212.5 m to 4346 m, and SST3 from 4474.5 m to TD. The sand quality was significantly better than observed in the neighbouring wells. When correlated with neighbouring wells well 15/3-8 showed significant lateral reservoir variations over small distances within the structure. SST1 contained a high-shrinkage volatile oil down to a contact at 4208 m, the SST2 pressure gradient proved a water bearing sandstone, although oil was sampled at 4332.9 m, while SST3 contained a near-critical gas-condensate down to a contact at 4485.4 m.Good shows were seen in the cores from the reservoir section as they were recovered on deck. It was no possible to give a reliable evaluation of the shows on cuttings during drilling due to background fluorescence from the oil based mud. In addition, some of the most marginal shows described from the cored section were hampered by the existence of formation derived kerogens in the mud. Some of the cores were also bleeding HC from very tight zones at surface and seepages from these zones might have contaminated better sandstone sections below. From the general fluorescence picture there seem to be a presence of heavier HC in the tight zones than in the more porous zones.A total of 158 m core was recovered in 7 cores from the interval 4167 to 4505 m in various Intra-Draupne Formation sandstone sections in the Late Jurassic. MDT fluid samples were taken at 4514.5 m (water), 4479.1 m (hydrocarbons), 4332.9 m (hydrocarbons), 4213.5 m (water), 4182.1 m (hydrocarbons), and at 4074 m (hydrocarbons).The well was permanently abandoned on 11 April 2006 as an oil and gas appraisal well.TestingTwo drill stem test was performed in Intra-Draupne Formation sandstones.DST 1 tested the interval 4141 - 4183 m. The well was opened to flow for a total of 28 hours. The main flow duration was 14 hours with an approximate oil rate of 739 m3/day a gas rate of 346600 Sm3 gas/day and a GOR of 469 m3/m3 through a 32/64" choke. This was followed by a 96 hours build up period. Maximum bottom hole temperature recorded in the test was 133 deg C.DST 2 tested the interval 4073 - 4087 m. The well was open to flow for a total of 26 hours. The main flow duration was 10 hours with an approximate oil rate of 650m3/day, a gas rate of 342400 Sm3 gas/day and a GOR of 500 m3/m3 through a 28/64" choke. This was followed by a 96 hours build up period. Maximum bottom hole temperature recorded in the test was 130 deg C. -
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]1020.004590.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom14167.04179.6[m ]24179.64200.5[m ]34202.04238.5[m ]44238.54275.2[m ]54275.24302.5[m ]64478.54492.5[m ]74494.04505.1[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]158.9Cores at the Norwegian Offshore Directorate Cores available for sampling?YES -
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 availableDST4141.004183.00OIL04.03.2006 - 08:17YES -
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 typeCONDUCTOR30179.036179.00.00LOTSURF.COND.201001.0261010.01.50LOTINTERM.142754.017 1/22765.01.71LOTINTERM.9 7/83910.012 1/43910.02.12LOTLINER74298.08 1/24590.00.00LOT -
Drill stem tests (DST)
Drill stem tests (DST) Test numberFrom depth MD
[m]To depth MD
[m]Choke size
[mm]1.04141418312.72.04073408711.0Drill stem tests (DST) Test numberFinal shut-in pressure
[MPa]Final flow pressure
[MPa]Bottom hole pressure
[MPa]Downhole temperature
[°C]1.03.5007.0001332.04.0007.500130Drill stem tests (DST) Test numberOil
[Sm3/day]Gas
[Sm3/day]Oil density
[g/cm3]Gas grav. rel.airGOR
[m3/m3]1.07334732.0670500 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]AIT DSI EMS GR27504590MDT40744514MDT MINI DST SAMPLE39464514MDT PT39464519MDT SAMPLE43324479MFC 801292007MSCT39454581MWD - GR RES DIR PWD ECD1822765MWD - GR RES DIR PWD ECD39104590MWD - GR RES DIR PWD ECD BCPM AP27653908OBMI-2 GR39004590VSP1294474VSP WAZO1303300VSP ZO10003901 -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit133658858102511361448179221642164222322772603274027402792321333413673368637943859387539333933407343924474 -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured1511.05SW / BENTONITE 11821.05SW / BENTONITE 19551.03SW / BENTONITE 110101.30SW / BENTONITE 116171.3518.0GLYDRIL 1219951.3622.0GLYDRIL 1228001.3929.0PARATHERM32171.4527.0PARATHERM35101.6240.0PARATHERM39081.6237.0PARATHERM39101.6140.0PARATHERM39311.03PARATHERM -
Thin sections at the Norwegian Offshore Directorate
Thin sections at the Norwegian Offshore Directorate DepthUnit4170.25[m ]4176.50[m ]4180.30[m ]4205.44[m ]4209.20[m ]4211.75[m ]4218.50[m ]4223.00[m ]4228.75[m ]4236.50[m ]4244.00[m ]4247.50[m ]4254.50[m ]4268.50[m ]4270.60[m ]4285.75[m ]4292.00[m ]4298.75[m ]4483.54[m ]4488.00[m ]4501.25[m ]