Abstract:

Many oil and gas fields are now entering (or already have) entered the end of their

productive lives and as of consequence, the hydrocarbon industry presently faces the

dilemma of decommissioning redundant oil and gas installations. The purpose of this report

is to probe into the various treatment options available to reduce pollution caused by

decommissioning and abandonment of offshore oil rigs, in accordance with both international

and domestic regulating bodies. According to the UK Offshore Operators Association

(UKOOA), decommissioned was defined as the process which the operator of an offshore oil

and gas installation goes through to plan, gain government approval and implement the

removal, disposal or re-use of a structure when it is no longer needed for its current

purpose.” Firstly, this report outlined the decommissioning process which comprises of well

abandonment, pre-abandonment, engineering, decommissioning, structural removal,

disposal and site clearance. It was observed that the choice of removal method depended

on cost, proximity to disposal sites, availability of removal equipment, location of the removal

relative to shipping lanes and fishing interests, and safety and environmental issues. In

addition, the disposal method played a key role in the decision on the removal method.

Furthermore, it was also found that, the planning phase of the decommissioning and

abandonment process took the longest time, since it had to be established at the time of

erection of the offshore platform by the operator involved. This was followed by outlining the

legal framework that is stipulated by international regulatory bodies and conventions, with

emphasis on the decommissioning phase in oil and gas industry. As of consequence, this

report looked into two general types of treatments namely: technological and alternative

treatments (i.e. re-use and recycling) which are adopted by oil and gas operators to conform

to the legal requirements stipulated by both international and domestic regulatory bodies.

Technological treatments dealt with well plugging and other decommissioning options which

included alternative treatments as a subset of a suite of remedies that could be utilized.

Finally, limitations of environmental laws and conventions was looked into, and the report

concluded that in some cases the definition of pollution in the law was ambiguous,

consequently mechanisms were established to limit the possible exploitation created in

claims for compensation for environmental damages.

INTRODUCTION - Chapter one

Background Information to Oil and Gas Installation Decommissioning

The offshore oil and gas industry had its beginnings in the Gulf of Mexico in 1947. The first

offshore development used a multiplied steel jacket to support the topside production

facilities, a design which has since been used extensively. Now there are more than 7000

drilling and production platforms located on the Continental Shelves of 53 countries (Day

2008). Over 4,000 are situated in the Gulf of Mexico, some 950 in Asia, some 700 in the

Middle East and some 600 in the North Sea and North East Atlantic. Some of these

structures have been installed in areas of deep water and treacherous climates, and

consequently structure designs have adapted to withstand the environmental conditions of

these areas. Commonly used structural designs are illustrated below:

FIGURE 1.1. Steel-jacketed structure (Day 2008)

FIGURE 1.2. Tension leg platform (Day 2008)

FIGURE 1.3. Concrete gravity base structure (Day 2008)

FIGURE 1.4. Floating production system (Day 2008)

Figure 1.5 Cell Spar (Day 2008)

The United Kingdom Continental Shelf (UKCS) is home to some 312 structures extracting oil

and gas. These include subsea equipment fixed to the ocean floor as well as platforms

ranging from the smaller structures in the Southern and Central North Sea to the substantial

installations in the Northern North Sea built to withstand very harsh weather conditions in

deep waters. Many of the structures were constructed in the 1970s and were hailed as

technological feats when they were installed (Gibson 2002). The table below shows the

location of North Sea installations by type and country:

Country Steel-Jacket Concrete substructure Subsea Floating Total

UK 227 12 56 17 312

Norway 69 13 54 9 145

Netherlands 118 2 7 127

Denmark 39 39

Germany 1 1 2

Total 454 28 117 26 625

The table 1.1 above shows the location of North Sea installations by type and country

(Gibson 2002).

In the proximal future

Many oil and gas fields are now entering (or already have) entered the end of their

productive lives and as of consequence, the hydrocarbon industry presently faces the

dilemma of decommissioning redundant oil and gas installations. The purpose of this report

is to delve into the various treatment options available to reduce pollution caused by

decommissioning and abandonment of offshore oil rigs, in accordance with international

environmental laws and conventions.

To date there is relatively negligible experience in removing structures from the North Sea.

Presently, approximately 30 small steel structures and sub-sea installations have been

successfully decommissioned in the shallow waters (30-50 metres) of the Southern North

Sea sector, including 20 from UK waters.

The largest structure decommissioned so far is the Odin platform in 1997. The steel

substructure, weighing 6,200 tonnes, was removed from the North Sea in waters 100 metres

deep. None of the largest structures, those weighing over 10,000 tonnes, has ever been

removed anywhere in the world

THESIS STATEMENT

Substructure, removal of topsides, well plugging, abandonment in-situ, recycling of waste, as

well as the use of non-explosives, are some of the treatment options employed as

containment measures to reduce pollution caused by decommissioning and abandonment of

offshore oil rigs, in accordance with international environmental laws and conventions.

Objectives:

To define what is decommissioning.

To encapsulate and to provide a comprehensive review of the decommissioning and

abandonment process.

To outline the legal framework of platform decommissioning.

To demonstrate the use of technology as treatment options in decommissioning and

abandonment, in adherence with environmental laws and conventions.

To examine limitations of environmental laws and conventions.

Chapter two

Definition

According to the UK Offshore Operators Association (UKOOA) defines decommissioning as:

“The process which the operator of an offshore oil and gas installation goes through

to plan, gain government approval and implement the removal, disposal or re-use of a

structure when it is no longer needed for its current purpose.”

Decommissioning is usually, a long-term process. For example, Petroleum UK began to

think about the decommissioning of their Maureen platform in 1993 – the platform was finally

removed in 2001.

The abandonment process

The entire abandonment process can be broken down into seven distinct activities:

1. Well abandonment: the permanent plugging and abandonment of non-productive

well bores.

2. Pre-abandonment surveys/data gathering: information-gathering phase to gain

knowledge about the existing platform and its condition. Governing ministries or

standards organizations should be contacted to determine permit and environmental

requirements.

3. Engineering: development of an abandonment plan based on information gathered

during pre-abandonment surveys.

4. Decommissioning: the shutdown of all process equipment and facilities, removal of

waste streams and associated activities to ready the platform for a safe and

environmentally sound demolition.

5. Structure removal: removal of the deck or floating production facility from the site,

followed by removal of the jacket, bottom tether structures or gravity base.

6. Disposal: the disposal, recycle, or reuse of platform components onshore or

offshore.

7. Site clearance: final clean-up of sea-floor debris.

Well abandonment

The precise formulae devised in order to determine cessation of production can be quite

challenging. However, a close working relationship between the reservoir, downhole and

salvage engineers should be developed to establish the timing of a well and platform

abandonment project. Before abandonment can begin, the salvage engineer must confirm

that all wells on the platform are abandoned. The wells should be permanently abandoned

according to the recommended procedures in adherence to the appropriate jurisdiction.

Generally this means isolating productive zones of the well with cement, removing some or

all of the production tubing and setting a surface cement plug in the well with the top of the

plug approximately 30–50 m below the mudline. The inner casing string should be checked

to ensure that adequate diameter and depths are available for the lowering of explosives or

cutting tools. If the well plug and abandonment are not performed properly, removal of the

conductor by explosive or mechanical means becomes unsafe and much more expensive.

To ensure no delays in structure removal, all well plug and abandonments should be

completed several months prior to commencement of offshore decommissioning. After well

plug and abandonment responsibility and schedules have been established, the following

step is the information-gathering phase (Day 2008).

Pre-Abandonment surveys/information gathering

This phase is of paramount importance for a successful abandonment program. Adequate

preparation requires a thorough knowledge about the platform to be decommissioned.

Information must be combined from the topside deck and support structure design,

fabrication and installation as well as any structural modifications that may have occurred

since installation. The pre-abandonment survey should assess the condition of the platform

facilities and structure prior to commencement of abandonment (Day 2008). The survey

should include the following:

i. File surveys. All available documentation concerning the platform design, fabrication,

installation, commissioning, start-up and continuing operations should be

investigated. The file survey will inform the project engineer with the other

appurtenances to the platform facility such as living quarters, process equipment,

piping, flare system and pipelines and any additions/deletions or structural repairs to

the jacket or the topside since the original installation.

ii. Geophysical surveys. Depending on the results of the file survey, the engineer may

choose to have additional data gathered by means of side-scan sonar. This survey

will indicate the amount of debris on the seafloor. In the case of deep-sea disposal,

the sonar can determine if there are any obstructions at the dump site. Proximity of

an available dump site or ‘rigs to reef’ site, water depths and obstructions along the

tow route should be investigated as part of the geophysical survey.

iii. Environmental surveys. This consists of an environmental audit of the offshore

platform to identify waste streams or other government controlled materials. At this

time items such as naturally occurring radioactive materials (NORM), asbestos,

PCBs, sludges, slop oils and hazardous/toxic wastes should be identified and

quantified. The problem of dealing with these waste streams should be addressed in

the scope of work for handling during the decommissioning phase of the project. The

project engineer should determine what permits or operating parameters are required

by the host government or international standards.

iv. Structural surveys. A structural engineer can use observation and non-destructive

ultrasonic testing techniques to evaluate the structural integrity. Items inspected will

include condition and accessibility of lifting eyes, obstructions on the deck which may

require removal and interfaces between production modules/deck and deck/jacket

which may require cutting for disassembly. Discrepancies between actual conditions

and as-built information identified in the files should be noted during this phase. The

platform legs should be checked for damage that may obstruct explosives or cutting

tools from accessing the proper cutting depth. If obstruction from damage is

anticipated or found, smaller diameter charges or cutting tools should be provided by

the removal contractor as a contingency. Information concerning the underwater

condition of the structure should be available from previous underwater inspections.

If not available, consideration should be given for gathering this information by divers

or remote-operated vehicles (ROVs).

Engineering:

Upon completion of pre-abandonment surveys, a strategy for decommissioning and

abandonment can be developed. The engineering phase takes all of the data previously

gathered and pieces it together to form a logical, planned approach to a safe

abandonment. Of major concern during the development of this strategy is the safety of

the operations. As with all offshore operations, there exists a high potential for accidents

involving bodily injury or loss of life and the accidental discharge of oil and flammable,

corrosive or toxic material into the environment. A risk analysis for all phases of the

decommissioning should be performed. The results of this risk analysis are used to

develop a decommissioning safety plan. Safety targets can be set and achieved

provided the appropriate attention is devoted to the elements of the decommissioning

plan. These procedural elements include the following items:

Regularly scheduled safety meetings;

Identification of safe work areas;

Safety equipment and training for emergency situations;

Working at high elevations and over water;

Safe operations of cutting tools and explosives;

Safe demolition to maintain structural integrity;

Proper use of rescue and evacuation equipment;

Diving and ROV operations;

Testing for and monitoring of toxic/explosive gases;

Pollution controls and containment;

Methods for handling and disposal of oil wastes, corrosive, NORM, or toxic

materials;

Weather monitoring/night watch procedures;

Addressing each of the aforementioned items will assist in the development of a safe

decommissioning and salvage plan. After all the safety and environmental aspects of the

project have been considered, details of the salvage process need to be identified. The

sequence of process equipment and structure decommissioning and the salvage and

disposal methods need to be determined. Any required government permits should be

submitted for approval.

A key element in the determination for an effective and efficient abandonment program is

proper selection of the salvage equipment. Equipment selection for lifting purposes is

determined by maximum weights of components to be lifted. Oceangoing derrick barges

or Heavy Lift Vessels (HLV) currently available to the industry range from approximately

135 to 7000 tonnes (as shown in figure 2.1 below).

Figure 2.1 showing a Derrick barge (Day 2008).

Cost comparisons must be made between the time savings afforded by heavier lift, more

expensive equipment and time-consuming, lighter lift, less expensive equipment. In

addition to costs, the project engineer must assess the safety and environmental risks

associated with sectional removal. Sectional removal will require significant time at the

site for dismemberment and removal of production piping and equipment prior to cutting

the topside deck into pieces. Additional hazardous tasks involved with decommissioning,

lifting and rigging operations need to be performed offshore in a sectional removal, and

thus the time during which personnel will be exposed to increased workplace hazards

will be increased.

Decommissioning

The main goal during the decommissioning is to protect the marine environment and the

ecosystem by proper collection, control, transport and disposal of various waste streams.

Decommissioning is a dangerous phase of the abandonment operation and creates the

possibility of environmental pollution. Decommissioning and removal or abandonment in

place should be carried out by personnel who have specific knowledge and experience

in safety, process flows, platform operations, marine transportation, structural systems

and pipeline operations. All contractors involved with the decommissioning should be

brought in early in the planning stage to further assure a smooth decommissioning

project.

The sequence of decommissioning the process system, utilities, power supplies and life

support systems is important. The platform’s power, communications and life support

systems should be maintained for as long as practicable to support the decommissioning

effort. Process systems throughout the platform will have to be flushed, purged and

degassed in order to remove any trapped hydrocarbons. Safe lock-out, tag-out, hot work

and vessel entry procedures must be in place to ensure safety. Procedures must outline

all duties of the standby/rescue teams including the use of breathing apparatus, air

purging and lighting and caution must be exercised in removing all amounts of gases,

oils and solids which may still remain in valves, production headers, filter housings,

vessels and pipework that could present hazards to the crew.

Platform decommissioning normally result in large amounts of waste liquids and solids.,

Waste liquids can be dealt with most cost effectively by placing them in existing pipelines

and sending them to existing operating facilities. If no ongoing operations are available,

then the waste streams will have to be pumped into storage containers and transported

onshore for disposal or recycling. The constituents of the waste stream is instrumental in

determining the cost of disposal. Solid wastes such as discarded batteries, glycol filters

and absorbent rags will also have to be handled onshore according to acceptable

disposal practices. Most times many platforms will have chemical treatment additives as

well as possible toxic/hazardous materials such as methanol, biocides, antifoams,

oxygen scavengers, corrosion inhibitors, paints and solvents, some of which may cause

damage to the marine environment if accidentally discharged. As of consequence, the

methods for handling and containing must be followed. The presence of radioactive

scale, NORM, PCBs, hydrogen sulphide, etc., should have been detected during the

environmental survey and a disposal plan developed. Disposal will generally entails

transporting this material in drums to disposal wells or approved landfills. Prior to

removal, a detailed plan on how each material will be disposed of should be developed

(for instance, in the case of Trinidad and Tobago, certificate of environmental clearance

and HAZOPS must be applied for). The plan should identify recyclable materials such as

steel, rubber and aluminium and the recycling centres that will take delivery of these

materials. For those items not to be recycled, the abandonment plan should include the

environmental impact that disposal will have on the dump site.

After the process piping and vessels have been cleaned and it has been determined that

there is no future utility for the pipelines, pipeline decommissioning should commence.

Pipelines departing the platform will either board another platform or commingle with

another pipeline via a sub-sea tie-in. A surface to surface decommissioning is the least

costly to perform. This requires pigging the line to vacate any residual hydrocarbons

followed by flushing with one line volume of detergent water followed by final rinsing with

one line volume of sea water. Upon completion of the pipeline purging operation, pipeline

ends should be cut, plugs inserted and the ends buried below the sea-bed. In the case of

a sub-sea tie-in, details of the sub-sea tap will have to be obtained so that pipeline

decommissioning plans can be developed. The flowline can be pigged, flushed and

disconnected if the receiving platform can accept the fluids, otherwise the pipeline

segment will have to be isolated from the adjoining trunkline and then decommissioned.

This usually involves a boat capable of mooring over the sub-sea tie-in, connecting

flexible piping to the tie-in using divers or ROVs, then pumping pigs, detergent water and

rinsing water toward the platform for handling. Decommissioning involves a variety of

waste streams, disposal handling methods and specialty contractors. This phase more

than any other will determine the success of the abandonment and salvage.

Structure removal

The procedure of a structure removal will be determined by the structure design,

availability of removal equipment, method of disposal and the legal requirements

governing the jurisdiction in which the abandonment occurs. The legal requirements will

usually be based on various parameters such as the social, economic, environmental

and safety concerns of the local governing bodies. All of these issues are interdependent

and will have a direct repercussion on the overall cost of the removal operation. The

economics of the removal are of prime importance to the party responsible for the

removal, whether it is third parties such as a contractor, local government or producer.

Each structure consists primarily of the topsides or deck above the water line and the

jacket below the waterline.

Deck removal

Topsides removal is essentially the reverse sequence of the installation. Any piece of

equipment obstructing the deck lifting eyes must be removed prior to the lift. The deck

section is removed by cutting the welded connection between the piles and the deck

legs. Slings are attached to the deck lifting eyes and the crane hook on the HLV. The

HLV’s crane lifts the deck section from the jacket. The deck is then placed on the cargo

barge and readied for transportation to a land based facility for offloading (Day 2008).

Jacket removal

The jacket portion of the platform comprises of the steel template which resides in the

water column. Prior to removing the jacket, the piles must be cut to dislodge the jacket

from the seafloor. The majority of structures in moderate environments will be totally

removed. Most regulatory bodies throughout the world require that the structure be

removed anywhere from the mudline to 5 m below. The predominant consideration when

developing a removal method is to determine if the piles or well bores will be severed

using explosive or nonexplosive methods.

(a) Extraction using explosives. Severing platform piles and well bores with explosives is

relatively effective compared with using non-explosive methods, as multiple cuts can

be made in a short period of time. This limits the amount of time that removal support

equipment must be on the site and limits personnel exposure to unsafe working

conditions. Generally, explosives are the least exorbitant and the method of choice

for structure removal. However, when explosives are used, more stringent

regulations may become effective, including consultations with the local fishery or

natural resource agencies. A project plan should allow lead time for consultations

and permit approval from these agencies. Explosives emit high-energy shock waves

that can be harmful to habitat fisheries immediately adjacent to a removal site and

some endangered species, such as marine turtles or mammals, in close proximity to

the detonations may be mortally affected by these shock waves. Local regulations

should be researched to ascertain limits to the amount and size of charges allowed

and to determine if moratorium periods exist during marine migration periods. In

some areas, a condition for approval requires that observers from the local regulatory

agencies and/or resource groups be present at the removal site prior to detonations,

to observe that permit requirements are being observed and to ensure that no harm

is done to endangered species that may be in the area. Other conditions that may be

imposed to limit the effects of explosives on habitat fisheries are predetonation aerial

surveys, daylight-only working hours and staggered detonations. The disadvantage

of focused charges is that they need to be properly set in the well bore or pile and

corrosion scale or damage in the piles can prevent the charge from applying its full

energy to the target. One approach used to reduce the effects of explosives on

habitat fisheries is to evacuate the platform piles of all water. This reduces the

resistance of the shock wave from the charge to the target. Also, special shock-

attenuating blankets can be placed at the mudline to limit the energy emitted from the

seafloor. Another approach is to avert fishes from entering the blast area. Small, pre-

set charges set off prior to the detonation of the severing charges, known as scare

charges, have been used. However, there are risks that scare charges may actually

draw some species of curious fish toward the blast site. The use of strobe lights

similar to those used to keep fish away from dam intakes may be warranted.

(b) Non-explosive Extraction. Another option for the project engineer is to eliminate the

use of explosives in the removal. Use of non-explosive removal methods eliminates

the impact due to shock waves. As a result, costs and time associated with observers

and additional permit conditions may be curtailed. However, salvages using non-

explosive methods can be more costly since only one pile or well bore can in practice

be severed at one time. Each nonexplosive cut will typically take several hours to

perform. The additional time and cost can be minimized depending on the scope of

work and with proper project planning. The project engineer should perform a precise

cost estimate, evaluating the costs and risks between using explosive and non-

explosive methods of severing. The following is a discussion of some non-explosive

severing techniques.

High-pressure water/abrasive cutters

This system uses a high-pressure water jet operating at anywhere from 200 to 4000

psi to perform the cut. In other systems, sand, garnet or other type of abrasive is

injected into the water stream to aid in the cutting process. The nozzle is lowered into

the hole attached to an umbilical hose line or a hard pipe supply line. The nozzle is

rotated 360° inside of the pile or well bore until the cut comes back on itself. A merit

to this system is its effective cutting ability. The casing strings do not have to be

concentric in the well bore. The wall thickness of the platform piles is generally not a

concern. The reaction of the water spray and the returns of the water indicates to the

operator that the cut is literally being made. However, the drawbacks of using this

system are the tendency for system downtime due to the high working pressures,

electrical and mechanical complexities, the delicate characteristics of the abrasive

injection and wear and tear on the nozzle. Interrupting the cutting operation requires

that the tool be placed in the exact location of the cut to avoid incomplete cuts. The

effectiveness of these cuts is reduced at deeper cutting depths owing to the

hydrostatic head that the water jet needs to overcome. As with all cutters, the tool

must be centred in the pipe to maximize cutting efficiency. This can be difficult in

heavily scaled pipes or in battered piles. Topside instrumentation can be used to

monitor the position of the cutting tool during the cut. Camera technology has been

used to inspect visually the status and effectiveness of a cut (Day 2008).

Mechanical cutters.

Mechanical cutters use tungsten bit cutters that are extended from a housing tool

with hydraulic rams. The tool is rotated constantly using friction to perform the cut.

Disadvantages include incessant downtime of the tool due to frictional wear and tear,

high labour intensity in handling heavy and bulky tools, the need for a work platform

around the piling/well bore to be cut and poor cutting performance on non-concentric

casing strings. Also, it can be difficult for the operator to determine if a cut is

complete. Shifting of the well strings or platform piles downward can jam the tool into

the kerf of the cut.

Diver cut.

Internal or external pile or well bore cuts can be accomplished by using diver’s

underwater burning equipment. This type of cut can be made internally if there is

access for the diver into a large-diameter casing or piling. If there is no internal

access and the cut must be made below the mudline, a trench must be excavated to

afford the diver access to the area to be severed. In some soils, keeping a trench

open to the required 5 m depth may be impractical and may put the diver at undue

risk from trench collapse. If the cut must be made below the mudline, it should be

consulted to the local jurisdiction of the required depth of the cut. This may require

obtaining a waiver to reduce the required cutting depth due to local soil

characteristics and safety concerns for the diver personnel. Another concern to the

diver’s safety is oxygen entrapment in the soil near the cut or on the backside of the

pipe being cut. Oxygen build-up can lead to an explosion if contacted with a

flammable source such as a burning rod.

Plasma arc cutting.

Plasma arc cutting can be accomplished by an extremely high velocity plasma gas jet

formed by an arc and an inert gas flowing from a small-diameter orifice. The arc

energy is focused on a small area of metal, thus forcing the molten metal through the

kerf and out of the backside of the pipe. Water can act as a shielding agent to cool

and constrict the arc. The procedure requires a high arc voltage provided by

specialized power sources. This method is not frequently used, and is therefore not

highly developed. For it to be effective, the tool must be set properly in the cut pipe. It

is difficult to determine if a cut is being made unless camera technology is utilized.

Regardless of which ever method is being used (i.e. explosives or non-explosives),

obstructions in the pile can interfere with the proper placement of charges or cutting

tools in the well bore or pile. Examples of such hindrance includes: scale build-up,

damaged piling, mud or pile stabbing guides. The removal of mud from the pile is

generally accomplished with the use of a combination of a water jet and air lifting

tools. When properly designed, these work well. This task is traditionally performed

after the topside deck has been removed by the heavy lift contractor. A more cost-

effective technique is the use of a submersible pump to excavate mud from the

platform pile prior to removal. A small inexpensive work spread can be mobilized to

the site prior to the arrival of the heavy lift equipment to perform this task. A window

is cut into the jacket leg/pile and the submersible pump is then lowered down the

jacket leg on a soft umbilical line.

Alternative removal techniques

Many installations are removed with heavy lift equipment such as oceangoing derrick

barges. In faraway areas of the world, another concern in dislodging the platform

from the seafloor is the availability of salvage support equipment. International

Maritime Organization (IMO) guidelines permit the host government to allow a

structure to remain in place provided that the structure is properly maintained to

prevent failure. Maintenance costs over the life of the installation may eventually

exceed the cost of the removal. When left in place, the platform may remain a hazard

to navigation, exposed to collapse during storms or become a haven for refugees.

These risks and liabilities may outweigh high removal costs to the host government

and the operator, thus the decision to remove the platform may prevail.

Another technique that can be used for the lifting of platform topsides is the

Versatruss system (see figure 2.2 below). The method uses a series of A-frames

mounted on tandem cargo barges. The combination of the A-frames, tension slings

and the topside deck create a catamaran and truss effect for lift stability. This lift

method also uses available equipment and requires relatively low-cost preparation.

Figure 2.2 showing Versatruss method (Versabar Inc. 2008)

Disposal

Once a platform or portions of a platform have been removed, the structure must be

disposed of. Some disposal options include the following:

● Transport inshore for disposal, storage or recycling;

● Toppling in place

● Disposal at a remote rigs to reef site;

● Emplacement;

● Deep-water dumping

Site Clearance

The final phase of the abandonment process involves restoration of the site to its original

predevelopment conditions by clearing the seafloor of debris and obstructions after platform

removal. If the abandonment was a partial removal, site clearance procedures may vary

from a total removal. In the case of total removal, debris should be removed, leaving the site

trawlable and safe for fishing or other maritime uses.

A site clearance plan may consist of two or three stages, depending on the information

gathered during the pre-abandonment surveys and the water depth at the location. The first

phase may occur before actual removal with divers making sector sweeps around the

platform site during pipeline decommissioning. High-frequency sonar can be used to locate

obstructions and direct divers to debris. Searches should be performed inside and outside

the platform a distance of at least 100 m. Following this initial debris removal, site clearance

can be discontinued until the structure removal has taken place (Day 2008).

Once the structure has been removed, the site is ready for a final clean-up if required. In

shallow waters, a trawling vessel can be used to simulate typical trawling activities that may

occur in the area after the platform removal.

Chapter Three

The legal framework of platform decommissioning

General Framework

The British Government’s policy with regard to the decommissioning of offshore oil and gas

installations on the United Kingdom Continental Shelf (UKCS) is stated quite clearly in the

Guidance Notes for Industry (Decommissioning of Offshore Installations and Pipelines under

the Petroleum Act 1998) produced by the Aberdeen-based Oil and Gas Office of the

Department of Trade and Industry (DTI):

“Government will seek to achieve effective and balanced decommissioning solutions

which are consistent with international obligations and have a proper regard for

safety, the environment, other legitimate users of the sea and economic

considerations. The Government will act in line with the principles of sustainable

development.”

International Conventions

International law has established the basic foundation of the legal requirements for the

removal and disposal of offshore structures. The removal of installations was addressed by

the 1958 Geneva Convention on the Continental Shelf, which stated that any installations

which are abandoned or disused must be entirely removed. However, several customized

local conventions were adopted by third parties to the Geneva Convention because it

allowed partial removal offshore installations. These local conventions were as follows:

i. United Nations Convention on the Law of the Sea

Internationally, the UK has a number of obligations concerning the decommissioning

of offshore installations which have their origins in the United Nations Convention on

the Law of the Sea (UNCLOS) of 19825 which entered into force in 1994 and was

finally ratified by the UK in 1997. Article 60(3) notes that:

“Any installations or structures which are abandoned or disused shall be

removed to ensure safety of navigation, taking into account any generally

accepted standards established in this regard by the competent international

organisation. Such removal shall also have due regard to fishing, the

protection of the marine environment and the rights and duties of other

States. Appropriate publicity shall be given to the depth, position and

dimensions of any installations or structures not entirely removed.” (Gibson

2002)

The International Maritime Organisation (formed in 1989 and based in London), which

adopted the IMO Guidelines and Standards setting out the global criteria for removal of

offshore installations, is the competent international organisation for UNCLOS (1982).

The IMO guidelines states that if the structure exists in less than 75 m of water and

weighs less than 4000 tonnes, it must be totally removed (Day 2008). If the removal is

done partially, the installation must maintain a 55 m clear water column. However,

exceptions to the same were as follows: for example, if the structure can serve a new

use after hydrocarbon production including enhancement of a living resource, or if the

structure can be left without causing undue interference with other uses of the sea or

where removal is technically not feasible, the installation can remain in place.

ii. The Oslo Convention of 1972 for the Prevention of Marine Pollution by Dumping from

Ships and Aircraft also provided some guidelines. However, its interpretation was

ambiguous, thus on these grounds it was not clear if this Convention applies to

dumping of platforms in place.

iii. In addition, 1992 witnessed a new regional convention, the Convention of the

Protection of the Marine Environment of the North East Atlantic (‘the OSPAR

Convention’). This convention, a replacement and modernisation of the 1972 Oslo

Convention on the Protection of the Marine Environment by Dumping from Ships and

Aircraft and the 1974 Paris Convention on the Prevention on Marine Pollution from

Land-Based Sources, came into operation in 1998. The Convention’s main roles are

to control disposal of all waste at sea and discharges from land. Including the EU,

there are 16 contracting parties of which the UK is one (Gibson 2002).

iv. Furthermore in 1992, 15 United Nations Environment Programme (UNEP) regional

conventions had been held. Here, local states have adopted varying degrees of

guidelines for potential legal concerns such as determination of the party responsible

for removal, responsibility and methods of payment, responsibility of owners in

default situations, owner designation upon non-use, maintenance responsibility and

liability for items left in place and such site-specific issues as bottom debris removal

and moratoriums for marine migrations. Some countries, depending on their

experience with removals, are fairly mature in their regulatory standards for

abandonment whilst others still have great strides to make in enacting requirements

for removals within their coastal waters (Predominantly third world countries).

v. In July 1998 a new binding framework (OSPAR Decision 98/3) for the

decommissioning of offshore installations was established by the First Ministerial

meeting of the OSPAR Commission. Generally, the primary decision was

unambiguous in that it states the following: “The dumping, and the leaving wholly or

partly in place, of disused offshore installations within the maritime area is prohibited”

(Gibson 2002). This recognition by OSPAR 98/3 of the difficulties involved in

removing in their entirety the ‘footings’ of large steel jackets weighing more than

10,000 tonnes and in removing concrete installations ensured that provisions were

made for a derogation from the main ‘general’ rule highlighted above (assessed on a

case-by-case basis). In particular:

a. The topsides of all installations must be returned to shore

b. All steel installations with a jacket weight of less than 10,000 tonnes must be

completely removed for re-use, recycling or final disposal on land;

c. For steel structures with a jacket weight greater than 10,000 tonnes it is

possible to consider whether the footings of the installation may remain in place;

d. For concrete installations it is possible to consider whether they should be left

wholly or partially in place;

e. All installations emplaced after 9 February 1999 (when OSPAR 98/3 came

into force) must be completely removed;

f. Exceptions can be considered for other structures when exceptional and

unforeseen circumstances resulting from structural damage or deterioration or other

reasons which would prevent the removal of a structure.

It is noted however, that pipelines were yet not covered by OSPAR Decision 98/3. There

were no international framework for the decommissioning of disused pipelines.

Chapter four

Technology as treatment options in decommissioning and abandonment, in

adherence with environmental laws and conventions.

There are various methods to remove and dispose of an offshore installation. Exactly which

are applicable to any individual installation will depend on a number of variables for example,

the type of construction, size, and distance from shore, weather conditions, and the

complexity of the removal operation including the safety considerations for the workers.

The diagram below depicts the main options open to offshore operators:

Figure 4.1 showing flow chart of decommissioning options (Gibson 2002).

After consideration of the relevant legislation and regulation, recommending which

decommissioning option is the most appropriate in any particular case has to take into

account at least five key factors:

• Potential impact on the environment;

• Potential impact on human health and safety;

• Technical feasibility of the plan;

• Economic impact;

• Public concern.

These criterion must be carefully balanced to ascertain the most beneficial (or the least

harmful) course of action.

Prior to decommissioning, well plugging and abandonment is the first decommissioning

activity to get underway offshore. It has been developed based on commencing

abandonment of water injection and low productivity wells while retaining high productivity

wells, simultaneous production and well abandonment. This philosophy maintains production

until its cessation is required for topside systems cleaning and preparation for topsides

removal, which then becomes the project critical path.

Wellbore-Abandonment Challenges and solutions

The key goal of any well abandonment is the permanent isolation of all subsurface

formations penetrated by the well. Although sealing depleted reservoirs is an important

concern in P&A procedures, ideal abandonment operations isolate both producing reservoirs

and other fluid bearing formations. Complete isolation prevents gas, oil or water from

migrating to surface or flowing from one substance formation to another (Barclay, Pellenbarg

and Tettero 2001).

Leaking seals pose risks to the environment – groundwater resources and the overlying land

or sea – and must be repaired, but remedial plugging operations are difficult and expensive.

Sealing a well correctly at the outset is significantly more cost effective, even if the initial

cost outlay is high. Considering well abandonment at the earliest stages of the well design

makes sense, because quality of the primary cement between the casing and formations is a

key factor for successful well abandonment later on.

Any deficiencies, in primary cementing tend to affect long term isolation performance. Wide

fluctuations in downhole pressure and temperature can negatively affect cement integrity or

cause debonding. Tectonic stresses can also fracture set cement. No matter the cause, loss

of cement integrity can result in fluid migration, impairment of zonal isolation or casing

collapse even when high-quality cement is placed properly. If fluids are migrating from a well

that has to be abandoned, then the first challenge is to locate the fluid-migration path.

Usually, subsurface fluids migrate through the completion components, leaky plugs, deficient

cement squeezes or flaws in the primary cement sheath or the caprock – the relatively

impermeable formation that encloses the reservoir. The caprock may be composed of

natural fracturing or by fracture stimulation treatments. When multiple reservoir exist,

identifying which one is leaking enables target remediation (Barclay, Pellenbarg and Tettero

2001). Knowing the condition of primary and secondary cement is of paramount importance.

The appropriate persons involved in the abandonment must be well acquainted with the

geology, wellbore geometry and accessibility, downhole equipment and its condition,

reservoir pressure and potential fluid migration path to abandon a well successfully.

Rigless Wellbore abandonment

Well abandonment begins with cleaning the production tubing and cementing or squeezing,

the production perforations. After the tubing the above the production packer is perforated,

cement is circulated between the tubing and the casing. At shallower casing-shoe levels,

multiwall perforations are shot and cement is circulated in an open annuli to achieve a wall to

wall cement barrier. Lastly, the tubing is perforated at a shallow depth of approximately 150

m (490 ft) – and a surface cement plug is placed. When all cement plugs have been placed

and tested, the wellhead and casing stump are removed.

Advantages of Rigless wellbore abandonment

The equipment cost less offshore and easier to mobilize.

Onshore its value lies in time savings over a comparable hoist operation.

Coil tubing allows precise placement of cement plugs even in deviated wellbores.

Also coiled tubing can operate without killing the well or removing the production

tubing or well head.

Challenges associated with Rigless wellbore abandonment

Heavy thick crude oil in the production tubing and annulus

Corrosion of the outer casing of some wells required additional plugging through

outer annulus of each well.

With regards to Rigless abandonment, diagram 4.2 below shows a diagrammatic

representation of a well before and after abandonment. Abandonment of Jisr-1 well, located

in southern Oman, represents an average of degree of difficulty for the PDO well

abandonment programme. Because the well was 12 years old, all valves on the Christmas

tree were backed up with new valves, and coiled tubing blowout preventers were rigged up

to ensure well control. Next, the tubing hanger plug, used for temporary well suspension was

removed. The production tubing and “A” annulus were cleaned by jetting cleaning fluids

down the tubing and up the annulus. The cleaning fluid contains surfactants and acids that

remove sludge, oil and paraffin. Cleaning is critically impertinent at this stage because seals

within the wellbore can shift if sludge or other material moves after setting cement plugs.

Also cement will not form a perfect hydraulic seal with materials coated with hydrocarbon.

The production tubing and 9 5/8-in casing pump were cleaned with a high pressure jetting

tool run on coiled tubing. The tubing and the “A” annulus were then displaced with 11.4-

kPa/m [0.5-psi/ft] salt brine. High pressure jetting has proved to be an effective,

environmentally friendly method for cleaning the tubing and sump, as waste generation was

significantly reduced.

Figure 4.2 a showing Jisr-1 before (left) and after (right) well abandonment (Barclay,

Pellenbarg and Tettero 2001)

Figure 4.2 b showing Jisr-1 before and after well abandonment (Barclay, Pellenbarg and

Tettero 2001).

With coiled tubing, a set of bentonite spacer on bottom to serve as a base for the cement

plug. On Jisr-1, the perforations were shot 342 m [1122 ft] above the base cement plug as

shown above. The PDO requirement was to set the reservoir installation plug from 50 m [164

ft] below the lower perforation to 50 m above the reservoir. In order to comply with

requirement at minimum cost, a 280 m [920 ft] bentonite spacer was spacer on bottom as a

filler. The first cement plug was set through coiled tubing across the perforations. A second

plug as shown above, was set higher in the wellbore, opposite the 133/8-in casing shoe, after

a bridge plug was set inside the 31/2-in production tubing using coiled tubing. The 31/2-in

tubing and 95/8-in casing were perforated and a wall to wall cement plug was placed. Next, a

bridge plug was set at 155 m [508 ft], and the tubing was perforated at 150 m. Finally,

the surface cement was plug was pumped. In contrast to procedures for the previous

cement plugs, PDO abandonment standards do not required pressure –testing of the surface

plug (Barclay, Pellenbarg and Tettero 2001).

Decommissioning Options

Options for decommissioning assume wells have been decommissioned and plugged and

topsides have been cleaned and removed, or made safe for toppling with the jacket.

Typically, topsides are taken onshore for disposal or recycling

The decommissioning options available for an offshore installation can be separated into

three groups:

1. Alternative Use of The Facilities, either in-situ or reused at another location.

2. Full Removal Schemes, entailing total removal of all facilities, subsea and topsides,

leaving a clear seabed

3. Partial Removal Schemes, entailing removal to leave a minimum clear water depth

of 55m above any remaining structure on the seabed in accordance with the IMO.

Alternative structure uses. In some areas of the world, the host government is either wholly

responsible for structure removal or, through participation by a national oil company, is

partially responsible for the cost of structure removal. The political entity may not want to

dedicate funds to a nonrevenue generating project. These states may decide that leaving the

structure in place is the only alternative. IMO guidelines give local states the discretion to

allow offshore structures to remain in place if the removal is not economically feasible. In

these situations, operators will need to review the contract terms for possible ongoing or

future liabilities.

The benefits of the alternative uses usually offset the costs to maintain the structure in place.

Some alternative uses may be as follows:

● Fish farm

● Marine laboratory

● Military radar support structure

● Weather station

● Oil loading station

● Spur for deep-water developments

● Aviation/navigation beacon

● Tourism/recreational

● Power generation, i.e. wind/wave.

Platform reuse. Reuse is another option. If a potential development can finance the removal

of a structure, this relieves the non-revenue producing property from absorbing the salvage

costs. Platform reuse can reduce the cycle time to get the new development in production,

generating cash. However, an immediate reuse should be identified when decommissioning

is undertaken. Storage of the platform onshore prior to identifying a reuse can result in costs

that may offset the savings from reuse.

Substructure

Complete removal. Complete Removal requires the structure to be entirely removed by lifting

either in one piece or in sections depending on the size of the jacket and the capacity of the

lift vessel. The foundation piles are left in place from about 5m below the seabed. The

refloating of “self-floating” jackets has been found to be impractical as the reuse of the

flotation control system was not a design consideration; similarly, the addition of buoyancy

tanks to barge-launched steel jackets has also been found to be impractical. The removed

jacket may be disposed of by taking it to deepwater for subsea disposal, or transporting it

ashore for recycling or onshore as seen below in figure 4.3.

Figure 4.3 showing total removal of an offshore installation.

Partial removals. In the North Sea, the abandonment issue is coming into focus as some of

the area’s fields are reaching the end of their productive lives. Some of the world’s largest

structures will need to be removed before the year 2005. The large component weights will

result in removal costs that may exceed the cost of the original installation. These removal

costs will largely be absorbed by the local governments because of tax breaks from removal

costs available to the operator. Thus, local governments may need to regulate and monitor

abandonment procedures to allow for a cost-effective removal strategy without

compromising safety or the environment. These partial removal methods will consist of the

following:

a. partial removal of jacket component

Figure 4.4 showing partial removal of jacket component (Day 2008)

The Toppling option involves toppling the upper portion of the jacket in-situ, to leave an

unobstructed water column. The high degree of precision and control required to ensure the

structure is safely toppled as planned make this is an extremely complex operation.

Explosive charges are used to sever designated critical members in a controlled sequence

of cuts, allowing the jacket to collapse under its own weight. A pull barge may be used to

provide forward momentum to the collapsing structure. This option can be achieved without

the need for heavy lift vessels. Reuse. The opportunities for reuse of jackets at another field

site are limited as they are designed for specific production requirements, water depth,

environmental criteria and soil conditions. Field life is also factored into the design of jackets

in terms of fatigue and corrosion considerations.

b. Toppling in place

Figure 4.5 showing toppling in place (Day 2008)

c. Total removal of topside and toppling in place of the jacket only

Figure 4.6 showing total removal of side (Day 2008)

d. Emplacement

Figure 4.7 showing emplacement (Day 2008)

Emplacement. Emplacement (Figure 4.7) is much the same procedure as

toppling except that the top section is completely cut from the lower section,

lifted off and placed next to the lower section

e. Transport to rigs to reef site. Rigs-to-Reefs is a process, managed by

Federal and State agencies, by which operators choose to donate – rather

than scrap – decommissioned oil and gas platforms to coastal States to serve

as artificial reefs under the National Artificial Reef Plan. Decommissioned

structures are typically toppled in place, partially removed near the surface, or

towed to existing reef sites or reef planning areas. The decommissioned

platforms, like artificial reefs and natural hard surfaces underwater, attract

various encrusting organisms such as barnacles and bivalves which colonize

on them and, in turn, attract fish and other marine life as found on natural

reefs.

f. Deep-water dumping. This method is particularly reserved for huge floating

systems located in the North Sea. Essentially, the structure is disconnected from

its moorings and towed to the deep ocean waters where it is then flooded and

sunk. Prior to any dumping operations, it is important to confirm that all

components placed in the ocean waters are free of hydrocarbons in harmful

quantities to avoid pollution of the open sea. Partial removal may consist of any

combination of the above-listed options. The method of structure and component

disposal should be based on legal, environmental, safety, financial and timing

issues. Identification of a disposal site and its proximity to the removal site must

be considered to perform a cost analysis on the most effective disposal method.

An inherent concern with any disposal method is tying down the salvaged

component on the transport barges, which can be particularly difficult and

dangerous in rough weather. A well thought out plan has to be enacted to assure

a safe and stable lift and placement on the transport barges. All components

should be tied down with a system that provides the same integrity as when the

platform was towed offshore for installation. A marine surveyor should be

available on-site to monitor the tie-down operations. The marine surveyor’s

responsibilities include confirming that the structure is secure for tow, certifying

that the tow route is free of overhead, width or bottom obstructions and verifying

proper ballast of the transport barge.

The choice of removal method will depend on cost, proximity to disposal sites, availability of

removal equipment, location of the removal relative to shipping lanes and fishing interests,

and safety and environmental issues. In addition, the disposal method will play a key role in

the decision on the removal method.

Chapter five

Legal limitations and applications associated with the Decommissioning,

abandonment and removal off obsolete offshore installations.

The extremely high cost of decommissioning and removal off offshore installations led to the

need to revise some of the national and international regulations adopted about 40 years

ago. Such a revision covered, in particular, the requirement set by the Convention on the

Continental Shelf (Geneva, 1958) and the United Nations Convention on the Law of the Sea

(Montego Bay, 1982) to remove abandoned offshore installations totally. At present, a more

flexible and phased approach is used. It suggests immediate and total removal of offshore

structures (mainly platforms) weighing up to 4,000 tons in the areas with depths less than 75

m and after 1998 - at depths less than 100 m. In deeper waters, removing only the upper

parts from above the sea surface to 55 m deep and leaving the remaining structure in place

is allowed. The removed fragments can be either transported to the shore or buried in the

sea. This approach considers the possibility of secondary use of abandoned offshore

platforms for other purposes.

From the technical-economic perspective, the larger the structures are and the deeper they

are located, the more appropriate it is to leave them totally or partially intact. In shallow

waters, in contrast, total or partial structure removal makes more sense. The fragments can

be taken to the shore, buried, or reused for some other purposes.

From the fisheries perspective, any options when the structures or their fragments are left on

the bottom may cause physical interference with fishing activities. In these cases, the

possibility of vessel and gear damages and corresponding losses does not disappear with

termination of production activities in the area. Instead, abandoned structures pose the

threat to fishing for many decades after the oil and gas operators leave the site. The

obsolete pipelines left on the bottom are especially dangerous in this respect. Their

degradation and uncontrolled dissipation over wide areas may lead to the most unexpected

situations occurring during bottom trawling in the most unexpected places. At the same time,

national and international agreements about the decommissioning and abandonment of

offshore installations refer mostly to large, fixed structures like drilling platforms. The fate of

underwater pipelines is still not affected by clear regulations.

In general the 1982 UNCLOS can best be seen as serving the interest of maritime states

within the exclusive economic zone, EEZ (a 200 nautical mile perimeter around the state.

Coastal states must have due regards for the right and duty of other states, including the

right of freedom of navigation. This freedom is largely protected by ensuring uniformity of

applicable pollution standard, and by preserving the ability of the maritime state to influence

the formulation of those standards within the IMO (International Maritime Organisation)

Interest groups (and sometimes referred to as “flags of convenience”) which have adopted

the UNCLOS include: environmental NGO’s, industry association and the maritime states

have dominated the discussions on policy and implementation. The USA is one such

example.

Secondary use of offshore fixed platforms

The options of reusing abandoned platforms, their foundations, and other structures that are

out of service have been actively discussed for the last 10 years.

An analysis of scientific potential of research stations permanently based on abandoned oil

platforms in the Gulf of Mexico revealed several promising directions of marine research at

such stations [Dokken, 1993; Gardner, Wiebe, 1993]. These include studying regulation of

the marine populations and coral reproduction, making underwater observations, monitoring

the sea level, and collecting oceanographic and meteorological information within the

framework of international projects. Some other suggestions consider transformation of

abandoned platforms into places for power generation using wind/wave and thermal energy

[Rowe, 1993]. These platforms also could be used as bases for search and rescue

operations or centres for waste processing and disposal [Side, 1992].

From the fisheries perspective, the most interesting projects are the ones aimed at

converting the fixed marine structures into artificial reefs. Artificial reefs are known to be one

of the most effective means of increasing the bio-productivity of coastal waters by providing

additional habitats for marine life. They are widely and effectively used on the shelves of

many countries.

The offshore structures can undoubtedly attract many species of migrating invertebrates and

fish searching for food, shelter, and places to reproduce. In particular, observations in the

Gulf of Mexico revealed a strong positive correlation between the amount of oil platforms,

growing since the 1950s, and commercial fish catches in the region. It became one of the

reasons to suggest the positive impact of offshore oil and gas developments on the fish

populations and stock. Wide popularization of this fact led to the mass movement using the

slogan "From rigs - to reefs" in the USA in the mid-1980s.

However, further analyses of the fishing situation in the Gulf of Mexico showed that the

growth of the fish catch in this case was connected not with increasing the total stock and

abundance of commercial species but with their redistribution due to the reef effect of the

platforms. A critical point here was the use of static gear methods of fishing (e.g., lines and

hooks) instead of trawl gears. Besides, the areas around the platforms became very popular

places of recreational and sport fishing. This also made a significant contribution to the total

catch volumes. Nothing similar was noted in the North Sea, where the number of oil

platforms has also been growing since the 1960s. However, the total catch did not correlate

with this growth at all and even decreased. This fact indicates the absence of any positive

impact of the reef effect of oil platforms on the commercial fish catches in areas where the

main way to fish is trawling.

At the same time, we should not forget about the danger that abandoned offshore oil

platforms and their fragments pose to navigation and trawling fishing. With an abundance of

such artificial reefs, this problem requires special regulations for negotiating the inevitable

conflict of interests. One such regulatory program has been developed and applied in the

USA in the Gulf of Mexico on the shelf of Louisiana [Pope et al., 1993]. It requires mapping

the area to indicate the locations of platforms, underwater pipelines, and other structures left

on the bottom. The program also includes monitoring, collecting data, developing a warning

system, and other activities necessary to control the situation and ensure safety in the

region.

It is of interest that the above argument in favour of rigs-to-reef has not been well received in

some quarters and the state of California has had some success in stalling the strong

challenge by interest groups lobbying for a change in the laws.

Until recently, law required that “decommissioned” oil and gas platforms be removed at the

end of production, and the surrounding marine environment be cleaned up and restored to a

natural condition. These obligations were known to the oil industry when the platforms were

installed. However, for several years, the industry lobbied to change existing law to allow

abandonment of offshore platforms in place after production ceases. Industry's motivation

was to avoid the costs for this previously agreed-to remediation.

Beginning in 1996, after the State of California required Chevron to remove four platforms

offshore Summerland in Southern Santa Barbara County, Chevron joined with other oil

corporations to lobby the State legislature to amend the law and allow platforms to be

abandoned in place.

The State of California’s position was based on the following concerns:

• Pollution

Oil platforms contain toxic materials and are surrounded by contaminated debris. Leaving

them in place defers full clean up and threatens the ocean environment with long-term

pollution impacts.

• Marine Resources

The University of California Marine Council found that research does not indicate that oil and

gas platforms enhance marine resources.

• Invasive Species

Oil and gas platforms can host non-native species that threaten the surrounding environment

and native fisheries.

• Safety Hazards

Leaving debris in the ocean creates a safety hazard for boaters, fishermen, and divers.

• Liability to California

If the platforms are left in place, the State of California would be left with the liability of

accidents or further mitigation efforts. Financial liability for abandoned platforms could thus

result in significant, ongoing costs for the state.

It is to be expected that similar concerns would be shared by the Trinidad and Tobago

population, its immediate neighbours and should provide awareness for the wider Caribbean

region.

These views were challenged by lobbyists so in order to protect the marine environment the

Environmental Defence Center, EDC led three successful efforts to defeat such legislation

and hold the oil and gas industry to the responsibilities it had previously agreed.

If consideration of alternate uses for decommissioned offshore oil and gas facilities were to

occur, EDC noted that the following issues should be addressed:

• Science-Based

The decision must be made based on objective scientific research addressing the potential

ecological implications platforms may have on regional fish populations (e.g. UC Marine

Council Report)

• Costs and Benefits

The full breadth and extent of environmental costs and benefits are considered

• Site Specific Analysis

Platform decommissioning is considered for each individual platform

• Burden of Costs

Platform owner should not be freed of costs associated with platform removal and

remediation.

If an artificial reef program is to be pursued, it should follow the State of California’s

established guidelines for artificial reef design and construction, such as mimicking in size

and substrate (e.g. rock and concrete) the reefs that naturally produce and maintain greater

numbers of fish, and incorporating various rock and crevice sizes in order to help fishes

recruit from the water column, find shelter, and reproduce. In many cases, platform

structures do not follow these guidelines.

The related guidelines relevant to Trinidad and Tobago are still not clear. (to be checked).

Scientific data in favour of rigs-to-reefs in the context of Trinidad and Tobago may be very

limited and with the need to encourage exploration and investment by international oil and

gas companies it is quite possible that relaxing such laws could serve as an incentive to

participate in our oil based economy.

Explosive activities

Complete or partial removal of steel or concrete fixed platforms that weigh thousands of tons

is practically impossible without using explosive materials. Bulk explosive charges have

been used in 90% of cases. This is very powerful, although short-term, impact on the marine

environment and biota, which should not be neglected.

It is extremely difficult to get any reliable estimates of possible mortality of marine organisms,

especially fish, during an explosive activity even if the initial data, such as the type of

explosive, depth of the water, bottom relief, and others, are known. This large uncertainty is

connected, in particular, with the high heterogeneity of fish distribution that strongly depends

on specific features of fish schooling behaviour. Calculations show that with a 2.5-ton (TNT

equivalent) charge, the mass of killed fish will be about 20 tons during each explosion. At the

same time, if, for example, a school of herring happens to get into that zone, the fish kill

figure may be much higher [Side, Davies, 1989].

One of the few known observations of fish damage in zones of explosive activity was done in

1992 in the Gulf of Mexico near the shore of Louisiana and Texas [Gitschlag, Herczeg,

1994]. In order to remove over 100 fixed platforms and other structures, more than 12,000

kg of plastic charges were exploded. The amount of dead fish floating on the surface was

visually recorded after the explosions. It totalled to about 51,000 specimens. The actual

number of killed fish was undoubtedly higher because many specimens could not float to the

surface or did not get in the zone of visual observation.

Whatever number of adult fish actually died during the explosions, it will hardly influence the

total abundance of commercial species. Much more hazardous for the fish stock are

explosive impacts on fish larvae and juveniles. The threshold of lethal impacts for the

younger organisms weighing up to several grams is tens of times lower than that for adult

specimens [Yelverton et al., 1975; Side, 1992]. Thus, the zone of mortality of fish at the early

stages of development is respectively wider. The quantitative estimates of possible effects at

the populational level are even more complicated because of the absence of corresponding

data and methods. Nevertheless, enough evidence exists to enforce strict regulations of

explosive activities and to forbid them in areas and in seasons of spawning and fry

development of commercial fish.

Removal of the offshore structures also decreases the number of habitats for structure-

related fish. For example, in the mostly soft-bottom environment of the Gulf of Mexico, these

structures provide hard substrates for marine organisms. The decline of stocks of reef fish

observed in this region within the past decade can be connected, in particular, with

elimination of over 400 oil-related structures that had served as an artificial habitat for marine

life [MMS, 1995].

Despite the fact that the State Legislature had rejected rigs-to-reefs proposals three times, a

new bill was introduced in 2010. EDC and other groups opposed the bill (AB 2503:

California Marine Life Legacy Act), due to the need for more scientific analysis and further

evaluation of the safety, management and economic ramifications of a state-sponsored rigs-

to-reefs program. See EDC's letter in opposition to A.B. 2503. AB 2503 was signed into law

on September 13, 2010.

Conclusions

Laws are proposed to protect economic states, interest groups while creating free and safe

access to the wider marine environment. The international maritime law and UNCLOS offer

some protection against some countries which, if allowed to, would impose fines to ships

that pass through their external economic zones.

In some cases where the definition of pollution in the law is so vague, mechanisms have

been put in place to limit the possible exploitation created in claims for compensation for

environmental damages. On the other hand compensation funds attract penalty payments

and associated restorative cost from the polluter.

As the cost of decommissioning and abandonment become financially prohibitive to oil

companies more efforts are being made to convert rig platforms to environmentally friendly

rigs-to-reefs havens.

Significant lobbying and lack of sufficient scientific data have contributed in several

environmental laws which govern decommissioning to them being changed or modified and

often to the possible detriment of the environment.

ReferencesBarclay, Ian, Jan Pellenbarg, and Frans Tettero. 2001. The Begining of the End: Preview of

Abandonment and decommissioning. New York: Schlumberger.

Day, M D. 2008. "Environmental control Technology in the Oil industry." In Decommissioning of offshore oil and gas installations, by Stefan T Orszulik, 188-228. New Hamsphire: Oxoid Ltd.

Gibson, Graeme. 2002. The Decommissioning of Offshore oil and gas installations: A review of current legislation, Financial regimes and opportunities for Shetland. London: Oxford Publishers.

1. http://www.offshore-environment.com/abandonment.html

2. International law and the Environment by Patricia Birnie, Alan Boyle and

Catherine Redgwell, 3rd edition, Oxford University Press, 2009

3. http://www.edcnet.org/learn/current_cases/offshore_oil/rigs_to_reefs/

4. http://www.environmentaldefensecenter.org/learn/current_cases/offshore_oil/

rigs_to_reefs/Final_EDC%20letter%20to%20OPC%20re%20OST%20study%206-

24-10.pdf

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Oil and gas accidents - information on drilling, transportation and storage accidents during

the offshore oil and gas activities.

Gas impact on water organisms - gas impact on fish and other marine organisms is

considered. Results of field and laboratory studies, including biological consequences of

accidental gas blowouts are discussed.

Natural gas in the marine environment - chemical composition and biological impact of

natural gas in the sea.

Spilled oil in the sea - fate, transformations and behaviour of oil and oil hydrocarbons in the

sea during an oil spill.

Environmental Impact of the Offshore Oil and Gas Industry, including the impact of

decommissioning, abandonment and removal off the offshore installations, click here.

Reviews of Environmental Impact of the Offshore Oil and Gas Industry by Stanislav Patin