An Assessment of Techniques for Removing Offshore Structures (1996)

Regulations governing the removal of offshore structures need to be sufficiently flexible to accommodate the complex requirements of a wide variety of structures, a spectrum of marine life, and various users in the Gulf of Mexico.

The many different types and locations of platforms, an array of potential interactions with other users of the ocean, and the complexity and variety of the biological communities associated with platforms indicate that regulations for platform removals must be flexible if they are to be both efficient and fair to all interested parties.

Existing Minerals Management Service (MMS) regulations have functioned well for many years. They are prescriptive in some areas (such as establishing the depth to which a platform must be removed). In other areas, the regulations are more flexible and can accommodate unusual cases by approving specific procedures in specific cases. Since the regulations have been in place, the oversight and approval processes have been continuously improved and modified. For example, the National Marine Fisheries Service (NMFS) Observer Program was instituted to minimize the incidental taking of sea turtles and marine mammals. Another improvement made in recent years is the requirement for verification of site clearance and written reports.

There are significant opportunities to satisfy some of the concerns of the interested parties without slighting the concerns of others. To take advantage of these opportunities, regulations must allow for individual circumstances and conditions.

Explosives are an economical and reliable tool for removing most structures, especially structures located in deep water.

At this time there is insufficient information about the mortality of fish from explosive removals to warrant changes in the current regulations and procedures. However, losses may be substantial, and continued efforts should be made to reduce them.

The available evidence on the effects of explosive removals on sea turtles and marine mammals does not support prohibiting or further restricting the use of explosives in the platform removal process. However, the effects on fish population dynamics are uncertain. Prohibiting explosive removals would incur risks to divers and other offshore workers and would substantially increase the cost of platform removals. Research and development on techniques to remove platforms without using explosives, and techniques that use smaller amounts of explosives more effectively, are progressing, as are research and development efforts on methods to mitigate the effects of explosives on marine life. Wider deployment and field testing are needed to evaluate the costs and benefits of these techniques. Suggested adjustments in MMS regulations and procedures that would encourage the development of nonexplosive techniques, as well as recommendations regarding research and testing that demonstrate the value of techniques for mitigating the damage from explosions, are discussed below.

The requirement that structures be removed to a depth of least 15 feet below the mudline is a disincentive to the development and use of nonexplosive techniques and advanced techniques using smaller explosive charges.

The 15-foot depth requirement significantly increases the risks to divers and the costs of nonexplosive cutting or advanced explosive cutting, which requires divers to place explosives. Divers can work much more efficiently and safely near the mudline. Relaxing the 15-foot depth of removal requirement could encourage the use of nonexplosive or advanced explosive techniques using smaller charges.

The NMFS Observer Program has significantly improved understanding of the effects of platform removals on sea turtles and marine mammals. However, the effects of explosive removals on populations of fish that frequently reside near platforms are not well understood.

The NMFS Observer Progam is valuable from both a research and an enforcement perspective. Continuing this program can significantly improve understanding of the effects of explosive removals on living marine resources and suggest ways to mitigate them. Available empirical information about the numbers, location, and variation of species of interest is too fragmented to support conclusions at this time about the effects on total fish populations or population

dynamics. Further research is needed for a definitive understanding of these effects.

The simplest means of blast mitigation are unlikely to reduce significantly fish killed from explosive removal operations.

Although there is considerable uncertainty about how to mitigate fish kills using existing methods, the evidence seems to indicate that blast effects of multiple detonations are severe enough that reducing the size of the explosive charge (e.g., using 25-pound charges instead of 50-pound charges) or setting deeper detonations (e.g., 32 feet instead of 16 feet) will result in only a modest reduction in the number of fish killed.

Devices to scare fish away from platforms during explosive activity are not currently applicable for use in open ocean water. However, this line of technological development offers promise for the future and should be encouraged.

Fish in shallow water (less than 50 feet deep) are vulnerable to the pressure wave generated by explosions (high compression followed by rapid decompression). There has been some success in frightening fish away using acoustic or “fish scare” devices, for example, near water intakes. If these techniques could be adapted to the fish species, water depths, and distances (e.g., 200 to 300 feet) associated with platform removals in the Gulf of Mexico, the number of fish killed could be significantly reduced. Mitigation techniques, such as reducing the size of explosive charges and increasing the depth of emplacement of explosives, when used in conjunction with other mitigation techniques, would then be more effective in reducing the number of fish killed.

Limiting the number of near-simultaneous explosions to eight and limiting the weight of individual charges to 50 pounds may have undesirable effects.

Although limits on the number of detonations and the weight of individual charges were motivated by concern about the adverse effects of explosions on marine life, these limits may increase rather than decrease damage. There are no data comparing the effects of a single explosive charge or near-simultaneous charges with the effects of a series of charges of the same size set off at timed intervals. In the absence of contrary information, estimates—based solely on existing data—of the number of fish killed from the explosive removal of a platform using a single charge must be assumed to be less than the number of fish that would be killed by a series of blasts set off at close intervals. Requiring a delay if more than eight explosions are necessary to remove a structure would expose surviving fish to subsequent explosions.

Because the 50-pound limit for individual charges is approved routinely under a generic permit, this limit may become a de facto industry standard, which would tend to discourage more discriminating analyses of the size of the charge needed to do a particular job. Such a standard could, in some cases, result in the use of a larger explosive charge than necessary. At other times, too small a charge might be used, which would necessitate using a second charge. In either case, more fish would be killed than if the appropriate-sized charge were used.

Nonlethal effects of explosive removals on living marine resources (e.g., temporary or permanent hearing loss or other physiological or neurological damage) on survival factors like reproductive performance or predator avoidance are not known. If species found near platforms represent specific year classes or are unique components of the reef ecosystem, the impact could be significant.

Studies are needed to determine the nonlethal morphological and physiological effects of high-level impulse noise on fish and other marine species affected by explosive removals.

Leaving platforms in place, partially removing them, toppling them in place, or using them for artificial reefs are options that are economically and environmentally attractive to many ocean users groups. Transport costs, concerns about liability, and regulatory issues now limit their use.

Commercial and recreational fishermen, environmentalists, and others concerned with maintaining or expanding the habitats provided by platforms (and reducing the damage they perceive when platforms are removed explosively) would, in some cases, prefer to leave platforms in place. Operators would avoid costs of removal. However, the potential liability and the costs of maintenance are perceived as outweighing these savings. Coastal states are hesitant to assume potentially unlimited liability for platforms left in place. Partial removal would solve most of the liability problems but is only feasible in deep water because of the need for navigation clearance. The cost of transporting a platform may limit its use as an artificial reef if a suitable site is far from the original platform site.

The committee recommends that the Minerals Management Service:

1. Change the minimum depth at which structures or well conductors must be severed from the current depth of 15 feet below the mudline to 3 feet below the mudline, provided that platform removal measures are employed that do not increase adverse environmental effects. Such measures include nonexplosive techniques, reduced charges, fish scare devices, or other effective mitigating methods. A 3-foot requirement would be consistent

with regulations for the burial of pipelines as well as extensive research indicating that a 3-foot limit would provide ample protection against exposure of the remaining structural elements by erosion or scouring of the seabed.

2. Work with industry representatives, explosives experts, and other interested parties and user groups to develop guidelines for determining the size of explosive charges necessary for cutting a specific structural element.

3. Allow partial removal of structures in 300 (or more) feet of water, with a cut at least 85 feet below the water surface when nonexplosive or advanced explosive techniques are used. If the top of the remaining structure is 200 feet or more below the water, a buoy should be installed and maintained.

4. Remove the limit of a maximum of eight detonations at any one time during the removal process, but retain the requirement of a 0.9-second delay between individual detonations.

5. Incorporate into the permit process the flexibility, including necessary request procedures, to encourage testing of removal techniques that could reduce the risks to living marine resources.

The committee recommends that the National Marine Fisheries Service in cooperation with the Minerals Managment Service and appropriate state agencies:

6. Maintain the procedures of the existing Marine Mammal and Sea Turtle Observer Program, including the ban on night-time detonations, but shorten the required period of observation from 48 to 24 hours prior to detonation. The 48-hour timeframe is costly in terms of human resources and support equipment and does not produce any additional benefits over a a 24-hour timeframe.

7. Systematically gather more information to augment available information about the species, numbers, and age distribution of fish killed and fish surviving when platforms are removed by explosives. Topics of particular importance include the following:

   • experimentally compare the fish kill for species of interest resulting from a series of equally buried detonations separated by the required 0.9 seconds, to the number of fish killed by a single detonation of the same size

   • experimentally determine the fish kill for species of interest at various depths and horizontal ranges for typical single explosion removal detonations

   • experimentally determine the effectiveness of acoustic systems, tailored for the species of interest, in scaring fish away from the sound source to a safe distance

The committee recommends that the offshore oil and gas industry, in cooperation with the appropriate federal and state agencies:

8. Develop a guidebook through appropriate industry-supported groups on recommended practices for using explosives in the platform removal process. The guidebook should deal with issues of reliability, environmental effects, and mitigation strategies including tradeoffs between depth of placement, size of charge, and associated environmental effects.

9. Sponsor and support programs to explore the feasibility and cost effectiveness of acoustic means of keeping fish, including the grouper/snapper complex, at a relatively safe distance from removal operations.

10. Investigate means of incorporating safe removal techniques and the reduction of environmental damage into the initial design.

The committee recommends that appropriate state agencies, in cooperation with the appropriate federal agencies and the offshore industry:

11. Evaluate existing state-administered, artificial reef programs to enhance their potential for accommodating more platforms (by increasing the number of sites, for example) as well as their potential for providing commercial, recreational, or environmental benefits to other ocean users. The evaluation should include considerations of potential liability as well as the longer-term issues raised by the eventual loss of marine habitat.