Tapping Prudhoe’s relic oil

Injections also help produce so-called “relic oil” stranded in the gas cap after most of Prudhoe’s oil migrated lower in the reservoir over many millennia.

BP estimates the gas cap holds 1 billion barrels of relic oil. The company likens this oil to “the film of sauce that remains on the sides of (a) sauce bottle when you can no longer get any more out even when it’s upside down.”

Injected methane vaporizes relic oil so that it will come to the surface when the gas is produced again.

—Bill White