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North Sea oil

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   North Sea Oil Platforms
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   North Sea Oil Platforms

   North Sea oil refers to oil and natural gas ( hydrocarbons) produced
   from oil reservoirs beneath the North Sea.

History

   North Sea oil was discovered in the early 1960s, with the first North
   Sea oil coming on line in 1971 and being piped ashore at Teesside,
   England, from 1975, but the fields were not intensively exploited until
   rising oil prices in the 1980s made exploitation economically feasible.
   Inaccessibility and dangerous conditions offshore require complex and
   expensive production methods.

   In reality, oil seeps had been known from coal beds on either side of
   the North Sea, but only a limited amount of development had occurred (
   Eakring oil field, Nottinghamshire, England; Edinburgh Oil Shales
   (which seem unrelated to later discoveries); and small discoveries in
   the Netherlands and Northern Germany). A "demonstration well" was sunk
   in 1938 in association with the "World Petroleum Congress" at The
   Hague. After the Second World War a small number of onshore gas and oil
   fields were found in In 1959, an academic well drilled at Ten Boer near
   Groningen, Netherlands was deepened and discovered a significant gas
   deposit. Appraisal and development wells over the next few years
   brought the realisation in 1963 that the Groningen field was not just
   "economic", nor even "big", or "large", or "giant", but was an
   "elephant" field of huge potential. Given that, extending exploration
   into adjacent areas was a "no-brain" decision.

   The exploration of the North Sea has been a story of continually
   pushing the edges of the technology of exploitation (in terms of what
   can be produced) and later the technologies of discovery and evaluation
   ( 2-D seismic, followed by 3-D and 4-D seismic; sub-salt seismic;
   immersive display and analysis suites and supercomputing to handle the
   flood of computation required).

Licensing

   There are five countries with North Sea Production. All operate a tax
   and Royalty licencing regime. The respective sectors are divided by
   median lines agreed in the late 1960s:
     * United Kingdom - licences are administered by the DTI ( Department
       of Trade and Industry- Website). The UKCS is divided into quadrants
       of 1 degree latitude and one degree longitude. Each quadrant is
       divided into 30 blocks measuring 10 minutes of latitude and 12
       minutes of longitude. Some blocks are divided further into part
       blocks where some areas are relinquished by previous licensees. For
       example block 13/24a is located in quad 13 and is the 24th block
       and is the a part block of this block. The UK government has
       traditionally issued licences via periodic (now annual) licensing
       rounds. Blocks are awarded on the basis of the work programme bid
       by the participants. The UK DTI has been very active in attracting
       new entrants to the UKCS via Promote licencing rounds (less
       demanding terms) and the fallow acarage initiative where non-active
       licences have had to be relinquished.
     * Norway - licences are administered by the NPD (Norwegian Petroleum
       Directorate Website in English ). The NCS is also divided into
       quads of 1 degree by 1 degree. Norwegian licence blocks are larger
       than British blocks, being 15 minutes of latitude by 20 minutes of
       longitude (12 blocks in a quad). Like Britain there are numerous
       part blocks formed by relicensing relinquished acreage.
     * Denmark - The Danish sector is administered by the Danish Energy
       Authority ( website in English). The Danes also divide their sector
       of the North Sea into 1 degree by 1 degree quadrants, their blocks
       however are 10 minutes latitude by 15 minutes longitude. Part
       blocks exist where partial relinquishments have taken place.
     * Germany - Germany and the Netherlands share a quadrant and block
       grid - quadrants are given letters rather than numbers. The blocks
       are 10 minutes latitude by 20 minutes longitude. Germany has the
       smallest sector in the North Sea.
     * Netherlands - The Dutch sector is located in the Southern Gas Basin
       and shares a grid pattern with Germany.

Reserves and production

   The North Sea contains the majority of Europe's oil reserves and is one
   of the largest non- OPEC producing regions in the world. While most
   reserves lie beneath waters belonging to the United Kingdom and Norway,
   some fields belong to Denmark, the Netherlands, and Germany.

   Most oil companies have investments in the North Sea. Peaking in 1999,
   production of North Sea oil was nearly 6 million barrels (950,000 m³)
   per day. Natural gas production was nearly 10 trillion cubic feet
   (280,000,000 m³) in 2001 and continues to increase.

   Brent crude (one of the earliest crude oils produced in the North Sea)
   is still used today as a standard reference for pricing oil.

   North Sea oil production fell ten percent (230,000 barrels) in 2004,
   and fell an additional 12.8% in 2005. This was the largest decrease of
   any other oil exporting nation in the world, and has led to Britain
   becoming a net importer of crude for the first time in decades, as
   recognized by the energy policy of the United Kingdom. . The production
   is expected to fall to one-third of its peak by 2020.

List of areas ("plays")

   A play is a collection of fields or structures with common features of
   source rock, thermal history, trap style and structure that make
   lessons from the discovery and development of one field on a play
   closely applicable to other similar structures. In stratigraphic order:

Devonian

     * Devonian Old Red Sandstone - see Buchan oil field

Carboniferous and Permian

     * Sub-Zechstein Gas - Gas fields sourced from the Carboniferous Coal
       Measures and reservoired in the Permian Rotliegend sandstone or
       Carboniferous sandstones in the Northern part of the Southern Gas
       basin. Zechstein dolomite reservoirs alos exist (e.g. Auk oilfield)
       . Seals are from Zechstein (also of Permian age) halite beds.
       Structures are mostly due to rifting in the pre-salt section.
       Example field - the discovery for the entire province at Groningen,
       Netherlands.

Triassic

   The Triassic play is located in the Central North Sea. The reservoir is
   composed of fluvial and lacustrine sandstones of the Skaggerak
   formation. Fields with Triassic reservoirs include J-Block (Judy, Jade,
   Joshephine) and Marnock

   Triassic reservoirs are also important in the East Irish Sea (Morecambe
   gas field, Sherwood Sandtsone) and Southern North Sea (Hewett gasfield
   complex - Bunter sandstone)

Middle Jurassic

   Northern North Sea tilted fault blocks; Brent Series deltaic sands of
   Bathonian age. In 1971 the Shell/ Esso joint venture drilled a poorly
   resolved structure in block 211 and found a classical prograding delta
   sand sequence (the Brent Sands overlain by a good source rock (the
   Kimmeridge Clay Formation, broke up into tilted fault blocks due to
   crustal extension, and the whole sealed by the lateral equivalent of
   the Chalk, the muddy Shetland Group. Several billion barrels of oil
   later, the Brent Field is being depressurised in the mid 2000s with
   shutdown looming on the horizon. Economically, this is the major play
   in the North Sea.

Upper Jurassic

     * Upper Jurassic Central North Sea, Fulmar Play - The Oxfordian Age
       Fulmar sandstone is a shallow marine unit present in the southern
       part of the Central Graben. It is also present in the Norwegian
       sector where it is called the Ula formation. This reservoir is very
       good quality with high porosities which can be preserved under deep
       (6000m) burial in high pressure high temperature (HPHT) fields such
       as Elgin, Franklin and Shearwater.
     * Upper Jurassic Turbidites - These Kimmeridgian/Volgian sandstone
       reservoirs are found in the Outer Moray Firth. The Buzzard Field,
       the largest discovery in recent years has an Ettrick formation
       turbidite reservoir.
     * Fanglomerates against faults. In the late 1980s seismic along some
       of the major "bounding faults" of the main basins of the North Sea
       revealed wedges of sediment which evidently piled up while the
       faults were still moving ( syndepositional faulting). Magnus,
       Tiffany, Toni and Thelma follow this play, with many smaller
       developments being developed along-strike since as sub-sea tie-back
       technology develops

Lower Cretaceous

   The Lower Cretacous play developed in the 1980s and 1990s. The
   reservoir rocks are Aptian / Albian turbidites. Most discoveries are
   stratigraphic traps . Examples include the Britania gas field and the
   Blake oil field

Upper Cretaceous

   Chalk oil - The first major oil discovery was in 1969 by Phillips in
   the Ekofisk field of the Central North Sea (56°30'N 3°10'E). Source is
   Kimmeridge Clay Formation. Oil and gas generated early after deposition
   invaded the Cretaceous Chalk sediments and displaced the water
   necessary for compactional diagenesis (with later consequences).
   Structures are broad anticlines cored either by salt diapirs or
   Pre-Cretaceous Horsts.

Palaeocene

   Central North Sea Tertiary turbidite sand fans - the Forties field
   (57°45'N 01°E) targeted a series of sand fans in mudstone surrounds and
   capped by Palaeocene Basalts. Source was Kimmeridge Clay Formation
   again. The Forties was discovered the year after Ekofisk, following
   several years of frustration in failing to adequately resolve these
   structures and find a major field.
     * Over-salt Sands. In the Central North Sea a large number of salt
       domes could early be seen to penetrate from the Zechstein up into
       the Tertiary cover rocks, but without adequate seismic they weren't
       considered good targets for development. Better seismic allows the
       development of numerous small fields around or above these
       structures. Individual fields are mostly small, but can be
       accommodated by tie-ing the fields back to existing facilities.
       Tie-in pipelines and control umbilicals of over 10 km are not
       unknown, despite serious technical difficulties (such as plugging
       of lines with methane hydrates or the rock stresses associated with
       piercement diapirs.)

List of fields

   South to north.

Netherlands

     *
          + Onshore
               o Rijswijk oil field - An Oilfield with a Lower Cretaceous
                 reservoir
               o Schoonebeek - largest onshore oilfield in Western Europe
               o Groningen gas field - huge gas discovery
          + Offshore (serviced from The Hague
               o Zuidwal
               o Ameland - (whether this will be developed onshore of
                 offshore is an open question)
               o Many fields in Quadrantrs P, Q, K, L, some in blocks E, F

United Kingdom

   Reference DTI Brown book
     *
          + Onshore
               o Wytch Farm - BP's largest onshore development
               o Singleton, West Sussex - beautifully situated across the
                 valley from Goodwood Racecourse
               o (several other prospects along strike on the South Downs)
               o East Midlands oilfield, centred on Eakring,
                 Nottinghamshire, and extending up to Eskdale, North
                 Yorkshire and the Pickering / Kirkby Misperton structure
                 under Ryedale.
          + Offshore (Southern North Sea) (serviced from Lowestoft, Monkey
            Town, Yarmouth and near Skegness)
               o Hewett - Triassic, operated by Tullow oil
               o Dotty - Triassic
               o Leman - Rotliegend
               o Vulcan - Rotliegend, operated by ConocoPhillips
               o Indefatigable - Rotliegend
               o Viking - Rotliegend - operated by ConocoPhillips
               o Audrey - Rotliegend - operated by ConocoPhillips
               o Ann - Rotliegend - operated by ConocoPhillips
               o Amethyst -Rotliegend -operated by BP
               o West Sole gasfield -Rotliegend
               o Rough gasfield - used for Natural gas storage
               o Cleeton gasfield - Rotliegend
               o Ravenspurn gasfield - Rotliegend
               o Caister gasfield - Carboniferous sandstone, - operated by
                 ConocoPhillips
               o Murdoch gasfield- Carboniferous sandstone, - operated by
                 ConocoPhillips
               o Gordon gasfield - Triassic
               o Forbes gasfield - Triassic
               o Esmond gasfield - Triassic
          + Offshore Irish Sea Serviced from Liverpool, Blackpool and
            Morecambe
               o Douglas gas field - Triassic, operated by BHP
               o Lennox gas field - Triassic, operated by BHP
               o Hamilton gas field - Triassic, operated by BHP
               o Morecambe gas field - Triassic, Operated by Centrica
               o Millom gasfield - Triassic, operated by Burlington
                 Resources
          + Offshore (Central North Sea) (serviced from Aberdeen
               o Argyll oilfield - Rotliegend / Zechstein
               o Auk oilfield - Rotliegend / Zechstein, Operated by Shell
                 Oil
               o Clyde oilfield - Fulmar sandstone operated by Talisman
                 Energy
               o Fulmar oilfield - Fulmar sandstone, Operated by Shell Oil
               o J-Block gasfield - Triassic, Chalk and Palaeocene,
                 operated by ConocoPhillips
               o Elgin and Franklin gasfields - Fulmar sandtone and Middle
                 Jurassic, operated by Total S.A.
               o Shearwater Gasfield - Fulmar - operated by Shell oil
               o Erskine gasfield -Middle Jurassic sandstone - operated by
                 Chevron
               o Gannet oilfield (A, B, C, D, E, and F) - Paleocene and
                 Jurassic - operated by Shell
               o Scoter oilfield -operated by Shell
               o Pierce oilfield - Paleocene (non-horizontal Oil-Water
                 Contact), Operated by Shell Oil
               o ETAP gas field comaplex includes Marnock, Machar, Monan
                 and Mirren fields, Operated by BP
               o Arbroath oilfield - Plaeocene, Forties Sandstone,
                 operated by Talisman Energy
               o Blane oil field - Paleocene, Forties Sandstone, operated
                 by Talisman Energy
               o Montrose oilfield - Paleocene, Forties Sandstone,
                 operated by Talisman Energy
               o Lomond gasfield - Palaeocene, Forties Sandstone operated
                 by BP
               o Everest gasfield - Palaeocene, Forties Sandstone operated
                 by BP
               o Armada gasfields - Palaeocene and Jurassic Fulmar,
                 operated by BG Group
               o Kittiwake oilfield -operated by Shell
               o Nelson oilfield - Palaeocene, Forties Sandstone, Operated
                 by Shell Oil
               o Forties oilfield - Palaeocene, Forties Sandstone operated
                 by Apache Corp.
               o Brittania gasfield - Lower Cretaceous, Operated by
                 ConocoPhillips and Chevron
               o Alba oilfield - Eocene operated by Chevron
               o Buchan oil field - Devonian Sandstone - Operated by
                 Talisman Energy
               o Ettrick oilfield - Upper Jurassic
               o Buzzard oilfield - Upper Jurassic operated by Encana,
                 largest discovery in last 10 years
               o Andrew oilfield - Palaeocene
               o Moira oilfield - Palaeocene
               o Maureen oilfield - Palaeocene (abandoned, platform
                 removed was operated by Phillips Petroleum)
               o Cyrus oilfield - Palaeocene
               o Balmoral oilfield - Palaeocene
               o Gryphon oilfield- Eocene Operated by Maersk
               o Harding oilfield - Eocene Operated by BP
               o Tiffany oilfield - Upper Jurassic
               o Toni oilfield - Upper Jurassic (subsea tie back to
                 Tiffany)
               o Thelma oilfield - Upper Jurassic (subsea tie back to
                 Tiffany)
               o Sycamore oilfield - Upper Jurassic (subsea tie back to
                 Tiffany and Brae)
               o Brae oilfield Upper Jurassic (several satellite
                 accumulations) operated by Marathon Oil
               o Miller oilfield
          + Offshore (Moray Firth) (Serviced from Aberdeen)
               o Beatrice oilfield- Upper Jurassic operated by Talisman
                 Energy
               o Unnamed, yet, Senergy
               o Claymore oilfield - Upper Jurassic operated by Talisman
                 Energy
               o Piper oilfield - Upper Jurassic operated by Talisman
                 Energy(produced from Piper Bravo platform after loss of
                 Piper Alpha
               o Tartan oilfield - Upper Jurassic operated by Talisman
                 Energy
               o Scott oilfield - Upper Jurassic operated by Talisman
                 Energy
               o Ross oilfield - Upper Jurassic (small development by
                 Talisman Energy; within sight of Peterhead)
               o Blake oilfield -Lower Cretaceous, operated by BG Group

     *
          + Offshore (Northern North Sea) (serviced from Aberdeen)
               o Beryl oilfield upper Jurassic operated by ExxonMobil
                 (with offshoots to Linhe, Ness...)
               o Bressay oilfield
               o Emerald oilfield
               o Strathspey oilfield (decommissioned? subsea tie-back to
                 Ninian Central)
               o Columba oilfield (extended-reach drilling from Ninian
                 platforms)
               o Ninian oilfield (3 platforms, including the dreaded "one
                 legged, fire-breathing giant from Nigg", if you believe
                 in Scotland's answer to Nostradamus, the Seer of Brathan)
               o Lyell oilfield
               o Heather oilfield Middle Jurassic operated by DNO
               o Brent oilfield Middle Jurassic operated by Shell (4 main
                 platforms, plus the Brent Spar fiasco.)
               o Dunlin oilfield Middle Jurassic operated by Shell
               o Hutton oilfield (produced from the innovative Tension-leg
                 platform; decommissioned 2001 was operated by Conoco)
               o Cormorant oilfield Middle Jurassic operated by Shell,
                 (production started sweet, but has turned slightly sour
                 over the decades. which is very interesting. And
                 worrying.)
               o Tern oilfield Operated by Shell Oil (The 'Black Pig' to
                 its friends. Captain Pugwash reference.)
               o Eider oilfield Middle Jurassic operated by Shell
               o Murchison oilfield Straddles the Norwegian median line.
               o Don oilfield
               o Magnus oilfield Big BP rust bucket. Crane is good at
                 dropping logging units.
          + Offshore (West of Shetland) (Serviced from Aberdeen)
               o Clair oilfield A large, but high viscosity field.
               o Schiehallion oilfield
               o Foinaven oilfield

Germany

     *
          + Onshore
               o Wietze "near Hanover", discovered in 1859!
               o The Schoenebeek field of the Netherlands extends across
                 the border.
          + No commercial developments offshore

Denmark

     *
          + Nothing onshore
          + Offshore developments abundant. (There is a strange kink in
            the German-Danish median line that begs for explanation.)
            Serviced from Esbjerg, most fields are operated by DONG Energy
               o Nils oilfiled
               o Skjold oilfield
               o Gorm oil and gasfield - Chalk reservoir
               o Roar oilfield - Chalk reservoir
               o Harald oilfield - Chalk reservoir
               o Dan oil and gas field - Chalk reservoir
               o Kraka oilfield - Chalk reservoir
               o Halfdan oil and gas field - Chalk reservoir
               o Tyra oil and gas field - Chalk reservoir
               o Tyra Southeast oil field
               o Svend oil field
               o Valdemar oilfield
               o Lulita gas field
               o Regnar oil field
               o Rolf oil field
               o Dagmar oil field
               o Siri oil field
               o Nini oil field
               o Cecilie oil field
               o South Arne oil and gas field

Norway

   Reference - Norwegian Petroleum Directorate fact pages on oil fields
     *
          + Onshore developments -none ( Oslo Graben oil seeps??).
          + Offshore developments. Serviced from Bergen, Stavanger,
            Kristiansund
          + Central North Sea
               o Hod oilfield - Chalk reservoir , Operated by BP
               o Valhall oilfield - Chalk reservoir, operated by BP
               o Eldfisk - Chalk reservoir, operated by ConocoPhillips
               o Ekofisk - Chalk reservoir, operated by ConocoPhillips
               o Embla oilfield - Devonian / Permian Reservoir, operated
                 by ConocoPhillips
               o Tor oilfield - Chalk reservoir, operated by
                 ConocoPhillips
               o Albuskjell oilfield - decommissioned
               o Ula oilfield- Jurassic sandstone reservoir, Operated by
                 BP
               o Gyda oilfield - Jurassic sandstone reservoir, Operated by
                 Talisman Energy
               o Cod oilfield- decommissioned
          + Northern North Sea
               o Sleipner oilfield, Jurassic and Palaeocene reservoirs,
                 operated by Statoil
               o Brisling oilfield
               o Bream oilfield
               o Balder oilfield - Palaeocene/Eocene, operated by
                 ExxonMobil
               o Frigg gas field Large Eocene reservoir gas field,
               o Hild gas field
               o Heimdal gasfield - Palaeocene reservoir, Operated by
                 Norsk Hydro
               o Oseberg oilfield Middle Jurassic sandstone reservoir
                 operated by Norsk Hydro (the only oil rig with a log fire
                 in the accommodation ?? Mad Noggins)
               o Brage oil filed, operated by Norsk Hydro
               o Troll Largest gas field in North Sea operated by Statoil.
               o Gullfaks oil field, Middle Jurassic reservoir operated by
                 Statoil
               o Statfjord along strike from Brent, but structurally
                 deeper, partially in UK sector. Operated by Statoil
               o Snorre oilfield, Middle Jurassic reservoir operated by
                 Statoil
               o Murchison oil field (part of; produced through UK)
                 Operated by CNR resources
               o Agat
          + Haltenbank; numerous developments in production, Heidrun
            gasfied, Draugen oil field, Ormen Lange etc.

Associated, but not strictly North Sea

     * Ireland (includes Northern Ireland)
          + Onshore
               o Larne; tiny prospect under the basalts.
               o Other small prospects, and significant coal-bed methane.
          + Offshore
               o Kinsale Head; gas development off the coast of Cork
               o Corrib Gas Field; about to start production to a
                 controversial onshore processing plant
               o Inishbeg; prospect announced to the NW of Donegal. Due to
                 be drilled August 2006.
     * Faroes
          + Offshore
               o Various blocks licensed for exploration, several
                 discoveries not yet developed.
     * Iceland
          + Offshore
               o Nothing published, but the idea is not inconceivable on
                 the ridges extending towards Iceland from the Faroes and
                 the East Greenland Coast.
     * East Greenland
          + Onshore
               o No prospects reported, though sediments analogous to the
                 Mesozoic and Caenozoic deposits of the North Sea are
                 known, so there is appreciable interest. Development
                 would be formidably difficult, technically, logistically
                 and politically.
          + Offshore
               o A recent conference on hydrocarbon prospects in arctic
                 Russia (Geological Society, London; February 2006) had
                 several speakers mention major gas prospectivity on the
                 East Greenland coast, but they cited no sources. A
                 conference volume is due towards the end of 2006, which
                 may elaborate.
     * Barents Sea
          + Onshore
               o No significant prospects or potential.
          + Offshore
               o Significant exploration, appraisal and development. Major
                 discoveries the Snøhvit gasfield, operated by Statoil in
                 Norwegian sector and the Stokhmanovskoye gasfield planned
                 to be operated by Gazprom in Russian sector.

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