tce OIL & GAS

34 www.tcetoday.com july/august 2010

Anatomy of a disaster

The tce team takes a closer look at BP’s efforts to stop the oil spill in the Gulf of Mexico

Containment

IN a bid to wrestle control of BP’s 60,000 bbl/d gusher, the Gulf of Mexico has become a frontier-land for on-the-hoof engineering filled with top hats, and robots wielding diamond-tipped saws.

In late May, BP decided to abandon efforts to plug its damaged well. Prior to that, the company had tried about every measure in the book to stop the oil – and a few that weren’t. All to no avail. So what went wrong?

top killThe so-called ‘top kill’ operation failed to stop the upwell of oil and gas despite BP pumping in 30,000 bbl of mud at pressures in excess of 10,000 psi and at rates as high as 80 bbl/minute. ‘Mud’ is industry parlance for a cocktail of heavy-density fluids, in this case made of barite and viscosifiers. To complement efforts to clog the 445 t blowout preventer (BOP), the failed series of multi-redundant high-pressure valves atop the well, BP also fired in a series of ‘junk shots’ containing shredded tyres and dense rubber balls. But the oil kept leaking from the well – along with the mud BP had pumped in; so BP’s engineers refocused their attention on containing the spill.

domes and top hatsPreviously, BP had built a 12 m tall dome made from steel and concrete and lowered it on top of the leak. Unfortunately, on contact with cold seawater the leaking gas chilled into hydrate crystals, blocking the dome. Worse still, because the crystals were less dense than the surrounding water the dome became buoyant and began floating away from the well. According to a senior process engineer working in the oil industry, this sequence of events was entirely predictable: “Methane gas and cold water...didn’t hydrates cross their minds before they started to construct and implement the dome?” A much smaller 4 m tall steel containment dome (the ‘top hat’) was more successful. While technical troubles prevented a snug fit and there is still some oil leaking into the sea, the injection of methanol antifreeze prevented further

july/august 2010 www.tcetoday.com 35

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formation of hydrate crystals. Despite minor hitches – the system had to be shut down for 11 hours after a remotely-operated subsea robot collided with it – the top hat works. As tce goes to print, this system, collectively called the lower marine riser package (LMRP) is siphoning some 16,000 bbl/d to a ship called the Discoverer Enterprise. BP set up a second containment system by connecting a 45 t manifold to the kill and choke lines used in the unsuccessful top kill operation. The flow of the system has been reversed and some 8000bbl/d of oil and gas is now pumped to the Q4000 rig.

stormy weatherAs the Gulf of Mexico has now entered hurricane season, Mother Nature has started to force ships collecting oil to disconnect from their containment systems and scurry back to the relative safety of port. The first hurricane of the season, Hurricane Alex, made landfall in Texas, hundreds of miles from the centre of the leak, and yet it forced ships involved in the cleanup to evacuate the area. Another hurricane passing closer to the site of the leak would give BP no option but to evacuate, usually five days before the storm hits, leaving their disconnected containment systems leaking into the sea at full capacity. To minimise downtimes, engineers have built two huge hollow steel cans called free-standing risers (FSRs) that will bob 90 m below the surface of the sea impervious to any hurricanes passing above. They will allow BP to quickly disconnect from the well should a storm appear and more quickly reconnect once it has gone. In the coming weeks, the first of these systems will be connected to a second manifold which together with the LMRP and Q4000 will collect some 40–50,000 bbl/d.

ramping up capacityThe Q4000 and FSR connect to the BOP’s kill and choke lines below the main pipe capped with the top hat so once installed these systems will limit the oil reaching the LMRP. At this point, BP will remove the cap and install a tighter-fitting valve that will allow collection at the top of the BOP to increase to a maximum of 30,000 bbl/d. By mid-July, BP plans to have replaced its Q4000 output with its second FSR. At this point BP’s system should be able to collect up to 80,000 bbl/d meaning it will have redundant containment capacity for the first time since the leak began. For arguments sake, if all these systems failed at once, it would take two years to bleed the formation dry at the current estimated leak rate of 60,000 bbl/d. Of course BP has no intention of allowing this to happen. The company is currently drilling two relief wells in a bid to cut off the failed well, the first of which is expected to reach the original well in early August. 1500 m below the surface of the sea, and 3300 m beneath the seabed preparations are under way to drill the final stretch of the most developed relief well. BP is using electrical signals to map the precise location of the failed well so that when the final few metres can be drilled, the failed well can be intercepted and the ‘bottom kill’ operation can begin.

All photos courtesy of United States Coast Guard. Main photo: Gas from the damaged Deepwater Horizon is flared by the drillship Discoverer Enterprise.

Left to right: Engineers prepare the first dome for deployment; the top hat is launched; the Q4000 flares captured gas; top kill operation underway

36 www.tcetoday.com july/august 2010

tce OIL & GAS

Clean-up

So the oil is in the water, what next? The movement of oil is affected by tides, currents, and wind direction,

and the first line of defence is to try to prevent the oil from washing ashore. There are several methods of doing this: skimming, controlled burns, containment with booms, and chemical dispersion.

skim and burnSkimming and burning are fairly self-explanatory. Skimmers may be deployed to the scene of a spill. These boats are fitted with equipment to separate oil, which can then be burned off. Almost 300 controlled burns have been carried out on oil from the Deepwater Horizon leak, removing an estimated 38b l of oil from the ocean so far. Both methods are only truly effective in calm seas.

boomsThere are two types of boom; containment booms and sorbent booms. Containment booms float on the surface of the ocean and are made of impermeable material such as plastic. They can be used to ‘corral’ oil in areas of the sea to facilitate skimming or to prevent oil reaching a certain place. In the Deepwater Horizon spill, booms have been used to try to protect the sensitive Louisiana shoreline, with limited success. Booms will only work in relatively calm seas – waves can cause the oil to wash over the top. Sorbent booms soak up the oil with an absorbent or adsorbent core, which is usually synthetic but may be natural. Booms made of hair were trialled in the spill but were ruled out for widescale use after they quickly became waterlogged and sank.

dispersants The use of dispersants is somewhat controversial. They reduce the quantity of oil reaching the coast by dispersing it throughout the water column but this presents its own problems. While much has been made of the fact that Corexit, the most-commonly applied pre-approved dispersant, is toxic to marine animals, Carys Mitchelmore,

Regulation

WHENEVER a disaster such as this hits the headlines, the question is asked: “How could

this be allowed to happen?”, usually followed by “We must learn the lessons and prevent it from ever happening again.” Some, including representatives of the Government Accountability Office and the Interior’s Inspector General have testified that there was too little critical oversight, that the rules weren’t tight enough, and that companies have enjoyed too much freedom to set their own rules and procedures when it comes to health and safety.

On the other hand, a kneejerk reaction resulting in an avalanche of prescriptive safety regulations could do more harm than good, warns Donald Dobson, principal inspector of well engineering at the UK’s Health and Safety Executive.

Dobson suggests that the US could learn a thing or two from the UK, which operates a goal-setting regulatory regime rather

Above: a clean-up crew member shovels and collects oily waste in Grand Isle, Louisiana.

Top left: response teams prepare booms

Top right: ships skim the sea for oil

aquatic toxicologist at the University of Maryland’s Center for Environmental Science says it is less harmful than the dispersed oil itself. Dispersed from the surface, oil droplets could badly affect creatures living in the top 10 m of the water column. Here live the larval stages of many marine creatures so a generation is at risk, as are the zoo- and phytoplankton, which form the bottom of the marine food chain. As this is the first time dispersants have been applied below the surface the potential effects are as yet uncertain. “This is one big experiment,” says Mitchelmore. “We really don’t know what will happen. It’s a learning curve for everybody.”

shoreline clean-up Once the oil is on the shore there are various options but Denise Reed, a professor of earth and environmental sciences at the University of New Orleans warns that there isn’t a ‘one-size-fits-all’ solution, as superficially similar coastlines may actually be quite different. Removing oil from sandy and rocky shores is relatively simple, it can be shovelled up and taken away from sand or pressure-washed off rocks. On marshes the operation is more complex. If the leaves of marsh plants become coated with oil, they cannot breathe and will die. Trying to remove the oil can force it into the soil where the conditions are anaerobic, preventing microbial breakdown. Microbial breakdown can be encouraged by one of two methods, biostimluation and bioaugmentation. With biostimulation, nutrients are added to the environment to encourage microbial growth. With bioaugmentation, additional microbes are added to the environment. Reed says that in places like Louisiana, where growth is already high due to a warm climate and abundant nutrients, this is likely to do more harm than good because it disrupts the existing balance. Sometimes the best option can be ‘do nothing’ – though BP may find it hard to convince politicians and the media of the wisom in this. But once the area is clean, animals will recolonise from other areas, so lasting impacts should be minimal.

july/august 2010 www.tcetoday.com 37

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than the more prescriptive approach used in the US. This gives the UK a measure of flexibility, while keeping operators on their toes, which he says is a key safety advantage.

Anyone wanting to drill offshore has to submit a safety case, follow the goals set by the Offshore Installations and Wells – Design and Construction regulation, and have their design and construction checked by an independent competent expert.

The regulations typically require operators to ensure equipment specified (such as the BOP) is suitable to the task. Operators may get suggestions for what constitutes “suitable” from the available guidance, but ultimately, UK regulators do not demand specific solutions.

“A weakness of the regime anywhere is that there aren’t any international standards for the design of a well,” says Dobson. This means that most of the industry works to its own corporate standards. Part of the problem is that company engineers are have far more experience and competence than regulators ever will, Dobson says. “Any regulator can only spot the fairly major blunders,” he admits, though the independent expert adds another pair of eyes in the UK.

The US requirement for regulatory consent adds its own problems, particularly when requests for a new drill site are often not made till the last minute, putting regulators under pressure to consent with insufficient time for a meaningful review. Dobson believes that while this apparently tighter regime may look good to outsiders, in practice it can give the operator a false sense of security, the warm fuzzy feeling of “regulator-approved”.

It may come as a surprise to some, given the huge effects of an accident, that there is no independent requirement or check to ensure that the safety, design and building standards used by firms are up to scratch – the industry is largely self-regulating.

The closest they come to independent scrutiny is the UK requirement of an independent expert – however this is a scheme set up and paid for by the oil companies. This person might be third party, but can also be from the operator’s own company, provided they have no direct responsibility for work they are examining.

“There is a trade-off between competence and independence,” Dobson admits. It works, he says, because “company insiders have a better understanding on how that particular company does things and is better able to spot errors that a complete outsider would not.” tce

The warm fuzzy feeling of ‘regulator-approved’ did not prevent drastic cleanup measures such as this controlled burn