7/12-8
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General information
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Wellbore history
GeneralWell 7/12-8 was drilled on the south eastern flank of the Ula Field in the North Sea. The well was drilled to evaluate the reservoir potential of the south eastern sector of the Field and to assist target future water injection wells. To enable a full evaluation of the reservoir the lower Ula Formation and the underlying Triassic section were penetrated.Operations and resultsAppraisal well 7/12-8 was spudded with the semi-submersible installation Vildkat Explorer on 3 October 1988 and drilled to TD at 3900 m in the Triassic Skagerrak Formation. Drilling down to top reservoir proceeded without any significant problems. The well was drilled with seawater and bentonite down to 167 m, with seawater/bentonite/spercell/CMC EHV mud from 167 to 955 m, with KCl/polymer mud from 955 m to 3721 m, and with oil based Safemul mud from 3721 m to TD.Top Mandal Formation was encountered at 3640 m, top Farsund Formation at 3663 m, and top Ula Formation at 3718 m, 78 m higher than prognosed. RFT measurements showed a pressure barrier at ca 3770 m. There was oil down to the barrier and water below. An effective oil/water contact was difficult to identify. The saturation profile across interval 3770 - 3796 is interpreted as water influx from the aquifer following production from the field since 1986. The RFT results supported that the Ula reservoir at the 7/12-8 location was depleted and in pressure communication with the crestal producing part of the Ula Field. There were no signs of hydrocarbons in the underlying Triassic.One core was cut in the Ula Formation from 3724.0 to 3750.5 m. Segregated RFT fluid samples were taken at 3772 m (water and oil) and 3808.5 m (water and OBM).The well was suspended on 23 December 1988 as an oil appraisal.TestingOne Drill Stem Test was performed in the Ula Formation in the interval 3719 to 3756 m flowed 274 Sm3/d of oil and 21800 Sm3/d of gas through a 254 mm choke. The GOR was 79 Sm3/Sm3. Maximum H2S and CO2 was 0 ppm and 2.5 %vol, respectively. Final BHT was 146.1 deg C. Two water injection tests followed the production test, the first over interval 3719 m to 3756 m and the second overt the interval 3719 to 3783 m.r -
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]1500.003897.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom13724.53750.0[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]25.5Cores 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 typeCONDUCTOR30167.032171.00.00LOTSURF.COND.20951.026957.01.63LOTINTERM.13 3/82338.017 1/22350.01.97LOTINTERM.9 5/83712.012 1/43721.02.24LOTLINER73787.08 1/23788.02.06LOTOPEN HOLE3900.063900.00.00 -
Drill stem tests (DST)
Drill stem tests (DST) Test numberFrom depth MD
[m]To depth MD
[m]Choke size
[mm]1.03719378316.0Drill 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]1.02742200079 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]00BGL GR9522344BHC GR37253770CBL VDL GR15003768CST GR23503721CST GR37963893DIL BHC GR23403726DIL BHC GR37263792DIL BHC GR37943903DIL LSS GR167350DIL LSS GR9522342LDL CNL GR37933902LDL CNL NGL37163794MWD37103788NGT37163794OBT GR37933902RFTB HP GR37303780RFTB HP GR37953887SAT VELOCITY3003900 -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit952757275727892882292929402940307533213391339134653640364036633718371838143814 -
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]pdf11.86 -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured5591.2522.512.0WATER BASED11.10.19889571.3023.513.0WATER BASED11.10.19889571.3019.09.6WATER BASED11.10.19889571.3018.513.4WATER BASED11.10.19889571.3023.513.0WATER BASED11.10.19889571.3023.513.0WATER BASED19.10.19889571.3024.013.4WATER BASED19.10.198810261.4232.010.6OIL BASED19.10.198813361.5230.010.1OIL BASED19.10.198814841.5242.09.6OIL BASED19.10.198816951.5254.016.3OIL BASED24.10.198819451.5259.514.9OIL BASED24.10.198820501.5457.514.9OIL BASED24.10.198821451.5459.014.9OIL BASED24.10.198823161.5563.017.3OIL BASED24.10.198833411.5644.510.1WATER BASED11.11.198834271.5644.010.6WATER BASED11.11.198834956.0145.510.6WATER BASED17.11.198835671.5644.510.6WATER BASED17.11.198836291.5844.010.6WATER BASED17.11.198836701.5843.510.1WATER BASED17.11.198837091.5844.510.1WATER BASED17.11.198837131.5845.510.6WATER BASED17.11.198837161.5845.010.6WATER BASED17.11.198837171.5845.011.5WATER BASED21.11.198837191.5844.512.0WATER BASED21.11.198837201.5842.512.0WATER BASED21.11.198837211.5841.09.6WATER BASED22.11.198837211.5842.011.5WATER BASED22.11.198837211.5842.011.5WATER BASED24.11.198837211.5846.011.5WATER BASED25.11.198837211.5822.024.0WATER BASED28.11.198837230.919.66.0WATER BASED28.11.198837510.929.68.0OIL BASED28.11.198837650.9310.89.0OIL BASED30.11.198837810.9416.02.9WATER BASED13.12.198837810.9520.53.8WATER BASED16.12.198837810.9520.53.4WATER BASED16.12.198837810.9420.03.4WATER BASED19.12.198837810.9619.02.9WATER BASED19.12.198837810.9522.03.8WATER BASED21.12.198837810.9624.03.6WATER BASED21.12.198837810.9622.03.4WATER BASED21.12.198837880.949.68.0OIL BASED30.11.198837880.9410.87.0OIL BASED01.12.198837880.9511.08.0OIL BASED02.12.198837881.4037.55.3WATER BASED06.12.198839001.4247.55.3WATER BASED09.12.198839001.4247.05.8WATER BASED09.12.198839001.4039.55.3WATER BASED13.12.198839000.0018.02.9WATER BASED13.12.198839000.9418.52.4WATER BASED13.12.198839001.4045.05.8WATER BASED06.12.198839001.4140.04.8WATER BASED07.12.198839000.9513.53.4WATER BASED13.12.1988