25/8-12 A
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General information
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Wellbore history
GeneralWell 25/8-12 A is a sidetrack from well 25/8-12 S, which encountered oil in Lower Jurassic, Upper Statfjord Formation sandstones. It was drilled to appraise the southern extension of the 25/8-11 Ringhorn discovery. In the Ringhorn structure, the BCU is also the base of the chalk and represents the overall top of the Lower Jurassic reservoir interval. The primary objective for well 25/8-12 A was Lower Statfjord Formation sandstones, in an eroded horst, fault block.Operations and resultsAppraisal well 25/8-12 A was drilled with the semi-submersible installation "Mærsk Jutlander". It was kicked of from 1014 m in the 8 1/2" section of 25/8-12 S on June 9, 1999 and drilled to TD at 2156 m in the Triassic Smith Bank Formation. The wellbore was drilled with oil based "Environment" mud. Top Statfjord Formation was found at 1945.7 m (1863.1 m TVD SS). Oil was encountered in Lower Statfjord Formation sandstones, as prognosed. Pressures and fluid sampling was undertaken with Schlumberger's Modular Dynamic Tester (MDT). Pressure measurements gave an oil gradient of 0.0719 bars/m (0.318 psi/ft), consistent with the oil gradient in the original 25/8-12 S wellbore (0.0749 bars/m) and in the 25/8-11 well (0.0741 bars/m). The oil and water gradients intersect to give an OWC at 1917.5 m TVD SS (2005 m MD RKB), in agreement with the Free Water Level defined in the 25/8-11. The deepest sands in the wellbore, the water bearing sands below 1970 m TVD SS, appear to record a separate, higher reservoir gradient. Four oil samples were collected in 450 cc MDT chambers at 1975 m, within the main Jurassic sand reservoir. No draw down was seen during the sampling. Temperature (measured, not static) ranged from 78.4 deg C to 79.3 deg C during the sampling. In addition to the 450 cc chambers, a single one-gallon chamber was filled with oil at the same depth. A one-gallon water sample was obtained at 2008.2 m. One core was cut in the interval 1951 - 1988.5 in the Statfjord Formation. Well 25/8-12 A was permanently abandoned on June 19 1999 as an oil appraisal well.TestingNo drill stem test was performed -
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]1600.002156.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom11951.01988.5[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]37.5Cores 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 typeLaboratory1948.0[m]DCRRI1951.0[m]DCRRI1958.0[m]DCRRI2002.0[m]DCRRI2014.0[m]DCRRI2020.0[m]DCRRI2032.0[m]DCRRI -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit15056067272872895411551166174817481815187519151921194620282028 -
Composite logs
Composite logs Document nameDocument formatDocument size [MB]pdf0.39 -
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].pdf2.04.pdf76.15 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]AIT-H DSI IPLT GR9862160MDT GR19482064MWD - DIR153213MWD - EWR4 DGR2132156VSP3002150 -
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 typeCONDUCTOR30211.036213.00.00LOTINTERM.9 5/8990.012 1/4990.00.00LOTOPEN HOLE2156.08 1/22156.01.62LOT -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured8251.3230.0OIL (ENVIRON)8601.3330.0OIL (ENVIRON)13401.3230.0OIL (ENVIRON)21561.3227.0OIL (ENVIRON) -
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]pdf0.20