Lithogenesis role in formation of zones with improved reservoir properties of subsalt carbonate sediments of venda and lower cambrian (Eastern Siberia)

Abstract

The object of research is pre-salt deposits of carbonate complexes from Vendian and Lower Cambrian Nepa-Botuobiya anteclise (NBA), located in the central part of the Siberian platform, administratively dedicated to the Irkutsk region. The problems of fluid dynamics within the basement ledges are considered. Their role in the high productivity of overlying carbonate deposits is assessed. Reconstruction of sedimentation conditions and subsequent diagenesis and katagenesis of Nepa formation sediments is made that have the greatest impact on morphostructure of the sedimentary cover. Cuts of Vendian-Cambrian sediments before and after diagenesis and katagenesis are given. Detailed construction helped to establish antiform structure of the sedimentary cover deposition over the basement ledges, allowing visually see in retrospect a sediment`s restructuring and its influence on the formation of hydrocarbon traps. The information on the rising pore pressure within the ledges is provided, due to which there is a subvertical fluid migration through both sulfate-carbonate rocks and interformational mudstones which to the beginning of elysion processes in Nepa formation were also unlithified porous sediments. It is suggested that the most permeable zones in the sulfate-carbonate rocks were formed over the edge portions of the projections as the most deformed during compaction of sand and clay deposits Nepa formation and restructuring of the upper section of the sedimentary cover. It is suggested that the elysion stage of sedimentary basin development within ledges and arched structure of Vendian-Cambrian deposits leads to dissolution and mobilization by aqueous solutions of the sedimentary rocks substance at depth and their migration mostly up. The results outlined in this paper are supported by the core data analysis.

Keywords

• Nepa-Botuobiya anteclise
• carbonate sediments
• Eastern Siberia
• Vendian
• Lower Cambrian
• sedimentation
• diagenesis
• katagenesis
• compression ratio
• fluid migration
• elysion stage
• basement ledges
• desalination
• reservoir properties