Место издания: Florence , Год издания: 2004

The Callovian-Oxfordian sediments are represented by mainly shallow-sea Vasugan Formation on the most part of the West Siberia Geosyneclise (WSG). In the west of WSG these sediments compose marine Abalak Formation and in the east - mainly the continental Naynak Formation. As the result of the discovering of number petroleum deposits in the horizon J1 (series of silt-sandstones beds), the Callovian-Oxfordian deposits became the main exploration objects of the WSG. The program of our work include a complex lithology-facies analysis, using of polarized microscope, XRD, IR spectra analysis. We used paleontological and geochemical data, too. As the result of the investigation it has been revealed that the formation of improved petroleum reservoirs (with porosity from 16 to 25%, permeability from 200 to 800 mD) depends on the content of medium-psammitic fraction, values of median and sorting coefficient, proportion of framework components of the rocks, amount and composition of rock cement. The Callovian-Oxfordian silt-sandstones have a feldspar-greywacke-quartz petrographic composition with predominance of the framework components (80-90%) and high quartz content (up to 60%). It was established that the porosity and permeability increase with the growth of median. The maximum values of these parameters are observed in sandstones with median more than 0,2 mm. Improved studied reservoirs are also characterized by the small amount of cement (2-7%) in sandstones that is made up of clayey, carbonaceous materials, quartz regenerations and diagenetic bitumen. The factors that are responsible for decompaction of Callovian-Oxfordian rocks of WSG are postsedimentary dissolution of framework components and cement, kaolinitization and presence of diagenetic bitumen. Rocks formation with improved reservoir properties occurred in: zones of bottom currents, bars of deltaic frontal part, along-shore and near-shore bars, beaches and shallow-water river channels. Numerous washouts and zones of pinching out of sandy layers are favorable for formation of traps of lithologic, texture-lithologic and texture-stratigraphic groups. The lithologic traps are typical for Vasugan and Naynak Formation. The texture-lithologic traps are confined to zone of facies replacement of the Vasugan Formation to Abalak and Naynak Formations. The texture-stratigraphic group represents the traps of pinching out of sandy layers and is confined to surfaces of washout.