Giant fields growing

Peggy Williams, Oil & Gas Interests Newsletter, May 1

Despite their maturity, 59 giant U.S. oil fields still contain more than 9 billion barrels of recoverable oil.

“The giant U.S. oil fields having significant remaining potential form a diverse group,” says James W. Schmoker, geologist and author of a new U.S. Geological Survey open-file report on the contribution of giant oil fields to U.S. production and reserves.

Most of the fields are in Texas, California and Louisiana. Alaska has eight giants, and its fields account for a good portion of that 9 billion barrels, Schmoker says.

Although many of the U.S. giants were discovered decades ago, changes in field sizes of tens of millions of barrels are still common. The number of fields that have increased in size since 1990 outnumber those that decreased in size by more than two to one.

All told, since 1990, a net of 5.8 billion barrels of oil was added to the estimated total recovery of the giant fields. “A number of giant U.S. oil fields have had extraordinarily long reserve lives and are declining at rates below expectations,” he says.

Reserve additions between 1990 and 1997 of more than 1 billion barrels were enjoyed by Alaska’s Prudhoe Bay and Kuparuk fields. Other giants that significantly increased in size were California’s Midway-Sunset and Belridge South fields, as well as Texas’ Spraberry Trend and Slaughter fields.