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Time and the river.

The legendary Swanson River oil field passes into a new phase of gas development.

Within the year, the legendary Swanson River field, Alaska's first major oil discovery and father of Cook Inlet petroleum development, will be converted to produce mainly gas as the oil reservoir nears the end of its natural life.

The North Slope today produces more oil in three months than Swanson River has during the past 35 years. However, it was Swanson River that launched Alaska into the oil age, serving as the inspiration for additional exploration that led to oil and gas development throughout the Cook Inlet basin. Discovered by Richfield Oil Co. in 1957, Swanson River spurred the largest rush for oil leases ever recorded in the nation.

Father Time has caught up with Swanson River, where crude production has fallen from a peak of 37,000 barrels a day in 1968 to current rates of about 4,500 barrels a day. Some 217 million barrels of crude have been extracted, or more than 98 percent of the field's oil reserves.

But Swanson River contains lots of natural gas -- an estimated 333 billion cubic feet -- most of which has been funneled into the reservoir over the years from the nearby Kenai gas field to maintain reservoir pressure for oil production.

Swanson River's new field operator, Unocal Corp., says the "redelivered" gas is just too valuable to keep in the ground. Unocal's share of the gas will be piped to the company's chemical plant at Kenai, which requires more than a quarter of the 200-plus billion cubic feet of gas consumed a year in the entire Cook Inlet region, including Anchorage.

"We're trying to secure enough gas and enough sources in various fields to maintain that plant's insatiable appetite," explains Kevin Tabler, Unocal's Alaska land manager.

Swanson River was included in a major property swap last year, involving the exchange of Unocal oil and gas leases in the Colville Delta region on the North Slope for Arco property in the Cook Inlet basin. Unocal and partner Marathon Oil Co. each hold a 50 percent share of the Swanson River gas, while Unocal owns 98.5 percent of the remaining oil reserves and manages the field.

The largest producer in the Cook Inlet basin, Unocal operates eight offshore platforms and seven of the nine producing gas fields in the region. The addition of Swanson River natural gas is expected to boost Unocal's daily inlet gas production by about 20 percent.

Tabler says roughly half of the estimated 333 billion cubic feet of gas in Swanson River is recoverable, adding that the field is expected to yield 40 million to 50 million cubic feet of gas per day.

Although Swanson River's crude reserves are nearly depleted, Tabler emphasizes the reservoir will continue to yield at least some oil long after the field is converted to produce gas. In fact, he says gas values will make the remaining oil economic to produce and will avert a total shutdown of oil operations.

"By slowing down oil production at Swanson River, we can actually recover more oil than would have been possible if we just maintained oil recovery solely in the field," says Tabler.
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Title Annotation:Swanson River oil field
Author:Tyson, Ray
Publication:Alaska Business Monthly
Date:May 1, 1993
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