DOE TO DEGASIFY 200 MILLION BBL OF SPR CRUDE

The U.S. Department of Energy plans to pump out more than one third -200 million bbl-of the oil stored in its Strategic Petroleum Reserve and degasify. it.

Natural gas has penetrated some of the salt dome storage caverns at Bayou Choctaw and West Hackberry in Louisiana and most of the caverns at Big Hill and Bryan Mound in Texas.

During many years, gas in surrounding salt formations has slowly intruded in the storage caverns and dissolved in the crude. The oil was gas free when it was stored but now contains 1-5 cf/bbl.

"The presence of dissolved gas in the crude oil poses no safety or other concerns as long as the oil remains in underground caverns," DOE said. "It does not mean the oil is unusable, only that the gas content will have to be reduced before the oil can be moved to commercial markets."

Some of the SPR crude has slightly higher temperatures due to geothermal heating, which has increased the vapor pressure of the oil. Such heating has raised the average temperature at a rate of about 2-3 F./year.

The caverns are 2,000-5,000 ft below the surface.

DOE said "As the temperature rises, the vapor pressure of the crude oil increases. Oil that has been in the caverns for long periods of time has a vapor pressure that is higher than permitted by commercial handling regulations. It poses a safety risk because of the potential for vapors to be released during transport or above ground storage."

CORRECTING THE PROBLEMS

DOE estimated a program to correct the problems will cost more than $60 million spread over 3-4 years but could be completed by January 1996.

DOE plans to install transportable separators, bring the affected oil to the surface, remove the gas, and then reinject the oil. Gas will be sold to help pay for the operation.

"It makes the most economical sense to do this with relatively small scale equipment over a period of about 3 years rather than building much larger and much more expensive gas separation units that would handle large quantities of oil at the time of a drawdown," DOE said.

"In the future, it may be necessary to routinely cycle crude oil through this equipment every few years to ensure that any gas buildup is removed."

DOE also plans to reconfigure drawdown pipes to cool the oil when it is pumped out.

"The most economical approach appears to be to reroute the initial section of the pipeline on the surface so that the water injection pipe and the oil removal pipe are installed in heat exchanger arrangements."

Remedial work will reduce the maximum drawdown rate from the 577.3 million bbl SPR. The rate will slip to 3.5 million b/d for a short time from the 3.9 million b/d rate existing before the problem was found.