Tectonic History of the U.S. Chukchi Shelf Region and Implications on the Play Concepts

Robert C. Scheidemann¹, John L. Shepard¹, Robert A. Foster¹, Charles J. Minero¹, Nina Lian¹, Attila Juhasz¹, Elli Tchouparova¹, Matthew Zechmeister¹, Douglas Collins¹, Lana Van Der Hurst¹, Pablo Buenafama¹, Steven Bergman³, Thomas X. Homza², and Guenter Jaeger^1
1SEPCO, Houston, TX.
²SEPCO, Anchorage, AK.
³SIEP, Houston, TX.

The U.S. Chukchi Shelf area reflects a tectono-stratigraphic history that differs from the “classic” tectonic evolution of the Alaska North Slope and U.S. Beaufort Shelf region. This difference created significant play diversity and the opportunity for multiple petroleum systems. Shell’s re-entry into Alaska is rooted in the prospectivity of this lightly drilled basin. This basin features giant traps, primarily within the Ellesmerian and Beaufortian Sequences, which share similarities with giant fields in N. Alaska.
Rifting initiated during earliest Ellesmerian time (Lt. Dev. to E. Miss. age) creating a rugose basin topography of stretched continental crust beneath the Hanna Trough region. This rifting phase is much more extensive than that of the North Slope, as evidenced by large half grabens filled by Endicott Grp. Eq. sediments sourced from the west (present day Russia) and east (present day Arctic Platform). During the post-rift sag phase, the remainder of the Ellesmerian Seq. (Miss. to E. Jur. age) was deposited by passive shelf margins that prograded into the region from both west and east (present day coordinates). Unlike the North Slope, the Lisburne Grp. Eq. contains abundant clastic material with diminished carbonate content, suggesting closer proximity to terrigenous input and lack of robust carbonate factories. The Hanna Trough region also contains a thick sequence of Sadlerochit Grp. Eq. sandstone and organic mudstone capped by a thick Shublik Eq. organic mudstone.

Rifting of N. Alaska from Canada was reestablished in the E. Jurassic to E. Neocomian, as reflected in the deposition of the Beaufortian Seq. Periods of basin margin uplift, extension and localized basin center subsidence, are evidenced by: 1) significant unconformities that are locally composite surfaces; and 2) accommodation space for juxtaposed prograding clastic systems that are age equivalent to the Kingak, Miluveach, Kuparuk and Pebble Shale Fms. It is also possible that the lwr Kingak may contain adequate source rock facies, as is seen within the Colville Basin.
The waning phase of Beaufortian rifting and onset of the Brookian Orogeny are evidenced by: 1) the LCU and LBU horizons as foreland bulge unconformities on the Arctic Platform and Outer Chukchi structural highs; 2) the northerly propagating Wrangel Island - Herald Arch fold and thrust belt; and 3) SW to NE prograding clastic margins that bury the primary source rocks and initiate the HC charge flux in the E. Cretaceous. This HC charge pulse was interrupted in the Lt. Cretaceous, as the Hanna Trough region experienced inversion through transpression with localized transtension, which resulted in extensive erosion or nondeposition during the upper Cretaceous. Relaxation of the Hanna Trough resumed in the Cenozoic, as witnessed by over 8,000 ft of Tertiary sedimentation and the development of keystone faulting. This renewed clastic load yielded a more recent early Tertiary HC charge pulse.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.