Fibreoptic cable arrivesCessation plan for Ekofisk I approved

Cessation plan for Ekofisk I

person By Norwegian Petroleum Museum
After 20 years of production, some of the offshore installations in the Greater Ekofisk Area were starting to become redundant by the 1990s. That reflected the impact of seabed subsidence, the Ekofisk II redevelopment and the fact that satellite fields were approaching the end of their economic lives. The Phillips group accordingly established the Ekofisk I cessation project in 1994, which began work on an impact assessment and plan for the unwanted Ekofisk I facilities. These were owned wholly or partly by the Phillips group, A/S Norske Shell and Norpipe Oil A/S.
Kjappe fakta:
  • The cessation plan covered:
  • 14 steel jackets (64 000 tonnes)
  • one concrete tank with breakwater (290 000 + 900 000 tonnes)
  • 15 topsides (107 000 tonnes)
  • 235 kilometres of buried pipelines (91 000 tonnes)
  • drill cuttings (about 31 000 tonnes)

The cessation plan was submitted to the government for approval on 22 October 1999. It provided an overview of which installations were to be shut down and removed, and when this would happen.

Measures proposed were weighed against criteria for safety, the environment and costs, and the interests of fishing, shipping and society.

Both national and international legislation had to be taken into account by the owner companies, including Norway’s Petroleum Act.

In addition came regional conventions (such as Ospar) and international guidelines from bodies like the International Maritime Organisation (IMO).

The Ekofisk I cessation plan was approved by the Ministry of Petroleum and Energy in 2001, and the Storting (parliament) agreed the following year that the Ekofisk tank should be left in place.

Costs

Implementing the cessation plan for Ekofisk I imposed substantial costs on Phillips, although a great deal was tax-deductible:

  • topsides to land for recycling – NOK 4.6 billion
  • steel jackets to land for recycling, tank left in place – NOK 3.2 billion
  • buried pipelines left in place – NOK 30 million
  • drill cuttings left – no specified cost.

The estimated total bill was about NOK 8 billion. Norway’s share (value creation) is put at 41-50 per cent and covered 5 700 work-years in all – or 200-500 per annum.

Schedule

2003-05 Cleaning storage cells in the Ekofisk tank.
2005-08 Removing superstructure from the Ekofisk tank.
2005-08 Removing light structures under 1 000 tonnes.
2006-13 Removing 11 platforms – Norpipe 36/22 A, Norpipe 37/4 A, Albuskjell 1/6 A, Albuskjell 2/4 F, West Ekofisk 2/4 D, Ekofisk 2/4 R, Cod 7/11 A, Edda 2/7 C, Ekofisk 2/4 P, Ekofisk 2/4 H and Ekofisk 2/4 Q.

The removal plan for Ekofisk 2/4 A, 2/4 B and 2/4 FTP  was to be determined in consultation with the Ministry of Petroleum and Energy.

Calculated emissions/recycling from the removal process

Total energy consumption: 7.6 million gigajoules (GJ)
Energy balance: 9.7 million GJ
CO2 emissions: 580 000 tonnes over 15 years
NOx emissions: 9 100 tonnes
SO2 emissions: 970 tonnes
160 000 tonnes of steel recycled
15 000 tonnes of waste for deposition

Plan for platform removal

In 2000, the Greater Ekofisk Area embraced eight different fields with 29 platforms. The cessation plan for Ekofisk I covered 15 of these structures, grouped in four different categories:

  • outlying platforms
  • Ekofisk Complex north installations
  • Ekofisk Complex south installations
  • pumping platforms in the UK sector
    In addition came flowlines between certain fields/facilities, as well as flare stacks, bridges and bridge supports.

“Outlying platforms” is the designation for installations located outside the Ekofisk Complex – in other words, the platforms on Albuskjell, Cod, Edda and West Ekofisk. These fields have been shut down because production is no longer economic.

Outlying platforms

Facility Function Installed Shutdown
Ekofisk 2/4 A (Drilling), production, accommodation 1972 2013 (plan: 2011)
Ekofisk 2/4 B (Drilling), production, (accommodation) 1972 On stream in 2019 (plan: 2004)
Albuskjell 2/4 F (Drilling), production, accommodation 1977 1990
Cod 7/11 A (Drilling), production, accommodation 1975 1998
Albuskjell 1/6 A (Drilling), production, accommodation 1976 1998
West Ekofisk 2/4 D (Drilling), production, accommodation 1973 1998
Edda 2/7 C (Drilling), production, accommodation 1976-78 1998

(Modules in brackets were originally installed but had been removed earlier).

Ekofisk Complex north

The platforms in the Ekofisk Complex were divided into northern and southern groups. Three owned by the Phillips group on the northern side were included in the plan – Ekofisk 2/4 R, Ekofisk 2/4 T with breakwater, and Ekofisk 2/4 P.

These installations were rendered redundant by the Ekofisk II development, while also being affected by seabed subsidence beneath the complex.

A separate plan was developed by Statoil for Ekofisk 2/4 S, the Statpipe riser platform, while BP dealt with the final disposition of Ekofisk 2/4 G – the riser platform for Valhall. Both were located on the northern side of the complex and linked to it by bridges.

Ekofisk Complex north platforms

Facility Function Installed Shutdown
Ekofisk 2/4 R Riser platform 1975 1998
Ekofisk 2/4 T Processing (and tank) 1973 1998
Breakwater (PBW) Protecting 2/4 T 1989 1998
Ekofisk 2/4 P Pumping platform 1974 1998

Ekofisk Complex south

The Ekofisk 2/4 FTP, Ekofisk 2/4 Q and Ekofisk 2/4 H platforms at the southern end of the complex were also included in the plan. Ekofisk II and seabed subsidence meant they had become redundant.

Ekofisk Complex south platforms

Facility Function Installed Shutdown
Ekofisk 2/4 Q Accommodation 1973 2013 (plan: 2008)
Ekofisk 2/4 FTP Processing, riser 1972 2013 (plan: 2004)
Ekofisk 2/4 H Accommodation 1977 2014 (plan: 2009)

Pumping platforms in the UK sector

Two platforms were installed along the oil pipeline to Teesside in northern England for pressure maintenance. The pipeline was relaid around them in 1991 and 1994, but they had ceased to be operational even earlier.

Pumping platforms in the UK sector

Facility Function Installed Shutdown
Norpipe 36/22 A Pumping platform September 1974 1983
Norpipe 37/4 A Pumping platform May 1974 1987

Pipelines

A total of 42 pipelines or pipeline segments were tied into Ekofisk I, and thereby became redundant once Ekofisk II had come on stream.

They included a number of small infield flowlines which had become surplus to requirements from the late 1970s, when Ekofisk converted from offshore loading of oil to pipeline transport.

The pipelines differed very considerably in both dimensions and type, from 4.5 to 34 inches in diameter and with lengths ranging from a few hundred metres to 75 kilometres.

All the pipelines covered by the cessation plan were buried (trenched) in the seabed at depths varying from 0.8 to 2.5 metres.

Drill cuttings

Seven of the platforms incorporated in the plan had been used for drilling production wells. These were Cod 7/11 A, Albuskjell 1/6 A, Albuskjell 2/4 F, Edda 2/7 C, West Ekofisk 2/4 D, Ekofisk 2/4 A and Ekofisk 2/4 B.

Over the years when drilling was under way, heaps of discharged drill cuttings (rock chips brought up as the well progressed) formed on the seabed beneath each platform.

The drill bit is cooled and lubricated by one or more types of drilling fluids, which also bring up the cuttings and balance downhole pressure. Such fluids normally comprise a base liquid such as water, oil or synthetic oil, and additives like barite and polymers.

With government permission, the usual practice up to 1990 was to discharge cuttings directly to the sea. Depending on its type, the fluid would first be separated out.

The regulations were then changed, and cuttings contaminated with oil-based fluid are now sent to land for treatment or injected into a well on the field.

Water-based fluid were primarily used on Ekofisk, with some diesel oil being added in exceptional cases for certain drilling activities.

Statistics indicate that seven per cent of the fluids used were synthetic, with the remaining 93 per cent water-based. No cuttings containing oil-based fluids have been discharged on Ekofisk I.

A survey of the cuttings heaps under the Greater Ekofisk Area platforms was conducted in the summer of 1998 to determine their size and to take samples of their content.

The results of this investigation are presented in the table.

Estimated drill cuttings

Platform Height (m) Area (m2) Volume (m3) Estimated weight (tonnes)
1/6A 3 3 000 1 800 3 400
2/4A 5 3 700 5 300 9 800
2/4B 5 3 200 4 200 7 800
2/4D 3 1 500 900 1 700
2/4F 3 3 500 2 400 4 400
2/7C 0.8 3 400 900 1 700

 

Cod 7/11 A had been investigated earlier and was not included in the 1998 study. The cuttings heap beneath this platform was estimated to be a metre high.

Tank contents

When cessation planning for Ekofisk 2/4 T began, solid sediments were assumed to have been deposited in the tank’s nine storage cells.

Disposing of these was therefore included as a separate point in the planning process. But investigations and sampling of the tank contents in the winter of 1998-99 encountered no such deposits. Sediments found in two of the cells were unconsolidated and could therefore be pumped out. The other seven cells contained no sediments at all.

As a result, the tank contents changed from being part of the planning work to becoming one of the jobs to be done at shutdown in order to prepare the structure for a cold phase.

Regardless of the disposal solution ultimately chosen for the tank and its breakwater, the cells would emptied and cleaned in accordance with the applicable regulations.

Solution adopted

The removal solution finally adopted for Ekofisk I involved the selection of a disposal option for each component, with an associated timetable.

These choices were the outcome of an overall assessment of technical condition, safety, environmental and social considerations and economics for each option.

Account was also taken of the impact on other users of the sea, in addition to the physical and operational restrictions imposed in the Greater Ekofisk Area.

Consequences of the solution adopted

These are summarised briefly below, together with a discussion of the solutions in relation to the international regulations which applied in this area.

Environmental consequences

The solution involved a total energy consumption of 7.6 million gigajoules – in other words, 35 per cent more than the energy-optimal options and 35 per cent less than the most energy-intensive ones.

Overall energy requirements for the solution were 9.7 million GJ, which represented the lowest overall figure of all the options (17 per cent down from the most energy-intensive choice).

Total CO2 emissions will be 580 000 tonnes, spread over a period of about 15 years. This is 36 per cent lower than the options with the highest emissions and 18 per cent up on those releasing the lowest amount.

Correspondingly, the figures are 9 100 tonnes for NOx, a saving of 30 per cent from the maximum solution, and 970 tonnes for SO2, down 35 per cent from the highest options.

The solution has had no consequences of any significance in terms of discharges to the sea. Habitat impacts and other physical effects are completely marginal.

Aesthetic effects primarily related to the noise caused by breaking up jackets and topsides. Odours deriving from rotting marine growth could also be a problem unless mitigatory measures were taken.

Potential problems associated with dust have been avoided by comparison with certain other options, while the scope of noisy work could also be reduced.

The solution meant that some 160 000 tonnes of steel were recovered. Waste in the order of 15 000 tonnes needed be deposited, with marine growth accounting for about half of this.

Leaving behind buried pipelines is unlikely to pose any real pollution potential. The tank is expected to decompose very slowly and to cause little pollution.

Doing nothing with the heaps of drill cuttings beneath the jackets has been identified as the best option in environmental terms.

This is based on a low risk of the leakage and spread of  potentially polluting substances from the heaps, and the fact that no good environmental solutions are available.

The field will be cleared of waste matter once the disposal process has been completed.

Consequences for society

The solution means that substantial areas will be opened for fishing in the longer term, with the tank as the only remaining obstacle – seen as a good overall solution for this industry.

Where maritime activities are concerned, the tank will remain the only remain risk. But it is very small, and the facility will be equipped with navigational markings to reduce any hazards.

The total potential loss of life (PLL) – in other words, expected fatalities per annum – for the solution adopted is 0.45. That represents an expected death rate of one person every other year during the removal operations. Other possible solutions had PLLs of 0.68 to 0.37.

In all, the solution adopted is expected to cost NOK 8 billion in 1998 money – NOK 3 billion more than the cheapest options and NOK 6.6 billion less than the most expensive.

Norway’s share (value creation) of the work with the solution adopted is in the order of 41-50 per cent. All overall options had a Norwegian proportion of around 50 per cent.

That adds up to a total of 5 700 work-years in direct and indirect employment effects.

Mitigatory measures, monitoring and follow-up

One of the purposes of an impact assessment is to propose measures which can mitigate possible negative effects. These include efforts to recycle all or part of the facilities in order to improve resource utilisation and limit the cost.

The solution for the Ekofisk tank called for a consultation over its acceptability in relation to Ospar. This process was led by the Norwegian government.

Backed by important technical support from the operator, these consultations with the other signatories to the convention led to agreement on leaving the structure in place.

A communication plan was developed in line with the cessation project’s objectives. This aimed to ensure that the solution adopted was acceptable to the Norwegian and international community. Society’s need for correct and adequate information would also be met.

Breaking up the structures on land required a site which took account of possible aesthetic consequences, as well as a possible noise measurement programme or reduction measures.

Such considerations were given emphasis in the contract strategy. Marine growth on jackets also had to be dealt with to avoid odour problems, and work procedures were developed for that.

The pipelines are to be visually inspected at regular intervals. If sections became exposed, measure will be taken to remove, rebury or cover them.

Furthermore, a programme for environmental monitoring of cuttings heaps was developed, with the pile under Ekofisk 2/4 A selected as the most suitable for this purpose.

The monitoring programme was initiated in 1999 and embraced 16 stations at 2/4 A. Sediment samples are analysed for their content of metals, organic compounds, oil components, benthic fauna and distribution of particle size.

Details of this programme have been further developed in consultation with the Norwegian Pollution Control Authority (SFT), now the Norwegian Environment Agency.

Epoke : information on the Ekofisk I cessation Project No. 1, 1997 and No. 12, 2002

Fibreoptic cable arrivesCessation plan for Ekofisk I approved
Published 12. August 2019   •   Updated 5. September 2019
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