25/11-21 A
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General information
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Wellbore history
GeneralWell 25/11-21 S was drilled on the Grane Field. The primary objectives of well 25/11-21 S were to calibrate the depth conversion model with reference to top and base of the Grane reservoir and the oil-water contact, and to investigate horizontal and vertical reservoir barriers and reservoir heterogeneities. The secondary objectives of well 25/11-21 S were to obtain reservoir and fluid data and to investigate uncontaminated initial water saturation values in the oil zone. The well location was selected to allow building up hole angle for later drilling of a horizontal section (25/11-21 A) at the required depth and coordinates and at the same time to provide an accurate seismic tie, i.e. an area with minimal compaction effects and away from faults, in an area where there are indications of a thick sand on the seismic data.Sidetrack well 25/11 -21 A was drilled to obtain 600 m to 900 m of horizontal reservoir information. The objectives were to appraise the reservoir in terms of reservoir quality and to confirm the structural top and base reservoir maps; to obtain lateral velocity information for calibration of the depth conversion model; to identify possible reservoir heterogeneities indicated on seismic; and finally to perform an extended test production in the horizontal section of the well.Operations and resultsAppraisal well 25/11-21 S was spudded with the semi-submersible installation "Treasure Saga" on 23 October 1995 and drilled to TD at 1957 m (1863.5 m TVD MSL) in Late Cretaceous Hod Formation. The well was drilled with seawater and hi-vis bentonite sweeps down to 1270 m and with KCl / Polymer mud from 1270 m to TD.Heimdal Formation sand was penetrated at 1788 m (1711.5 m TVD MSL). A reservoir thickness of 88 m (79.5 m TVD) was defined, giving a net pay of 57.9 m. The pressure data from the Heimdal Formation indicates a 0.4 bar pressure difference to well 25/11-18 T2 and 1.7 bar difference to well 25/11-15 based on HP gauge measurements. The oil-water contact (FWL) in the well was found at 1765 m TVD MSL, i.e. more or less the same as in well 25/11-18-T2 and 2.5 meters deeper than in well 25/11-15. No free gas cap was found.& Both the top and base reservoir seismic reflectors and the depth conversion model were proven to be correct in the area, and the reservoir characteristics as found in wells 25/11-15 and 25/11-18 T2 were confirmed. A walk away VSP and walk away AVO VSP were acquired in well 25/11-21 S yielding good qualify high resolution data. The entire reservoir section was cored from 1778 m to 1880.5 m. The wire line logging programme was followed successfully except for an operational failure of the GHMT-tool. MDT Oil samples were taken at 1790 m (1713.09 m TVD MSL), 1796 m (1718.6 m TVD MSL), 1813 m (1734 m TVD MSL), 1828 m (1747.4 m TVD MSL), 1830 m (1749.4 m TVD MSL), 1837.5 m (1756.2 m TVD MSL), and 1845 m (1763 m TVD MSL). MDT water samples were taken at 1850 m (1767.5 m TVD MSL), 1855 m (1772.1 m TVD MSL), 1861.5 m (1777.9 m TVD MSL), and 1874 m (1789.2 m TVD MSL). Well 25/11-21 S was plugged back to the 13 3/8" casing shoe and suspended as an oil appraisal on 14 November 1995.The well was re-entered with the semi-submersible installation "Treasure Saga" on 15 May 1996. Well 25/11-21 A was kicked of at 1262 m and drilled down to 1973 m in the Heimdal Formation. The hole was drilled with a too low angle to reach the 10 3/4" casing point within acceptable tolerances. Thus the hole was plugged back from 1973 m, and a technical sidetrack, 25/11-21 A T2, was drilled from 1783 m, continued inclined to horizontal, and drilled to TD at 3006 m (1801.4 m TVD MSL) in the Late Paleocene Lista Formation. The sidetrack was drilled water based with KCl / Polymer mud from kick off to 2448 m and with CaCO3 / NaCl mud from 2448 m to TD. In well 25/11-21 A T2, the top of the Heimdal Formation sand was penetrated at 1837.5 m (1705.7 m TVD MSL). At a depth of 1749 m TVD MSL a 820 m horizontal section was drilled. Here a 3 m thick calcite cemented layer, corresponding to an intra reservoir reflector, was penetrated at 2514.5 m. A deformed shaly zone, penetrated at 2627.5 - 2652 was probably due to drilling very close to top reservoir in this area. The Base of the Heimdal Formation was reached at 1765.7 m TVD MSL. The reservoir quality of the Heimdal sand is good, showing average porosities of 33%, and a general porosity increase from the SW towards the NE along the well path. The net to gross ratio of the Heimdal Formation is 0.98, due to the penetrated cemented and shaly zones. The oil-water contact (FWL) was found at 1765.6 m TVD MSL, confirming the results from the wells 25/11-21 S and 25/11-18 T2. The average oil saturation within the oil zone is 90%. Only MWD logs were obtained in the sidetrack. No wire line logs were run; consequently no fluid samples were taken on wire line. No conventional or sidewall cores were cut in the sidetrack. After an extended well test well 25/11-21 A was permanently abandoned as an oil appraisal on 1 October 1996TestingAn extended well test (25/11-T-21 A) from the interval 2048 m to 2606 m (1904.2 +/- 0.2 m TVD) in the horizontal section of well 25/11-21 A was carried out during the summer of 1996. The produced oil was stored on the storage tanker "Hellespoint Energy" and the associated gas was flared off from the "Treasure Saga" burner boom. After installation of sand screens and external casing packers, the screen washing and the setting of screen packer were halted for about a month due to a NOPEF strike. During this period the formation around the well bore received approximately 800m3 of drilling mud, kill pills and completion fluids. After the strike the well was put on production. At high production rates (up to 3000 Sm3/day) and especially after the well had started to produce water loss of pressure was observed. The reason for this was probably plugging by particles from the completion fluid. With careful increases in the production rate and with production rates between 800 to 1000 Sm3 the well was flowing with a Productivity Index of approximately 150 Sm3/d/bar at the end of the extended well test period. The static bottom hole pressure was 170 bar and the maximum temperature measured during the test was 81.4 deg C. An extensive fluid sampling programme was carried out. Based on single stage flash analyses of bottom hole samples to 1 atmosphere and 15 deg C the oil density was 0.94 g/cm3, and the corresponding GOR was 14.7 Sm3/Sm3. Gas gravity of separator samples was 0.632 (air = 1). -
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]1270.003000.00 -
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 availableDST0.000.0001.05.1996 - 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 typeLINER10 3/42034.012 1/42034.00.00LOTOPEN HOLE3006.09 1/23006.00.00LOT -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]LWD CLLS - SONIC20002970MWD DPR - GR RES12401550MWD MDL/MNP - NEU DEN20202990MWD RNT - NAVIGATOR15503000 -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit1557207967969059259449559781000102810741087110211151221123017361736174517571838262826302633264026452652271027132968 -
Composite logs
Composite logs Document nameDocument formatDocument size [MB]pdf0.42 -
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]pdf7.32 -
Drilling mud
Drilling mud Depth MD [m]Mud weight [g/cm3]Visc. [mPa.s]Yield point [Pa]Mud typeDate measured10301.30WATER BASED12621.3724.0WATER BASED14241.3721.0WATER BASED17151.3721.0WATER BASED18411.3726.0WATER BASED18941.3722.0WATER BASED19361.3724.0WATER BASED19731.3724.0WATER BASED20241.3726.0WATER BASED24481.2927.0WATER BASED27601.20WATER BASED29981.3029.0WATER BASED30061.3029.0WATER BASED -
Palynological slides at the Norwegian Offshore Directorate
Palynological slides at the Norwegian Offshore Directorate Sample depthDepth unitSample typeLaboratory1730.0[m]DCRRI1735.0[m]DCRRI1737.0[m]DCRRI1740.0[m]DCRRI1742.0[m]DCRRI1745.0[m]DCRRI1752.0[m]DCRRI1760.0[m]DCRRI1767.0[m]DCRRI1775.0[m]DCRRI1782.0[m]DCRRI1790.0[m]DCRRI1797.0[m]DCRRI1805.0[m]DCRRI1812.0[m]DCRRI1827.0[m]DCRRI1832.0[m]DCRRI1837.0[m]DCRRI2650.0[m]DCRRI2652.0[m]DCRRI2655.0[m]DCRRI2710.0[m]DCRRI2715.0[m]DCRRI2982.0[m]DCRRI