Alwyn North Triassic main gas-condensate; drilling deeper promotes production

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doi: 10.1144/1354-079302-550
Authors:Harker, S. D.; Richardson, G.; Sides, L. E.; Cooper, R.
Author Affiliations:Primary:
TotalFinaElf Exploration, Aberdeen, United Kingdom
Volume Title:Petroleum Geoscience
Source:Petroleum Geoscience, 9(2), p.133-143. Publisher: Geological Society Publishing House, London, United Kingdom. ISSN: 1354-0793
Publication Date:2003
Note:In English. 10 refs.; illus.
Summary:Production of oil and gas in the Alwyn North Field, UKCS, commenced in 1987 from Middle Jurassic Brent and Lower Jurassic Statfjord reservoirs. In 1988, a deepened Statfjord producer well (3/9a-N21) detected gas in the underlying Triassic, but testing was not possible at that time. The 3/10b-2 exploration well, drilled in 1992 to the east of the field, tested gas at low rates from a poor quality Triassic reservoir section. In 1995 well 3/9a-N33, a deviated well, was drilled from the Alwyn platform to evaluate the productivity of the deep Triassic. This well penetrated 770 m of the upper Lunde section, which was tested at 1.3×106 m3 per day of gas plus 4400 STB per day of condensate. The Alwyn trap comprises a westerly dipping fault panel structure. Erosion over the crest of the tilted panel and the eastern-facing scarp slope by the Base Cretaceous Unconformity (BCU) truncates the Jurassic section down to the Upper Triassic. Sealing of the Triassic Main accumulation is by uppermost Triassic shales of the overlying Statfjord Formation and by Cretaceous mudrocks onlapping onto the BCU. Hydrocarbon charging of the Triassic upper Lunde sandstones is from mature Late Jurassic Kimmeridge Clay source rocks that are juxtaposed against the reservoir along parts of the eastern frontal fault of the Alwyn panel. The upper Lunde (of Carnian to Rhaetian age) is a low net:gross reservoir section up to 800 m thick. The sediments are of semi-arid fluvial, floodplain and lacustrine origins, with the best reservoirs occurring in fluvial channel sandstones. The Late Triassic comprises four informal zones from A (top seal), through B and C to D reservoirs, above the middle Lunde Shale. The Triassic reservoir fluids are gas-condensate in the B and C units with an intraformational seal at the C-D boundary, beneath which lies volatile oil in the D unit. A total of eight further Triassic production wells were added to the Alwyn North Field by the end of 2001, as the development plan for Triassic Main progressed. These wells contribute in the order of 60% to the Alwyn North daily production.
Sections:Geochemistry
Subsections:Organic geochemistry
Subjects:Clastic rocks; Condensates; Erosion; Faults; Floodplains; Fluvial features; Jurassic; Kimmeridge Clay; Lacustrine environment; Mesozoic; Middle Jurassic; Oil and gas fields; Petroleum; Petroleum engineering; Production; Reservoir properties; Reservoir rocks; Sandstone; Sedimentary rocks; Shale; Source rocks; Statfjord Formation; Traps; Triassic; Upper Jurassic; Atlantic Ocean; North Atlantic; North Sea; Alwyn North Field; Brent Formation
Abstract Numbers:03M/4364
Record ID:2003070076
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
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