Petroleum System of the Khatanga-Anabar Region

Bernhard Cramer¹, Nikolay Sobolev², Christian Ostertag-Henning¹, Karsten Piepjohn¹, Anton Shmanjak², and Evgeny Petrov^2
1BGR, Hanover, Germany.
²VSEGEI, St. Petersburg, Russia.

The Laptev Sea and surrounding onshore areas are believed to contain significant resources of petroleum. The geological structure of the Laptev Sea is well known from seismic imaging. It is governed by deep rift basins filled with sedimentary rocks most probably of Cenozoic age. No deep well was drilled so far in the Laptev Sea giving direct evidence for the existence of oil or gas resources. Nevertheless, surface geochemical prospecting revealed traces of oil associated gas proving the existence of an active oil prone petroleum system in the Laptev Sea. The discussion still continues whether petroleum source rocks and reservoirs are situated within the young sedimentary sequence, or whether the active petroleum system in the Laptev Sea belongs to the supposed Mesozoic basement.

The Khatanga-Anabar region on the south-western edge of the Laptev Sea is part of a large sedimentary basin, filled with predominantly clastic rocks of Paleozoic to Mesozoic age. This basin is believed to extend below the Laptev Sea. Even though oil occurrences are known onshore from natural spills and shallow drilling, the petroleum system of this area was not systematically investigated during the past decades. Russian-German collaborative field work in summer 2007 investigated accessible outcrops in the area. In order to unravel the source rock potential and the origin of petroleum one formerly produced crude oil sample from Uryung Tumus, rock samples from outcrops and core samples from wells in the vicininty have been sampled and analysed. According TOC and RockEval pyrolysis data, many stratigraphic intervals sampled have remaining hydrocarbon potential, some especially for oil. Many samples have been classified as being impregnated with biodegraded oil.

All oils belong to one oil family most likely sourced from the same source rock interval. The maturity of the oils is similar and corresponds to the beginning of the peak oil generation stage. Characteristic features of the biomarker composition point to a carbonate or evaporitic marine source rock deposited under elevated salinity. This signature of the oil does not correspond to any potential source rock of the region investigated. High gammacerane concentrations in the crude oil, low δ13C values and the ratio of C28/C29 steranes below 0.5 is consistent with a Paleozoic source rock in evaporitic facies. These findings argue for a marine source rock in the Khatanga Anabar area associated with the known Devonian evaporates.

AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia