The work deals with a conceptual geological model creation that is necessary for further geocellular modelling and field development scheme optimization. The object of the study is Lower Jurassic terrigenous formations U15 and U14 of Urman-Archin fields group located in south-eastern part of West Siberian basin. Low quality of these reservoirs requires detailed geological analysis for allocation of the most perspective zones. This work integrates the results of seismic, paleogeographic, palaeotectonic, logging, well testing, macroand microscopic core analyses. It was discovered that the formations were deposited in fluvial conditions. Moreover, the evolution of the river system is observed across the interval of U15-U14 formations – braided streams change to meandering ones. The sedimentary processes determine vertical and lateral lithological heterogeneities as well as the primary distribution of grains of different size characterizing the activity of depositional agent. However, it was found that lithology and grain size is not directly related to the presence of reservoirs, so sedimentary conditions are not the key factor of reservoir continuity. Analysis of diagenetic alternations of the formations’ rocks showed that their compaction influenced reservoir quality and its lateral heterogeneity. In some parts of the studied area the rocks are more compacted, and, consequently, they have lower porosity and permeability. Tectonic movements caused non-uniform rock compaction across the area. In addition, they led to reservoir compartmentalization. There are hydrodynamically isolated blocks, which may influence fluid distribution within the formations and should be considered during development scheme planning. Significant influence of diagenetic alternations on the reservoir properties is not typical for the deposits in terrigenous rocks within West Siberian basin, so this conclusion should be taken into account when analyzing similar reservoirs in this region.

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