Gull Island Oilfield

From Wikipedia, the free encyclopedia

Gull Island is a small island off the Arctic coast of the U.S. state of Alaska near Prudhoe Bay. It is claimed that in 1976 exploratory drillings there proved the existence of a separate oil field from the main Prudhoe Bay field that could contribute up to 1 million barrels a day to Alaskan production. The wells were capped because it was discovered that they were outside the allowable drill area currently outlined in Prudhoe Bay, or so it is alleged. Oil composition and pressures have proven that this oilfield is separate from both the Prudhoe Bay oilfield and the new field at Alpine.

The accumulation of oil at Gull Island is indeed separate from the Prudhoe Bay Field. Oil at Prudhoe Bay occurs in the Ivishak Sandstone member of the Sadlerochit Group, a sequence of sedimentary rocks deposited during late Permian and early Triassic time. Rocks saturated with oil at Gull Island are the much older Kekiktuk Conglomerates of early Mississippian age. Sadlerochit Group rocks are not present at Gull Island, as they were removed by erosion during Lower Cretaceous time. That period of erosion may have produced one of the largest natural oil seeps ever seen (by dinosaurs, anyway), as the Ivishak oil sandstones may have contained some oil from older sources before they were removed by erosion. Production at Gull Island was not considered economical at depressed prices, but may be possible now that worldwide demand has balanced production, causing prices to jump since 2004.

Oil at the Alpine Field is also distinct from that at Prudhoe Bay, as it occurs in channel sandstones of Jurassic Age. The oils are lighter and lower in sulfur than oil sourced from the Cretacous shales that provided the hydrocarbons that filled the Ivishak and Lisburne reservoirs at Prudhoe Bay.