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Topic 36: Deep Sea Disposal of Oil and Gas Installations – Acceptable risk?

Brenda Amanda's picture

The subject cannot be discussed
without reference to the Brent Spar incident in which Shell, with the UK
government permission, decided to sink the Brent Spar (a redundant oil storage
installation) into the North Sea as a decommission and disposal [1]. Greenpeace,
an Environment protection organization, rallied public support against the
move, culminating in Shell changing their stand even though they had earlier
met all conditions satisfying that the option was environmentally safe.

I would like your views on this: If it can be proved through commissions,
investigations and adherence to existing regulations that disposal of a
particular decommissioned installation will not have adverse environmental
effects; should this method of disposal be accepted?



Brenda Amanda's picture

The OSPAR 98/3 decision on the
Disposal of disused offshore installations prohibits the dumping and leaving wholly
or partly in place of these installations within the maritime area. A provision
is made for derogation under certain conditions.

Jorgensen (2012) argues that the
above decision excludes the exclusion of rigs-to-reefs in the North Sea as a
viable decommissioning option. The author goes on to argue that this option
should not be categorically excluded but be assessed on a case by case basis.

I would like to agree with
Jorgensen on the issue of having the rigs-to reefs option left open and
assessed on a case-by- case basis since artificial reefs have proved to be an
improvement in the maritime environment especially in the Gulf of Mexico where
they are a common practice. Artificial reefs have been used for providing an
environment that is conducive for the growth of particular marine creatures
such as algae, corals, oysters. The reefs have also been used to study marine
environments for research purposes.

In light of the above, deep sea disposal
of oil and gas installations should indeed be considered as an option if it can
be proved that their presence is a positive addition to the maritime


D. Jorgensen, OSPAR’s Exclusion
of Rigs-to-Reefs in the North Sea; Ocean &Coastal Mangement, Vol 58, March
2012, p.57-67 [Online]. Available at [Accessed
on 3 November 2012]

OSPAR Decision 98/3 on the Disposal of Disused
Offshore Installations [Online] Available at
[Accessed on 3 November 2012]


Brenda, I will agree with you on the rig to reef option but not the sinking of the Brent Spar. I want to point out here that the rig to reef project as a decommissioning option is very good but how many of these structures can a particular area take over time if all the operators see it as an easy way to decommission.

There should be proper regulation guiding these structures. Subsea structures, no matter how perfectly built will definitely succumb to the forces of nature. The metals must corrode and as such posing safety concern for marine life.

For the Brent Spar, I give Greenpeace kudos for rallying people to oppose the sinking of "a whole oil storage installation!!". Looking at the moral point of view, if that installation was built onshore and towed to its storage site offshore for profit making, after its productive life, why can't it be towed back? is it because money will not be made from its journey back?



Menelaos Michelakis's picture

(Answer to Brenda_Amanda)

Dear Amanda, i like to see good friends like you commencing new topics.

In my opinion rigs-to-reefs solution should not be banned, and there are many reasons for that. It is the cheapest method to get rid of an old istallation. A natural reef is created and as you have already written, certain species are favored, such as corals for instance. If the reef is to be created in milder climates, it can be very attractive to divers.

Safety considerations: By the aspect of safety it is a much better solution especially when the platform is far away from the coast, in deep waters, and also too big to be cut and removed with safety. So i cannot understand why the state has taken such a decision and the only reason i can imagine is that it will be benefited somehow, by other types of decommissioning.

Ref : JCMackay (2008) - Offshore engineering, an introduction 

Brenda Amanda's picture

Menelaos, are you arguing that it
should be widely accepted simply because it is the cheapest option? Do keep in
mind there are more than 600 installations in the North Sea. Would we not have
a situation where the ocean floor is mangled with all this steel and the maritime
creatures have to compete for space with these? That would definitely make the
ocean floor unsafe and endanger the maritime creatures that we should be trying
to protect. This is was the Green Peace argument in the Brent Spar case.

Of course, as we all seem to
agree on this blog, the rigs-to reefs conversion does have its advantages.
Whether these outweigh the possible negative environmental effects is a
discussion that is on-going among different stakeholders.

Uko Bassey's picture

I will like to adjust Brenda’s conclusion on this deep water disposal of offshore structures. The agreement to take all possible steps to prevent and eliminate pollution from offshore sources took place during the 1992 Convention for the Protection of the Marine Environment of the North-East Atlantic, known as the OSPAR Convention and this commitment was reiterated in 1998 by Ministers on the Disposal of Disused Offshore Installations. This option of deep sea disposal can only be considered as a last resort which is subject to approval as stated here. The dumping, and the leaving wholly or partly in place, of disused offshore installations within the maritime area is prohibited", but adds that "…if the competent authority of the Contracting Party concerned is satisfied that an assessment …shows that there are significant reasons why an alternative disposal …is preferable to reuse or recycling or final disposal on land, it may issue a permit for …a concrete installation…to be dumped or left wholly or partly in place …".( 

Disposing anything to the marine environment is an artificial pollution/ contamination of the environment and should be strongly discouraged except where it is however found to be the only viable option. There could be possible reuse or recycle of the of the intended disposables. There is a higher tendency that people/organizations will take the advantage and dump all manner of things thereby turning deep water to shallow water. This action will affect water current, aquatic lives, free of passage, fishing activities, etc. 

Uko Bassey

Subsea Engineering.

Richard Milne's picture

I would like to agree, at least partly, with all commenters so far on this topic. I agree with Uko, in that current projects should only be disposed at sea if there are no other options, and I would agree with Menelaos and Amanda in that Rigs-to-Reefs is a good plan, however, I feel that only those rigs, or other structures, which have been designed to fit into a certain environment should be turned into a reef. For example, the structure must not alter the seabed too dramatically, by having dimensions larger than a pre-set amount. This would apply to all structures curently on the seabed.

With the Ospar regulations currently stipulating that "Ospar guidelines were drafted – guidelines that have restricted the definition of “artificial reefs” to artificial structures built specifically for the reproduction of living organisms." [1] Then I don't see why companies can't 'build in' these types of structures to their designs, making rigs, or other structures, capable of supporting marine life while in use, and after their useful life. This would mean that many more structures could be left on the seabed with very few complaints, and in most cases, with encouragement.

However, I feel there would have to be strict guidleines on this, in terms of the marine growth. For example, I think the companies who own the structures should have to prove the amount of marine growth that has been achieved over a 10 year period, and if it is not in line with that expected of the more conventional artificial reef, then the structure should be removed altogether when decommissioning comes around.

I beleive that this would go some way to both helping the marin environment instead of wrecking it, and also in improving safety during the decommissioning stage.


Brenda Amanda's picture

Richard, I like your suggested
solution of having ‘structures with dimensions no larger than a pre-set amount’.
However, I have a concern which I hope can be set straight. It can be generally
agreed that as the installations are taken deeper offshore, the conditions and
forces that they have to withstand increase greatly. So as the Engineers design
these deeper offshore structures to withstand all manner of forces, I would
imagine more elements are integrated into the structure to make it structurally
stable in these environments. If this is the case, how possible is it for there
to be fixed dimensions to which the installations can be constructed?

Richard Sedafor's picture


Richard, I agree that if designs of rigs incorporate the feature for reefs it would eventually reduce risk. But how many companies are ready to spend more money to do that. Cost of operation on a rig per day is incredibly high.

But there are more benefits to converting rigs-to-reefs. An article by the sciencedaily website stated that reefs could control coastal erosion.[1] This benefit will help save lives and money. Happisburgh, on Norfolk's North Sea coast experienced over 250m of coastal Land erosion between 1600 and 1850[2]. Though erosion defences have been constructed to prevent further erosion, erosion still persist but on a smaller scale. Rise in Sea level caused by Global warming and climatic change could cause further erosion not only on the shores of Norfolk but on other coastal lines on the north sea. In 1953 a tragic flood killed 76 Norfolk residents and destroyed properties[2]. This event could still re-occure with the rapid rise in sea levels due to climate change. Building more Artificial reefs from rigs will help prevent this problem though it might be on a small scale, some lives could be saved by preventing massive flooding and erosion by storm waves.

Therefore, as companies think of reducing cost through rig-to-reef constructions, stakeholders and residents may also be thinking of the long term savings they would be making by preventing flooding.


Richard Sedafor

(Msc Oil and Gas Engineering)





Discussion Topic 36: Deep Sea Disposal of Oil and Gas Installations – Acceptable risk

Well, me I will disagree with deep sea disposal of oil and gas installations to form reefs. First and foremost, although artificial reefs have been used for providing an environment that is conducive for the growth of particular marine creatures such as algae, corals, oysters as stated by Brenda, artificial reefs may result in water pollution in a long run especially if potentially harmful contaminants (hydrocarbons) are not removed prior to disposal or due to corrosion of the reef at the point of disposal. Most metallic structures begin to corrode over time releasing toxins to the environment. This problem is likely to occur irrespective of whether the rigs are  treated  while being decommissioned or not. These contaminants could harm marine creatures  such as fish. In addition, artificial reefs do not meet the weight requirement  for them to remain in one place in the sea floor thus they keep floating  on the sea floor leading to damage of wildlife or even destroying their nests. Artificial reefs /structures dumped in the sea can also facilitate the spread of invasive species and may interfere with fishing or other vessels since they are not marked.

It is obvious that disposal of disused offshore installations/platforms by dumping them deep in the sea to form reefs substantially reduces the cost of decommissioning such structures however, I am of the view that instead of dumping offshore installations in the sea, companies are better off taking such structures onshore and reusing them in a way that is economical  and by so doing, this will greatly save the environment.  For complex structures that are hard to move onshore, partial decommissioning can be done in which case a substantial part of the platform can be reused in an environmentally friendly manner for example for offshore wind energy or wave energy generation.

John Bosco Aliganyira
Msc.Oil and Gas Engineering.

1. (Accessed on 06/11/2012)

2.Peter I Macreadie*, Ashley M Fowler, and David J Booth. Rigs-to-reefs: Will the deep sea benefit from  artificial habitat? Front Ecol Environ 2011; 9(8): 455–461, doi:10.1890/100112 (published online 24 Mar 2011) (Accessed online on 06/11/2012)

3. online on 06/11/2012)

4.Fábio M. Ruivo, State University of Campinas - UNICAMP and Celso K. Morooka, SPE, UNICAMP ,SPE 71748 .Decommissioning Offshore Oil and Gas Fields. Copyright 2001, Society of Petroleum Engineers Inc.. This paper was prepared for presentation at the 2001 SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, 30 September–3 October 2001.

Menelaos Michelakis's picture

(Answer/comments to John Bosco)

Dear John Bosco,

i partially agree with you that some problems might occur, but the advantages cannot be compared with the disadvantages in this case.

Firstly hydrocarbon leekage cannot be important for 2 reasons. 1) engineers have sealed boreholes before abandoning, 2) the reservoir is depleted . So the quantities you mention are minor.

I also agree with you in the point you make, that recycling is better. But as you have written in prior decommissioning in certain cases is not able to be done and what it to be done then ?

Safety considerations : 1) If the jacket cannot be removed with safety because it is too big, then it is a great hazard for shipping too - if it remains. If certain parts can be removed and recycled this good, but something must be done for the remaining part. The creation of a reef is a permanent solution.

2) You refer to corrosion of metallic parts, (oxidation) in the water, but this type of contamination is minor, because corrosion in the sea water is very fast due to salinity and if the metalls are  not somehow preserved it happens very fast. So i disagree in this part because it is not as important as it may appears.

To conclude, there are no serious environmental problems occuring when a reef is created, so if there are not any other viable solution, this type of solution can prove very useful.

Regards M.M

Toby Stephen's picture

I disagree respectfully, Menelaos, with your point that "there are no serious environmental problems occurring when a reef is created". While I acknowledge that the environmental issues attached to the oil and gas industry can sometimes be overcooked by the general public and the media, they are still valid issues (for the most part).

With reference to your first point, hydrocarbon leakage can occur even if the well is plugged and while this may be minor on a global scale (compared to the observed levels of natural hydrocarbon seepage) it can still have profound effects on the immediate environment  


Toby Stephen
MSc Oil & Gas Engineering

mohamed.elkiki's picture

I actually agree also with Toby. Rigs to Reefs must have disadvantages to the environment because when companies such as Chevron who started this idea started to convert the platform into a reef, they were doing that in a way to minimize the cost of decommissioning and to rotate around the legislation tell them to remove the platform in environmental way after finishing with the production. Therefore, companies all concern were with money not environment. Also, in California, the legislation refused to convert the platform into reefs three times regarding environmental issue. However, EDC refused the bill that introduced in 2010 because they thought that the program of rigs to reefs need further investigations that can lead to approval that this program is environmental. In my opinion, the whole case is a way from oil companies to save some money instead of paying it in decommissioning and as usual the only way that will stop rigs to reefs is by environmental accident.

Reference :

Emmanuel Mbata's picture

yes elkiki, i agree with you. it appears to be a win win solution to both the oil companies and the environmentalist, but it sure has its own disadvantages. 

That is why OSPAR and any other regulatory body should consider rig to reef not as a disposal method for offshore installations but rather as an alternative use of existing materials to create intentional artificial reefs for environmental enhancement under the right conditions.

Installations that will have negative impact on the environment should be decommisioned onshore.

That way, oil and gas companies will not use the sea as a dumping ground for their waste. 





Dear Menelous:
I still disagree with you and i believe the advantages of recycling/reuse do over weigh the advantages of deep sea damping to create reefs. For cases where decommissioning of the entire platform is complex, part of the platform can be reused for other purposes other than damping the entire structure in the sea for example, the abandoned platform could be used for power generation through the use of wind turbines or for geothermal power generation and the rest of the platform taken onshore for recycling which i believe is more environmentally friendly than formation of reefs and when you talk of the creation of the reef being a permanent solution, I don’t believe you because this will definitely have impacts on marine life in a long run and thus it is a temporary solution.
For the case of the steel jacket being a hazard for shipping if not removed, this would not be the case as long as it is put to other uses as described above and of course if the platform is put to other uses, there will be measures to manage such hazards just like what happens during the usual oil production on offshore platforms.
Concerning the issue of corrosion, this is a very serious issue which we cannot under look because it results in water pollution. It may not look a serious issue if you are only looking at one platform but if this is done for as many as 100 platforms, the impact can not be minimal thus our environment will be at risk. There is nothing minor when it comes risk management because what you think is minor today will be a serious hazard tomorrow. What do others have to say?

John Bosco Aliganyira
Msc.Oil and Gas Engineering

Toby Stephen's picture

This is a really interesting discussion point and one that raises a lot of conjecture due to the associated environmental concerns. I think that the key point Brenda makes is that this option needs to be assessed on a case-by-case basis, and that there is no overarching framework that can or should guide deep-sea disposal other than that the operator should have a pretty strong case in order to gain approval to leave a platform at sea.

The environmental concerns that John raises are all very real and very significant and I agree that toxin release (through corrosion) and remnant hydrocarbons would have to be carefully monitored. To expand on this, I believe that should an operator choose to (and gain approval to) dispose of a platform at sea, this would need to be on the back of a comprehensive Environmental Impact Assessment and very strict ongoing monitoring plans to regularly assess contaminant levels, ensuring that a certain degree of liability still remains with the former operator. If, for example, a threshold contaminant level is then exceded (ie total hydrocarbon levels) then the operator would need to act immediately to remediate against this breach or face legal action.     



Toby Stephen
MSc Oil & Gas Engineering

Kyeyune Joseph's picture

Deep sea disposal is one of the options for disposal of oil and gas installations. It mainly concerns concrete substructures since their re-use value is very low. The OSPAR (Oslo- Paris) convention allows deep sea disposal of oil and gas installations after removal of topside facilities. Option has a number of Pros that include less carbon foot print since little energy is used in comparison to onshore disposal, less technical risks, lowest exposure of workforce to accidents and least cost. Additionally, the option enables such installations to be used as artificial reefs for the benefit of fishing industry. The Brent Spar platform operated by Shell UK in the North Sea was destined to be disposed off in deep waters in the Atlantic Ocean. Shell had evaluated all other possible options and finally decided to implement deep sea disposal. However, the proposal faced stiff resistance from the public especially in UK and Germany as well as the Greenpeace movement. Indeed it became a global issue that damaged the reputation of Shell. Therefore, a few concerns have to be clearly sorted out before this form of disposal can be engaged. Some of these include:

Environmental impact to marine life from pollutants like crude oil, heavy metals, sludge, radioactive scales, asphaltenes and polychlorinated biphenyl (PCB) has to be evaluated and threats reduced to ALARP levels. This calls for treatment of any storage residues on the structure or inside the cells.
Structural integrity of the structure being sound and tenable for re-flotation and towing to deep sea site for disposal. Otherwise, operation may turn be fatal and disastrous.
Technical feasibility of the option is quite important since in some cases deep water sites are quite far in remote areas as in the case of Brent Spar at North Fenni Ridge. Option presents technical challenges that need serious attention.
Public acceptability is crucial in this disposal option. The Brent Spar deep water disposal faced challenges yet in reality it was the best. Engaging as many stakeholders as possible can lead to acceptance if they are convinced. Shell UK ignored some stakeholders and this cost them!
Levels of safety to the work force executing activities like towing of the structure, lifting, diving is crucial. Risks should be minimised so as to lower cases of accidents.
Long term liability over the structure in deep waters needs to be critically understood and if possible the consequences evaluated. Otherwise, if structures are disposed off in deep waters and in the future they turn out to be sources of pollution to maritime environment, then companies involved may be in serious trouble.
In summary, this option of disposal seems to be good considering costs involved and energy consumed. However, with the failure of the Brent Spar project, few companies seem to be ready to take this route to decommissioning with fears of public backlash as in the case of Shell with the Brent Spar project.


Della Greca, A. 1996, "Decommissioning & Removal Options: Which Choice?" The International Society of Offshore and Polar Engineers,26-31 May 1996. 1-96-045 ISOPE conference Paper, available at onepetro.

Brent Spar Dossier: released by Shell UK, available at http//

Brenda Amanda's picture

I am glad the discussion has
taken shape. You all argue very interesting points. However, I’ll play the devil’s
advocate this time.

The OSPAR 98/3 allows for
derogation or leaving in place steel installations that weigh more than 10,000
tonnes in air. It should be noted, however, that as the installations were
taken deeper offshore, the number of installations falling into this category
increases. The installations in this category obviously have more steel so are
we solving the initial problem of clearing the ocean or sea floor? For example the
North Sea ‘Troll’ weighs over 1 million tons (Wilson, 2001). This makes it
liable for derogation under OSPAR 98/3 when the time comes for it to be

I would like to hear your take on


Wilson III C.A. and Heath J.W.
(2001) Rigs and Offshore Structures,
Encyclopedia of Ocean Sciences Volume 4 pp. 

faizakhatri's picture

The challenge concerning with deep sea disposal arises with Environmental impacts ans it starts when activities starts at deep water when  platform constructed it include all stages of oil and gas activities, including initial exploration, production And final decommissioning but a lot of potential challenges related with marine environment like releases of oil and chemicals from cuttings piles including equipment failure, or human errors and drainage of sea sumps. There are concerns that the ageing of infrastructure may increase the risk of accidents resulting in spills of oil and chemicals spills and emissions because of installations of equipment’s  which should include effect on water quality , contaminations, noise pollution under water and interference with other uses of the sea such as fishing, shipping, cable laying etc. Faiza khatri  M.Sc oil and gas engineering 


Charles Stuart's picture

I would absolutely agree with the statement any proposal for disposal at sea would need to be assessed on an individual basis.  

What I'm not clear on is exactly what criteria would separate one installation from another in terms of its suitability.  

If the argument in favour of rigs to reefs is that the environmental cost (from damage to the marine habitat surrounding the jacket) of removal (or benefit from non-removal) is such that disposal at sea is justified, then surely this same rational must be applied to all installations, ultimately leading to this approach being adopted 100% of the time.  What would differentiate one from another? Surely such an approach wouldn’t be acceptable or desirable for all 600 North Sea installations (to quote the figure from Brenda's earlier post).  

There is a danger that this would be viewed by the operators as a convenient and economic way of disposal.  I would agree with the point made by Toby that they must retain a degree of responsibility for the ongoing management of the site if this option is taken.  Perhaps a financial penalty equivalent to the removal cost should be applied, which could be used for any future management of the sites.

Hanifah N. Lubega's picture


Amanda, thats a good one.Smile

As more installations/platforms fall into the 98/3 OSPAR decision  to derogate them from completely removing structures, what is going to become of the Northsea?

I dont want to imagine because if all responsible parties can prove that the decomissioning method is beyond reasonable practicability or exceed normal risk acceptance (present good cases as required by the dicision), with evidence of danger to the environment and high exposure to safety hazards, the decision may be taken to leave them at sea. What happens to the physical environment of the sea and impact on marine life? Since we have approved rigs-to-reef sites, these structure may not be fit for the purpose especially concrete platforms and may keep detoriorating and probably releasing hazardous components with time. The impacts of possible pollution may be minimal given the volume of water, but they still pose a safety hazard.

I acknowledge that thaere is little experience in decomissioning but i believe this era of improved technology can identify ways of decomissioning such facilities before we find these water bodies uninhabitable to marine ecosystem or even causing accidents/fatalities to other sea users or divers.


Department of Energy and climate Change, 2011, Guidance Notes Decommissioning of Offshore Oil and Gas Installations and Pipelines under the Petroleum Act 1998 


YAKUBU ABUBAKAR 51126107's picture

Disposal of oil and gas installation in deep offshore is one
of the modern days decommissioning options even though is yet to be recognising
under OSPAR agreement treaty of 1999.Do we consider the exercise safe is a Yes
and No answer to me. Yes because in the deep offshore there is minimal or no
human interaction and no navigational risk and commercial fishing activities
because it’s a deep offshore or natural reef as the case may be. So it can be
argue that it has a minimal risk in that regard. No because even though it has
no human interaction it can affect the ecosystem of the marine bio diversity
which can be issue to the environment even though there is no any scientific
proof to that claim.

But I’m of the opinion that the disposal may have a serious environmental
impact to the geological stability which can result to massive floods, hurricanes
and other unforeseeable environmental issues in the future, and also is worth
nothing that more that 90% of the platforms are made of steel and iron that
when they rust can release some chemical to the sea environment which will affect
the chemical balance of the ecosystem. For me there is massive risk to that
exercise is just a short cut of spending money by the oil and gas operators.

Yakubu Abubakar

Oil and Gas engr.


Toby Stephen's picture

Respectfully, I think that your statement "there is no scientific proof to that claim" (regarding the effects of hydrocarbons on marine ecosystems) is an invalid one. The assertion itself implies that companies are wasting their time and money with the marine and environmental teams they put in place for this very reason. I agree that these environmental impacts can sometimes be overcooked by the media, general public and activist groups but there is no doubting the immediate and short-term toxic effects of hydrocarbons on marine environments, not to mention the significance of petroleum-derived carcinogens.


Source: Petroleum hydrocarbons in aquatic ecosystems — behavior and effects of sublethal concentrations: D. W. Connella, G. J. Millera & J. W. Farringtonb, pages 37-104.



Toby Stephen
MSc Oil & Gas Engineering

Craig Donaldson's picture

"But I'm of the opinion that the disposal may have a serious environmental
impact to the geological stability which can result to massive floods, hurricanes
and other unforeseeable environmental issues in the future"

I think you need to clarify what you mean by this statement since disposing of a rig on the seabed is not going to affect geological stability of the area on which it lies. It may affect the immediate seabed and the area around it as discussed in other posts; however, the reservoir will have been sealed separately and its weight is not going to suddenly compact the seabed either.

Furthermore, I don't understand how disposing of a rig at sea will cause massive floods, hurricanes or other things like that. Yes, the weather is influenced by the movements of currents in the seas and oceans as well as their respective temperatures (the sun is the main influencer though), but a disposed rig no matter the size could not have a noticeable effect on these factors due to the scale of these natural systems.

Derek Porter.'s picture

I will refer back to the original post topic ‘Deep sea disposal of oil and gas installations – acceptable risk?’ There are several forms of risk which can be included such as:

·         Environmental

·         Company reputation

·         Health and safety

·         Financial

In hindsight of the Brent spar incident, the company reputation has now become the most important risk to an organisation, thus ruling out this decommissioning method completely. The brent incident showed that the environmental risk was much higher than the risk posed by health and safety and company finances. I make an argument that the environmental damage posed by the decommissiong such as cutting, transport, disrupting current marine life at the site coupled with the increased health a safety dangers and extra cost potentially greatly outweighs the deep sea disposal.

chukwuemeka uzukwu's picture

Decision 93/3 provides the regulatory framework for decommissioning all off­shore
structures. The Decision states that “the dumping, and the leaving wholly or
partly in place, of disused offshore installations within the maritime area is
prohibited”, but adds that “…if the competent authority of the Contracting
Party concerned is satisfied that an assessment …shows that there are
significant reasons why an alternative disposal…is preferable to reuse or
recycling or final disposal on land, it may issue a permit for…a concrete be dumped or left wholly or partly in place…”.

Health and safety of the workforce is crucial in any
decommissioning work of offshore instal­lations. the level of safety should be
the same as during installation and operations and work should be carried out
in accordance with the principle that the risk for the workforce should be as
low as is reasonably practicable.

There is
very little experience of managing hazards and risks associated with offshore
decommissioning e.g. gravity concrete structures.

During the
tow out to the deep-water location it is assumed that no personnel would be
onboard the platform. Preparations for sinking the substructure are likely to
be made with people located on a nearby vessel. However, it may be necessary to
put people on board in the event of a failure of the mechanical systems
initiating the sinking process. A deep-water disposal of a substructure would
eliminate high risk to personnel during inshore and onshore deconstruction

There are some factors o consider when disposal oil platforms

• Technical feasibility

• Safety for personnel

• Environmental impact

   • Cost


Environmental Impact

Disposal of the concrete substructures in deep water may cause
minor environmental impact due to leakage of oil from temporary tanks used for
pumps necessary to control the buoyancy of the structure during re-float,
towing and sinking operations.

If the concrete substructure has been used for oil storage,
residual sludge and other deposits inside the storage tanks may have some local
environmental impact at the disposal site.

During the sinking process, it is likely that the platform will be
more or less pulverised or severely deformed due to overpressure and impact
when it hits the sea bottom. The surfaces of the inner storage tanks will
immediately be exposed to seawater. However, since the residuals are assumed to
be relatively immobile (due to high wax content) and will be contained in pores
in the inner walls of the storage tanks, a very slow leaching of hydrocarbons
from the surfaces to the seawater is anticipated.

A seabed inspection and environmental survey will normally be
performed prior to leaving the deep-water site.

disposal will eliminate major environmental impacts onshore during the decon­struction


    Uncertainties associated
with decommissioning include: structural integrity of the concrete installation
when it is released from the seabed; weight and buoyancy of the re-floated
structures; safety and issues associated with-long term liability.

• Effective consultation mechanisms have been developed to engage
stakeholders and other users of the sea in considering the options for

• A comprehensive environmental impact assessment (EIA),
undertaken by independ­ent parties, is a vital element when considering the
implications of deep sea disposal. The environmental impact assessment should
include consideration of the long-term impact on the marine environment from
any contaminants that may be left in the substructure. It is important to allow
the stakeholders to review and comment upon both the proposed scope of work for
the EIA and the subsequent outcome from the assessment.

• Concrete structures left in place in the marine environment are
extremely durable, will degrade very slowly and may be expected to remain
standing for years.

• Contamination of the marine environment in the vicinity of the
decommissioned instal­lation is not expected to be significant, especially
given strict controls on cleaning during decommissioning. 

As my classmates have cited here, RTR program is an approach to turn an obsolete platform to artificial reefs. I share the idea that this approach may pose risks to ecosystem but I would like to elaborate on this topic by discussing some standards regarding a safe RTR program.

  • reef material must be stable and without any debris and it should be built with the most stable condition.
  • reef material must be free from any hazardous material which may pose risks to ecosystem. So, all pipes, vessels and extra equipments should be removed before.
  • reef site must be in a place where it does not hinder any future energy activity such as oil and gas exploitation, renewable activities, etc.

By taking standards and regulations into consideration, companies can pose less risks to the environment. However, considering a large number of platforms operating in the north sea, we can come to conclusion that it is impossible for all of them to turn to reefs instead of being decommissioned. 


farman oladi's picture

More than 100 offshore structures will be removed this year in the Gulf of Mexico, which are known as "Idle Iron ". Clean up by oil companies sounds good, however many Scientists, Scuba Divers and Fishermen aren’t happy about it. According to Bob Shipp at the University of South Alabama, the platforms do attract some marine species for shelter and food.

Removal of platforms usually involves using explosives, will have has its own distractive effect on the environments. Therefore under federal Rig To Reefs program, conversion of platforms to an artificial reef will become a part of marine habitat.

Therefore Re-evaluation of the platform removal with so much at stake seams a reasonable request.

Refrences: Gulf Coast Oil Platforms: Save the Rigs?


Emmanuel Mbata's picture

When most of these offshore platforms where constructed, decommisioning in the sea was not considered. Most companies are embrassing it now because it looks cheaper in the short run, mean while most of the offshore installations are built with material that can have negative effect to marine life.

I think to minimise the future effect if the rig to reef descision is endorsed since it is the cheapest way out now, the regulatory bodies should produce guidelines on future construction of offshore platforms ensuring that only materials that are not prohibited to be dumbed at sea is used, forbading the use of recycled materials

Dike Nwabueze Chinedu.'s picture

Decommissioning of offshore installations is as important as its contruction. In almost all the offshore markets, there are regulations which a duty holder must comply with when decommisioning is required. The OSPRA 1992, IMO guideline, UNCLOS etc are some of these. The requirements may differ for different markets. In the North sea, all structures must be removed while in the US, subsea equipment is to be completely removed is in water depth of less than 800m.

The piper Alpha platform was toppled over onto an unused part of the sea, the Brent spar was to be sunk to sea but public outcry led to the spar being cut off and used for quary construction. It is clear from these two offshore installations as stated above that the disposal of oil and gas installations pose environmental, safety, health, and competency risks. It will alter marine life, pose some threat to trawlers and vessel movement as well as safety risks to the operators and decommissioning team (as seen in the maureen platform). Complying with the complex regulation associated with decommisioning is another bottle-neck. Legislative risks are also associated with this process.


MyAberdeen (2012), Introduction to subsea systems and networks, [online],
Available from:

Kelvin Arazu's picture

Deep sea disposal of Oil and gas installation is one of the methods of disposing oil and gas facilities after use.

This option seems less expensive and easy to execute. A quick one indeed, this activity has raised eye brawl as Greenpeace is against it. They have used the masses to ensure that they put a stop to this act of ‘'Dumping'' by the oil and gas operators after exploiting their reserves.

The likely risk associated to this operation includes:

Destruction of aquatic life, ship wreck, chemical discharge from rusted steel and alloy, flooding as these equipments will displace water by volume due to occupied space. In fact dumping could damage other existing subsea installations since they can be carried alongside with the flowing water body.

The (Oslo- Paris) convention supports deep sea disposal of oil and gas installations after removal of topside facilities.  As they argued that this will promote less carbon foot print because little energy is needed when compared to onshore disposal. Low exposure of personnel to accident since it is easier to cut and topple the facilities into the water [1].

Since this option presents formidable challenges to health and safety. My take on this issue is that, dumping should be stopped. Because if the operators could spend money to exploit the reservoirs, they should also spend money to ensure that the health and safety of the site on which they operate is not jeopardised.

sreehariprabhu's picture

It is good to have a talk on this topic since there is a big concern now about what to do with the platforms where production is stopped. I would agree with uko since you have to anyway dumb the structures in the deep water if there is no other proper way. Also a rigs to reef brings a good idea to do since it is very helpul for the marine environment and it also brings a lot of new opporunities for the environmentalists and oil companies to study about the rig to reef idea. If this idea is successful, it will defenitely be a good solution to many problems leading to leaving structures in deep water. But care should be taken that while dumping that no toxic fluids or any harmful fluids are released in the water. This could lead to a harmful condition to the sea life which will make environmentalists to act against this situation. So it must go hand to hand and the structures disposed must be made sure that they didnt affect the marine life.

But a problem which must be studied is the corrosion of these structures when they are left in deep water. Even if we can make rigs to reef, corrosion is one of the main factor which must be considered. If we find a suitable method to prevent it, this will be a bigg boost for the oil industry since leaving structures in deep water is one of the cheapest way.

Sreehari Ramachandra Prabhu 

Maxwell Otobo's picture

In the UK, the principle of 'Best Praticable Environmental Option' (BPEO) is applied by the environmental protection policy which also seeks to eliminate or minimize releases of harmful substances to the environment as a whole while considering the safety, pratical feasibility and financial aspects.

Other than the complete deep-sea  disposal of oil and gas installations, other options for decommissioning and disposal include;


  • Complete removal ashore, dispose and recycle
  • partial removal where only the lowest part of the structure 'the stump' is left in place
  • toppling or emplacement; where the topside is severed and placed alongside the stump leaving at least 55m distance to the surface of the sea.


Selecting the BPEO is a very complex procedure. The required activities are listed and a comparative assessment is carried out for the environmental impacts on land, water, and air, the health and safety implications, the technical steps and risk involved as well as financial costs and other relevant factors.

Where the BPEO involves disposal at sea, the necessary licences/approvals need to be sought out.

As stated above by Brenda, this subject cannot be discussed without reference to the Brent Spar incident where the BPEO method was used and the deep-sea disposal option waas considered the preferred option because it poses fewer safety risks, was cheaper and much more technically feasible. Although this was not finally done due to the rally/street protest by Green peace, an environment protection organization.

In conclusion, i dont see the reason why deep sea disposal should be halted in a case where the environmental considerations, safety and risk implications are of low or no significant issue.


adavis's picture

Though I haven’t dove on the world's largest artificial reef, the "USS Oriskany", I have dove on several other artificial reefs in Florida.  Speaking as a diver, artificial reefs are wonderful.  The amount of marine life is absolutely amazing.  However, if you happen to swim a few hundred feet on either side of the wreck, you'll see nothing but sand.  It looks

like an underwater desert.  The reefs seem to act as underwater sanctuaries.

Having said that, I'm sure there are environmental effects caused by this large foreign object that is suddenly plunged into this subsea environment.  However, I wonder if there are any alternatives that have no environmental impact or have more net benefit?  A few individuals have mentioned recycling as an option or even disposal on land.  Though that may be an option, I seriously doubt there is the environmental impact is less.  As I understand it, scrap yards general have problems with ground water and air pollution. As with most things, I don’t believe there is one ideal solution.'s picture

As the offshore oil and gas becomes more and more popular, many countries pour their attention to the deep sea oil and gas exploit. This situation may bring us some risk which may lead to several serious issues.

Last year, the BP project in Golf of Mexico gave rise to the oil leak under sea and in order to eliminate the pollution and the reputation lose, the company spent nearly 42 billion for this problem. However, this is not the end, the leaking oil pollute the adjacent areas as well as some sea animals. Hundreds and thousands sea birds were died due to the pollution. On the one hand, human need conventional energy to live, on the other hand, if the technology is not so mature, it probably bring many terrible consequences.

Then, the other example is that Shell decided to sink The Brent Spar oil platform into the bottom of the North Atlantic. However, this action received the protest from thousands of people and several governments. Finally, Shell claimed that the platform would not be sunk into the sea any more. The decommission platforms are also the problem for the deep sea installation. Before the end of the life span, the platform should be dealt reasonable.

Consequently, we cannot deny the necessary of offshore oil and gas industry, but we also cannot ignore the potential risk in the installations. The best way is to set up relevant management principles so that to decrease the risk as low as reasonable practicable.

amir masoud bayat's picture

Recently the issue of deep water disposal of platform whether it is more safe in comparison with the other ways or not has become disputable. There are several ways for disposal of platform. I would like to elaborate on this issue by dicussing the differences between onshore disposal through Horizontal dismantling and deep water disposal.

The horizontal dismantling have small negative effects on the marine organisms. But sometimes the process of rotating of the platform structure into the horizontal state fails which leads to releasing any contaminated ballast water into the coastal environment. Also, the structure of platform may sink which creates a hazard to fishing and navigation.

 On the other hand, for deep water disposal, the environmental effects are negligible while the impacts are considered to be largely physical. For instance, the burial of a lot of marine species. Since there are low dencities of species in the deep water, local toxic can effect on organisms. Moreover, the site should be selected to avoid dangers which associated with other uses of deep water such as submarine cables and military activities.

To sum up, what I would like to stress is that before disposal of platform, a review of technical methods and other assessment issues should be done to identify the best diposal way and reduce the risk to ALARP.


Ber_Mar's picture

Having done some research on the topic, i believe it to be unnaceptable. One cannot state that the ocean is an infinite garbage for human purposes. This legacy might prove unsastainable for future generations. While considering a smaller scale it evenutally might not even be important, nevertheless and since the absence of worldwide cartography (subsea equipments and pipelines) is huge, i believe it to be an obligation of the UN to make the oil companies and other players with interst on the subsea world to pay the organismo to create and nurture this cartography. Other measurments should be also carried out as extra cleaning of dirty zones, near costal areas. Using expertise and ROV's both available for the Offshore Oil players we could bring better oceans for our future genearations and animals.

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