Why Offshore Oil Rigs Explode
Only mere weeks had passed since BP finally capped its rupturing Deepwater Horizon well before a fire broke out on another rig in the Gulf of Mexico this week. Fortunately, the Mariner Energy platform – a production, not a drilling rig like BP's ill-fated vessel – did not explode, nor does it appear to have leaked oil, contrary to early reports.
Nevertheless, the incident goes to show that harvesting "black gold" and natural gas from beneath the ocean floor is a high-risk endeavor, despite oil companies' assurances of using the latest and greatest in safety tech.
"You would think that technological advancements would have reduced the number of incidents over the years," said Markus Huettel, a professor of oceanography at Florida State University.
Yet according to the National Wildlife Federation and other groups, accidents have indeed not let up.
As far as official statistics go, from 2006 up through last year, the U.S. Mineral Management Service (MMS, and now the Bureau of Ocean Energy Management, Regulation, and Enforcement) recorded 23 "loss of well control" incidents – blowouts, essentially – and some 500 fires on the nearly 4,000 oil and gas drilling and production rigs in the Gulf. (The former MMS changed its incident reporting guidelines in 2006, resulting in a three- to fourfold uptick over the first half of the decade.)
The vast majority of these fires lasted just a handful of seconds before rig workers extinguished them. The Mariner Energy incident, however, rather like a three-alarm blaze on land, required several boats with fire hoses to douse its rollicking flames.
Source of fire undetermined
The exact source of that fire remains under investigation. Many fires since 2006 were the result of minor equipment failures or welding procedures that led to nuisance fires, and only 26 exceeded $25,000 in damage.
Big, dangerous explosions, though rare, come about due to the very nature of offshore petroleum prospecting. Squeezing the complexity of oil drilling on land into a size-limited vessel atop storm-tossed waters with equipment descending into the blue for many hundreds of feet is about as easy as it sounds.
"One of the things that is really different about offshore oil production is that everything is in this very confined space; you can't spread out like you can in a cow pasture," said John Rogers Smith, an associate professor of petroleum engineering at Louisiana State University (LSU). "There's this balance between trying to separate ignition sources from fuel sources that is really difficult."
The fuel sources, of course, are the crude oil and natural gas burbling up from the hole drilled into a fossil fuel reservoir buried in the Earth's oceanic crust.
And the ignition sources include all the heavy equipment needed to locate, contain and draw these highly pressurized gas and fluids to the surface.
"Simply put, we're dealing with extremely high pressures, and it's hard to design equipment that doesn't leak," said Martin Chenevert, a senior lecturer in petroleum engineering at the University of Texas at Austin.
Chenevert notes that the pressure of gas in a typical home is only about five pounds per square inch (.35 kilogram per square centimeter). In contrast, the pressure of gas in an offshore field can be around 20,000 pounds per square inch (1,406 kilograms per square centimeter).
"You're moving these inherently flammable materials . . . and you have to have mechanical and electrical equipment to move them," LSU's Smith said. "So you inherently have got this combination of potential ignition sources and big fuel sources that are right there in close proximity."
Smith said some basic examples of efforts in keeping possible ignition sources safe include thick insulation around heated exhaust pipes and specially-designed fireproofed electronics. Another is "negative" air pressure in sensitive electrical areas so flammable vapors do not seep in.
An exposed circuit panel is suspected of igniting the spark that triggered the Deepwater Horizon rig explosion, killing 11 workers and unleashing the biggest oil spill in United States' history.
A sensor designed to let personnel know that the blowout preventer control panel in the driller's cabin was under negative pressure had been bypassed, Smith explained.
Arcing electricity here could have lit the burp of methane gas that shot up the riser pipe to the Deepwater Horizon rig and exploded on deck around 9:56 PM Central time on April 20.
Investigators continue to probe what in turn led to this natural gas bubble from the abyss; the ongoing raising of the failed blowout preventer by BP for inspection might help answer these questions.
Human error, of course, can and has contributed to oil rig explosions at sea, Smith said. This error can come in the form of an administrative decision – for example, the myriad safety shortcuts BP managers stand accused of making to cut costs and time on the Deepwater Horizon – to worker negligence and everyday "oopses."
Despite the degree of risk involved in drilling for petroleum offshore, Smith said he never felt scared all the times he worked and slept out at sea on rigs. "You’re very conscious of where you are, and it's deserving of a lot of respect and attention," he said.
When asked, however, if a flicker of danger exists in the back of one's mind – floating in a pipe-riddled, building-sized platform over a long, thin tube thrusting into a vast, flammable sea of goop and gas deep below – Smith said, "Oh yeah, it's there."
Samantha Murphy contributed reporting to this article.