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Exploration wellbore: 2/7-26 S

General information

Wellbore history

General

Well 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 results

Appraisal 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-26

Testing

Two 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 available at the NPD

Interval [m]: 579.00 - 4547.60

Cores available at the NPD

Core length [m]: 258.96

Scanned core photos

5480-5487ft	10500-10510ft	10510-10522ft	10522-10534ft	10534-10545ft
14103-14118ft	14118-14133ft	14133-14148ft	14148-14153ft	14417-14432ft
14432-14447ft	14447-14453ft	14457-14472ft	14472-14480ft	14481-14496ft
14496-14511ft	14511-14526ft	14526-14541ft	14541-14545ft	14558-14573ft
14573-14581ft	14586-14592ft	14598-14613ft	14613-14628ft	14628-14635ft
14636-14651ft	14651-14658ft	14660-14675ft	14675-14690ft	14790-14693ft
14696-14711ft	14711-14726ft	14726-14741ft	14741-14743ft	14746-14761ft
14761-14776ft	14776-14791ft	14791-14806ft	14806-14807ft	14807-14822ft
14822-14837ft	14854-14869ft	14869-14884ft	14884-14899ft	14899-14903ft
14903-14918ft	14918-14933ft	14933-14935ft	15312-15327ft	15327-15342ft
15342-15357ft	15357-15372ft	15372-15387ft	15387-15402ft	15402-15403ft
15404-15419ft	15419-15434ft	15434-15449ft	15449-15464ft	15464-15479ft
15479-15494ft	15494-15495ft	15844-15859ft	15859-15874ft	15874-15889ft
15889-15904ft	15904-15907ft

Palynological slides available at the NPD

No palynological slides in this wellbore.

Oil samples available at the NPD

Casing and leak-off tests

Mud

Drill stem test (intervals and pressures)

Drill Stem Test (recovery)

Available logs

Lithostratigraphy

Composite log

No composite log presently available.

Geochemical information available at the NPD

No geochemical data presently available. Regional geochemical studies which include data from this well may however be filed on a different well.

Documents reported by the licencees (period for duty of secrecy expired)

No documents presently available.

Old NPD WDSS reports, NPD papers and other related documents

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