The Precambrian Petroleum Systems of Eastern Siberia: Evidence from Oil Geochemistry and Basin Modeling

Uncertainties regarding the number, location, and areal extent of Precambrian petroleum systems in Eastern Siberia are primarily attributed to a lack of direct source rock data. This study provides an indirect characterization of source rocks contributing to petroliferous areas (PAs) in the southern Lena-Tunguska region through an assessment of available geochemical data from oils and gases contained in reservoirs from the Vendian through lower Cambrian. Geochemical data and basin modeling were used to: (1) establish the number of source rocks contributing to hydrocarbon accumulations; (2) define source rock depositional systems and lithology; (3) estimate source rock thermal maturity; and (4) predict source location and migration patterns.

In this study, geochemical interpretations are made on oil and gas data available from the published literature and GeoMark Reservoir Fluid Database and include comparisons of samples from the Nepa-Botuoba, Angara-Yenisey, Katanga Saddle, and Baykit PAs. Analysis of these data within the paleogeographic context of Eastern Siberia indicate significant geochemical differences among oils from the Nepa-Botuoba, Angara-Yenisey, and Baykit PAs, strongly supporting hydrocarbon generation from three distinct source rocks. Biomarker evidence and bulk fluid properties indicate long distance, lateral migration of Nepa-Botuoba oils across the anteclise, resulting in hydrocarbon accumulations nearer to the inferred source that are heavier and contain relatively more gas and sulfur, although these trends are somewhat complicated by local structures and multiple, stacked reservoirs.

One-dimensional maturity models of pseudo-wells in the Nepa-Botuoba and Angara-Yenisey PAs are constructed incorporating inferred source rock characteristics to constrain the timing and thermal histories of the petroleum system components. The drowning of the Siberian platform and formation of thick salt layers during the Early Cambrian controlled both accumulation and preservation of hydrocarbons in the Eastern Siberian PAs. In addition, the highly saline porewaters created during this period prevented biodegradation of hydrocarbons in the reservoirs, independent of reservoir temperature history. These results suggest that large accumulations of hydrocarbons in the Nepa-Botuoba PA are more likely to be limited by the lateral continuity of reservoir units than by the timing of hydrocarbon accumulation and preservation.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California