In the past, abandoning fields on land was relatively easy, with the major consideration being to seal wells to prevent contaminating freshwater aquifers.
But as government regulations have proliferated, the process has become more complicated and costly, encompassing not just wells but, in some locations, also cleaning up and restoring the adjacent land to a relatively pristine state.
In the US, states began regulating well abandonments in the 1930s. Prior to that, many wells were left without any seals or plugged with material such as lumber or tree limbs. The fact that regulations differ from state to state complicates the abandonment process in the US.
For many fields, an operator's abandonment liabilities are in the distant future. At present it is difficult to accurately assess these costs or determine what will be appropriate in the future, although much of the controversy surrounding the process has subsided.
Costly process
For fields requiring abandonment, the process, even on land, can be costly. For instance, a US General Accounting Office report released last month said that $2.7-6.0 billion may be required to dismantle the production infrastructure on Alaska's North Slope. The re quired work lacks definite guidelines, and an official at Alaska's Department of Natural Resources wrote that adopting specific standards today is premature because the producing operations likely will continue for another 50 years.
Offshore, abandonment costs in crease with water depth and the size of well-supporting structures that are re moved. Structures range in size from single caissons to towering structures more than 1,000 ft tall, in the case of compliant towers. Also subject to re moval are subsea items such as well templates, manifolds, wellheads, and interconnecting flowlines and umbilicals.
Floating facilities are easiest to remove because one can tow them to a dock for decommissioning, although disposing of floating-facility supporting structures such as spar towers, with their 600-ft height, is likely to be more complicated.
Gulf of Mexico waters have seen a continual removal of offshore platforms since operators dismantled the first structures in 1973. As discussed in a special report article on p. 39, decommissioning costs of these structures in the gulf typically range from $300,000 to $13 million. To date, operators in the gulf have removed mostly smaller struc tures in shallower water. Costs likely will increase when abandonment starts for platforms in water deeper than 600 ft.
A November 2000 study, prepared by Houston-based Twachtman Snyder & Byrd Inc. for the US Minerals Management Service, estimated decommissioning costs for three large platforms off California. These platforms sit in 430-1,198 ft of water and weigh 21,000-65,000 tons. The estimated cost for disposing of each platform, depending on removal method, is $44-123 million for complete removal, $15-20 million for partial removal and reefing in place, and $18-35 million for remote reefing.
The study said that, even though the industry is developing several new technologies for removing offshore platforms, standard removal technologies still remain the best option for decommissioning deepwater structures. It indicated that existing heavy-lift vessels are the most cost-effective and dependable topsides and jacket removal technology and that explosives remain the safest, most dependable, and reliable severing technique.
The costs for abandoning fields off the US are low compared with the costs facing operators of some larger facilities in the North Sea. As discussed in a second special report article, on p. 42, costs for abandoning Frigg field in the Norwegian North Sea will total 4.4 billion kroner (about $560 million).
Subdued controversy
Currently, field abandonment issues, especially offshore, have lost much of their controversy compared with the time Greenpeace activists occupied the North Sea's Brent spar in June 1995 to protest planned deepwater disposal of the spar. That incident created public awareness of abandonment issues, but new guidelines-such as those promulgated by international maritime groups Ospar and the International Maritime Organization-and more openness by operators about their plans have quelled the debate. And now no one in the North Sea proposes deepwater dumping of decommissioned structures.
Facility abandonment in the Gulf of Mexico still has some controversy concerning fish and turtle kills because of the explosives used to sever the conductors and structure legs. Although decommissioning companies still mainly rely on explosives, other cutting technologies are increasingly being used. To prevent harming turtles, regulations now require that the water be monitored prior to detonating explosives.
Also, both Louisiana and Texas still encourage operators to provide rigs for artificial reefs that serve as prolific fish breeding grounds.
