Fixing oil wells(Extracted from Economist)

The price of staying in the game
Oil companies are now developing a system that could cap deepwater wells in the Gulf of Mexico in a hurry
Aug 12th 2010

WITH 500 barrels of hard-set cement now gumming up the Macondo well, a number of inquiries are looking back at the loss of the Deepwater Horizon rig and the subsequent spilling of 5m barrels of oil. How much of the fault is found to lie with the well’s design, how much with the way the design was implemented and how much with the way the rig was run will determine how such ventures will be regulated from now on. It will also settle whether BP, the well’s operator, was grossly negligent—a finding that could be worth well over $10 billion in fines and liabilities.

Meanwhile, the oil industry is already getting to grips with the question of what to do if such a thing should happen again. This is in part prudent politics: credible assurances that a future blowout could be better dealt with will be vital to restoring the industry’s fortunes in the Gulf of Mexico. It is also a matter of economic self-interest. The costs facing BP would have been far smaller if it had been possible to shut the well down a lot quicker.

The position taken by ExxonMobil, Chevron, ConocoPhillips and Shell, which are clubbing together to put $1 billion into creating and equipping a new not-for-profit firm, the Marine Well Containment Company, is that the capability to do much better than at Macondo depends on having hardware designed for the job and available from day one. The companies outlined their plans at a public meeting held in New Orleans on August 4th by the Bureau of Ocean Energy Management.

As the first diagram shows, the main component would be a containment assembly that could fit on top of a damaged blowout preventer, such as the one from which the Macondo oil poured forth. In the absence of a preventer, the assembly could fit on top of various other bits of wellhead equipment, or even on a bare pipe if it was in good enough condition, thanks to a set of adaptors and vice-like grips designed to let it mate with all the different forms of piping known to be in use at deepwater wells in the gulf.

This assembly would have powerful rams that could seal off the flow once it was attached to the relevant bit of broken plumbing. But it would also have outlets that could divert that flow, if need be, into undersea piping. If a well was badly damaged, the pressure that would build up if it were capped might cause it to spring another leak somewhere else. There were worries for some time that something like this would happen at Macondo.

Despite the assembly’s versatility, there might be times when it would have nothing to latch on to—if, say, all the sea-floor kit had toppled over, or if oil was gushing out of a hole in the seabed some distance from the well proper. For cases like this the system will have a range of watertight structures called caissons, which are based on the suction-pile technology used to emplace deep-sea moorings and foundations.

A giant sucking sound

A suction pile is open at one end. That end is put into the sediment into which the pile is to be stuck. The air is then pumped out and water pressure pushes the pile into the ooze, as shown in the second diagram. To make an oil-collecting caisson, such a pile would be used as a collar around a funnel-topped tube that would sit over the leak. Various sizes of caisson will be built, including one 15 metres (50 feet) or so in diameter, large enough to fit over a whole blowout preventer.

Once the caisson was in position, the pile would be pumped out and driven into the ooze. The caisson would fill with oil from the leak. A containment assembly would then be attached to the top of the caisson to send the oil elsewhere. The caisson could not simply be capped, because the oil pressure would blow its suction pile out of the sea floor.

Whether or not a caisson was used, the oil from the containment assembly would then pass through a manifold—a sort of switching yard for pipes—to one or more floating risers leading to the surface and held vertical by buoys. Here, as the third diagram shows, it would be collected by “capture vessels” kitted out with special modules that would flare off dissolved gas and pump the liquid into adjacent tankers. The whole system could cope with a flow of 200,000 barrels a day—more than three times the 63,000 barrels a day the government estimates was the Macondo well’s peak flow rate. The capture vessels could take other jobs around the gulf, but on contracts that allowed them to break off immediately in case of emergency.

Throughout the system there would be ways of warming things up and injecting antifreeze to stave off the formation of icelike methane hydrates. If the capture vessels had to leave in the teeth of a hurricane, there would be a system for injecting dispersants into any oil that spilled out of the risers. That should lessen its impact.

If this equipment had all been available in April, its proponents say it might have capped Macondo in weeks. The companies also say the system should never be needed if wells are properly designed and operated, and that they hope their billion-dollar backstop will never have to be used. The various reports into the Deepwater Horizon disaster will doubtless say the same, while endorsing the newly planned capabilities, or some variant thereof, and making some further drilling conditional on having them in place.

Perhaps it is not too much to hope, though, that some of those reports might shed light on two deeper questions: why did such a technologically astute industry not see fit to develop such useful equipment before it was needed, rather than after? And how might that underlying and disastrous lack of foresight be corrected?

ref: http://www.economist.com/node/16789834