Field operator of the yearEkofisk South – 2/4 VC starts up

Seabox – research project for seabed water treatment

person by Kristin Øye Gjerde, Norwegian Petroleum Museum
Water has been injected into the Ekofisk reservoir through dedicated wells since the 1980s to improve recovery of oil and gas. Injection has taken place both from platforms and subsea.
However, a large and heavy plant is needed to treat the seawater used for such waterflooding. That requires a lot of space and energy, and is thereby expensive.
— Illustration: Seabox
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Seabox concept

seabox
The Seabox logo

Moving the whole seawater treatment plant to the seabed was the solution which occurred to David Pinchin and Helge Lunde in the early 2000s.

Producing from subsea wells and placing parts of the process on the seabed had become increasingly common. So the question was whether the same could be done for treating seawater.

Performing this function at source and with the injection well close at hand, without having to pass via a platform, was an attractive thought – particularly given the volumes involved.

With that in mind, Pinchin and Lunde established the Seabox company in 2004 to develop a complete subsea treatment, processing and injection module.

This project received backing from the Research Council of Norway and several oil companies. That meant long-term tests of the technology could be conducted by the Norwegian Institute for Water Research (Niva) in the Oslo Fjord in 2010 and 2013.[REMOVE]Fotnote: Teknisk Ukeblad, “Seabox”, 16 May 2016.

National Oilwell Varco acquired a stake in Seabox in 2015, and the company secured further support from Norway’s Demo 2000 research programme as well as several oil companies.

The latter included ConocoPhillips, and the aim was to build a prototype in order to qualify the technology for treating water on the seabed.

Seabox. This subsea treatment plant can produce sulphate-free seawater with the aid of microfiltration and membranes.

Seawater must be treated before injection into a sub-surface formation to prevent undesirable bacterial activity and to avoid particles which could block pores in the reservoir.

If barium and strontium are present, for example, untreated seawater can cause chemical reactions in these “soft” metals with oversaturation of salts and minerals in the reservoir water.

That in turn could block the formation pores should pressure and temperature fall, which poses the risk of reducing or losing production.

A reservoir can also “go sour” if sulphate-reducing bacteria are allowed to flourish. That not only increases production costs but reduces the value of the hydrocarbons produced.

Treatment process

The Seabox process uses electricity to produce chlorine from salt water in electrolytic cells. Seawater being treated spends up to two hours in the presence of this chlorine.

That kills the bacteria before the water is exposed to hydroxyl radicals (OH molecules), which ensure that all organic material is killed and dissolved.

 

In practice, this removes all bacteria and most of the particles in the first stage of the process. The water then passes through a microfiltration plant and nano- or RO-membranes.

Everything takes place inside the box, which eliminates emissions or discharges. The treated water is virtually fit to drink.

 

Ekofisk test well

Seabox received one of the most distinguished awards at the Offshore Technology Conference (OTC) in Houston in 2018, as well as a contract with ConocoPhillips.

The latter assignment covered a first unit which would be put into test production on Ekofisk.[REMOVE]Fotnote: Teknisk Ukeblad, “Seabox ble den store vinneren i oljeindustriens ‘Oscar’”, 30 April 2018. At that point, almost NOK 300 million had been devoted to developing the concept.

Åpning av Ekofisk Sør,
Ekofisk 2/4 Z seen from the east. Photo: Kjetil Alsvik/ConocoPhillips

ConocoPhillips made a platform and a well available for the research project, and the Seabox unit was installed on the seabed in August 2018 close to Ekofisk 2/4 Z and the West Linus rig.

In the first instance, treated seawater was conducted up to the rig to have its quality checked. Once it had passed muster, treated seawater began to injected in well Z-02.

This was a former production well which had been converted for injection. The project continued until August 2019, and its results will be significant for future work.[REMOVE]Fotnote: Pionér, no 3, 2018.

Field operator of the yearEkofisk South – 2/4 VC starts up
Published 21. August 2019   •   Updated 12. October 2019
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Ekofisk 2/4 VC

person Norwegian Petroleum Museum
Injection water from subsea installation Ekofisk VC (Victor Charlie) began to be pumped down well VC-03 on 28 September 2018. Well number two came on line just under a week later. 
Kjappe fakta:
  • Plan for development and operation (PDO) was approved by the Ministry of Petroleum and Energy on 7 September 2017.
  • Part of Ekofisk South
  • Installed September 2017
  • On stream September 2018
  • Gets electric power and signals from Ekofisk 2/4 M
  • Also called "Victor Charlie"
— Illustration of Ekofisk 2/4 VC (Victor Charlie). Illustration: ConocoPhillips
© Norsk Oljemuseum

The aim of this facility – an extension to the Ekofisk South project – was to increase waterflooding on the southern flank of the Ekofisk reservoir in order to maintain oil and gas production. 

An amended plan for development and operation (PDO) of Ekofisk South was approved by the Ministry of Petroleum and Energy on 7 September 2017. 

This involved installing a new seabed template with four water injection wells, and represented a continuation of the well-established Ekofisk production strategy based on waterflooding.[REMOVE]Fotnote: https://www.regjeringen.no/no/aktuelt/okt-utvinning-pa-ekofiskfeltet/id2570011/. 

The template was installed in September 2017, with a technical solution similar to that used on the seabed facilities already installed – Ekofisk 2/4 VA and 2/4 VB.[REMOVE]Fotnote: Pionér, no 2, ConocoPhillips, 2018.

In addition to the structure itself, including wellheads and Xmas trees, the installation comprised control modules with umbilicals connected to the existing waterflooding system. 

The 2/4 VC facility receives injection water from Eldfisk 2/7 E, while power and control signals come from Ekofisk 2/4 M. It is run from the Ekofisk 2/4 K control room. 

When fully developed, overall injection capacity for this subsea installation will be 80 000 barrels per day through the four wells. 

The water pipeline and umbilical to 2/4 VB were extended to 2/4 VC. Well operations on the latter began on 24 May 2018 with a view to starting injection before the end of the year. 

Published 15. October 2019   •   Updated 15. October 2019
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Ekofisk 2/4 Z

person Norwegian Petroleum Museum
This installation is a wellhead platform in the Ekofisk Complex.
Kjappe fakta:
  • Wellhead platform
  • Installed summer of 2013, on stream 25 October
  • Also known as Ekofisk Zulu
— Ekofisk 2/4 Z. Photo: ConocoPhillips/Norwegian Petroleum Museum
© Norsk Oljemuseum

This platform rests on a steel jacket built by Dragados at Cadiz in Spain. The module support frame (MSF) and topsides were fabricated by Energomontaz at Gdansk in Poland and completed at Kværner Egersund. 

The topsides were installed in July 2013. Petroleum and energy minister Tord Lien performed the official inauguration of 2/4 Z and the Ekofisk South project on 29 October 2013,13 just four days after the platform came on stream.14 

No control room is provided on 2/4 Z, but it has a local equipment room (LER) which is not permanently manned. The platform is monitored and remotely controlled from the control room on Ekofisk 2/4 J, but can also be run from the operations centre in Tananger.

2013-10 – Historisk dag for Ekofisk og Norge åpning av Ekofisk 2-4 Z – regjeringen-no

Published 1. October 2019   •   Updated 25. October 2019
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Ekofisk 2/4 VB

person by Gunleiv Hadland, Norwegian Petroleum Museum
The 2/4 VB subsea installation began injecting water in May 2013, three kilometres south of the Ekofisk Complex. It formed part of the Ekofisk South project approved by the Storting (parliament) in 2010.
Kjappe fakta:
  • Ekofisk 2/4 VB was a part of the Ekofisk South project
  • Installed 2012
  • Producing May 16. 2013
  • Also called “Victor Bravo”
— Ekofisk 2/4 VB (Victor Bravo) lowered into the sea. Photo: Bob Bartlett/ConocoPhillips
© Norsk Oljemuseum

 So successful had the 2/4 VA facility proved to be that it was copied for 2/4 VB as an eight-well template, also delivered by FMC at Kongsberg.

Similarly, the wells on 2/4 VB were drilled by Maersk Innovator. The well operation department completed installation of the template, manifolds and casing for the eight subsea wells.

Seabed installations carried out by Subsea 7 comprised a five-kilometre pipeline for water from the Eldfisk Complex as well as a diver-installed T piece welded into the existing pipeline from Eldfisk 2/7 E to Ekofisk 2/4 K.

This assignment also covered laying three kilometres of umbilicals combining hydraulic lines and fibreoptic cables from 2/4 VA, so that 2/4 VB could also be remotely operated from land.

Published 23. September 2019   •   Updated 7. February 2020
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What’s in a name

person By Björn Lindberg
Confusion can easily arise over the terms used in connection with Ekofisk, where the Greater Ekofisk Area (GEA) is a collective designation for a cluster of no less than eight fields. The largest of these is Ekofisk itself.
— Older poster showing The Greater Ekofisk area. Illustration: ConocoPhillips/Norwegian Petroleum Museum
© Norsk Oljemuseum
Kjære barn har samme navn, kart
The Greater Ekofisk Area (GEA) and its constituent fields lie primarily lie in PL 018 (red frame). Those with dotted boundaries have ceased production, while those with lilac borders were producing at 29 August 2019. Note that Valhall and Hod in the south-east corner of the map are not part of the GEA.

Primarily located in production licence PL 018, along with Ekofisk, the other seven fields are West Ekofisk, Tor, Eldfisk, Albuskjell, Edda, Cod and Embla. 

Furthermore, six of the eight – with Embla and Cod as the exception – comprise two geological formations. One is known as the Ekofisk formation, with the Tor formation as the other. See the article on sea scurf. 

The graph in figure 2, which presents collective production of oil, gas and condensate over time in million standard cubic metres of oil equivalent (scm oe), shows Ekofisk’s dominant position – both historically and today.

Kjære barn har samme navn, grav
Historical production from the Ekofisk area since the start of output in 1971 until the end of 2018. The base data were acquired from the norskpetroleum.no website on 29 August 2019.

With the exception of four years, overall output from the seven other fields has never achieved the same volume as Ekofisk’s own production. 

The effect of waterflooding on Ekofisk, which got going seriously in 1987, can be clearly seen in the production curve. This rose from less than 10 million scm oe per annum to more than 20 million. 

On 1 July 2019, operator ConocoPhillips submitted a plan for development and operation (PDO) which covered reopening the Tor field (Tor II). 

This will involve the investment of about NOK 6 billion, with a planned production start in late 2020, and is expected to yield an estimated 10 million scm oe. 

Furthermore, the licensees have initiated concept studies for further development of the northern flank of Eldfisk (Eldfisk II). Both subsea solutions and a simple unmanned platform are under consideration.[REMOVE]Fotnote: https://petro.no/nyheter/conocophillips-vurderer-a-bygge-ny-plattform-pa-eldfisk-nord  

Development of the Tommeliten Alpha formation, which has only ranked as a discovery so far, is also being assessed.[REMOVE]Fotnote:  https://petro.no/nyheter/forbereder-mulig-utbygging-tommeliten-alpha  

Published 23. September 2019   •   Updated 9. October 2019
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Sea scurf – the geology of Ekofisk

person By Björn Lindberg
The oil and gas in Ekofisk lies in a chalk reservoir composed of countless tiny shelly fragments derived from coccolithophores – microscopic algae which make calcium carbonate (CaCO3) scales.
— The image was taken using a scanning electron microscope (JEOL JSM-6330F), the colors are therefore artificial. Scale = 1.0 µm. Photo: NEON yes, colored by Richard Bartz
© Norsk Oljemuseum
havets flass
Microscope image from of cookoliths from the Ekofisk reservoir.

Known as coccoliths, these plates are so minute than 30 of them laid side by side would be no wider than a strand of hair. But what they lack in size, they make up for in numbers. 

Their colossal accumulation is helped by the fact that coccolithophores reproduce asexually. When one dies, its coccoliths sinks to the seabed at a rate of about 15 centimetres per day. 

If conditions are right, the scales remain lying and are eventually buried in their billions of billions 

Estimates indicate that coccolithophores globally produce more than 1.5 million tonnes of calcium carbonate per annum – equal to the weight of the Gullfaks C platform, which ranks as the heaviest structure ever moved by humans. 

Three things must be in place for an oil and/or gas field to form – a source rock, a reservoir rock and a cap rock which prevents the petroleum from escaping. 

In the case of Ekofisk, we know quite a bit about how these three components originated. 

Source rock – Draupne

havets flass,
Core sample from a well in the Vikinggrabenen field, with large content of Draupne shale. The Draupne formation is found over large parts of the Norwegian continental shelf. Photo: Norwegian Petroleum Directorate (Fact pages)

The Ekofisk source rock dates from the Jurassic period, 161-145 million years ago, and comprises organically rich black shales known as the Draupne formation. 

In Norse mythology, Draupne was the gold ring worn by the god Odin which formed another seven rings every ninth day – in other words, an endless source of prosperity. 

So the name is appropriate for a formation found over most of the Norwegian continental shelf (NCS), which has put huge volumes of petroleum into most of Norway’s fields – including Ekofisk. 

Cretaceous reservoir rock – Tor formation

The Cretaceous period followed the Jurassic and lasted for 145-66 million years, with the last 10 million of these forming the Campanian and Maastrichtian stages. 

Conditions then were favourable for coccolithophores over much of the southern and central North Sea as well as England, Denmark and France. 

Countless coccoliths were deposited on the seabed. Since the latter was neither flat nor stable, they were moved around by small slips, landslides and/or mud flows which could be activated by earthquakes, before being finally buried by their successors.

havets flass
Chalk cliffs along the French Channel coast (Etretat, Normandi). Photo: ConocoPhillips

Asteroid

The Cretaceous ended in a mass extinction event, when up to 70 per cent of all life on Earth vanished – including the dinosaurs. 

This wipe-out was unleashed by a massive asteroid strike in what is now the Gulf of Mexico, where the Chicxulub crater is about  150 kilometres in diameter and 20 kilometres deep. The asteroid itself may have measured 80 kilometres. 

havets flass,
Bioturbert chalk: Small animals on the seabed have eaten and dug into the chalk layers.

Palaeocene reservoir rock – Ekofisk formation

That impact nevertheless failed to destroy all marine life, and the “sea scurf” continued to rain down in the following Palaeocene period. 

During its first million years, known as the Danian stage, further tens of metres of calcium carbonate were deposited. But changed seabed conditions and a colder climate had an impact. 

The amount of reworking which the material experienced varied and decreased, while the content of silica derived from microscopic diatoms and radiolarians increased. 

Lower sea levels also meant an increased influx of sediments from land (terrigenous material) in the chalky plates heaping up on the seabed. 

Porosity and permeability

These sediments usually have up to 50 per cent porosity (cavities) when deposited. But this will be considerably reduced by burial and diagenesis (the physical, chemical and biological changes which occur during conversion from sediment to stone). 

In some case, that reduction can be down to well below 10 per cent. However, the good conditions around the Greater Ekofisk Area (GEA) meant that much of the porosity in the chalk was retained.  

It has been calculated at 25-40 per cent. By comparison, a good sandstone reservoir – which is the kind usually found on the NCS – has a porosity of 30 per cent. 

Permeability is also needed to get much oil out of a rock, and the “primary permeability” of Ekofisk chalk is low since the connections between its pores is poor/constricted. 

But the field has enjoyed another stroke of luck here. A large number of fractures in the reservoir have improved its permeability and provide good production properties – at least initially. See water injection. 

Cap rock and trap formation

havets flass,
Geological layers are folded and deformed. Etretate, Normandy. Photo: ConocoPhillips

After the deposition of the Ekofisk formation, conditions changed so that the overlying sediments lost all their porosity when buried and became tight (impermeable). 

That allows them to function as a cap rock which seals the reservoir formed by the Tor and Ekofisk formations. 

The fractures mentioned above were created at the same time as the rocks were subject to movement when large quantities of underlying salt shifted. This also produced large domes and thereby created trap structures where oil and gas can accumulate. 

In other words, the oil migrating from the source rocks has gathered in the reservoir formations under the cap rock – and in amounts which can be difficult to imagine. 

Havets flass – geologien i Ekofisk, Vanninnsprøyting for økt utvinning, graf
Produced and remaining oil reserves in fields on the Norwegian continental shelf. Ekofisk has the largest total oil reserves, but not the largest proportion of recoverable reserves. Source: Norwegian Petroleum/Norwegian Petroleum Directorate

The Ekofisk reservoir is as thick as the Eiffel tower is tall and covers an area of 40 square kilometres – the same size as 5 500 football pitches. 

Recoverable oil in Ekofisk totals 3.5 billion barrels, which would be sufficient to supply the whole world with crude for 35 days. 

Roughly 1.1 billion standard cubic metres (scm) of oil (about 6.9 million barrels) and 300 billion scm of gas were present in Ekofisk when production began. 

That corresponds to twice Norway’s annual water production. It also represents more than 100 times annual Norwegian energy consumption and just over 100 days of global oil usage. 

Havets flass,
Visualization of oil and water in one of the reservoir layers in Ekofisk. Red: Oil. Green: Oil and water. Blue: Water

It is impossible to get all the oil out of a reservoir, and a distinction is therefore drawn between reserves in place and recoverable reserves. 

However it is measured, though, Ekofisk ranks as one of the very largest fields on the NCS. The original estimate for petroleum recovery from the field was 17 per cent. It is now expected to exceed 50 per cent – in part through waterflooding. 

 

(figures) 

Figure 1 Oil quantities produced and remaining in fields on the NCS. Source: norskpetroleum.no. 

 

Figure 2 Coccoliths, which collectively form a coccosphere to surround the coccolithophore. A single coccolith measures 1-10 µm (0.001-0.01 mm) and is invisible to the naked eye. This photograph has been taken using an electron microscope. Photo: Alison R Taylor, University of North Carolina Wilmington Microscopy Facility 

 

Figure 3 A bloom of phytoplankton and the coccolithophore Emiliana huxleyi, which has coloured the Barents Sea pale blue. Photo: Nasa Earth Observatory 

 

Further reading

Halbout, Michel T, Giant Oil and Gas Fields of the Decade: 1968–1978. AAPG Memoir 30, 1980.  

 Ivar B. Ramberg – Inge Bryhni – Arvid Nøttvedt – Kristin Rangnes (ed.’s), The Making of a Land, NGF 2008

 

Published 23. September 2019   •   Updated 16. October 2019
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