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Petroleum Assessment of the Lomonosov Ridge Microcontinent, Arctic Ocean

Moore, Thomas E.1; Pitman, Janet K.2; Grantz, Arthur 3
1 U.S. Geological Survey, Menlo Park, CA.
2 U.S. Geological Survey, Denver, CO.
3 Consulting Geologist, Palo Alto, CA.

The Lomonosov Ridge (LR) is a narrow asymmetric continental fragment that transects the Arctic Ocean between the North American and Siberian margins via the North Pole. The LR was formed first by rotational opening of the oceanic Amerasia basin in the Early Cretaceous and later by rifting and seafloor spreading in the Eurasia ocean basin in the Paleocene. Seismic profiles across LR show that it contains a reflective sequence of shelf to passive-margin clastic strata that overlies a basement composed of crystalline and metamorphic rocks and competent sedimentary rocks. Seismic and dredge data suggest that the clastic sequence prograded across LR from source areas on the Barents shelf from the Mesozoic until the depositional system was sundered in the Paleocene by rifting of the Eurasia basin. Following rift-related erosion, separation from the Barents shelf, and subsidence below sea-level during formation of the Eurasia basin, LR was covered by a drape of Cenozoic sediments. Scientific coring by the ACEX expedition revealed that these deposits rest unconformably on Upper Cretaceous (Campanian) strata and consist of about 500 m of Cenozoic mudstone that is organic-rich in its lower half.

Petroleum source rocks in LR are inferred from Triassic and Jurassic strata of the Barents shelf and in the Amerasia basin in Alaska and Canada. Good quality source rocks on the LR are present in the Paleogene section in ACEX cores but these are likely to be thermally immature due to insufficient burial. Reservoirs are hypothetical but could include shelf-margin clastic units, especially those overlying the Early Cretaceous and Paleocene breakup unconformities, and Lower Cretaceous low-stand turbidites along the Amerasia basin margin. Traps are probably largely stratigraphic, although unconformity, growth-fault, and half-graben structural traps could also be present. Peak generation probably occurred during Paleocene rifting when high heat flow conditions prevailed.

The Cretaceous progradational deposits of the Amerasia (Makarov) basin margin in the LR were thought to be sufficiently prospective to be assessed (14% probability of at least 1 field >50 MMBOE). Our assessment yielded fully-risked estimates of 123 MMBO oil (range of 0 to 914 MMBO at 95 and 5 percent probability) and 740 BCF gas (range of 0 to 5528 BCF at 95 and 5 percent probability). Significant risk factors are source and reservoir rocks, thermal maturation, and preservation history.


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