The Disposition of Old Oil Rigs: To Reef or Demolish?

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Over the years, the world’s energy requirements have led to off-shore oil extraction. The first submerged oil wells were drilled from platforms built on piles driven on the bed of Grand Lake St. Mary’s in Ohio in 1891. In the early 20th century, many of these started as simple oil drilling platforms built a few miles off-shore. The first ones made off the coast of Louisiana and Texas were drilling over shallow waters (around 14 feet deep). Once these dried up and the oil demand rose, more oil platforms were built further off-shore.  

Oil platforms belong to two main types: those placed on platforms anchored on the sea (or lake) bed and those on floating platforms kept in place with anchors fixed at the bottom of the ocean. Some recent estimates place the number at approximately 7500 of these oil rigs operating worldwide. A vast majority of all these oil rigs are on shallower waters.

Oil platforms and wells built off-shore disrupts shipping routes and fishing areas. Moreover, most of these are on continental shelves, which are usually traditional fishing areas. The well will be capped off, and the oil platform will be disused once the yield is not economically feasible anymore. Once in disuse, these will have to be removed. The mode of removal depends on the type of oil platforms were present.  

Many oil drillers, especially those operating over deeper seabeds, purchase the used floating oil rigs after their initial service life. This is more common among oil drilling operators based in Southeast Asia. Once the oil platforms are unusable, these are usually scrapped the same way as ships. However, the disposition for those oil rigs suspended on fixed platforms or compliant towers, the situation is more complex.  

The usual method for demolition work for disused platforms is by the use of explosive charges. Divers will place explosives on the most sensitive parts of the “jacket” and platform. However, the explosive force creates a lethal shockwave to all marine life within the blast radius. Within 30 years of operation, a considerably more teeming ecosystem forms around the base of the platform. Destroying these can have a significant impact on future fish yields. 

Aside from considering marine life when deconstructing oil platforms, other items need to be looked into. The height of the stub protruding from the surface should not be high enough to entangle fishing nets or be a threat to the hulls of ships passing above it. In the case of the Gulf, Engineers will have to cut platform legs 15 feet below mud level to account for frequent changes of current and weather. However, to do that, shaped explosives are employed by some demolition companies. 

The Gulf of Mexico sees 150 to 200 oil platforms being decommissioned yearly, making deconstruction companies based in the area dealing with decommissioned oil rigs the most experienced. Bluegrass is one of the more specialized companies dealing with non-explosive demolition work on oil rigs. They are pioneers of a cutting method for platforms where wires embedded with diamonds are used. Divers are usually tasked with positioning the wire cutters. However, for depths below 300 meters, remotely-operated vehicles (ROVs) do the job of divers. The platforms are first to cut into 10 to 20-foot sections. Then the members are loaded into barges and transported to the shore for recycling. 

 

As for the disposition of the seabed, the viable option used by many oil companies and governments is to create artificial reefs. Reefing requires demolition work, and there are three ways to do it:

  1. Cutting the jacket at the level of the mudline.
  2. Leave a stub from the jacket so that the top won’t threaten passing boats.
  3. Repurpose the cut jacket and platform section by displacing these to a more favorable location for reefing.

Reefing is seen as beneficial for developed countries such as Denmark, which saw its fish yields dwindle after considerable damage on its sea bed. Reefing is also the plan seen viable for deconstructed oil rigs located on the North Sea. 

The disadvantage of reefing is that if the reef location is not planned correctly, the reef can serve as a staging point of disease vectors that can drift to the natural reefs at one point. Another disadvantage is that the unnatural reef location can be a staging point for invasive species as well. 

Settling the matter on whether or not to do reefing is becoming more urgent. But one thing is for sure, 7500 oil rigs are due for deconstruction at some point. For one, preserving the ecosystems formed around the rigs is vital to maintaining the fish stocks. Development in the engineering of demolition work and proper consideration of the location of reefing are crucial for the future of marine life on the seabed where the platforms used to be placed.

 

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