Petroleum Assessment of the Eurasia Basin, Arctic Ocean
Thomas E. Moore1 and Janet Pitman2
1U.S. Geological Survey, Menlo Park, CA.
2U.S. Geological Survey, Denver, CO.
The Eurasia basin (EB) is a rectangular oceanic basin formed by slow to ultraslow seafloor spreading at the Gakkel ridge beginning at about 56 Ma. The high-standing Gakkel ridge bisects the EB into the Nansen basin on the European side and the Amundsen basin on the Lomonosov Ridge side. Sediments are ponded adjacent to the respective continental margins but attain their greatest thickness in the Lena prodelta which was constructed where EB terminates against the East Siberian margin in the Laptev Sea.
For the purpose of hydrocarbon assessment, the EB was divided into Nansen basin, Nansen basin margin, Amundsen basin, and Lena prodelta assessment units (AUs). Nansen basin margin sediments range from progradational Cenozoic shelf deposits to continental slope and rise deposits that are 3 km to as much as 7 km thick. Source rocks may include correlatives of the high-TOC Paleocene and Eocene section identified in ACEX cores on the Lomonosov Ridge. Thermal modeling suggests that, if present, these strata may have attained thermal maturation and have active petroleum systems. The sedimentary sections in Nansen basin AU and Amundsen basin AU are typically thinner (<3 km and ~2 km, respectively) and finer grained than in the Nansen basin margin AU. Assuming decreasing heat flow typical for 30-56 Ma oceanic crust, sediment in neither basin has attained thermal maturities sufficient to generate hydrocarbons. In contrast, the Lena prodelta at the apex of EB is shed from the ninth largest river system in the world and contains subbasins >8 km thick. Seismic reflection data suggest trap and reservoir configurations typical of large deltas. Locally high heat flow and active extensional faulting associated with the Gakkel ridge may have produced complex petroleum systems sourced from either correlatives of the high-TOC Paleocene-Eocene deposits in deeper parts of the prodelta or from intradeltaic condensed intervals that are inferred from deltas worldwide. Although our analysis suggests that the Amundson and Nansen basin AUs are not prospective, we concluded that the Nansen basin margin AU and the Lena prodelta AU are prospective for hydrocarbons (25%, and 43% probability of containing at least one field >50 MMBOE, respectively). Our assessment yielded fully risked mean estimates of 364 MMBO and 3.4 TCF gas for the Nansen basin margin AU and 980 MMBO oil and 14 TCF gas for the Lena prodelta AU, all with very broad probability ranges.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia