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Basin Modelling in the Chukchi Sea Area-Alaska Offshore-Usa

Veiga, Ricardo D.1; Gruenwald, Robert 1; Franques-Faixa, Jordi 1; Gomez, Irene 1; Legrand, Xavier 1; Castañares, Luis M.1; Gutierrez, Manuel 2; Riveira, Manuel 3
1 Repsol, Madrid, Spain.
2 Gessal, Madrid, Spain.
3 Aurensis, Madrid, Spain.

The Chukchi Sea is a frontier basin located in the Northwest Alaska offshore. A regional study was performed to evaluate the main risks in the area.

Five wells were drilled with a discovery well (Burger-1) in Lower Cretaceous sandstones and four dry wells. The dry wells had oil and gas shows with poor reservoir quality.

The sedimentary section shows four major stratigraphic sequences: Franklinian Basement (Lower Paleozoic), Ellesmerian-Passive Margin (Carboniferous-Triassic), Beaufortian-SynRift (Jurassic-Lower Cretaceous) and Brookian-Foreland Basin and Passive Margin (Upper Cretaceous-Cenozoic).

The main source rocks are: the Shublik Fm.(Triassic), Kingak Shale (Jurassic) and Pebble Shale/HRZ (Lower Cretaceous). They area mainly gas prone with Kerogene type III & II. However Klondike-1 well proved the presence of an oil-prone source rock in Shublik Fm based on rock-eval data.

Potential reservoirs are included in the following formations: Echooka (Permian), Ivishak (Lower Triassic), Sag River (Upper Triassic), Kuparuk A-B (Lower Cretaceous), Kuparuk C (Lower Cretaceous) and Sagavanirtok (Lower Tertiary). They are all clastic units deposited in shallow marine environments.

The main structural elements are: the Barrow High in the Northeast and the Chukchi Platform to the Southwest. They are separated by three regional depocenters: North Chukchi, Central Hanna and South Hanna.

The main kitchens are located in the South Hanna, Central Hanna and North Chukchi depocenters. The peak of expulsion took place at Albian times in the South Hanna and North Chukchi depocenters and at Late Cretaceous times in the Central Hanna Trough. Only small areas expelled hydrocarbons during the Late Tertiary.

Vertical and lateral hydrocarbon migration is inferred. The gas accumulation proved by the Burger well, requires both vertical and lateral migration from the Central Hanna and South Hanna kitchens; a fetch area measuring some 5000 sq km.

Three general play concepts can be defined:

a) The four-way dip closure involving pre-Lower Cretaceous sandstones. It was proved by the Burger well.

b) The pinch out of the pre-Lower Cretaceous sandstones onto the southwestern flank of the Barrow Arch. The main risk in this play is the trap integrity of the up-dip lateral seal

c) Structural traps involving Paleocene sandstones that overlie the kitchen areas and are connected to the source rocks through vertical faults. The main risk in this play is the migration pathways


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009