Abstract

The Beaufortian megasequence in the National Petroleum Reserve in Alaska (NPRA) includes Jurassic through lower Cretaceous (Neocomian) strata of the Kingak Shale and the overlying pebble shale unit.  These strata are part of a composite total petroleum system involving hydrocarbons expelled from source rocks in three stratigraphic intervals, the Lower Jurassic part of the Kingak Shale, the Triassic Shublik Formation, and the Lower Cretaceous gamma-ray zone (GRZ) and associated strata.  The potential for undiscovered oil and gas resources in the Beaufortian megasequence in NPRA was assessed by defining eight plays (assessment units), two in lower Cretaceous (Neocomian) topset seismic facies, four in Upper Jurassic topset seismic facies, one in Lower Jurassic topset seismic facies, and one in Jurassic through lower Cretaceous (Neocomian) clinoform seismic facies.

The Beaufortian Cretaceous Topset North Play is estimated to contain between 0 (95-percent probability) and 239 (5-percent probability) million barrels of technically recoverable oil, with a mean (expected value) of 103 million barrels.  The Beaufortian Cretaceous Topset North Play is estimated to contain between 0 (95-percent probability) and 1,162 (5-percent probability) billion cubic feet of technically recoverable, nonassociated natural gas, with a mean (expected value) of 405 billion cubic feet.  The Beaufortian Cretaceous Topset South Play is estimated to contain between 635 (95-percent probability) and 4,004 (5-percent probability) billion cubic feet of technically recoverable, nonassociated natural gas, with a mean (expected value) of 2,130 billion cubic feet.  No technically recoverable oil is assessed in the Beaufortian Cretaceous Topset South Play, as it lies at depths that are entirely in the gas window.

The Beaufortian Upper Jurassic Topset Northeast Play is estimated to contain between 2,744 (95-percent probability) and 8,086 (5-percent probability) million barrels of technically recoverable oil, with a mean (expected value) of 5,176 million barrels.  No technically recoverable gas is assessed in the Beaufortian Upper Jurassic Topset Northeast Play.  The Beaufortian Upper Jurassic Topset Northwest Play is estimated to contain between 733 (95-percent probability) and 3,312 (5-percent probability) million barrels of technically recoverable oil, with a mean (expected value) of 1,859 million barrels.  No technically recoverable gas is assessed in the Beaufortian Upper Jurassic Topset Northwest Play.

The Beaufortian Upper Jurassic Topset Southeast Play is estimated to contain between 2,053 (95-percent probability) and 9,030 (5-percent probability) billion cubic feet of technically recoverable, nonassociated natural gas, with a mean (expected value) of 5,137 billion cubic feet.  No technically recoverable oil is assessed in the Beaufortian Upper Jurassic Topset Southeast Play, as it lies at depths that are entirely in the gas window.  The Beaufortian Upper Jurassic Topset Southwest Play is estimated to contain between 2,008 (95-percent probability) and 9,265 (5-percent probability) billion cubic feet of technically recoverable, nonassociated natural gas, with a mean (expected value) of 5,220 billion cubic feet.  No technically recoverable oil is assessed in the Beaufortian Upper Jurassic Topset Southwest Play, as it lies at depths that are entirely in the gas window.

The Beaufortian Lower Jurassic Topset Play is estimated to contain between 0 (95-percent probability) and 210 (5-percent probability) million barrels of technically recoverable oil, with a mean (expected value) of 83 million barrels.  The Beaufortian Lower Jurassic Topset Play is estimated to contain between 0 (95-percent probability) and 1,915 (5-percent probability) billion cubic feet of technically recoverable, nonassociated natural gas, with a mean (expected value) of 793 billion cubic feet.

The Beaufortian Clinoform Play is estimated to contain between 0 (95-percent probability) and 71 (5-percent probability) million barrels of technically recoverable oil, with a mean (expected value) of 12 million barrels.  The Beaufortian Clinoform Play is estimated to contain between 0 (95-percent probability) and 2,180 (5-percent probability) billion cubic feet of technically recoverable, nonassociated natural gas, with a mean (expected value) of 822 billion cubic feet.

The Beaufortian Upper Jurassic Topset Northeast Play will be the main focus of exploration in NPRA because it is estimated to contain numerous oil accumulations large enough to be developed as stand-alone or satellite fields, and because it is near existing infrastructure.  The total volume of oil assessed in the Beaufortian Upper Jurassic Topset Northeast Play (mean estimate 5.2 billion barrels) suggests it has the potential to contribute significantly to Alaska North Slope oil production.

 The Beaufortian Upper Jurassic Topset Northwest Play may become a focus of exploration in NPRA if infrastructure is extended closer to the play area, as it is estimated to contain several oil accumulations that may be large enough to be developed depending on infrastructure proximity.  All other Beaufortian plays are estimated to contain accumulations of modest size that may be developed as satellites if larger accumulations in the Beaufortian Upper Jurassic Topset Northeast Play or the Beaufortian Upper Jurassic Topset Northwest Play are developed as fields.