East Arctic Basins Offshore Eurasia and Hydrocarbon System Prediction Nikolay Malyshev, Victor Obmetko, Aleksey Borodulin Rosneft Oil Company, Moscow, RU

Victor Obmetko

Offshore the Eastern Arctic we defined the large areas of subsidence - Laptev Sea (LB), East Siberia (ESB), the North and the South Chukchi (NChB and SChB) basins. The thickness of the LB sedimentary cover reaches up to 15 km. This is a young rift Aptian-Cenozoic basin with preserved pericratonic (PZ2-K1) sedimentary complex in its western part. The thickness of the ESB and NChB sedimentary formations reaches 18 km. These are old basins ((D3?-C-T), developed on the Late Caledonian folded basement with the superimposed large Jurassic-Cretaceous rift troughs. The thickness of the SChB sedimentary cover is less than 7 km. This is a young (K1a-KZ) rift basin, developed on the Late Cimmerian folded basement. On the LB margins the Permian to Paleogene interval contains the organic-rich rocks. The content of sapropelic and humus-sapropelic organic matter varies from 0.5 to 7%, reaching 11-16% in the Lower Triassic rocks of the New Siberian Islands. Humus-type organic matter is determined mainly in the Cretaceous-Paleogene sediments (TOC 0.26-19.54%), reaching up to 3% in the Eocene clay and silica Azolla layers on the Lomonosov Ridge. Also, recent studies of the rocks from the Wrangel Island demonstrated high organic matter content in the Triassic (1-4%) and Carboniferous (2.5%). The Upper Cretaceous - Paleogene formations have good gas generation potential (TOC: 5-12.3%). Reservoir presence in LB is expected in the thick Lower Permian marine sandstones and deltaic and coastal marine Upper Cretaceous - Cenozoic sandy formations. In the ESB and NChB reservoir development is predicted in the Carboniferous-Permian carbonate and clastic formations, prospective in the eroded places under the Triassic and Jurassic clays. In the SChB, ESB and NChB Cretaceous-Cenozoic formations, the reservoirs are associated with the coastal-marine and continental sandstones. Despite of numerous uncertainties and, consequently, multi-variant description of hydrocarbon systems, all models point to HC saturation in most of the basins in the East Arctic shelf of Eurasia. The LB, ESB and NChB basins are described as oil and gas prone and SChB is predicted as predominantly gas basin. The defined kitchen for the Permian-Cretaceous LB formations is the South Laptev depression, and for Upper Cretaceous-Cenozoic formations – the Ust-Lena-Omoloy rift system. The main kitchen for ESB and NChB was related to the North Chukchi and Vilkitsky troughs, in contrast to the American sector of the Chukchi Sea, where the Colville foredeep played the main role. Significant impact, both on the HC destruction and re-accumulation, was provided by structural changes in the region (K1nc, Pg1, and N1).

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013