The Department of Energy has begun moving 72 million bbl of oil out of its Weeks Island, La., Strategic Petroleum Reserve site because a naturally occurring fracture threatens the integrity of underground storage chambers.
Meanwhile, at other SPR sites, DOE is removing high levels of methane that have rendered some of the stored crude oil temporarily unusable. DOE said high gas content has reduced its access to about 130 million bbl, or 22%, of SPR inventory.
More than 12 million bbl of crude have been treated so far, and degassing operations continue at a 270,000 b/d rate.
DOE said the SPR's emergency response capability should be fully restored early in 1998, when the Weeks Island crude is transferred to other sites and degassing operations are complete.
Use of heat exchangers has solved a problem of excessive heat in some SPR storage caverns.
The SPR is the largest emergency crude oil inventory in the world. It holds 592 million bbl in caverns on the Gulf Coast that have a capacity of 750 million bbl.
WEEKS ISLAND
The Weeks Island site, near New Iberia, La., has been geologically compromised by one or more natural fractures leading from the surface to the 700 ft deep storage chambers.
Weeks Island is different from other SPR sites because it is a converted salt mine. The other sites, created by leaching cavities in salt domes, are deeper and much less susceptible to fractures.
Water has seeped through a fracture into the Weeks Island storage chamber.
Although no oil has leaked, DOE fears a sudden washout might force large amounts of crude into the surrounding area.
DOE has stabilized the flow of water with a "freeze wall," a 200 ft high, 60 ft diameter cylinder of ice around the large fracture where it runs into a water aquifer.
That enabled DOE to begin transferring Weeks Island crude in early November to the Bayou Choctaw SPR site near Baton Rouge, La. Later, the crude will be moved to the Big Hill site near Winnie, Tex.
Drawing down the entire inventory will take 12-16 months, depending on availability of commercial pipeline space between Weeks Island and Big Hill.
When the oil is removed, the Weeks Island cavern will be refilled with brine. The entire decommissioning process will take 2-3 years.
DOE is paying for Weeks Island operation with funds previously earmarked for improvements at other sites. An appropriations bill awaiting action in Congress would allow the sale of 7 million bbl of Weeks Island oil to pay for the decommissioning.
GAS, HEAT PROBLEMS
DOE found in 1993 that high levels of methane had accumulated in crude stored for the longest time at the other four sites, apparently from a slow intrusion from surrounding salt formations.
It also found that geothermal heating at the extreme depths of the caverns had raised the temperature of some of the crude. The tops of caverns are about 2,000 ft below the surface and they descend another 2,000 ft.
DOE said high temperature and gas content would create safety, environmental, and transportation problems when oil is drawn down.
Nearly 143 million bbl of oil had enough methane to warrant corrective action, although some of it could be used in an emergency by blending it with unaffected oil from other caverns.
Earlier this year, DOE installed degassing units at the West Hackberry site near Lake Charles, La., and the Bryan Mound site near Nederland, Tex.
West Hackberry oil is being withdrawn, degasified, and reinjected at a rate of as much as 150,000 b/d. At Bryan Mound, the rate is as much as 120,000 b/d.
When the West Hackberry job is finished, the degassing unit will be moved to Bayou Choctaw and then to Big Hill. Degassing at the three sites will be complete by May 1997. Bryan Mound degassing is to be finished by April 1998.
DOE said it may have to degasify stored crude every 5-10 years to prevent methane buildups.
To resolve the heat buildup problem, DOE has installed heat exchangers in line with surface piping that would remove crude from the caverns during a drawdown.
Most of the SPR caverns have two or three wells, one or two for water injection and another for removing oil.
DOE routed the surface piping so water pumped to the caverns to force oil out during a drawdown would pass through the heat exchangers, absorbing heat from the oil being withdrawn.
Tests have confirmed that the heat exchangers are effective.
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